Social Jet Lag, When Our Body Rhythms Are out of Sync with the Day-Night Cycle

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IY_[dj_ij Lebkc['&+DkcX[h,Del[cX[hÄ:[Y[cX[h(&'- Departments Feature Articles 322 From the Editors 348 364 323 Letters to the Editors 326 Spotlight Proprietary algorithms 328 Infographic Living with fire 330 First Person: Sally C. Seidel New insights on particle physics 332 Sightings Seeing the heart’s power 334 Briefings 335 Computing Science Bitcoins maybe; blockchains likely Peter J. Denning and Ted G. Lewis 340 Engineering 348 Adapting Your Body Clock to a 364 The New Language of Problematic pedestrian bridges 24-Hour Society Mathematics Henry Petroski Can new research help address the dis- Is it possible to take all words out of 344 Perspective connect between the body’s sleep-wake mathematical expressions? cycle and the rhythms of modern life? The forgotten mystery of inertia Daniel S. Silver Alexis Webb and Erik Herzog Tony Rothman 372 The Persistence and Peril of Scientists’ 356 Cassini and the Rings of Saturn Misinformation As one of its final scientific feats, Many challenges arise while battling Nightstand Cassini conducted a detailed tour of the widespread falsehoods. 376 Book Reviews material encircling the giant planet. Brian G. Southwell, Emily A. Picturing science rBig data in law Matthew S. Tiscareno Thorson, and Laura Sheble enforcement From Sigma Xi 356 381 Sigma Xi Today Q&A with new editor-in-chief of American Scientist rSymposium will address climate and health r Members share solar eclipse stories rNew quarterly conversations 372 The Cover

Technology has extended the times of day when people can be active and has allowed for connectivity at any time of day. A growing body of research shows that the biological clock is affected by light exposure, especially at certain times of day, which in turn can affect all sorts of biological processes necessary for health, including sleep, focus, and metabolism. More people seem to be experiencing social jet lag, when our body rhythms are out of sync with the day-night cycle. This lack of synchrony can have serious public health consequences; for example, it has been linked to sleep disorders, obesity, and mental disorders. In “Adapting Your Body Clock to a 24-Hour Society” (pages 348–355), circadian biologists Alexis Webb and Erik Herzog explain how the biological clock sets and keeps time, and what solutions are under study to help people sync up with healthy daily routines for sleeping and eating. (Cover illustration by Michael Morgenstern.)

FROM THE EDITORS AMERICAN Modern Challenges IY_[dj_ij decade ago, the robotic spacecraft Cassini had nnn%Xd\i`ZXejZ`\ek`jk%fi^______Aalready become a huge success. It had released its Huygens probe onto Saturn’s moon Titan, and it was returning spectacular imagery of the giant VOLUME 105, NUMBER 6 planet itself, as well as its other moons. At that time, we asked Carolyn Porco, leader of the imaging team Editor-in-Chief Fenella Saunders for the Cassini-Huygens mission and director of the Senior Consulting Editor Corey S. Powell Cassini Imaging Central Laboratory for Operations, Digital Features Editor Katie L. Burke to fill in American Scientist readers on the mission Contributing Editors Sandra J. Ackerman, Marla Broadfoot, Catherine Clabby, Brian Hayes, results so far. Her resulting essay in the July–August Anna Lena Phillips, Diana Robinson, David 2007 issue showcased the early results from the first Schoonmaker, Michael Szpir, Flora Taylor 1,000 days of the mission. Editorial Associate Mia Evans In this issue, we are returning to Cassini as its mission recently came to a preplanned end. To preclude Cassini from crashing into Art Director Barbara J. Aulicino one of Saturn’s moons as it ran out of propellant and potentially spreading terrestrial contamination there, the spacecraft was instead deliberately plunged into SCIENTISTS’ NIGHTSTAND Saturn. But before its final encounter with the planet, Cassini spent much of the Editor Dianne Timblin final year of its mission taking a detailed look at Saturn’s rings. As Matthew S. AMERICAN SCIENTIST ONLINE Tiscareno explains in “Cassini and the Rings of Saturn” (pages 356–363), this con- Digital Managing Editor Robert Frederick cluding year has been practically a whole new mission for the spacecraft, with some spectacular results. Publisher Jamie L. Vernon Space exploration uses remarkable technology, but the devices we use daily are also pretty amazing, even if we’re not paying attention to how they work. ADVERTISING SALES This issue tackles from multiple angles topics related to technology and how it af- BEWFSUJTJOH!BNTDJPSHt______fects us. In our cover story, Alexis Webb and Erik Herzog look at the role that late- EDITORIAL AND SUBSCRIPTION night viewing of backlit devices, such as cell phones and tablets, is having on our CORRESPONDENCE biological clocks, and our health, as a result. In “Adapting Your Body Clock to a American Scientist 24-Hour Society” (pages 348–355), the authors look at research that might help P.O. Box 13975 reset our biological clocks to be more in tune with our modern style of living. 3FTFBSDI5SJBOHMF1BSL /$ Mobile devices offer us the convenience of information at our fingertips, but tGBY are they also a conduit for making us more susceptible to falsehoods? In “The FEJUPST!BNTDJPOMJOFPSHtTVCT!BNTDJPSH______Persistence and Peril of Misinformation,” Brian G. Southwell, Emily A. Thorson, PUBLISHED BY SIGMA XI, THE SCIENTIFIC and Laura Sheble review what is known about how people evaluate information RESEARCH HONOR SOCIETY and discuss how knowledge of these processes could be used to battle hoaxes President Stuart L. Cooper and fake news. Treasurer David Baker Two articles in this issue discuss machine learning and its supporting algo- President-Elect Joel R. Primack rithms, which are increasingly framing our lives whether we are aware of it or Immediate Past President Tee Guidotti not. In the Spotlight section (pages 326–327), Simson L. Garfinkel reports on a Executive Director Jamie L. Vernon recent panel discussing proprietary algorithms and who should have access to American Scientist gratefully acknowledges how they work. Garfinkel points out that these types of algorithms not only can support for “Engineering” through the Leroy control what music you hear or what news you see on social media, but also are Record Fund. increasingly used to screen which job applicants to interview or determine how long a jail sentence should be—and there is currently little recourse for those af- Sigma Xi, The Scientiﬁc Research Honor fected to dispute the results from the software. Society is a society of scientists and engineers, One specific use of machine-learning algorithms is what’s calledpredictive polic- GPVOEFEJOUPSFDPHOJ[FTDJFOUJmD ing, where law enforcement agencies use software to help determine everything achievement. A diverse organization of from where officers patrol to which members of the public might be more likely members and chapters, the Society fosters to be a victim of a crime. In the Scientists’ Nightstand section (pages 376–380), an interaction among science, technology, and society; encourages appreciation and support excerpt of Andrew Guthrie Ferguson’s latest book, The Rise of Big Data Policing, of original work in science and technology; and digs into such programs, and why efforts in New Orleans were successful when QSPNPUFTFUIJDTBOEFYDFMMFODFJOTDJFOUJmDBOE similar programs in other cities didn’t have such dramatic results. engineering research. As Garfinkel points out, going back to a world where nothing is filtered isn’t really an option; we would all end up buried in spam and cat videos. Science is Printed in USA helping society find the balance between technology that is useful and applications that, maybe, step too far for human comfort. —Fenella Saunders (@FenellaSaunders)

322 American Scientist, Volume 105

LETTERS

Alone in the Universe? where in the universe lasts long enough in the Drake Equation are the ones to broadcast its existence for a sufficient estimating the proportion of planets To the Editors: amount of time to be found by another harboring conscious life, because we I found Howard A. Smith’s article short-lived technological civilization. know the least about them. Regarding “Questioning Copernican Mediocrity” I presume that whatever direction the lifetime of civilizations, however, (July–August) interesting, especially the evolution might take on other planets Stephen Hawking famously echoes discussion of the radius within which will be governed by the same principles sentiments similar to Dr. Cushing’s we might reasonably hope to communi- that Charles Darwin discovered here on when he speaks out against contact- cate with alien life forms. His article also Earth. Like us, such planets’ intelligent ing aliens. He simplistically claims that reminded me why I’ve long thought species (if any) will find it difficult or because they will be much more ad- that the last term in the Drake Equation, even impossible to overcome their ten- vanced than we are and presumably which famously estimates the number dency to overpopulate and overexploit will have also evolved through Dar- of intelligent extraterrestrial civilizations their ecological niche, ultimately lead- winian processes, they will be, to his in our galaxy, is the most significant in ing to their rapid extinction or reduc- way of thinking, dangerously violent. understanding the Fermi Paradox. tion to a pretechnological state of living. I am more hopeful than either Dr. Among the many factors in the equa- If there is intelligent life on other plan- Cushing or Hawking; after all, evo- tion that Frank Drake considered in ets, it is most likely to be either prein- lutionary biologists have pointed 1961, the length of time that a techno- dustrial or post-technological. In either out that sentiments such as altruism logical civilization releases detectable case, we wouldn’t be likely to find it. and gratitude are also the products signals into space now seems the weak- If my speculations are true, Smith’s of evolution. My opinion is that if an est link. We have been releasing such plea that we treat our special planet advanced civilization is able to last radio signals for barely more than 100 with more respect takes on even more than a few millennia without de- years. It seems possible that within an- greater significance. We may indeed stroying itself or its world, it will have other 100 years there will be no one left be alone, but in case we are not, per- learned how to master its negative im- on Earth sending such signals. Our ex- haps we should try harder to last long pulses. Perhaps the biggest benefit we ploding population, rapid exhaustion enough to be found. can derive from challenging our cos- of the necessary resources to support a mic mediocrity is the added impetus John Cushing technological civilization, already vis- to learn this lesson ourselves. Evergreen State College (Emeritus) ible destruction of a climate and envi- Bend, Oregon ronment that can sustain life on Earth, To the Editors: and threats of nuclear annihilation—all Dr. Smith responds: In his recent feature, Howard A. Smith of these suggest that perhaps no tech- I thank Dr. Cushing for his comments. seems to be asserting that the fact of nological civilization that evolves any- I think that the most uncertain factors something being rare means that it is

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ONLINE @ ______Wc[h_YWdiY_[dj_ij$eh] nonetheless prefer to believe we are cosmically average—or the opposite: that we are a cosmically amazing species. But personal beliefs such as these are What Makes Science Scientiﬁc Check out AmSci Blogs matters of taste, and it is worth asking A degree in science should require http://www.amsci.org/blog/ ourselves what underlies that belief. students to evaluate their process of Perhaps some philosophical attachment producing knowledge. Find American Scientist or psychological need prompts us to see http://bit.ly/2wgNtgy on Facebook ourselves as being either insignificant or Studying the Light of the Eclipse facebook.com/AmericanScientist significant. Still, we must try to ground Solar eclipses offer rare opportunities our personal beliefs in the scientific to better understand both the Sun’s Follow us on Twitter facts. (3) Admitting we are rare: While we wait, perhaps forever, to find out corona and the Earth’s atmosphere. twitter.com/AmSciMag whether there are aliens, we meanwhile http://bit.ly/2fw8yQZ ought to recognize that in the volume of Slide Show: Ecology’s Colonial Legacy Follow us on Google Plus the universe in which Homo sapiens can This set of historical images expands plus.google.com/+Americanscientist______ever exert influence, which is perhaps beyond the visuals in “The Colonial Org/about_____ thousands of light years in diameter, Origins of Tropical Field Stations,” we are probably unusual and could be in the July–August issue. Join us on LinkedIn unique. Does that make us rare, that is: “a thing not found in large numbers http://bit.ly/2hrI2J4 ______https://www.linkedin.com/company/ ______american-scientist and so of interest or value?” I would say Podcast: The Moment of Totality so. The Earth is too. The word “special” For thousands of years, people have Dr. Foster uses is loaded with subjectiv- Read American Scientist been computing the timing of eclips- ity and I try to avoid it. Both Dr. Foster, using the iPad app es. We’re really close. But with a little whom I thank for his question, and I are more data, we could be closer still. Available through Apple’s App Store probably average examples of Homo sa- http://bit.ly/2wgO4ii piens, but I daresay we are both special. It does not follow that if we are special and intelligence is rare, a theological ex- necessarily special. This error has been sponds that we are just a collection of planation is required. decried by numerous scientists, includ- molecules in a universe filled with lots ing Richard Feynman, who mocked the of planets and molecules, then it is im- Illustration notion in his unique way: “You know, portant to include the “priors” of the the most amazing thing happened to case before calculating the statistics, Credits me tonight.... I saw a car with the license as one would in a detailed Bayesian Infographic plate ARW 357. Can you imagine? Of all analysis: If one knows ahead of time Pages 328–329 Eleanor Lutz the millions of license plates in the state, that the very particular license number what was the chance that I would see “ARW 357” entitles one to win $1 tril- Perspective that particular one tonight? Amazing!” lion, then one must admit that all other Page 345, 346 Tom Dunne If the universe averages one planet license plates are worthless. We don’t Adapting Your Body Clock with intelligent life per galaxy, Earth- know whether the collection of intelli- to a 24-Hour Society lings would never detect other intelligent molecules here on Earth is so very Pages 350, 352 Barbara Aulicino gent beings but would nonetheless not particular, but it might be. be special in any way. In other words, We moderns are becoming accus- The Persistence and Peril of Misinformation one of 100 billion examples of intel- tomed to living with the realization Page 373 Michele Rosenthal ligent life in the universe is hardly spe- that some things are fundamentally cial. Frankly, the notion that humans not knowable: quantum mechanical are special is still theological. predictions, the outcome of determin- istic but chaotic systems, and events John Foster in the universe beyond our (receding) Columbus, Ohio cosmic horizon are examples. My article asks the reader to puzzle Dr. Smith responds: over three consequences of the limits of The “ad hoc fallacy” that Feynman il- knowing (and I talk more about these How to Write to American Scientist lustrates is not applicable to this situa- matters in the 2016 Zygon article I cite). Brief letters commenting on articles tion. “The state” cited in the example (1) Living with uncertainty: From what appearing in the magazine are wel- has millions of other license plates, we do know, for hundreds or thousands comed. The editors reserve the right and each one is indeed equally “amaz- of human generations (maybe even lon- to edit submissions. Please include ing” a priori. But the universe has no ger) we are likely to be the only intel- an email address if possible. Address: other intelligent life we have seen (nor ligent beings around, though we prob- Letters to the Editors, P.O. Box 13975, do we know whether any exists). We ably will not know for sure that we are. Research Triangle Park, NC 27709 or are an example of one. If a person re- (2) Recognizing beliefs: Yes, we might [email protected].______

324 American Scientist, Volume 105

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Spotlight

Computer programs running ad- A Peek at Proprietary Algorithms vanced machine-learning algorithms are now everywhere, and are making deci- Software increasingly determines what people see online or even how long sions about people for which we often have little or no recourse. Go shopping they might spend in jail, but few can access how such programs work. online, and algorithms decide which products you see and what special deals you might be offered—and which are Let’s say you start using a music stream- email from spam, or even helping busi- withheld. Apply to a university, and an ing service online. You pick a few songs nesses sort the flood of résumés received algorithm may determine if a human you like, and the site creates a playlist in response to an advertisement. even sees your admissions essays. In of similar music for you based on that To complete such tasks, software fol- New York City and Santa Cruz, Cali- input, using its huge database of infor- lows algorithms, which have been part of fornia, among other places, predictive mation classifying songs into different computing since the dawn of computer policing algorithms may determine how genres, along with data about other us- science: Ada Lovelace wrote the first often the police patrol a neighborhood. ers’ likes and dislikes. Each time the ser- one back in 1840. More recently, how- And if you commit a crime in Wiscon- vice plays a song, you rate it, and the ever, the term algorithm has evolved to sin, an algorithm might determine how service refines its statistical model of mean “a self-contained step-by-step set much time you spend in prison. your preferences. This is machine learn- of operations that computers and other These uses of algorithms all share ing at work, and it’s one of computing’s ‘smart’ devices carry out to perform several important characteristics. Like fundamental tools for helping people calculation, data processing, and auto- the music service scenario, they all ap- make choices in the face of information mated reasoning tasks,” according to the pear to be based on advanced statistical overload, no matter whether the task in- public policy council for the Association machine-learning techniques, devel- volves choosing songs in a catalog, clas- for Computing Machinery (ACM), the oped over the past two decades, which sifying the overflow of posts and photo- world’s largest educational and scientific use large amounts of training data to graphs on social media, filtering wanted computing society. create models that can then make predictions or perform classifications. In addition, these algorithms are propri- Principles for Algorithmic Transparency and Accountability etary: So far, the public (or regulatory 1. Awareness: Owners, designers, builders, users, and other stakeholders of officials acting on the public’s behalf) analytic systems should be aware of the possible biases involved in their design, has no right to inspect algorithmic implementation, and use and the potential harm that biases can cause to implementations or the training data, individuals and society. even when the algorithms are used for 2. Access and Redress: Regulators should encourage the adoption of mechanisms public purposes. And finally, in many that enable questioning and redress for individuals and groups that are cases, the algorithm is being used by an adversely affected by algorithmically informed decisions. organization with institutional power, 3. Accountability: Institutions should be held responsible for decisions made by to make decisions about people who the algorithms that they use, even if it is not feasible to explain in detail how frequently have no right to appeal if the the algorithms produce their results. algorithm makes a mistake. 4. Explanation: Systems and institutions that use algorithmic decision-making are On September 14, the ACM’s U.S. encouraged to produce explanations regarding both the procedures followed Public Policy Council (USACM) held a by the algorithm and the speciﬁc decisions that are made. This is particularly panel discussion at the National Press important in public policy contexts. Club in Washington, D.C., to discuss the 5. Data Provenance: A description of the way in which the training data was effect of algorithmic decision-making on collected should be maintained by the builders of the algorithms, accompanied society and the technical underpinnings by an exploration of the potential biases induced by the human or algorithmic of algorithmic models. I moderated the data-gathering process. Public scrutiny of the data provides maximum opportu- panel, and I cochair the USACM’s work- nity for corrections. However, concerns over privacy, protecting trade secrets, or revelation of analytics that might allow malicious actors to game the system ing group on Algorithmic Transparency can justify restricting access to qualiﬁed and authorized individuals. and Accountability (ATA). 6. Auditability: Models, algorithms, data, and decisions should be recorded so that Jeanna Matthews, an associate pro- they can be audited in cases where harm is suspected. fessor of computer science at Clarkson University in New York and also a co- 7. Validation and Testing: Institutions should use rigorous methods to validate their models and document those methods and results. In particular, they chair of the USACM group, opened should routinely perform tests to assess and determine whether the model the panel’s discussion by introducing generates discriminatory harm. Institutions are encouraged to make the results the “Principles for Algorithmic Trans- of such tests public. parency and Accountability” (see box) Source: https://www.acm.org/binaries/content/assets/public-policy/2017_usacm_statement_algorithms.pdf______that USACM issued earlier this year. Modeled on the various principles of

326 American Scientist, Volume 105

fair information practice developed Legal Robot’s advantages, he says, is known biases. In other cases, algorithms by privacy regulators worldwide over the way it has collected and labeled its have been shown to have unintended the past 40 years, these principles are training data, instead of the actual algo- consequences, such as causing users to designed to provide a framework for rithms. For example, many programs see on social media only news that con- thinking about the challenges posed by that were developed to process English forms to their own political leanings, or the increasing use of algorithms in our fail when presented with legal docu- repeatedly sending police to the same society. The seven principles address ments, because the vocabulary and style neighborhood because there were no re- many of the concerns that have been of language usage is so different. ports of crime in others. voiced about the growing use of algo- There is certainly a growing interest rithms, without placing limits on the Algorithmic Bias among computer scientists and academ- possible beneficial uses of algorithms Geoff Cohen, a vice president at Stroz ics in developing approaches for algo- currently being explored. Friedberg, an Aon company, has per- rithmic transparency and accountability. Nicholas Diakopoulos, an assistant formed many computer forensic inves- Since 2014, for example, a workshop professor at Northwestern University, tigations of algorithms used by com- called Fairness, Accuracy, and Transpar- spoke about his website, Algorithm panies. He said that in recent years, ency in Machine Learning has explored Tips (http://algorithmtips.org/),______which U.S. patent law has weakened while this topic with significant mathematical tracks the growing use of algorithms by legislation regarding trade secrets has rigor. Increasingly, academics are reach- the U.S. government. The website aims become more powerful, and many ing out to corporations and policy mak- to promote accountability and transpar- companies have reacted by trying to ers, with the hope of establishing norms ency, and specifically to assist investiga- keep their algorithms more secret. But so society can benefit from algorithms tive journalists in writing about these inspection is possible, Cohen said, add- while preventing individuals from being topics. The database contained more ing that inspection typically happens inappropriately harmed by them. than 150 algorithms in September. when an algorithmic-based company With the rise of the information Dan Rubins, one of the two industry is being considered for acquisition or economy, it would be unworkable to representatives on the panel, is cofound- is the subject of a lawsuit. In the future, go back to a world in which nothing er of Legal Robot, an artificial intelli- government regulators might instead is filtered. Without algorithmic assis- gence startup that is using algorithms perform such inspections. tance, social media, Internet search en- to analyze case law and contracts. Ru- Finally, Ansgar Koene, chair of a Stan- gines, and even email would all be un- bins said that his company is using the dard for Algorithm Bias Considerations usable. Companies are now exploring ATA principles as the framework for the working group under the auspices of the ways of using algorithms to filter not transparency report that Legal Robot is Institute for Electrical and Electronics just spam, but also fake news and even publishing on its website. It is possible Engineers (IEEE), discussed the efforts hate speech. Just how far such filtering for companies to be open about how under way to create an international goes, and whether it is possible to turn their technology works without giving standard that organizations could use it off, needs to be the subject of public up commercial advantage, Rubins said, to understand and eliminate uninten- debate. —Simson L. Garfinkel but doing so requires focusing on where tional algorithmic bias in their offerings. the company’s added value happens to For instance, there has been increased Simson L. Garfinkel is an adjunct faculty member be. For example, he said, it can be dif- attention to cases in which algorithms at George Mason University, where he teach digi- ficult to move algorithms from one do- have developed “racist” classifying ten- tal forensics. He is the author of Database Na- main to another, because the training dencies, some of which could be tied to tion: The Death of Privacy in the 21st Century data may not be representative. One of underlying data sets that contained un- (O’Reilly, 2000). Internet: https://simson.net/

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www.americanscientist.org 2017 November–December 327

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www.americanscientist.orgFor an animated version of this infographic, go to at www.amsci.org. 2017 November–December 329

First Person: Sally C. Seidel

Sally C. Seidel is the faculty member of the University of New Mexico’s Collider Physics Group and a collaborator on the ATLAS experiment at the Large Hadron Collider housed at CERN, the European Organization for Nuclear Research, in Switzerland. The ATLAS experiment focuses on activity involving massive particles and was part of the effort to discover of the Higgs boson in 2012. Seidel’s research focuses on improving the understanding of heavy quark bound states, which in turn can help to elucidate the strong force, one of the four fundamental forces of nature. Her group also works on developing particle-tracking detectors. Seidel, one of Sigma Xi’s Distinguished Lecturers, spoke with editor-in-chief Fenella Saunders about her research.

How many particles do physicists What are the strong force and the think are out there? weak force? If we are talking about the most funda- The strong force is the strongest of the mental particles, there are only about fundamental forces, and it’s the one a dozen, the quarks and the leptons that binds the quarks into a nucleus. and so forth. Often particle physicists It’s the one that is able to overcome heavier quarks as signatures of those. speak somewhat casually about par- the repulsion that the quarks that have The bottom quark, in particular, is the ticles, and we include what we would the same electromagnetic charge oth- second heaviest quark. We typically think of as bound states, combinations erwise experience and which would look for signatures that involve a bottom of quarks and so forth. In that case, otherwise cause the nucleus to disin- quark for a number of reasons—for ex- there are hundreds of them. tegrate. The weak force is something ample, because its coupling to the Higgs entirely different. It’s one of the forc- boson is the strongest. Typically, it’s one What is the difference between es that allows quarks and leptons to of the easier signatures to reconstruct. fundamental particles and something change their identity, and it’s at the like bound states, or particles that are basis of radioactive decay. What did you find in your study that made from other particles? combined two quarks? The fundamental particles, as far as we What do you see as the purpose of a The University of New Mexico group know, are typically pointlike objects. particle collider? contributed an analysis published by They might have mass, but sometimes The purpose of a particle collider is to the ATLAS experiment, that involved they don’t have any physical dimen- collect a lot of energy at a very small the discovery of the first excited state sion. The particles that are like protons point, and we do that by colliding two of the BC meson, which is a bound are physically extended, and when we particles that are carrying a lot of en- state of a bottom and a charm quark. collide them in colliders like the Large ergy. Mostly these particles are carrying Hadron Collider, we can determine that energy in the form of their momen- This study described the excited state that they actually have structure. tum, and some of it in the form of their as being almost like one of the quarks mass. Typically the moment of colli- was orbiting the other, like an elec- How can a fundamental particle have sion creates a little microscopic fireball, tron in an atom. Is that accurate? mass, but no volume? Can you explain which evolves according to the laws That’s a reasonable model. One could how that works? of nature. Then, we look and see what think of the bottom quark as being I cannot. It’s a mystery. That’s some- nature produces when you give it that so heavy that the motion of the two thing we’re still working on. much energy. In that sense, we are rep- particles relative to each other in the licating a tiny Big Bang sort of event. bound state might be approximately Is there a defining line between a nonrelativistic. particle and a force? For instance, be- What particles is your group studying? cause there are certain particles that Members of my group are part of the If you’re talking about an excited are responsible for forces, where does ATLAS Experiment at the Large Hadron state, is it analogous to the orbitals that defining line happen? Collider. There are four general-purpose of an electron being moved up to an It is the case that some of the particles experiments at the LHC, and ATLAS excited state? seem in nature to be constituents of is one of them. Within the collabora- Yes. Our initial motivating interest was physical bodies or things, like the pro- tion, there are people who are study- to learn what bound states can be sus- ton, and some of them seem to have ing the Higgs boson, properties of the tained in nature, which may give us the role of transmitting forces. We top quark, people who are searching for an opportunity to understand better are able to relate the photon, which new exotic particles that have properties how the strong force works and what is the particle of light, as also being that might help us see some unifying the binding principles of the strong the transmitter of the electromagnetic principle in nature. My group is inter- force are. We’re experimentalists, so force. There are particles like that for ested in searching for new particles, new we made the measurement. We’re not the strong force, the weak force, and principles, and new properties, and we, theorists, but in principle theorists so forth. particularly historically, have used the who build quantum chromodynam-

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ics models might use the information Someone might wake up in the morning together, moving forward together of the mass of this particle combined ing and connect to a meeting and talk to toward a solution. with other bound states to infer some 20 people about a technology that’s in features of the strong interaction. development. Then they might have a What is it like to work with such an video conference with a different group international team? Many scientists collaborate on work of 15 or 20 people and talk about an anal- The collaboration draws upon expertise at the Large Hadron Collider. What are ysis that’s searching for a new particle, almost without consideration of national the advantages of working in large and then maybe later in the day talk with borders. A typical meeting that I might collaborations? yet some other small group, maybe 15 or have with collaborators does not require There are four collaborations on the so people about some other new devel- me usually to travel any place other than Large Hadron Collider. The ATLAS opment, maybe a new method for data as far as my laptop, where I can run collaboration, the one that I work on, storage, data reconstruction, electronics, some video conferencing software, and has 3,000 people. The members of something like that. I may connect and meet with 20 people the collaboration form subcollabora- In the end, the fact that there are who are in 20 different locations, and tions so that people who have related 3,000 people is barely visible to a typi- I may not even know where they are, expertise, people who naturally will cal collaborator. We have very small what their nationality is, or where they’re support, enhance, and stimulate the and tightly networked communities physically connecting from. We’re just work of one another, work together. that we work within. That seems to working together on the science. People who do, for example, particle have evolved naturally. That’s not tracking, as the University of New imposed by the collaboration. It’s a What advice would you give to stu- Mexico does, form smaller groups, natural way that scientists work. It’s dents working on a PhD? and then within particle tracking good for the students, because they I think a student who has decided to there are people who are interested in find themselves working in a commu- attempt a PhD should select the single smaller and smaller, more and more nity that is largely without any hierar- topic that they think is most important specific aspects of that topic, until in chy of age or experience. There could and most interesting to them. If you’re the end the number of people who be people who are graduate students working every day on something that were talking to each other about a who are communicating with people is the most important thing to you, particular question may be only five who are very experienced, distin- it’s the easiest thing in the world to people or may be only 15 or 30 people, guished members of the community, do. You don’t feel conflicted about it, despite the fact that there are 3,000 of all talking about the same problem, and you feel encouraged by the worth- us in the entire collaboration. same questions, and everyone grow- whileness of the topic.

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www.americanscientist.org 2017 November–December 331

Sightings

Ao RCL

RV NCL

AVCA

LBB MA

LPN

Seeing the Heart’s Power

The first 3D imaging of the intricate cardiac conduction system provides new detail for researchers and surgeons.

ven in the fast-paced world of digital imaging, it Replacing thin-slicing and tissue-staining techniques, which took seven years for researchers to develop the have been in use for more than a century with light micros- technique to make these three-dimensional (3D) copy, is also not an option, Jarvis says. That’s because 3D images (above). Manchester University’s Halina Do- imaging of an intact heart provides no interior access to the Ebrzynski, Liverpool John Moores University’s Jonathan tissue to label particular proteins, which is the key to under- Jarvis in the United Kingdom, and a team of international standing what each population of heart cells is doing. researchers undertook the effort because they thought high- But results from the new technique already are improv- resolution 3D imaging of an intact heart would provide ing upon previous research. For example, tracing the car- new insights into how the organ works. diac conduction system previously required researchers to “We also pretty soon realized that in the 3D image,” says follow the route layer-by-layer through perhaps hundreds Jarvis, “we could tell the difference between the working of thin slices of cardiac tissue from the same heart. With the myocardium—that’s the cardiomyocytes that produce the team’s 3D images has come the understanding that “com- pumping action—and the cardiac conduction system, which monly accepted anatomical representations [of the cardiac is the electrical side of the heart.” The conduction system is conduction system] are oversimplified,” the researchers made from specialized cardiomyocytes. Segmented conduc- write in the August 2017 issue of Scientific Reports. tion networks of these cells are represented by different col- Although the imaging technique is new, the technology ors and overlaid on semitransparent heart images. behind it is not: Microcomputed tomography (micro-CT) Dobrzynski says the group hopes the technique will also scans have been in use for decades. Initially, micro-CT scan- help heart surgeons better visualize the locations of different ners could only image the human body’s harder tissues, components of the heart’s conduction system. The technique such as bone and teeth, because those tissues better absorb is not intended to replace any tools and imaging guides. the x-rays that give the technology its imaging power.

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RBB LCL RVOT RCL Ao NCL

FO AVCA

RPN TA RV

Robert S. Stephenson et al. In each pair of images, colored diagrams represent the segmented blood to the rest of the body. Other parts of the cardiac conduction network of the cardiac conduction system, displayed both sepa- system and visible anatomy include the aortic root (Ao), atrioven- rately and overlaying a high-resolution microcomputed tomogra- tricular conduction axis (AVCA), coronary sinus (CS), fossa ovale phy scan. The intact heart has been sliced virtually in half and is (FO), left/right bundle branch (LBB/RBB), hinge of left/right coro- presented semitransparently. The right half (above) has the thin- nary leaflet (LCL/RCL), left/right Purkinje network (LPN/RPN), ner right ventricle (RV) for pumping blood only to the lungs. The mitral annulus (MA), hinge of noncoronary leaflet (NCL), right left half (far left) has the thicker left ventricle (LV) for pumping ventricular outflow tract (RVOT), and tricuspid annulus (TA).

Imaging softer tissues has been more challenging, also too does the amount of iodine required, because iodine is though many labs around the world have developed mul- toxic at such levels. Ideally, imaging techniques could guide tiple techniques for doing so by injecting soft tissue with surgeons performing real-time operations on patients, dur- contrast agents that better absorb x-rays. That means those ing which the cardiac conduction system is currently in- labs already have access to everything they need to make visible. “It would be very unwise to say that something is such 3D images of intact hearts. “I think we were success- impossible,” Jarvis says, “because the progress in medical ful because we knew how to handle and prepare the tissue imaging has been so spectacular over the last 50 years— very carefully,” says Jarvis, a muscle physiologist. things which we thought were impossible even 10 years Still another challenge in this kind of research is obtaining ago are now possible.” access to normal, intact heart tissue, which is usually reserved With this imaging technique, then, next steps include for heart-transplant patients. With collaborators at the Univer- imaging older and damaged hearts to address whether, sity of Minnesota’s Visible Heart Lab, the team gained access for example, the stretching or scarring of the heart muscle to human hearts that had been intended for use in transplanta- that often occurs in heart-disease patients is associated with tion, but which had not been transplanted for varying reasons. strains on or interruptions to the cardiac conduction system. The team’s experimentation with actual human hearts was In the meantime, the detail from these kinds of post- minimal, though, because they only needed to scale up from mortem scans may be used today for exploring 3D cross- having perfected the imaging technique using the hearts of sections virtually, as shown above, or for printing 3D smaller mammals, including rats. “So you do have to modify models, both of which can aid medical professionals in your technique a little bit,” says Jarvis, such as by allowing a visualizing any cross-section of the heart with the visible longer period of time for the contrast agent to diffuse into the location of the cardiac conduction system. For the 3D human heart tissue. Theirs was an iodine-based agent, and models, Jarvis says, “You have to use a transparent ma- that diffusion took two weeks. terial with some colored material incorporated into the That lengthy diffusion time, of course, makes this par- print, and that is fairly challenging, but we have done it.” ticular technique useful only with post-mortem tissue, but —Robert Frederick

www.americanscientist.orgFor related video and podcast, see the online version of this article at www.amsci.org. 2017 November–December 333

Briefings

n this roundup, digital features microRNAs identified affect plant size and ment for peanut allergies. The study editor Katie L. Burke summarizes color. When present in bee bread fed to participants were given either a daily I notable recent developments in larvae, the microRNAs affect genes that treatment of a probiotic combined with scientiﬁc research, selected from reports delay reproductive development to keep a peanut protein, or a placebo. The trial compiled in the free electronic newslet- worker bees sterile. Further study of en- released preliminary results in 2013, ter Sigma Xi SmartBrief. Online: https://_____ vironmental changes in plants that could showing that after one month of treat- www.smartbrief.com/sigmaxi/index.jsp affect microRNAs could help entomolo- ment 82 percent of children receiving gists understand current problems with the probiotic could eat peanuts. This fol- honeybee health. low-up study shows that four years later, The Birth of a Black Hole 70 percent of the participants in the Astronomers have captured the clearest Zhu, K., et al. Plant microRNAs in larval food treatment group can still ingest peanuts picture yet of the birth of a new black regulate honeybee caste development. PLOS without an adverse reaction. The probi- hole from a catastrophic stellar explosion. Genetics 13(8):e1006946 (August 31) otic used was a bacterium, Lactobacillus Gamma ray bursts are one of the most rhamnosus, which is thought to allay powerful Fish Fossil Doesn’t Fit Family Tree some allergic symptoms. Larger clinical explosions A fossil dating to about 360 million years studies are now needed to determine in the uni- ago, when fish evolved into land-dwelling long-term safety outcomes, say the re- verse and are animals, does not fit clearly in the current searchers at Murdoch Children’s Research short-lived evolutionary tree, because it possesses Institute in Australia. They are also study- (sometimes features of two lineages thought to be ing whether the peanut protein is neces-

NASA/Goddard Space Flight Center NASA/Goddard lasting a few distinct. The new species of lobe-finned sary in conjunction with the probiotic or seconds). So it is challenging to react to fish, called Hongyu chowi, was found in whether the latter is effective alone. one in time to study the comprehensive northern China. The shoulder girdle and event. Using data from several ground- support for the gills of this 1.5-meter- Hsiao, K.-C., et al. Long-term clinical and im- and space-based telescopes, an interna- long ambush predator, resemble those munological effects of probiotic and peanut tional team of astronomers assembled of early four-legged animals and their oral immunotherapy after treatment an unprecedentedly detailed description closest fish relatives, indicating that the cessation: 4-year follow-up of a ran- of a recent gamma-ray burst (called GRB fossil belongs to an extinct group of fish domised, double-blind, placebo-controlled 160625B) that showed up in the sky in called elpistostegids. But other features trial. The Lancet Child & Adolescent Health June 2016. They were able to characterize resemble a group of fish called rhizodonts 1:97–105 (August 15) the emission and jets of the gamma-ray that were thought to have branched off burst to settle some longstanding ques- from a com- Long-Lasting Structural Colors tions about how the explosion and black- mon ancestor Inspired by certain vivid colors in nature, hole formation progress. Immediately before the such as those of some birds and but- after the explosion, the prompt emission lineage that terflies, polymer scientists have figured comes from electrons bouncing around in gave rise to how to make long-lasting a magnetic field. In the following seconds four-legged “structural” colors. or minutes, powerful magnetic fields sur- animals Such colors are rounding the black hole organize emerg- emerged. formed through ing matter and energy into tight jets. Changes in Nature Publishing Group light’s interac- the shoulder girdle and gill bones are tion with nano- Troja, E., et al. Significant and variable linear central to the story of the evolution of structures rather polarization during the prompt optical flash of weight-bearing limbs and jaws charac- than through its

GRB 160625B. Nature 547:425–427 (July 26) teristic of land-dwelling vertebrates. This absorption by a pig- Ming Xiao, University of Akron fish’s mix of features means that either ment. Pigments fade Plants Affect Bee Development different groups of lobe-finned fish, in- when their molecules break down, A new study clarifies how honeybee lar- cluding the rhizodonts, independently so structural colors can be longer lasting. vae develop into worker bees or queens, evolved this shoulder girdle and gill struc- Oddly enough, the researchers used a showing that plants are more important ture, or the rhizodonts are more closely pigment to form the structural color by for controlling bee development than had related to four-legged animals and elpis- changing the nanostructure of clumps been recognized. It’s long been known tostegids than was once thought. of its molecules. The pigment melanin that food influences honeybees’ role in changes skin color in animals and appears the colony—for example, royal jelly is fed Zhu, M., P. E. Ahlberg, W.-J. Zhao, and L.-T. black in its individual nanoparticles. The to larvae that develop into queens—but Jia. A Devonian tetrapod-like fish reveals color was changed from olive to orange it had not been known that worker bees’ substantial parallelism in stem tetrapod evo- to blue by varying the spacing in clusters development is also influenced by an ac- lution. Nature Ecology & Evolution 1:1470– of the nanoparticles using a silica coating tive ingredient in bee bread, their pollen- 1476 (September 4) to limit how closely they pack together. and honey-based food. That ingredient turns out to be a type of microRNA, a Treatment for Peanut Allergy Xiao, M., et al. Bioinspired bright nonirides- short noncoding RNA that plays a regula- A clinical trial with 48 children suggests cent photonic melanin supraballs. Science tory role, derived from plants. The the first successful long-lasting treat- Advances 3(9):e1701151 (September 15)

334 American Scientist, Volume 105

Computing Science

Bitcoins Maybe; Blockchains Likely

The innovative foundations of the cryptocurrency may outlive the currency itself, as its verification method finds applications everywhere.

Peter J. Denning and Ted G. Lewis

n January 3, 2009, Satoshi Na- same coin. This double-spend problem that cannot be hacked by breaking into a kamoto began selling a new plagues all concepts of virtual money. single database fills this bill. form of money and operating Nakamoto wanted a system that could Thus, Nakamoto defined bitcoins as an associated support system ensure that a sum of money can be spent “a chain of digital signatures.” To un- Ocalled the bitcoin cryptocurrency sys- exactly once—no double payments. derstand what he means, consider the tem. The name bitcoin (BTC) comes from it being digital money that can be used like coinage, and the crypto term indicates that the bits are secured by cryptographic methods. The currency has secretive roots: It is still unknown who Nakamoto was, but it may have been Harold Thomas Finney II, a known cryptologist who created a secured transaction system similar to that used in BTC exchanges, and a developer employed Erik Tham / Alamy Stock Photo by the PGP (Pretty Good Privacy) Corporation. (PGP is a protocol widely used in personal encoding keys.) Finney was the first recipient of BTCs in 2009. But we may never know for certain who Nakamoto was, because Finney died in 2014. Bitcoin users purchase paper certificates or plastic cards for the convenience of storing their encryption keys for transactions. Some of the key-storing cards are elaborate and employ The term bitcoin conjures up an image antitampering technologies such as holograms, as in the close-up image of this card. Storage of a real coin encoded as a bit pattern. devices in the form of actual coinlike tokens are also available. The big problem with bit patterns is that the owner can retain a digital copy and Banks already know how to prevent example of Alice wanting to pay 1 BTC try to make another payment with the double payments: A digital transaction to Bob. Alice can create a certificate that is completed by the bank, not the con- says “Alice pays 1 BTC to Bob, signed sumer. The bank has full control over the Alice.” The certificate is signed by Alice’s Peter J. Denning is Distinguished Professor of Com- database of all accounts and can safely secret digital key, which is paired with puter Science and Director of the Cebrowski Institute transfer an amount from the payer to her public digital key that anyone can for information innovation at the Naval Postgraduate the payee accounts. Banking is based on use to validate her ownership. The cer- School in Monterey, California, and editor of ACM Ubiquity. The author’s views expressed here are not trust in the banking system. Nakamoto tificate is a record of a transaction stored necessarily those of his employer or the U.S. Federal rejected the idea of a centralized data- in the ledger of all transactions. Alice’s Government. Ted G. Lewis is a cofounder of the Cen- base, seeking instead a system without a ability to pay is determined by the enter for Homeland Defense and Security at the Naval trusted intermediary or a single point of tire history of all transactions that flow Postgraduate School. Email for Denning: [email protected]______failure. A distributed ledger of accounts to or from her. When the transaction is

www.americanscientist.org 2017 November–December 335

5,000 The value of bitcoins in U.S. dollars over the past year shows extreme volatility. 4,500

4,000 completed, the ledger will show her net worth decreasing by 1 BTC and Bob’s in- 3,500 creasing by 1 BTC. In other words, cryp- 3,000 tographic coins are the value generated by transactions recorded in a ledger. We 2,500 scan the ledger to find out anyone’s net 2,000 worth at any moment of time. The idea of calculating value based 1,500 on a history of transactions is used in

value of bitcoins in US dollars value many places. A familiar example is the 1,000 title to a property. It is a certificate that 500 says, “As of this date, Alice is the sole owner of the property described here; 0 signed, notary.” When Bob wants to buy 9/19/16 12/28/16 4/17/17 7/16/17 10/24/17 the property, the escrow company hires date a title search firm to review all the records of previous sales and liens back to the beginning to validate that Alice is indeed the legitimate sole owner. The trail Does Majority Consensus Work? of transactions on the property is called a chain. Although the current title is an With any distributed ledger, there is a serious problem in deciding which integral part of the chain, the validity of copies of new blocks are valid and which should be discarded. The problem that title depends on the entire history. is complicated by the fact that some of the miners may be dishonest and are Nakamoto’s definition of value is paral- seeking to insert fraudulent blocks that pay them a lot of money. In 2017 lel to this scenario if the title company there were nearly 5,000 miners in the bitcoin blockchain. Nakamoto’s Point- is replaced by a computer system and of-Work (POW) is a clever way of using the computing power of the major- the transactions are all electronic fund ity to overcome a dishonest minority. In addition, mining requires very fast transfers. computers that consume lots of electricity. Miners only get paid when they The records of all bitcoin transactions win the POW race. What happens if one miner becomes so powerful that it are compiled into blocks of about 4 starves out all others? The mining community shrinks to a handful that can megabytes in size. The linked list of all afford very expensive, fast, energy-hungry computing machines. blocks going back to the beginning in In 1982 Lamport, Shostak, and Pease proposed a solution to a very similar 2009 is called a blockchain. Although the problem, called the Byzantine Generals Problem. A general in charge of an blockchain could be stored in a central army wants to distribute attack or retreat orders to N lieutenants. M lieuten- database, Nakamoto wanted to distrib- ants are disloyal and will not relay the orders properly. The loyal lieutenants ute it among many computing nodes in can use a majority vote to decide if the messages they received are legitimate. the network to remove the risk of single Lamport and his colleagues proved that the vote can be trusted only if the point of failure. Thus, there are many honest majority is at least 2N/3, and N must be at least 3M+1. Under those copies of the blockchain in a distributed conditions the minority votes cannot prevail. The figures below illustrate a network of nodes, but the entire chain simple case. The honest lieutenants (green) relay the order correctly; the dis- is protected from tampering by a com- honest ones (red) lie. The honest lieutenants go with the majority vote of the plex arrangement of links made from confirmations. In the left figure, each green node receives votes 2:1 favoring digital signatures and hashes, mathe- attack, and act as the commander ordered. In the right figure, each green matical functions that scramble all the node receives votes 1:1 and cannot reach an affirmative decision to attack. bits of a file into a fixed-length code. A form of majority voting is used to decide which blocks are valid and can be added to the chain. Changing the commander commander contents of a copy in any node without being detected is next to impossible. The bitcoin system comes with user orders orders lieutenants lieutenants interface software called a wallet. A user to attack to attack logs into a wallet and specifies transactions. The wallet handles all the details, such as representing the transactions as signed certificates, broadcasting them into the network, and receiving trans- VOTE VOTE actions from the network that would 2:1 to attack 1:1 to attack (tie) affect the funds in the wallet. The wallet converts currencies such as the U.S.

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dollar into bitcoins through a system of recomputing all the block hashes all The number-of-zeroes parameter in brokers called BTC exchanges. the way to the end of the chain. bitcoin is frequently adjusted so that POW takes an average of about 10 min- Signatures and Hashes Proof of Work utes. That means that a hacker expects In the world of online transactions, two Using an algorithm called a Proof-of- to spend about 10 minutes of comput- concepts are absolutely fundamental: Work (POW), the time to compute a ing time to find a nonce that generates the digital signature and the hash. Us- new hash of a block is made to be time- a valid hash for a fraudulent block. In ing a bitcoin wallet, a user can obtain a consuming and expensive, on purpose turn that means that the hacker has a matched pair of encryption keys (one and for good reason. If the time need- very small chance of overtaking who- public and one private, each consist- ed to make a hash is approximately ever is linking a new valid block to the ing of patterns typically 256 bits long), the basis of a public key cryptosystem. In the blockchain, message secrecy is unimportant, but authenticity is. Al- The value of cryptographic coins ice’s transaction “Pay 1 BTC to Bob” is encoded as “Pay 1 BTC to public-key- is calculated based on a history of of-Bob,” signed with her private key, and submitted to the blockchain. Only transactions recorded in a ledger, similar Bob can “cash” the transaction—in other words, use his secret key to unlock to verifying the title to a property through the transaction. The digital signatures guarantee the validity of the transac- a review of all its previous sales and liens. tions recorded in the ledger. But the signatures do not protect against double spending, which could the same as the time it takes for the chain. Nakamoto set up the system to happen if Alice inserted two identical network to add a new block to the make POW progressively harder (with “pay Bob” transactions into the blockchain, it becomes impossible for a more leading zeroes) so that new nonces chain. The blockchain protocols would hacker to catch up and substitute the are progressively harder to find. Finding not accept Alice’s duplicate transaction, recomputed chain for the original. new nonces becomes impossible when but if Bob can cash them before the pro- The nonce plays a pivotal role in the total number of bitcoins is 21 million. tocols reject the duplicate, Bob gets paid POW. The nonce is not just any num- twice and Alice pays once. Nakamoto ber, but a random number that causes Miners solved this problem by a complex se- the hash of the block to begin with a A miner is a special node that com- ries of cryptographic techniques based certain number of leading zero bits. putes the POW for new blocks pro- on what are called hashing functions. A For example, if the number-of-zeros posed for the chain and builds the hash is the output of a special function parameter is 60, the block hash must blockchain by performing POW and that takes all the bits of a file, scrambles begin with 60 zero bits. The only way adding blocks. It works as follows: them, and condenses the scramble into this format can be met is to find a New transactions are broadcast to a fixed number of bits, typically 256. nonce that, when combined with all all nodes. A well-designed hash function will so the other hashes of the block, yields a completely scramble the original file that block hash beginning with 60 zero bits. Each node collects new transac- altering a single input bit causes most Because hash functions are not invert- tions into a block. bits in the output to change. The hash ible, this process can only be done by function is not invertible: Given the out- repeatedly trying a nonce that is one Each miner node does the POW put, the only way to find the input that larger than the previous nonce. to find a hash for the new block. generated it is an exhaustive search of all possible inputs, which would take block n – 1block n block n + 1 more time than the remaining life of the universe. To guarantee that no one block hash < target can tamper with any transactions in the previous Merkle blockchain, each is entered into the chain nonce hash hash along with its hash. It is easy to verify that a transaction is valid simply by computing its hash and comparing with hash34 hash12 the hash stored with the transaction. hash4 hash3 hash2 hash1 The hash of a block of transactions in the chain can be computed by com- trans4 trans3 trans2 trans1 bining the hash of the previous block with the hashes of all transactions in the current block and a nonce (a ran- A blockchain is a linked list of blocks, each of which contains transactions, a previous block’s dom number used once). This method hash (a unique string of bits that is generated based on the bits in the file), a Merkle hash of the of linking blocks is called a ratchet be- transactions (which is a way to repeatedly hash pairs of hashes until only a single, total hash cause any change to a block requires remains), and a nonce or random number produced as a byproduct of Proof-of-Work (POW).

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end of chain ed. These issues include performance, trust, volatility of cryptocurrencies, reli- ability, and overall world energy cost from operating blockchains.

Performance A1 A2 A3 A4 A5 A6 A7 By design, updates in the Nakamoto blockchain are computationally intensive. The result is that the overall throughput of the bitcoin network is about 7 transactions per second, and it B4 B5 B6 B7 takes about 10 minutes to close a transaction after it is submitted. In contrast, credit card companies and banks to- A normal blockchain of valid transactions consists of blocks A1 to A7. A hacker tries to insert day can handle thousands of transac- a fraudulent block B4. Because of the use of a Proof-of-Work (POW) algorithm, the hacker has tions every second, and give almost to fork the chain by copying all the blocks from A4 to A7, and recomputing their hashes. The instantaneous response times to close POW makes the time to recompute a block’s hash the same as the time to add the next new transactions. On August 1, 2017, the block to the chain. The hacker can never catch up and is unable to force the forked chain to BTC blockchain experienced a hard substitute for the correct chain. fork when the block size was changed from 1 megabyte to 4 megabytes, and Different miners working in par- can also be used to populate the chain a lighter version of BTC called bitcoin allel will find different nonces with fraudulent blocks. cash was created to improve transac- and hashes. To prevent such fraud, Nakamo- tion processing speed. When a miner node completes a to’s system depends heavily on self- In addition to massive computational POW, it broadcasts the block and interest rather than trust. He claims, power, the blockchain requires massive its hash to all nodes. “If a greedy attacker is able to assem- storage. In 2017, the blockchain occu- ble more CPU power than all the hon- pied 100 gigabytes, and it took many A node validates the new block by est nodes, he would have to choose days to download and verify a new verifying the signatures and hash- between using it to defraud people copy on a personal computer. This es of all the transactions and then by stealing back his payments, or us- blockchain clearly cannot scale up to the adds the block to its local copy of ing it to generate new coins. He ought size that would be needed to support a the blockchain. After accepting a block, a miner node begins working on creating Blockchain verification is intended to be the next block in the chain, using the hash of the accepted block as computationally expensive, which means the previous hash. All the other miners drop their attempts to it is also energy intensive. validate a block and start over to mine the next block. to find it more profitable to play by cryptocurrency with billions of users. The first miner to find a hash for the rules, such rules that favor him There are at least a dozen alterna- the new block gets a reward of a with more new coins than everyone tive blockchain architectures that all few bitcoins. else combined, than to undermine the aim to reduce the computational work system and the validity of his own to verify a new block and add it to Miners are constantly looking for wealth.” But Nakamoto overlooked the chain. The most promising is Ethe- ways to amass so much computing the possibility of a 51-percent cartel. reum, which uses a Proof-of-Stake (POS) power that they can always win the rather than Proof-of-Work: In POS, race to add the next block to the chain, Blockchain Spinoffs nodes with larger amounts of currency and thereby reap the reward. Mining is Although blockchains were invented get greater weight in a vote determin- such a big business that there are now for the bitcoin currency, many see their ing when a new block will be added special-purpose chips for computing potential for other purposes, such as to the chain. But these alternative cur- hashes. This environment encourages dealing with public and organization- rencies appear to be more susceptible the formation of a cartel of miners, who al records in a decentralized network. than bitcoin to a 51-percent attack. It together control 51 percent or more of There are proposals to move the Inter- will take some time to test out all these the computing power in the network, net’s DNS (Domain Name System) to alternatives to find out which ones are to collaborate on producing new blocks a blockchain, which would be much reliable, scalable, and hackproof. and share the rewards. With at least 51 faster as well as resilient against out- Another alternative is being ex- percent of the computing power, the ages. Despite the enthusiasm, there are plored by the Hyperledger.org proj- group can complete POW faster than also a number of important issues that ect, which aims to produce an open any nodes in the network. This scenario give pause and will need resolution be- architecture for business blockchains. is called a 51-percent attack because it fore blockchains will be widely adopt- They have defined a set of layers, each

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providing a critical function. One of nential increase in bitcoin exchange Coining a New System the most critical to performance is the rates during the 2016–2017 seasons It seems most likely that bitcoins will consensus layer, which adds a pro- may be a reaction to political changes remain limited in use until there are posed new block to the chain once a in Europe and the United States. affirmative answers to questions about consensus of the nodes is achieved. Economist William Luther of Ken- their security and resilience, but such They are experimenting with alterna- yon College in Ohio claims that bitcoin solutions are not obvious right now. tives to POW that are much less com- has failed to catch on because of the On the other hand, the idea of block- putationally intensive, such as using a steep switching cost in moving away chain ratcheting is already spreading lottery to select a node that then pro- from government-backed currencies. to related technologies and could grow vides the proposed new block or ac- Bitcoin adopters need to have their further, assuming some of its issues cepting the proposed block only if a own copy of the ledger (taking up 100 can be resolved. For example, the Sig- majority vote for it. These new options megabytes in 2017) and enough com- nal Protocol used by social networks are possible when assumptions about puting power to do the hashes and such as Instagram and Facebook em- trust are relaxed. In Nakamoto’s net- signatures rapidly. And even if they do ploys ratchets inspired by blockchain work, no one trusts anyone; the system make the switch, the volatility could technology. It’s another case where the is designed to achieve consensus on easily rob them of their wealth. adoption of a technology has taken additions to the blockchain when each an unexpected turn, and determin- node is anonymous and considers the Energy Cost ing which new developments will other nodes as untrustworthy. In the We think the biggest problem of all is in stand the test of time can be difficult new system, people within an orga- the POW idea itself. It is intended to be to predict. nization may reveal themselves and computationally expensive, even when have a greater basic level of trust. the world’s most powerful computers Bibliography and special chips are deployed. This Cocco, L., and M. Marchesi. Modeling and Trust computation load means that POW is Simulation of the economics of mining in Miners of the blockchain network are be- also energy intensive. Various estimates the bitcoin market. ______https://arxiv.org/ pdf/1605.01354v1.pdf. coming highly specialized professionals are that the current electrical demands ______Franco, P. 2015. Understanding Bitcoin: Cryptog- relying on expensive chips specifically of world data centers consume about 7 raphy, Engineering, and Economics. Chichester, designed for POW. Because many ordi- percent of the world’s electricity. Mas- UK: John Wiley & Sons. nary users cannot afford to be miners, sive use of blockchains would signifi- Lamport, L., R. Shostak, and M. Pease. 1982. The much of the computing power is con- cantly boost that total. Do we want a Byzantine Generals Problem. ACM Transac- centrating in a relatively small minority system of currencies that requires so tions on Programming Languages and Systems 4:382–401. doi:10.1145/357172.357176. of the network. After a recent $79 million much of the planet’s energy to power? Luther, W. J. 2013. Cryptocurrencies, network heist of Ethereum coins, the miners pro- Or that becomes ever more susceptible effects, and switching costs. Mercatus Cen- posed to collaborate so that they could to total collapse if someone finds a way ter Working Paper No. 13–17. ______https://ssrn. go back and revise the blockchain to de- to shut down the power grids? com/abstract=2295134. lete the transactions performing the heist. Although this act would deprive the criminals of their bounty, it also would undermine trust in the network. What else might a coalition of miners do?

Volatility The exchange rates for cryptocurrencies can be quite volatile, which encourages speculators to buy up bitcoins and hoard them. The satura- tion limit of 21 million BTC adds to the volatility because of the scarcity of the coins. There is no central government bank monitoring the currency and keeping its value stable. For this reason, the Chinese government has banned speculation in ICOs (Initial Coin Offers) that exchange cryptocurrency for investment in startups. The volatility of bitcoin values is likely to be correlated with social and political uncertainty, especially as confidence in government declines. At one point, rumors that China held most bitcoins in circulation led to price spikes because of fears that China might devalue its currency. The expo-

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Engineering

Problematic Pedestrian Bridges

Crowds walking, running, dancing, and even standing still on these spans often prove to be the ultimate test of a structure’s soundness.

Henry Petroski

edestrian bridges are ubiqui- accompanied by friction forces that pre- of countervailing movements) were tous, but most are unremark- vent a foot from slipping and sliding. added to the bridge in London to keep able and anonymous. They The component of friction force point- in check any motion that developed. span interstate highways to ing straight ahead is what propels the For whatever reason, even highly Pcarry hiking and biking trails over walker forward; the effect of its reaction experienced engineers sometimes fail heavy traffic, thus keeping walkers, on a bridge deck is usually negligible. to take into account all the possible runners, and cyclists safely above the The sideways component of the friction dynamic effects of people walking, fray. Some pedestrian bridges rise to force exerted on the bridge deck, how- running, marching, and dancing on prominence, however, often because of ever, can move it left and right. bridges. Perhaps pedestrian bridges controversies or problems associated Engineers generally check the nat- are not considered as seriously as the with their location, design, construc- ural frequency of a structural design heavier, wider, and usually much lon- tion, or performance. against the typical frequency of the ger and grander structures that carry This was the case with the now- vertical tramp of human footsteps, railroad and vehicle traffic. infamous London Millennium Bridge which can range from one to four cy- Yet even crowds of people stand- connecting across the River Thames cles per second. Unfortunately, in the ing still have proven time and again to the tourist areas of St. Paul’s Cathedral case of the London Millennium Bridge, represent the ultimate test of a bridge and Tate Modern art museum, housed engineers neglected to check the struc- structure. In Missouri, the Kansas City in the repurposed Bankside Power Sta- ture’s natural frequency against the Hyatt Regency Hotel’s elevated walk- tion. As originally built and opened in frequency of sidewise motion, which ways, which were essentially bridges 2000, the bridge was the result of an is typically about half that of footfalls, spanning the building’s atrium, col- imposed collaboration among an engi- because pushing off sideways with the lapsed in 1981 under the sheer weight neer, an architect, and an artist. Within right (or left) foot occurs only half as of people, some evidently moving to three days of its opening, the low- frequently as the two feet alternately the music of a band playing for a tea slung suspension bridge was closed coming down on the pavement. Ig- dance. The tragedy claimed 114 lives because it swayed too much under the noring this lower-frequency excitation and injured many more. The structural crowds of people who walked across it of human footsteps set the unusually engineers responsible for the design in synchrony with its movement. low-slung suspended bridge deck de- were found negligent in approving a The problem was traced to neglect- sign into a swaying motion and made suggested change in a support detail ing to consider that as people walk, it unsuitable for its purpose. without giving it sufficient thought. they naturally exert on the pavement To celebrate the 50th anniversary of sidewise forces, in addition to the more Elephants and Human Stampedes the opening day of the Golden Gate commonly recognized vertical ones as- There is indeed a long history of bridg- Bridge in San Francisco in 1987, the sociated with their feet pushing down- es moving too much beneath the feet structure was closed to vehicle traf- ward. The downward pushes are re- of pedestrians and marchers. Just the fic, and pedestrians were allowed to acted to, according to Newton’s Third year before the London Millennium crowd onto virtually every square Law, by an upward force from the Bridge problem came to light, the foot of the bridge’s roadway and pavement. And such vertical forces are new passerelle Solférino (now called sidewalks. The resulting shoulder- passerelle Léopold-Sédar-Senghora) in to-shoulder mass of celebrants rep- Paris behaved poorly. In each case, the resented the largest load the bridge Henry Petroski is the Aleksandar S. Vesic Profes- sor of Civil Engineering and a professor of his- structure had to be modified to alter its had experienced in its half-century of tory at Duke University. His most recent book is natural frequency that coincided with operation, a condition evidently not The Road Taken: The History and Future of that of pedestrian footfalls. In addi- anticipated by its design engineers. America’s Infrastructure (Bloomsbury, 2016). tion, tuned mass dampers (devices that The center of the bridge’s roadway, Address: Box 90287, Durham, NC 27708. ameliorate vibrations, often by means which under normal circumstances

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has a distinct camber to it, flattened ning leg of the annual New York City adjacent to the famous structure was out noticeably, and engineers observ- Marathon, whose route crosses sev- dense with piers, to and from which ing the phenomenon expressed genu- eral bridges to touch each of the city’s goods from all around the world were ine concern. Thankfully, the Golden five boroughs. loaded onto and off of ships. This Gate Bridge survived its trial by pe- Pedestrians or runners have never commerce was in part what made destrian, and subsequent anniversa- caused any of these great suspension the East River, over which the great ries have not been the free-for-all of bridges to move in an unsafe manner, bridge spans, so busy, and it was pre- the 50th. It is reasonable to expect that to my knowledge, but an unfortunate cisely to alleviate some of the conges- limitations on the crowd size will be incident occurred just a week after the tion on the water that the bridge was imposed when the 100th anniversary Brooklyn Bridge opened in 1883. A ru- supported financially, politically, and is celebrated. mor that the new bridge was about popularly. The Brooklyn waterfront The most recent debacle involving a to collapse, with about 20,000 people began to change dramatically in the bridge and the people designing and crowded onto its walkway, touched 1950s with the introduction of con- using it occurred in New York City, in off a panic that resulted in a stampede, tainerized shipping, which marked the shadow of the Brooklyn Bridge. leading to the death of a dozen peo- the development of larger ships re- Ironically, that historic 130-year-old ple and the injury of three times that quiring larger piers. In time, much of structure carries one of the most cel- many. The bridge was never in any the dockside commerce was driven ebrated and successful pedestrian danger of collapse, but some people across the harbor into Newark Bay. All cargo ship operations in the vicinity of the Brooklyn Bridge ended in 1983, the centennial of the structure’s opening. With the piers obsolete and abandoned, there remained the question of what to do with the properties. The idea for a Brooklyn Bridge Park was pushed in earnest when the Port Author- ity of New York and New Jersey announced plans to sell the piers for commercial development, a

Brian Jeffery Beggerly/Wikimedia Commons move that could The London Millenium Bridge, which opened in 2000, was the first new bridge to cross the Thames River in more than have resulted a century, and was London’s first dedicated pedestrian bridge. Within a few days, it closed because it swayed too much in high-rises from the sideways load of a crowd’s footsteps. After repairs, the bridge no longer wobbled and was reopened in 2002. blocking views from preexist- walkways in the world. The walkway remained unconvinced until the cir- ing buildings of the river, its bridges, of the Brooklyn Bridge was thought- cus came to town the following year and lower Manhattan. Activists pre- fully designed to rise above the traffic and the great showman P. T. Barnum vailed, and in 2002 an agreement was on either side, thus giving amblers a led a parade of 21 elephants across the reached to create a Brooklyn Bridge clear view of the surroundings. De- structure. It had long been believed Park on 85 acres, some reaching out pending upon which way one transits that by some sixth sense even a single into the East River and incorporating the bridge, there are spectacular and elephant would balk at setting foot on the remains of the obsolete Brooklyn virtually unobstructed views of New an unsafe bridge. Indeed, an elephant piers. Parts of the parkland would be York Harbor, the Statue of Liberty, the or two was often called upon to test a landfill built from soil excavated from Manhattan skyline, and other mas- new bridge to prove its safety. the construction site of the new One sive New York City bridges, including World Trade Center, also known as the Manhattan to the north and the Aesthetics and Views Freedom Tower, located south of the Verrazano-Narrows to the south. This Even before the Brooklyn Bridge was site of the twin towers that terrorists latter bridge is the site for the begin- completed and tested, the waterfront destroyed in 2001.

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community when in 2009 he was the recipient of one of the genius grants from the John D. and Catherine T. MacArthur Foundation, which identifies him as “a structural engineer who is leading the design of elegant and enduring bridges around the world.” Besides being a MacArthur Fellow, Zoli is a visiting lecturer at Princeton University, his alma mater, and an adjunct professor at Columbia Univer- sity. He was the principal designer of the Squibb Park Bridge. Zoli’s vision for the Squibb Park Bridge was at the same time pedestrian and exotic. In plan, it resembles, depending on your point of view, an elongated M or W or a distorted Greek Ȉ. Any way you look from it, the zig- zag of its walkway gives the person walking down to Brooklyn Bridge Park changing views, from lower Manhattan across the river to the Brooklyn Bridge just upriver. The feel underfoot of the @Painet Inc./Alamy Stock Photo 120-meter-long bridge was intended by During the 50th anniversary of the Golden Gate Bridge in 1987, the bridge was closed to vehicles, design to evoke the sensation of walk- and pedestrians were permitted to pack the span, adding far more weight on the bridge than ing across the kind of bouncy bridge would any vehicle traffic. Engineers expressed concern, but fortunately the structure held. often found in state parks. But the Squibb Park structure is not Construction of the park began in waterways in heavily industrialized a conventional suspension bridge. It 2008, and it was opened in stages. As parts of cities. Various types of inten- has no network of vertical suspenders attractive as the park was to people tionally moveable bridges swing, rise, dropping from curving steel cables to living in the neighborhood, they were or lift out of the way to allow ships to support its walkway of unconvention- cut off from easy access to it by the pass along the rivers, canals, and navi- al black-locust wood, a rot-resistant heavily trafficked Brooklyn-Queens gations they span. Many engineers of hardwood that is expected to last a Expressway, which separated a land- the late 19th and early 20th centuries long time in the vicinity of the estu- locked section known as Squibb Park cut their professional teeth designing arial East River. from Brooklyn Bridge Park proper. The such structures. But it is not only what was above the original design for a pedestrian bridge In 1941, the firm of Harrington, bridge’s walkway that is remarkable. connecting the waterfront park with Howard, and Ash changed its name The structure’s concrete piers are not simple cylinders or prisms, as are those of so many highway bridges. The piers of the Squibb Park structure rise out of The bridge had become so weighed the ground like tree trunks, and branch out to suggest perennially leafless down with hundreds of thousands of limbs. And the wooden trusses spanning between the arboreal supports are locks that its fragile-looking ironwork supplemented by steel cables, which are the mechanism that at the same was in danger of buckling. time give the bridge both its strength and its limited stiffness, or bounce. The bridge opened to critical ac- the residential area of Brooklyn fell to to Howard, Needles, Tammen, and claim in the spring of 2013. After a HNTB, a world-class infrastructure Bergendoff, after the surviving little more than a year, however, it was firm based in Kansas City, Missouri. founding partner and his new part- abruptly closed. The walkway was not HNTB is an employee-owned corpora- ners. The mouthful corporate name only bouncing more than desired, it tion that traces its roots to the founding was formally changed to the simpler was also twisting in ways that were in 1914 of the firm Harrington, How- HNTB in 1993, and in 2000 the firm considered potentially unsafe. Zoli ard, and Ash, which ironically special- became employee-owned. Today, and other HNTB engineers sought to ized in the design of moveable bridges. HNTB’s most prominent engineer is fix the structure by “retensioning” it The movement of those bridges was probably Theodore P. Zoli III, usually to bring it back into alignment, and by deliberate, however, because they were called simply Ted Zoli. He came to adding cross bracing and otherwise typically built with low clearances over prominence beyond the engineering retrofitting it to maintain that align-

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ment. An impatient Brooklyn citizenry was told the bridge would reopen in a matter of months, which soon dragged on past a year. When HNTB did not seem able to bring the repairs to a satisfactory conclusion, the Brooklyn Bridge Park Corporation, the operator of the park, announced that it was suing the engineering company for the $3 million cost of the bridge and that a different firm would take over responsibility for developing a plan to fix the structure. The company chosen to do the retrofitting was an international engineering firm called Arup. Incidentally, this is the same firm that was embarrassed to be responsible for the engineering of the Thames-crossing London Mil- lenium Bridge, nicknamed “Wobbly” by the British. But Arup did eventually fix that structure. Among the fixes Arup applied to the Squibb Park Bridge were improve- ments to the connections between Lee Snider/Alamy Stock Photo the timber truss and steel cables un- The Squibb Park Bridge in Brooklyn, New York, opened in 2013 but was closed within a year der the walkway. In addition, tuned because it was deemed to bounce and twist too much for pedestrian comfort. After false starts on mass dampers, in the form of heavy repairs, the bridge reopened 32 months later with retrofittings to damp out the effects of footsteps. metal plates attached by springs to the underside of the main structure, were again began to attract a new collection morous spin on the bridge. They read: installed to reduce the bounce. Move- of locks, many etched with the names no locks… yes lox, the first phrase ment of the walkway was not meant to or initials of the lovers. followed by the image of a padlock be completely absent underfoot, but it In 2015 it was estimated that the in a red circle with a slash through it. would be more muted and less alarm- Pont des Arts had become so weighed The second was illustrated with a New ing to walkers with a low tolerance down with hundreds of thousands of York bagel loaded with smoked salm- for motion of an unexpected kind and locks that its fragile-looking ironwork on and a schmear of cream cheese. amplitude. The modifications were not was in danger of buckling. By one es- That the offense was no laughing mat- expected to alter much of the appear- timate, the collection of love tokens ter was emphasized by the punch line: ance or experience of using the bridge, amounted to an extra 45-ton load on fine $100. Still, padlocks can often be but it was believed to be much more the structure, about the same weight found hanging from the same light safe when it reopened in the spring of as the entire amount of black-locust structures that hold the signs. Hu- this year. wood planking in the Squibb Park mans, after all, aren’t known for con- Bridge. To keep the Pont des Arts from sidering how their small actions can Too Much Love being pulled down into the Seine, in affect the greater good or even their Just as a large assemblage of people the spring of 2015 city workers re- own potential safety. on a bridge can cause it problems, a moved entire sections of lock-laden bridge can also receive too much love. bridge grills and replaced them with Selected Bibliography Around 2010 in Paris, a fad gained side panels decorated with designs Foderaro, L. W. 2016. Repairs coming for popularity: A pair of lovers would af- too wide to allow a common lock to bridge that bounced too much. New York fix a metal padlock to the ironwork of be affixed to them. Authorities had no Times (July 14). a bridge across the Seine and throw plans about what to do with the esti- Foderaro, L. W. 2017. Rhythmically but safely: the key into the river as a symbol of mated 700,000 keys resting on the bot- That’s the way the bridge bounces. New their permanent attachment to each tom of the Seine. York Times (April 18). other. By 2015 the Pont des Arts—the When the French tradition moved Nir, S. M. 2016. Dear John… Token of love Seine crossing located just downriver across the Atlantic, padlocks began discouraged at landmark. New York Times from the Pont Neuf at the foot of the to be left along the walkway of the (November 15). Île de la Cité—had accumulated so Brooklyn Bridge. But after a wire sup- Rubin, A. J., and A. Breeden. 2015. Showing many heavy locks that entire sections porting a light fixture snapped under love for historic bridge, Paris removes tons of padlocks. New York Times (June 2). of balustrades and the meshwork be- the weight of too many locks, the city low had to be replaced lest they be moved quickly. Workers using heavy Webster, N., and D. Shirley. 2016. A History of Brooklyn Bridge Park: How a Community pulled by gravity onto the deck of a wire cutters tried removing locks one Reclaimed and Transformed New York City’s passing tour boat. But as soon as a at a time, but the Sisyphean task soon Waterfront. New York: Columbia Univer- section of meshwork was replaced, it led to the posting of signs with a hu- sity Press.

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Perspective

The Forgotten Mystery of Inertia

A century after Ernst Mach and Albert Einstein cast doubt on absolute space, we still don’t know how a gyroscope stays pointed in a fixed direction.

Tony Rothman

n days of yore, at a World Science ly honest. Despite a gyroscope’s ut- In his magnum opus, Principia Math- Fiction Convention in Boston, a ter simplicity—it is, after all, nothing ematica, Newton proposed a thought Harvard graduate student pol- more than a wheel on an axle—it re- experiment to prove that rotation takes ished his reputation as a brilliant mains the most fascinating and myste- place with respect to absolute space. Imad scientist by roaming the conven- rious device ever created. Spin up the He imagined a bucket partially filled tion halls, brandishing what at first wheel, set it on a pedestal, and there it with water and hanging from a rope, glance appeared to be a rather peculiar stays, pointed at…? which an experimenter has twisted steel bowling ball. Portholes perfo- That is the question. At what, exact- up. When the experimenter releases rated its surface, providing a glimpse ly, is the gyroscope pointed? Accord- the bucket, the rope untwists, and the of electronic hardware inside; tangled ing to the law of inertia, objects tend bucket begins to spin. At first the wa- wires sprouted from the same holes, to continue doing what they’ve been ter remains flat, but as the pail speeds and a gear train surrounded the mys- doing: If at rest, they remain at rest; if up and drags along the water, its sur- terious object’s equator. moving, they continue moving at the face eventually becomes concave due “What’s that?” I asked him. same speed in the same direction. The to the centrifugal force of the rotation. “It’s the gyro platform for an inter- gyroscope also bends to inertia’s will, At that stage, the water and vessel are continental ballistic missile,” he re- but in confounding ways. Touch it, rotating together, and there is no rela- plied. “If you put it on a Titan rocket, it and the gyro opposes you by veering tive motion between them. Yet some- will fly to Kiev.” in unexpected directions. If it is spin- how the water “knows” to create a “How do you know?” ning extremely rapidly, the gyroscope concave surface. “It’s an inertial guidance system, remains rigidly locked in the direc- Newton insisted that the concavity stupid. It knows where Kiev is.” tion it has been set, its sights set on... must be due to the water’s rotation with “I know how inertial guidance sys- Kiev—hence the term inertial guidance respect to something else—absolute tems work, but how do you know it systems. If a rocket veers off the gyro’s space. Rotation is absolute, not relative. knows where Kiev is?” fixed course, a sensor detects the error, That answer stood largely unchallenged “Oh, that. It was stamped on the box.” and a servomechanism realigns the for two centuries, until the Austrian This sorcerer’s apprentice had dis- missile with the gyroscope axis. physicist Ernst Mach flatly declared covered that for $900 you could buy a But this is just the explanation Newton to be wrong. surplus intercontinental ballistic missile, stamped on the box. What tells the 10 years before the electronics were de- gyro it is set on the Great Gate of Kiev? Relative Revolutions classified. His Titan was delivered on Isaac Newton would argue that the In his 1883 book Science of Mechanics, two railway cars, “Kiev Titan Missile” gyro is pointed in a fixed direction rel- Mach wrote that Newton’s thought stamped on the crates. He junked the ative to “absolute space,” what physi- experiment “simply informs us, that body, donated the engines to an art mu- cists term an inertial reference frame— the relative rotation of the water with seum, and saved the electronics for his indeed, the ultimate inertial reference respect to the sides of the vessel pro- research. A tall tale? Sounds like one, but frame. Think of it as an invisible ref- duces no noticeable centrifugal forces, the gyro platform was there for all to see. erence grid somehow etched into the but that such forces are produced by its I didn’t understand it, nor did my fabric of the universe. But if absolute relative rotation with respect to the mass mad interlocutor, and anyone who space is a highly abstract concept, the of the Earth and the other celestial bod- claims otherwise is not being entire- gyro’s behavior is very tangible. Set ies.” Mach continued, that “no one is up a gyro on a lecture table at a uni- competent to say how the experiment Tony Rothman teaches in the applied physics versity (or a coffee table at home), and would turn out if the sides of the vessel department at New York University. His latest as the day progresses it appears to ro- increased in thickness and mass till they book is The Course of Fortune (iBooks, 2015), a tate with respect to walls…or is it vice were ultimately several leagues thick.” historical novel about the Great Siege of Malta in versa? Are the rotations relative, or are He dismissed absolute space as an “arbi- 1565. Email: [email protected] they absolute? trary fiction of our imagination.”

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Albert Einstein’s general theory of relativity, inspired by Ernst Mach’s rejection of absolute than usual, as if the gravitational pull space, predicted that spinning black holes or other massive objects would drag around the sur- of the Earth has suddenly increased. rounding reference frame of space; such “frame dragging” should deflect a gyroscope placed With “the happiest thought of his there. The effect has been verified, but its broader implications for inertia remain unclear. life,” Einstein realized that within the elevator’s confines, it is impossible to Mach never gave a precise formula- questions: Inertia is not a property in- distinguish acceleration from grav- tion of what became known as Mach’s trinsic to an object but depends upon ity. To explain the origin of accelera- Principle. Nevertheless, the essential all the mass in the universe. Mach’s tions, then, he would need to create idea is simple enough. According to suggestion proved heretical, not least a theory of gravitation. Furthermore, Mach, Newton’s conception of absolute because Newton’s laws, with their because free fall abolishes gravity in an space lacks all meaning. Inertia—that assumption of absolute space, work elevator, the origin of inertia cannot be tendency of massive objects to move so exquisitely. It furthermore went found in the interaction with nearby at constant velocity—must depend against our human intuition that our bodies such as Earth. Inertia’s origin on other bodies, because motion itself experience of the world is fundamen- must depend on the distant matter in must be measured relative to other bod- tal, not contingent. the universe, as Mach had insisted. ies. Rotations and accelerations along Mach’s arguments had a profound Einstein hoped that, within the straight paths take place with respect to effect on Albert Einstein, who devised framework of general relativity, the the reference frame of the distant stars the general theory of relativity largely distribution of matter of the universe and galaxies. The centrifugal forces that to abolish the idea of absolute motion, would fully determine the inertia of throw you to the side of an automobile and indeed it was Einstein who, in material objects. Most modern discus- as it rounds a corner arise because you 1918, coined the phrase “Mach’s Prin- sions of Mach’s Principle (when the are accelerating with respect to the dis- ciple.” The basis of Einstein’s general topic comes up at all) center on wheth- tant matter in the universe. theory was his observation that the er general relativity succeeded in this Reframed as a question, no proposi- gravitational force the Earth exerts on goal. As simple as the question sounds, tion goes straighter to the fundamen- you is canceled out in a freely falling there is as yet no definitive answer. tals than Mach’s Principle: Would you elevator. When accelerating down- While still formulating general feel centrifugal forces in an empty uni- ward in an elevator whose cable has relativity, Einstein calculated that the verse? Does the law of inertia mean snapped, you feel weightless. By the gravitational field of a shell of matter anything in an empty universe? Mach same token, when accelerating up- rotating around a gyroscope (picture a would give a resounding “no” to both ward in an elevator, you feel heavier gyro inside a spinning, hollow Earth)

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would displace the gyro’s axis culating the effects of curved relative to the fixed stars. The space around the Sun, Einstein gravitational field literally needed to assume that at large drags around the gyro’s “in- distances from the Sun, space- ertial compass.” In 1918, Aus- time becomes flat—and abso- trian physicist Hans Thirring, lute. In other words, he had to with Einstein’s input, published impose by fiat “boundary con- a similar calculation based on ditions” at infinity to complete the completed relativity theory. his solution. General relativity, Josef Lense, an Austrian math- in and of itself, did not entirely ematician, later provided rele- determine the precession of vant astronomical observations. Mercury’s orbit. Inevitably, this concept of frame Mathematician Kurt Gödel dragging has come to be known brought the point home in as the Lense-Thirring effect. 1949 when he published a cos- In the paltry gravitational mological model designed to field of the rotating Earth, the show that Mach and Einstein predicted amount of frame were incompatible. Gödel as- dragging is enough to dis- sumed the same uniform displace the axis of an orbiting tribution of matter as Einstein gyro by only 0.042 seconds of did in his first cosmological arc annually. That is roughly model of 1917, but Gödel’s the angular size of a quarter solution exhibited fundamen- held aloft by the Statue of Lib- tally different behavior. That erty in New York as viewed discrepancy directly contra- by William Penn atop Phila- dicted Einstein’s premise that delphia’s city hall. Despite the the universe’s matter distribu- challenge of measuring such a tion should uniquely deter- minuscule effect, frame drag- mine gyroscopic behavior. ging has been detected by The key difference was the Laser Geometric Environ- that Gödel’s universe rotated, mental Observation Survey meaning that distant galaxies (LAGEOS) and Gravity Probe rotate with respect to a gyro- B satellites, although the re- scope sitting on my desk, and sults were too uncertain to that anyone, anywhere in the confirm the exact prediction of universe would observe the Einstein’s theory. same behavior. (It does not In 1963, New Zealander mean that the universe is ro- Roy Kerr, then at the Univer- In Isaac Newton’s thought experiment, water forms a flat surface tating around some central sity of Texas, discovered the in a still bucket but a concave surface in one that is spinning. He axis.) For true followers of general-relativistic description asserted that this behavior is determined relative to absolute space. Mach, a gyro should track the of rotating black holes. Soon bulk matter of the cosmos, and physicists recognized that so it should remain stationary frame dragging can become far more orbital precession of Mercury’s peri- with respect to distant galaxies. Since pronounced around extreme astro- helion: the small but puzzling 43 sec- Gödel, researchers have found other nomical bodies. Several teams have onds of arc per century by which the rotating models of the universe, all claimed to find observational evidence point of the planet’s closest approach of which similarly contradict Mach’s of frame dragging in the disks around to the Sun shifts with time, a move- premise. Such models can be declared supermassive black holes, although ment that Newton’s laws could not unphysical, however, because they fla- the results are indirect and imprecise. easily explain. Einstein described the grantly contradict observations of the gravitational field of the Sun in terms real universe. Nevertheless, as theo- The Cosmic Connection of curved space and showed that the retical solutions they demonstrate the There is no longer a question in any curvature caused Mercury’s perihelion difficulties that come with defining in- physicist’s mind that general relativ- to shift by precisely the right amount. ertia purely in relation to other objects. ity predicts Machian effects on gyro- As physicist Erwin Schrödinger The litany of counterexamples even- scopes, and so far, the data seem to wrote, however, in a striking 1925 ar- tually convinced Einstein to abandon support Einstein’s predictions. The ticle on Mach’s Principle, “…every Mach’s Principle. In 1990, however, question of how the distant reaches of naïve person has to ask: With respect Harry King, then at the University of the universe give marching orders to a to what, according to the theory, does Texas, proved that a closed universe— gyroscope spinning on my desk is an the orbital ellipse perform this pre- one that is destined to stop expanding altogether trickier issue. cession, which according to experience and eventually recollapse—can exhibit The first triumph of general rela- takes place with respect to the aver- no rotation. Any rotation of galaxies as tivity was its exact prediction of the age system of the fixed stars?” In cal- in Gödel’s model is cancelled out by

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gravitational waves moving in the op- are concerned. A nonrotating universe Mach irrelevant for doing science: “Sci- posite direction. If Gödel’s result was still does not necessarily explain the ence for me was always a bunch of a setback for Mach, then King’s result forces that push you back into the seat tools, not a branch of philosophy.” was a definite victory. Unfortunately, of a car when you accelerate along a The greater obstacle is one of fash- today’s cosmologists believe that the straight line. ion. Today’s cosmologists constantly real universe is open—destined to ex- To most contemporary physicists, wade into shallow philosophical wa- pand forever—demonstrating again Mach’s Principle is not merely redun- ters if they align with tastes of the cur- how difficult it is to connect a theo- dant, it is forgotten entirely—as un- rent scientific Pradas and Versaces. retical understanding of inertia to the known to them as it may have been to They worry about creating Big Bang actual cosmos. the madcap graduate student flaunt- models whose input parameters oc- More recently, Christoph Schmid of ing his missile guidance system. Yet cur “naturally” rather than needing the Swiss Federal Institute of Technol- the mystery is never far away. To this to be “fine-tuned” by hand. They ogy claims to have vindicated both day, we do not truly understand how consider the “cosmological constant Einstein and Mach. Schmid has con- the distant universe gives gyroscopes problem”—why the “dark energy” cluded that vorticity added to a realis- their marching orders. driving the universe’s expansion is tic cosmological model would indeed The backwater of Mach’s Principle some 125 orders of magnitude less drag gyroscope axes. But according to holds many lessons. One is that the than what you’d “expect”—to be the Schmid’s calculations, the influence of teaching of undergraduate physics has outstanding dilemma of their field. matter diminishes exponentially be- become divorced from the practice of Physics or philosophy? Each year hun- yond a critical radius, related to the physics. From arbitrary conventions dreds of papers are published on the distance that light has traveled since that are presented as natural laws, to string theory landscape and on the the Big Bang, and the exact shape of the insistence on precise answers to un- universe of universes—the multiverse. space at much larger distances be- realistic problems, to the banishment Each year dozens of conferences take comes irrelevant. In this way, he by- of concepts such as centrifugal force, place on particle physics or string the- passes the necessity to impose bound- university physics has evolved to in- ory. The only conference on Mach’s ary conditions at infinity, the problem hibit creativity rather than encourage Principle took place in 1993. that bedeviled Einstein. The matter it. How can one hold high the tenants But replace the quaint-sounding distribution of the universe in and of of relativity—that physics can be per- words “Mach’s Principle” with “Why itself determines the behavior of gyro- formed in any reference frame—while does a gyroscope point in a direction fixed relative to distant quasars?” and one stands face to face with one of the most striking questions nature pres- Does the law of inertia mean anything in ents to us. It is more of a question than “How does the Higgs boson impart an empty universe? Would you feel mass to other subatomic particles?” It is hardly less a question than “Why centrifugal forces? Mach would say no. does time move forward when the basic laws of physics do not?” It is perhaps more fruitful than the vastly scopes. Schmid claims that general rel- simultaneously declaring that New- more popular question, “What lies ativity then perfectly embodies Mach’s ton’s laws hold only in inertial frames? behind quantum mechanics?” And Principle; on the other hand, some of How can one begin to discuss Mach’s Mach’s Principle outshines virtually his calculations are performed in a Principle if one denies the very exis- all other riddles in one other category: closed universe, which would seem to tence of centrifugal forces? Aye, centrif- It is pure romance. run afoul of King’s proof. ugal forces disappear in inertial frames; We have a working theory of grav- In independent analyses, Cam- gravity disappears in free-falling eleva- ity, one that has been tested more pre- bridge University’s Donald Lynden- tors. Does that mean that gravity is a cisely than any other theory ever de- Bell and his collaborators have accept- fictitious force? vised. It accounts for the expansion of ed certain aspects of Schmid’s results. Part of the difficulty in tackling the universe; it describes the behavior Modern studies of the cosmic micro- Mach’s Principle lies in its similar- of black holes; and it has successfully wave background radiation, however, ity to the utterances of the Delphic predicted the existence of gravitation- largely rule out any large-scale rota- Oracle. Julian Barbour and Herbert al waves. It should tell us why gyro- tions in the universe. Many cosmolo- Pfister, organizers of a 1993 conference scopes point at the stars. gists believe that the universe went on Mach’s Principle in Tübingin, listed through an early inflationary period, no fewer than 21 different interpreta- Bibliography in which the size of the universe in- tions. An exit poll at the conference’s Barbour, J., and H. Pfister, eds. 1995. Mach’s creased exponentially. Such inflation end revealed that only three attendees Principle: From Newton’s Bucket to Quantum would likely have damped out any ro- believed that general relativity perfectly Gravity. Boston, MA: Birkhauser. tation, leaving a still cosmos in which embodied Mach’s Principle, whereas Bondi, H. 2010. Cosmology. Mineola, NY: Dover gyroscopes would naturally be at rest 21 did not. Fourteen viewed it as “very Books on Physics. relative to distant matter, rendering Machian,” and seven did not consider it Sciama, D. W. 1953. On the origin of inertia. Mach’s Principle redundant—at least Machian at all. An illustrious colleague Monthly Notices of the Royal Astronomical as far as rotating objects such as gyros recently remarked to me that he found Society 113:34–42.

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Adapting Your Body Clock to a 24-Hour Society

Can new research and technology help people address the disconnect between the body’s sleep-wake cycle and the rhythms of modern life?

Alexis Webb and Erik Herzog

unt Lexie!!!” came the ear- timing of her new environment, and that are at odds with internal rhythms. piercing squeal from my jet lag will be a thing of the past. But Modern 24-hour lifestyles have similar niece as she ran toward so far, our access to technology has effects because society no longer relies my legs. I (Webb) smiled mostly been exacerbating the problem, on the day-night differences in external “Aweakly, exhausted. My husband and not alleviating it. conditions that human bodies evolved I had been awake for nearly 20 hours, Having studied biological rhythms to track and set processes to. The ever- rising at the equivalent of the night and timing for decades, the two of us present access to food, technology, before, local time, to travel to America (Webb and Herzog) are usually the go- and, most notably, electric light means from our home in London. How do to people for friends and colleagues that people are regularly exposed to you explain jet lag to a six-year-old? seeking advice on how to beat the stimuli that are not coordinated with She was having none of it—our visit transatlantic travel blues. Our basic the body’s internal time. Couple this should mean that she had two of her tenets include: Spend time outside, development with the constraints of favorite playmates at her disposal. But preferably in direct sunlight, when the standard working day, which may after little rest over the course of a day you arrive. Eat a meal on local time. necessitate waking before preferred spent on planes and sitting in airports, Try to stay awake until your normal morning rise time, and the clash of my husband and I were desperate for bedtime where you are, not where you body time with environmental time is some peace and quiet. Convincing a arrived from. For most people, flying continual. Researchers have described child that your body still thinks it’s on west, which prolongs your wake-sleep this phenomenon as social jet lag— the other side of the Atlantic is nearly rhythm relative to normal, feels easier going through daily life at odds with as difficult as convincing your body than flying east. Although you may the circadian rhythm—which can have that it’s not. Unlike our phones and find yourself unable to sleep in the profound consequences for health. other wired technologies, our bodies early morning hours and flagging at The good news is that advances in can’t read the new time off the local the end of the day, flying west tends to research and technology are providing network tower once we have arrived be kinder to the body. It’s not always better ways to track and train the body in a new location and adjust instantly. so easy to follow these rules, however, clock to cope with modern living. At Perhaps when my niece is my age, and it gets harder still as our daily rou- the same time, scientists are improving her activity tracker or some future de- tines keep changing in ways that can their understanding of possible targets vice will be able to tell her brain the sacrifice well-being. for drugs, making better use of data The feeling of jet lag, of being just a from wearable devices, and bringing bit off and out of sorts, arises because together citizen scientists to examine Alexis Webb has a PhD in neuroscience and spent of a discrepancy between internal time real-world behavior, which can be vast- her early career researching the role of biological clocks in behavior and development in both the and the environment. In the brain sits ly different from what is observed in United States and Europe. She is a senior research a biological clock that coordinates the the controlled conditions of the labora- funding manager for the world’s largest cancer regular daily timing of nearly all of the tory. New technologies that are chang- research charity and is based in London. Erik Her- body’s processes. This clock is set or ing our lifestyles and challenging our zog is a chronobiologist studying the molecules, entrained to local time through light clocks will also be able to provide ex- cells, and circuits that underlie daily rhythms in input from the eyes. The change in quisite details about our biology, lead- physiology and behavior. He is professor and as- time experienced when people travel ing to solutions never realized before. sociate chair of biology at Washington University across time zones cannot be processed in St. Louis, where he is also the codirector of instantly by the clock in the brain; Entrainment in a Modern World the Graduate Program in Neuroscience and the there is no watch hand to wind to a The modern world increasingly makes director of the St. Louis Neuroscience Pipeline Program, a National Institutes of Health–funded new time. The internal clocks must re- possible or even demands nighttime initiative to increase diversity in the neurosci- adjust to the new environment through activity. Thanks to social media and ences. He serves as the President-elect of the Soci- experience of the new day-night cycle. other modes of connectivity, people ety for Research on Biological Rhythms. Email for These days, people don’t need to get from anywhere in the world can see Webb: [email protected] on a plane to experience conditions what our planet looks like from the

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Edwin Eemsberg/Alamy Stock Photo People around the world, including crowds under ornate lights in Taksim Square in Istanbul, sible for coordinating essential daily Turkey, are becoming more active at night with the rise of connectivity and technologies that processes, such as metabolism and began with the electric era nearly 100 years ago. The rhythms of modern life are often out hormone release, has enormous impli- of sync with the day-night cycle that sets many of our bodily routines, contributing to sleep cations for human health. problems, obesity, and other disease risks. Alleviating this social jet lag is at the forefront of Nurses working the night shift at circadian biology research. a hospital have an 8 percent greater chance of developing breast cancer, International Space Station at any time the wee hours. More than 20 percent of and that chance continues to rise for and see that the surface of the Earth the workforce in industrialized coun- every year that an individual works looks much different than it did 100 tries has irregular, rotating, or unstable a rotating night shift. Nighttime fast- years ago. Aside from the changes to shifts. Not only are people working at food employees and their hungry cus- the landmasses, oceans, and ice sheets, all hours, they have constant access tomers are fighting against the body’s the area now covered by electric lights, to technology, information, and, well, metabolic rhythms by eating food which resemble millions of fireflies stuff. Since the advent of Amazon.com around the clock, including at times shining out into darkness, is immense. in the 1990s e-commerce has boomed; when the body expects to be at rest Although large parts of Africa, South more than half of all purchases are now and fasting. This kind of metabolic jet America, and Asia still face night in made online, where we have 24-7 ac- lag is linked to obesity, which brings relative darkness, North America and cess to shopping. And thanks to this with it a whole host of additional Europe appear as glowing lattices of change toward a retail-focused econo- health problems. On the whole, soci- cities and towns. my, more people are working jobs with ety is working more and sleeping less, In contrast to the circumstances of antisocial hours. Modern society no increasing the risk for depression and previous generations, the end of the longer requires citizens to rest and reset. anxiety issues. Such disobedience to day no longer means the end of work The world is nonstop, and the conse- the circadian clock, a behavioral prob- and activity. Thanks to the inventions of quences are beginning to show. lem arising from changes in modern Nikola Tesla and Thomas Edison, hu- Evolution has not caught up to living, is adding to the growing finan- mans can remain active at night. One of these changes in day-to-day life. Hu- cial strain on health services world- those lights below is a hospital in Man- mans, as well as nearly every other wide. In the United States alone, an chester, where nurses and doctors are organism on the planet, are adapted to estimated $14 billion per year is spent working their rotating overnight shift. the 24-hour rhythm of light and dark- on health care for sleep disorders, ac- Another is an all-night fast-food restau- ness that arises from the spinning of cording to the U.S. Institute of Medi- rant in Atlanta, where employees serve Earth on its axis. Fighting against this cine Committee on Sleep Medicine burgers and greasy fries to patrons into finely tuned clock, which is respon- and Research.

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master clock suprachiasmatic nucleus (SCN)

suprachiasmatic light lateral nucleus geniculate endocrine clock nucleus pineal gland

behavior right lungs retina heart muscle

liver

optic chiasm left retina gut renal A master clock in the brain, the suprachiasmatic nucleus (SCN), helps keep the schedule for clocks in tissues throughout the body (left). The stron- reproductive gest signal for setting this master clock is light. Specialized nerve cells for light detection in the retina connect the eyes to the SCN, which is a pair of bilateral nuclei sitting on top of the crossing of the optic nerves at the base of the brain within the hypothalamus.

The word circadian, from the Lat- nerve cells connect the eyes to an area night cycle. The size of the adjust- in circa diem, meaning “about a day,” at the base of the brain within the hypo- ment needed is flexible; depending describes the body’s near 24-hour thalamus called the suprachiasmatic nu- on the latitude and the time of year, internal clock that is set to the local cleus (SCN). Scientists have studied this humans experience different lengths environment. This clock is intrinsic; structure for decades—first observing of day and night. Therefore, our in- it will persist even in constant condi- that animals with lesions in this area ternal clock must change its relation- tions that do not change, such as in lose all behavioral rhythms. Pioneering ship with the light cycle to be awake a cave or deep in the ocean. Modern transplantation studies led to the con- and asleep at the optimal times. This working environments are quite dif- clusion that the SCN structure is both offset is otherwise known as the phase ferent from conditions in a cave, but necessary for generating daily rhythms relationship between the body clock in either setting the body must use and sufficient for providing them. and the environment, signifying how internal time must speed up or slow down to fall in line with the daily experience of light and dark. An added On the whole, society is working more complication for many people is that the times they need to be awake and and sleeping less, increasing the risk for asleep change throughout the week and may be at odds with what is hap- depression and anxiety issues. pening in the environment. Changing the body clock to the right phase relationship underlies the pro- information from the sensory system The rhythm provided by the SCN cess of entrainment. This process is at to tune the intrinsic circadian clock to is not exactly 24 hours in length. De- the heart of improving circadian fitness the environment—put simply, to tell pending on the organism, it can be and is likely the reason that more and whether it is day or night. slightly longer or slightly shorter more people will struggle with their Specialized cells in the retina, called than 24 hours, with humans fall- health. Sunlight is the most powerful intrinsically sensitive retinal ganglion cells, ing into the former category. Light entraining signal for the body clock. are primarily used for light detection detection through the eyes sets But in the modern era of electricity and rather than for image formation. These the internal rhythm to the day- nonstop access to information, it’s the

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light received via a computer screen the discrete model and the continu- training signal) given at a certain point after dinner or a smartphone screen be- ous one. To understand the difference, on the route around the track allows fore bed that counteracts the day-night imagine two cyclists going around a cyclist 2 to immediately overcome the cycle provided by the Sun. Too many circular track—they are cycling at the distance and jump to a new point on constant inputs are in conflict with the same speed, but there is a distance be- the track, the same point as cyclist 1, daily biological cycle we evolved for. tween them. This distance represents so that the internal clock is in sync Historically, there have been two the phase difference between cyclist 1 with the actual environment. conceptual models that explain the en- (the environmental clock) and cyclist Essentially, according to the discrete trainment that takes place to synchro- 2 (the internal clock). In the discrete model, light can immediately shift nize the internal and external rhythms: model, a light stimulus (or other en- the internal clock to the phase of the

Biological Clocks: There’s an App for That pps and smartphone settings of Satchidananda Panda’s laboratory, Forger’s laboratory, which is based at are helping people learn about who are based at University of Califor- University of Michigan, found that bed- Atheir daily rhythms and how nia, San Diego, and are creators of the time, not wake time, predicts how long this information can improve their app, found that over the course of 16 people sleep, and that those people who sleep and entrainment. These technolo- weeks, overweight, healthy adults lost experience outside light during the day gies also can be used for crowdsourc- weight, improved energy levels, and go to bed earlier and sleep more. Avail- ing data to study the connections be- slept better when eating in the restrict- able for Android and iOS. tween daily activities, biological clocks, ed time window prescribed by the http://entrain.math.lsa.umich.edu and disease risks. Several ground- app. Available for Android and iOS. breaking examples are detailed here. https://mycircadianclock.org Night Shift and f.lux [not related to data collection] My Circadian Clock Entrain The Night Shift setting is part of the Use this app to track your sleep-wake If you are traveling across the country iPhone operating system, designed to cycle, exercise, and meals through- or around the world, this app will help minimize the impact of the blue-light- out the day. Feedogram data help shift your clock to local time faster. En- emitting screens on delaying the circa- you track when you eat throughout ter information about your trip: where dian clock and making it harder to fall the day; you may be surprised at how you are traveling from, what’s your asleep at night. Using a set time, your frequently across the day and night destination, when do you leave. The screen will automatically filter out blue you are consuming food. Activity data app then collects data on your sleep and light and enhance warmer colored light can help inform when you should be activity, as well as light exposure, which from your phone in the evenings. Simi- restricting your meals according to is fed into a mathematical model of the lar modifications are available on some your circadian cycle. By eating during circadian clock. The model uses phase models of Android phones. A program a window that corresponds to when response curves based on your circadi- called f.lux will also automatically ad- your metabolism is ramped up (dur- an rhythm to make predictions on when just the brightness and color of your ing the day when your clock knows you should see light before and dur- laptop screen based on time of day and you’re active), you may find it easier to ing your trip to best enhance your en- lighting within the room: maintain a healthy weight. Members trainment. Creators of the app in Daniel https://justgetflux.com

MY CIRCADIAN CLOCK ENTRAIN

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+4 Bright light exposure after dusk has are particularly sensitive to the blue light the ability to delay the clock, shifting from these screens. +2 activity later, as if one were experienc- Avoiding phone use at night to pre- advance ing a longer day. Light exposure before vent body clocks from shifting is not zone dawn has the ability to advance the the only option; technology has been 0 clock, shifting activity earlier to start developed that can purposefully block delay zone a new day. Night-shift workers face the blue light from being emitted (see –2 light exposure that can both advance sidebar on preceding page). On an over- phase shift (hours) phase shift and delay their clocks; rotating-shift cast day, the eyes still receive around –4 workers struggle between “regular” 2,000 lux. But the illumination level of and shifted schedules, never success- indoor lighting is often much lower, dawn mid-day dusk night dawn fully entraining to either. Models sim- and can be as low as 50 lux. Limited time of light stimulus ulating phase-response curves based bright light exposure for elderly pa- on data from the underlying circadian tients in care homes could be one rea- Bright light exposure after dusk has the abil- rhythm can now help frequent travel- son for the disrupted sleep and activity ity to delay the internal clock, shifting one’s ers predict when they should be ex- rhythms observed in those populations. activity later, as if the day were longer. Light posed to light to best exposure before dawn has the ability to ad- entrain their body illuminance surfaces vance the clock, shifting activity earlier to clocks to their current (lux) illuminated by start a new day. This phase-response curve, a local time (see sidebar plot of the change in the internal clock rela- on preceding page). colorless 0.0001 moonless, overcast tive to the external environment based on the vision night sky (starlight) time of light exposure, shows that the biggest Although most of phase shifts occur at two points in the night: the world won’t be 0.001 and 10 moonlight to early just after dusk and just before dawn. attempting to inten- twilight tionally shift circadian 0.002 moonless, clear night environmental light-dark cycle. The rhythms in this way, limited sky with airglow continuous model argues that an en- it is the transitions in color training stimulus would cause cyclist 2 light at dawn and dusk vision 0.05 to 0.36 full moon on a clear to increase or decrease her speed over that help entrain the night the subsequent cycles until she is at slightly longer internal 3.4 dark limit of civil twilight the same point on the track as cyclist rhythm to the 24-hour under a clear sky 1. This process happens over multiple day-night cycle of the 10 to 50 public areas with dark loops as the internal clock is continu- environment. Studies surroundings ously adjusting to fall in line with the have shown that two environmental cycle. Although aspects light stimuli, one when 30 tablet/smartphone screen of both discrete and continuous en- diurnal activity starts trainment are still favorably regard- and the other when it 50 family living room lights ed in the literature today, these two stops, provide enough (Australia, 1998) models of entrainment have failed to time information to 80 office building color unify the field. Recently, an alternative the circadian system hallway/toilet lighting theory has been proposed, which pos- to set it to the environ- vision tulates that changes in how the circa- mental rhythm. 100 very dark overcast day dian system integrates light signals at How much light is 320 to 500 office lighting different times of day allows it to tune necessary to shift and 400 sunrise or sunset on a to the environment. set the body clock? Al- clear day In both the continuous and discrete though bright sunlight models, depending on what time the with an intensity mea- 500 to 1,000 computer screen light stimulus arrives, the extent of the sured at 100,000 lux is 1,000 overcast day; typical TV light shift varies. For example, light ex- most efficient, recent studio lighting posure during the day has little effect studies by researchers 10,000 therapeutic light box on the intrinsic clock. This idea seems at Harvard Medical intuitive—if the purpose of light is to School have shown that pupil 10,000 to 25,000 full daylight (not direct shift the clock, then either limiting ex- even the light emitted constriction sun) and phase posure to the light, or in the case of the from the LED (light- 32,000 to 120,000 direct sunlight circadian system, limiting when light emitting diode) screens shifting has a shifting effect, would be benefi- of smartphones and tab- cial. Plotting the change in the phase lets, when seen before Entrainment is stronger when people are exposed to brighter of the internal clock relative to the ex- bed, is enough to de- light. Sunlight is ideal, because it is bright enough to cause pupil constriction and phase shifting. Most office lighting is not bright ternal environment based on time of lay the circadian clock enough to entrain the body’s clock. Light with a brightness of at light exposure, otherwise known as and disrupt sleep. In- least 10 lux is detected by both rods and cones in the eye. Light the phase-response curve, shows that the deed, the light-sensing with an illuminance below 0.0001 lux allows for detection with biggest shifts occur at two points: just retinal ganglion cells rods only (colorless vision). The rods and some cones can detect after dusk and just before dawn. that project to the SCN dim light (0.001–10 lux), allowing for limited color vision.

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Can We Entrain Faster? S cones Being in tune with the environment intrinsically is a boon for organisms, not only for photosensitive “the early bird that gets the worm,” retinal ganglion cells but also for nocturnal animals who rods time their activity cycle to minimize M cones predation and improve survival. As L cones mentioned in the previous section, the strongest entraining signal for the cir- sunlight cadian clock is light. Unlike the brains of birds, human brains cannot experience light directly through the skull intensity sensitivity/relative fluorescent light and must rely instead on a specialized part of the visual system. Indeed, research over the past 20 years in hu- 400 500 600 700 800 mans (and mice) lacking parts of the wavelength (nanometers) image detection apparatus of the eye— the rods and cones—showed that they Bluer light has a stronger effect on entrainment than other wavelengths of light. The specialized still maintain daily rhythms; that re- cells that detect light and send the signal to the SCN, called intrinsically sensitive retinal gangli- search contributed to the discovery of on cells, contain the photopigment melanospin, which is especially sensitive to the blue part of those specialized light-detecting gan- the light spectrum peaking around 460 nanometers. Rods and cones, on the other hand, can pick glion cells crucial for entrainment. up the full color spectrum and play a larger role in image formation, not light detection. People Many people, such as parents of who have blindness caused by the degradation of rods and cones can still detect enough light to have a weakly entrained circadian rhythm. (Figure adapted from Hatori and Panda, 2010.) young children and business travelers, would surely benefit from an internal clock that can be set to local time faster. jet lag is likely years away, but studies tor in the SCN, who then relays this The nurse and the fast-food worker suggest that certain drugs may be able information to the rest of the neurons, who are forced to work against their to influence the timing of brain cells or and in turn, to the rest of the body. daily rhythms would be able to im- their ability to respond to entraining Many studies have tried to identify prove their health with a clock that signals. Human SCNs are comprised the roles of different areas and cells was easier to shift and reset. Can cir- of tens of thousands of neurons, elec- types in the SCN and to elucidate how cadian biology provide any insights? trically active cells that can send tim- the symphony comes together. Bad news first: There are lots of ing information to the rest of the brain When neurons in the SCN fire, a gimmicks that are not based on sound and body. These neurons are them- neuropeptide, vasoactive intestinal science. Probably one of the most in- selves rhythmic; their firing is cyclic polypeptide or VIP, is released. Under famous published studies in the field over a 24-hour period and it is light in- normal conditions, VIP plays an im- claimed that light exposure to the back put (and the neurochemicals released portant role in keeping the cells of the of the knees improved entrainment fol- by those light-receiving cells) that in- SCN synchronized to the same beat. lowing a long-haul flight—a conclusion fluences the timing of activity. Researchers in one of our (Herzog’s) based on a faulty correlation. There are no photoreceptors located behind the kneecap. Plenty of other proposed time- shifting quick-fixes exist that haven’t In addition to light, one of the other been published in scientific journals, but they still are sometimes promoted rhythmic signals that may help realign in the pages of in-flight magazines or newspapers. Many of these treatments, the clock faster is shifting meals such as therapy with melatonin or ben- zodiazapines, are designed to promote to local time at the destination as sleep, but they won’t necessarily aid in entraining your circadian rhythm to a soon as possible. new external time. In addition to exposure to light, one of the other rhythmic signals that may help realign the clock In addition to maintaining their tim- labs have shown that high concentra- faster is shifting meals to local time at ing relative to the outside world, SCN tions of VIP, however, can throw the the destination as soon as possible. neurons are also set in time with one SCN symphony into disarray. This lack More recent research has examined another. Imagine a symphony of musi- of synchrony in the rhythms may be the effects of chemicals, such as kinase cians. They may not play all at once, beneficial when it comes to speeding inhibitors or DNA damage regulators, but an individual section must keep up entrainment. on the behavior of the SCN, specifi- time relative to the others, with the To explain how this role might work, cally to find out whether exposure to conductor setting the overall pace of we collaborated with computational them can speed up the adjustment to the performance. Light input commu- scientists, who built a mathematical a new time. A pill that could help beat nicates external timing to the conduc- model of the circadian rhythm in an

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16 and heart rates. They could use this wealth of information to make better 12 and more informed decisions about their daily behavior. Activity trackers encourage wearers to think about how 8 much and what they do on a daily basis—and also about when they are 4 doing each of their routine activities. Those who want to learn more about percentage of population percentage their circadian behavior now have 0 access to apps and websites offering midnight 1234567891011 noon more information. Scientists also are mid-sleep on free days (local time) utilizing the internet to connect with other members of the public who early type normal late type would like to contribute to research. These citizen scientists can use mobile extrememoderateslight slight moderate extreme technology to generate and share data with researchers, essentially turning the world into a giant laboratory. The Munich Chronotype Questionnaire places individuals on a frequency distribution based Developers of research-based apps on the midpoint at which they prefer to be asleep on an ideal day (when they are not sleep have empowered people to become deprived and wake without an alarm). Most people’s preferred midpoint of sleep is between 5 AM and 6 AM. This survey has been important in collecting anecdotal evidence about people’s part of the scientific process of under- sleep habits. Now, with activity trackers collecting information through smartphones and standing their biology. Using an app wearables, the scale of raw data available on people’s daily behaviors is enormous, with the to track behavior can provide a win- potential to transform what is known about disease risks and solutions related to out-of-sync dow into daily life in the real world, biological clocks. (Figure adapted from Roenneberg and Merrow, 2007.) without the constraints of a controlled environment in the lab. These sorts SCN neuron. Our model predicted how light may help trigger phase tumbling of data are particularly useful to ob- desynchrony could make entrainment in our SCN and hasten readjustment serve the changes seen in 21st-century happen faster. In the model, neurons re- to a new time. lifestyles compared with lifestyles of sponded to high doses of VIP with a be- Researchers have also been examin- 50 or even 100 years ago. Large-scale havior described as “phase tumbling.” ing whether the introduction of other surveys such as the Munich Chrono- Essentially, lots of VIP produces a tran- compounds could improve entrain- type Questionnaire, whose questions sient phase decoupling across the cells, ment. Screens of libraries of small mol- place individuals across a distribution shifting them in time relative to one ecules, including primarily synthetic based on the midpoint of when they’d another. This dispersion likely occurs compounds that can bind to genes and prefer to be asleep, have been impor- due to molecular variability or noise in proteins that could produce or lead to tant in collecting anecdotal evidence the levels of gene activity and protein enhanced shifts, is a high-throughput about the when, where, and how of amounts in individual cells—evidence way of identifying candidates. A fu- people’s sleep habits. But with activ- our lab has also observed. In the model, ture for improving entrainment may ity trackers, the scale of raw data that the shifted cells are also quicker to re- rely on a combinatorial approach. By we have about people’s daily behavior adjust and entrain to new times, sug- using light together with drugs, timed from around the world is enormous. gesting that high VIP levels might help meals, and other stimuli, humans may Apps that track sleep and wake times, alleviate jet lag. be able to better tune and enhance the food intake, and other aspects of bio- To test this idea, researchers in our phase relationship between their inter- logical rhythms, such as My Circadian lab recently measured the rhythmic nal and external timing. Clock and Entrain, have already pro- activity of mice provided with run- vided new information about obesity ning wheels. They simulated jet lag for Technology to Improve Entrainment and recovery from jet lag (see sidebar the mice by shifting the light schedule The past 10 years have seen an explo- on page 349). Now and in the near fu- to either advance or delay the envi- sion in constant connectivity by way ture, researchers could use such apps ronmental signal by six hours relative of mobile devices and other technolo- in combination with other personal to the previous schedule. Researchers gies. In addition to listicles and cat pic- data, such as medical records and ge- examined when the mice would be ac- tures, the internet now contains vast netic predispositions, to paint a more tive on their running wheels following amounts of data generated by the pop- detailed picture of how the circadian the shift. Mice that received injections ulation, including information about clock contributes to overall human of high concentrations of VIP in the sleep and wake patterns, food intake, health as well as disease risk. area around their SCN were able to en- and location. This era of quantified The challenge now is figuring out train faster to the new schedule com- self, collected through activity trackers how to spread the word to people pared with control mice that received and apps, means that there are more about the effects of a healthy circadian injections of saline instead. Because data than ever before about people’s rhythm on conditions such as obe- VIP is released from the neurons that daily lives. Some fast-food workers, sity, cancer, and mental health, and receive input from light-sensing cells for example, might have a Fitbit that how best to encourage more people in the eyes, a good dose of bright sun- measures their steps, exercise, sleep, to examine the data they generate to

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feedogram (baseline) p<0.05 26 caloric containing eating duration 5 (2.5–97.5 percentile interval) p<0.05 24 baseline 22

20 0 18 days 16

14 time (hours) –5 12

feedogram (intervention) change in body weight (kilograms) 8 16-week intervention

6 –10 12345678 B161Y subjects B: weight change during 3-week baseline 16: after 16-week intervention 1Y: 1 year after intervention start

Shubhroz Gill and Satchidananda Panda created the app My Circadian Clock to study the timing of food intake and its effects on weight loss among healthy individuals. They first monitored the times that study subjects ate food without any intervention and found that people tended to eat frequently and erratically throughout the day and consumed more daily calories in the afternoon and evening (top left). When the app coached the same individuals on the time window in which to eat, so that they stopped any food intake earlier in the evening after peak circadian activity (bottom left), subjects overall lost weight (above). days

body clock, aided by wearable technol- Herzog, E. D. 2007. Neurons and networks in ogy and apps, may someday be possible. daily rhythms. Nature Reviews Neuroscience 8:790–802. But achieving it will require more research to understand the ways in which Lucas, R. J., et al. 2013. Measuring and using light in the melanopsin age. Trends in Neu- biology and the rhythms of modern life rosciences doi:10.1016/j.tins.2013.10.004. can work together in harmony. Roenneberg, T. 2017. Internal Time: Chronotypes, Social Jet Lag, and Why You’re So Tired. Cam- Bibliography bridge, MA: Harvard University Press. An, S., et al. 2013. A neuropeptide speeds circa- Roenneberg, T., and M. Merrow. 2007. Entrain- dian entrainment by reducing intercellular ment of the human circadian clock. Cold synchrony. Proceedings of the National Acad- Spring Harbor Symposia on Quantitative Biol- emy of Sciences of the U.S.A. 110(46):E4355– ogy 72:293–299. E4361. doi:10.1073/pnas.1307088110. Schibler, U., et al. 2015. Clock-talk: Interactions Chang, A.-M., D. Aeschbach, J. F. Duffy, and between central and peripheral circadian C. A. Czeisler. 2015. Evening use of light- oscillators in mammals. Cold Spring Harbor 06 1824 emitting eReaders negatively affects sleep, Symposia on Quantitative Biology 80:223–232. time (hours) circadian timing, and next-morning alert- Walch, O. J., A. Cochran, and D. B. Forger. ness. Proceedings of the National Academy of 2016. A global quantification of “normal” Sciences of the U.S.A. 112(4):1232–1237. sleep schedules using smartphone data. discover how their rhythms could be Chen, Z., S.-H. Yoo, and J. S. Takahashi. 2013. Science Advances 2(5):e1501705. doi:10.1126/ Small molecule modifiers of circadian clocks. sciadv.1501705. improved. Until better solutions for Cell Molecular Life Sciences 70(16):2985–2998. circadian dysfunction exist, those of us Dunlap, J. C., J. J. Loros, and P. J. DeCoursey. prone to late-night Netflix streaming or 2009. Chronobiology: Biological Timekeeping. scrolling through our Instragram feed Sunderland, MA: Sinauer Associates. before we turn out the light can take Foster, R., and L. Kreitzman. 2017. Circadian steps to be healthier by acknowledging Rhythms: A Very Short Introduction. Oxford, UK: Oxford University Press. For relevant Web links, consult this our circadian rhythms and trying to issue of American Scientist Online: minimize disruption to our clocks. Gill, S., and S. Panda. 2015. A smartphone app A couple of straightforward changes reveals erratic diurnal eating patterns in www.amsci.org/magazine/issues/2017/ humans that can be modulated for health november-december can make a marked difference in allevi- benefits. Cell Metabolism 22(5):789–798. ating entrainment problems: removing Hatori, M., and S. Panda. 2010. The emerging all technology from the bedroom and roles of melanopsin in behavioral adapta- ensuring that some time is spent out- tion to light. Trends in Molecular Medicine doors every day. An instantly adjusting 16:435–446.

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Cassini and the Rings of Saturn

As one of its final scientific feats, the accomplished robotic spacecraft returned unprecedentedly detailed data on the material encircling the giant planet.

Matthew S. Tiscareno

he rings of Saturn are deli- et Saturn. The chunks range from cate, enigmatic, beautiful, marble-size to house-size. The ring and useful. NASA’s Cassini system is confined to the plane of spacecraft has been study- Saturn’s equator and is arguably the Ting them (and the rest of the Saturn flattest structure known to human- system) over the course of a spec- ity, with an end-to-end dimension tacularly successful 13-year mission, equivalent to circling the Earth seven but its concluding year has been the times, but a vertical height about that most spectacular of all—practically of a house. a whole new mission. In December Saturn’s rings are useful to scien- 2016, Cassini commenced weekly tists because they provide physical plunges through the ring plane just and chemical clues regarding the off the outer edge of the main rings formation and history of the entire (activity termed the “Ring-Grazing Saturn system, they serve as detec- Orbits”), and transitioned in April tors and amplifiers for planetary phe- 2017 to weekly plunges between the nomena around them, and they help rings and the planet’s cloud-tops (the us understand more generally how “Grand Finale” orbits). The mission disk systems operate, providing clues concluded in September 2017 with a about other kinds of disks, such as final descent into the planet’s atmo- baby solar systems. A few of the most sphere, to preclude possible terrestrial compelling science questions regard- contamination of Saturn’s moons. ing Saturn’s rings are: How do ring The science goals of the Ring-Grazing particles interact with one another, Orbits and the Grand Finale orbits in- with moons embedded within them, cluded direct sampling of particles from and with moons farther away? Are Saturn’s rings and atmosphere, de- ring particles made of ice that is fluffy tailed measurements of Saturn’s grav- or dense, pristine or sooty? What are ity and magnetic field to probe the their shapes and sizes? What struc- planet’s interior, and unprecedentedly tures do we see in the dusty parts of close-range imaging of Saturn and its the rings, and what can we continue rings with the spacecraft’s main cam- to learn from them? era and similar instruments. These observations followed up on discoveries made through the prime and extended Matthew S. Tiscareno is a senior research sci- Cassini missions, continued monitor- entist at the SETI Institute in Mountain View, ing seasonal or evolving phenom- California, and a participating scientist and imaging team associate for the Cassini spacecraft. ena, and took advantage of Cassini’s He received his PhD in planetary science from unique proximity to Saturn in these the University of Arizona in 2004. His research closing stages of the mission. focuses on the orbital and rotational motions of Saturn’s planetary ring system is rings, satellites, and planets. He is the coeditor of made up of countless chunks of ice, Planetary Ring Systems (Cambridge University each in its own orbit around the plan- Press, 2018). Email: [email protected]______rg

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An illustration shows the Cassini spacecraft orbiting Saturn, where it operated for 13 years. In September the mission came to a preplanned end because the spacecraft was running out of propellant. The craft was deliberately plunged into Saturn, so that there could be no risk of it accidentally crashing into one of Saturn’s moons and potentially contaminating it. (All images are courtesy of NASA.)

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The structure of Saturn’s ring system is dominated by occur at many locations within the rings, as well as streaky concentric bands and tightly wound spirals. Very few of texture and other types of texture. Each of these textures these bands are empty gaps, so it is better to think of the en- likely indicates a different mode of mutual interaction among tire system as a disk, rather than as “countless rings.” Much the ring particles, and/or different ring particle properties. of the structure is not well understood by scientists, but the The main rings are largely free of dust (that is, of icy most common type of understood structure are waves that particles that are smaller than the period at the end of this propagate through the rings at locations where ring particle sentence), because dust tends to collect as a layer on the sur- orbits resonate (or essentially “hum in tune”) with the orbit faces of larger ring particles. In the few places where dust of a moon orbiting beyond the rings. Cassini scientists dis- does coexist with larger particles, it indicates the presence covered in recent years that a few of these waves are excited of vigorous ongoing activity that is keeping the dust in mo- by structures within the planet Saturn. tion. In locations that are far from the main rings, only dust Moons that orbit within the rings deflect nearby ring paris present, and the dust then can be sculpted into shapes ticles with their gravity and thus create a disturbance around that reflect the forces surrounding it. themselves. The moons Pan and Daphnis are large enough Perhaps the most fundamental mystery surrounding Sat- that this disturbance becomes a sharp-edged empty gap ex- urn’s ring system is its age. Certain aspects of the dynami- tending around the entire circumference of the rings. Extrapo- cal interactions between the rings and moons can only be lating from this archetype, scientists expected each of the rewound for about 100 million years, indicating either that a dozen other sharp-edged gaps in the rings to also host a moon significant reworking of the ring system’s structure occurred apiece; however, careful searches by Cassini have shown that within that time, or that the entire ring system is only that old. this is not the case, so these gaps must have a more complex An important clue in this mystery is the rate at which the rings origin. Moons in a smaller size class than Pan and Daphnis cre- are being polluted by “soot” falling in from the Solar System. ate a propeller-shaped disturbance that is filled back in by the If that infalling rate is low, or if the rings have a relatively rings before it can extend circumferentially. large mass of water ice with which to mix the pollution, then The interior and surface properties of ring particles are it would be reasonable to conclude that the rings are as old as poorly known. Are they more like ice cubes or snowballs? Saturn and still sport the relatively pure water ice we see them Are their surfaces fluffy or slushy or frosty? The answer may to have. However, if the infalling rate of pollution is high and be all of the above. Images from the Ring-Grazing Orbits and the mass of the rings is low, then the rings are likely no older Grand Finale have shed new light on the collective interac- than 100 million years. Cassini’s dust detectors were working tions of ring particles. A speckled strawlike texture occurs on a definitive measurement of the pollution rate, and the within waves at locations where the particles had been re- mass of the rings will be measured directly from the gravi- cently compressed but that pressure has now been released, tational pull of the rings on Cassini during the Grand Finale perhaps as a result of temporary clumps falling apart. More orbits. After analysis of the final Cassini data has been com- surprisingly, sharp-edged bands of similarly speckled texture pleted, these questions should find more concrete answers.

The spiral density wave at left occurs at the location where ring par- pull of the moon Janus, but at a location where ring particles orbit ticles orbit Saturn twice for every time that the moon Janus orbits Saturn four times for every three Janus orbits (a 4-to-3 resonance). once (called a 2-to-1 resonance). Because Janus trades orbits with its The peaks of the wave are dark, and the broad, bright troughs contain partner moon Epimetheus every four years, this wave sports several a speckly, strawlike structure, likely due to transient clumps of ring “glitches” that trace the wave’s history going back several decades. particles that are now falling apart. The corduroy-like structure at The spiral density wave at right is also caused by the gravitational center and right is a result of a recent pass of the moon Pan.

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The moon Daphnis is seen orbiting within its sharp-edged gap. Ring particles that have recently passed the moon are perturbed into wavelike structures in the gap edge, but Daphnis’s influence is waning by the third wavecrest back, which is disintegrating into a collection of small clumps.

The quasi-moon “Peggy” appears at the outer edge of the main rings, looking as though it might spiral away from the rings and become a freely orbiting moon. Subsequent Cassini images have shown Peggy’s story to be more complicated, because it has broken into several pieces and has remained within the rings.

At left, a sharp-edged bright band (called a plateau) has an unknown cause. The central strip, from which the first-order brightness has been removed so that local structure becomes more visible, shows that the plateau has a streaky texture whereas the surrounding region has a speckly texture. The different textures must indicate different modes of particle properties and/or interactions. Also visible to the right in this image is a spiral density wave driven by structure inside the planet Saturn.

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The moon Prometheus dips into the dusty F ring and sculpts its material. The resulting channels flatten out as they move downstream from Pro- metheus. Also visible in this image are several strands of dust comprising the F ring, with some bright knots that indicate embedded moons.

Swarms of small propellers of debris (above) surround a density wave (with a 9-to-8 resonance with the moon Prometheus). Each propeller contains a 100-meter moonlet at its core, which creates the disturbance around itself.

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An inner-central part of the planet’s B ring is shown in what is the highest- resolution true-color image of any part of Saturn’s rings produced to date. The reason for the tan color is poorly understood, as is the origin of the sharply defined banded structure.

Close-up views show giant propellers caused by ring-embedded moons. The figures immediately below and to the right show the lit side of the rings, where brighter tones indicate more material reflecting light. The figures at far bottom and on the facing page bottom show the translucent, unlit side of the rings, where most dark tones indicate more material, such that the ring becomes opaque. Cassini has tracked the orbits of these individual propellers for more than a decade and has found subtle changes in the orbits that are likely due to moon-disk interactions. These individual propellers have been nicknamed “Santos-Dumont” (below), “Earhart” (right), and “Blériot” (facing).

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Ghostly white markings called spokes appear in the central region of the main rings, in a wide-angle image (above) and in a more detailed image (left). These spokes are composed of dust levitating above the ring plane. The dust was likely ejected by meteoroid impacts and then caught up into Saturn’s magnetic field, although the details are not well understood.

Dusty lanes occur within the D ring, the innermost ring of Saturn. Some of the bands comprise a spiral that preserves traces of an inferred meteoroid impact that took place in the 1980s. The brighter bands at bottom-left are the innermost portion of the main rings.

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Earth and Moon

A panoramic view of Saturn shows both its main rings and its outer, that are more closely aligned with the Sun appear even brighter. The dusty rings. Because the Sun was behind Saturn when this image bluish E ring is composed of material ejected from the geysers on was taken (that is, Cassini was inside Saturn’s shadow), the dusty the south pole of the moon Enceladus. The Earth and its Moon are rings appear nearly as bright as the main rings, and dusty regions visible to the lower-right of Saturn.

An impact ejecta cloud tells the tale of a meter-sized object that plowed through the rings some hours before this image was taken. The ejecta cloud is near the center of the image and is nearly horizontal, canted at an angle from the concentric bands of the ring structure.

For relevant Web links, consult this issue of American Scientist Online: www.amsci.org/magazine/issues/2017/ november-december

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The New Language of Mathematics

Is it possible to take all words out of mathematical expressions?

Daniel S. Silver

omething strange is happening about replacing mathematics require- and again in red. By arranging all in in mathematics seminar rooms ments for the bachelor’s degree with rectangular fashion as we have, it is an around the world. Words and foreign language courses, Gibbs rose easy matter to count the total, which is phrases such as spider, birdtrack, and forcefully declared: “Gentlemen, 5t6 = 30. In order to find our original Samoeba, sandpile, and octopus decomposi- mathematics is a language.” sum, we need only divide by 2, there- tion are being heard. Drawings that Gibbs wasn’t the first notable scien- by correcting for our double counting. resemble prehistoric petroglyphs or tist to call mathematics a language. Gal- The novelty of the picture is that we ancient Chinese calligraphy are being ileo Galilei beat him to it by more than can grasp the idea at a glance. More- seen, and are being manipulated like 200 years. In Il Saggiator (The Assayer), over, there is nothing special about 5 the traditional numerals and symbols published in Rome in 1623, the Italian columns of dots. We could just as easily of algebra. It is a language that would astronomer wrote: “[The universe] can- imagine 100. So 1+2+. . .+100 must be have been alien to mathematicians of not be read until we have learnt the equal to 100×101 divided by 2, which is past centuries. language and become familiar with the 5,050. Similarly we can find the sum of The words and symbols of math- characters in which it is written. It is the first N integers, for any N whatso- ematics are intended to stimulate written in mathematical language.” ever. The answer is N(N+1)/2. thought, promote curiosity, or simply Galileo wrote in Italian rather than Just as the 19th-century musician amuse. At times they ignite public scholarly Latin, hoping to reach readers Felix Mendelssohn enjoyed writ- Commons Alamy Stock Photo; Wikimedia Robert Garrigus / imagination. Occasionally they inter- who were literate but not necessarily ing Lieder ohne Worte (Songs Without fere with understanding. Always they scientific. But just as students at Pla- Words), so mathematicians like to craft are evolving. Today, as the boundaries to’s Academy were reputedly greeted Proofs Without Words. Since 1975 the of mathematical inquiry expand, their with the warning “Let no one ignorant Mathematical Association of America evolution seems to be accelerating. of geometry enter here,” so Galileo’s has published a column devoted to The words and symbols of mathemat- readers were being cautioned that the them in its Mathematics Magazine. Its ics have helped bring the subject to its book before them had some language examples are intended to leave the present, bountiful state. But the ques- prerequisites. For Galileo, the letters of reader speechless. tion remains: Can the symbols of math- mathematics were triangles, circles, and Despite the many proofs without ematics stand up on their own, without other geometric figures. Gibbs, who is words, mathematical thought ohne any words to support them? responsible for much of the vector cal- Worte might be impossible. Words culus that we use, would have added a come to us automatically when we Is Mathematics a Language? modern symbol or two of his own. view images. Images come to mind Josiah Willard Gibbs navigated confi- If mathematics is a language, then when we see words. It seems that we dently in a sea of mathematical words just as any ordinary language, such as need words after all. and symbols. Gibbs was a founder of French or Russian, does not rely on an- The role that words play in math- statistical mechanics and a professor of other one to be understood, so mathematics was on the mind of the French mathematical physics at Yale Univer- ematics should be independent of ordi- mathematician Jacques Hadamard sity during the latter half of the 19th nary languages. The idea does not seem when, during the 1940s, he asked col- century. Colleagues knew this out- so far-fetched when we consider musical leagues around the world how they wardly plain and unassuming scholar notation, which is readable by trained thought about their subject. Did they as someone who rarely made public musicians everywhere. If mathematics think in images or think in words? He pronouncements. Imagine their sur- is a language, then we should be able to summarized his findings in The Psy- prise when, during a faculty meeting understand its ideas without the use of chology of Invention in the Mathematical words. Let’s see how that might be done. Field. One of the respondents was Al- Consider the task of adding the bert Einstein, who wrote: Daniel S. Silver is an emeritus professor of mathematics at the University of South first few integers, say 1, 2, 3, 4, 5. Easy Alabama. His research explores the relation enough. Their sum is 15. But what The words or the language, as between knots and dynamical systems, as well about adding the first 100 integers? they are written or spoken, do not as the history of science and the psychology of The figure on page 366 displays seem to play any role in my mech- invention. Email: [email protected] 1+2+3+4+5 dots twice, once in black anism of thought. The psychical

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Symbolic representation of words and ideas has an ancient history, from North American ory, which won him the prestigious petroglyphs (top) to early Chinese calligraphy (above, left). Modern mathematicians are ex- Fields medal seven years later. Al- ploring the usefulness of wordless symbols, including the “birdtracks” notation (above, right) though the dot was not entirely gra- created by mathematician Predrag Cvitanovi°. tuitous—it came about by thinking of factors in terms of concentric black entities which seem to serve as posed by the use of images alone. In circles—it was intended as a humor- elements in thought are certain 1983 the New Zealander and Ameri- ous commentary on the constraints of signs and more or less clear im- can mathematician Vaughan Jones imagery. “Some people have enjoyed ages which can be “voluntarily” made the point by reproducing the the joke,” Jones told me. reproduced and combined. image of a big black dot to illustrate Whether or not mathematics is a

the projection lattice of II1 (read as language, its words share with ordi- Even those mathematicians who “type two-one”) factors, a sophisti- nary language an important function: would agree with Einstein recognize cated algebraic object that Jones later They transport essential images from the severe limitation on thought im- used to create new tools for knot the- one mind to another. For that reason

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notion of entropy, introduced by Ru- Third, the wide popularity of Shan- dolf Clausius in 1864, was noted with non’s information theory has been wonder by many, including the math- helped by his use of a word that is rec- ematician John von Neumann. Shan- ognized, if not truly understood, by non is said to have told an interviewer everyone. Its associations with disor- the following anecdote in 1961: der in everyday life evoke a sympa- thetic response with everyone, much My greatest concern was what like another popular mathematical to call it. I thought of calling it word, chaos. “information,” but the word was overly used, so I decided to call it What’s in a Name? “uncertainty.” When I discussed “Must a name mean something?” asked it with John von Neumann, he Alice doubtfully. “Of course it must,” had a better idea. Von Neumann was Humpty Dumpty’s emphatic reply told me, “You should call it en- to Alice’s question in Lewis Carroll’s tropy, for two reasons. In the first Through the Looking-Glass. place your uncertainty function Mathematician James Yorke of the has been used in statistical me- University of Maryland would have chanics under that name, so it al- given Alice the same answer. In a re- ready has a name. In the second Wikimedia Commons cent discussion I had with him, Yorke place, and more important, no Josiah Willard Gibbs, a 19th-century math- recalled his decision to adopt the word one knows what entropy really ematician at Yale University who was known chaos for a mathematical phenomenon is, so in a debate you will always for being reserved, nonetheless expressed associated with a type of unpredict- have the advantage.” very strongly his opinion that mathematics able behavior found everywhere in was itself a language. Although von Neumann’s second rea- the world, from the drip patterns of son presumably was intended as a joke, water faucets to long-range weather the choice of words that we make is the exchange highlights the importance behavior. “Your terms should mean important. of careful language choice in fostering something,” he insisted. He dismissed

Multiple Meanings In 1948, Claude Shannon, working on communication theory at Bell Tele- Mathematical monikers usually slip phone Laboratories, created a beautiful and useful algebraic expression for through the world quietly. The term a measure of average uncertainty in an information source. Its similarity chaos was an exception; it seized the in form to the statistical mechanics public imagination.

understanding. Like Shannon, many the advice of colleagues urging him mathematicians agonize over the words to choose a more dispassionate term. that they invent, hoping that those they Yorke wished to capture the feelings choose will survive for decades. Shan- that we all have about the randomness non’s choice proved to be brilliant for in our lives. three reasons, two in addition to those Mathematical monikers usually slip proposed by von Neumann: through the world quietly, recognized First, mathematicians enjoy the bor- by only the researchers who use them. rowed authority of words from science, Chaos was an exception. In 1975 Yorke especially from physics. Von Neumann and his co-author, mathematician Tien- was correct when he said that the use Yien Li of Michigan State University, of entropy conferred an advantage on proved a surprising theorem about the speaker. Audience members either continuous functions on an interval, know the meaning of the term or else the sort of functions that students they feel that they should. learn about in calculus. They wrote Second, Shannon’s appropriation of up their proof in a short paper titled the term entropy provoked an insight- “Period Three Implies Chaos.” An array of dots can be used as a nonverbal ful debate. Did his term in fact have a What did Yorke and Li prove? Think demonstration that the sum 1+2+3+4+5 is meaningful connection with statistical of such a function as a machine: Insert equal to 5 (the number of columns needed to mechanics? The debate has been pro- a number a from the interval and get a represent all the digits) multiplied by 6 (the ductive. Today Clausius’s entropy is value b. If we put b into our machine, number of rows needed to represent the larg- regarded by many as a special case of then we get a third number c. Now in- est digit) and then divided by 2. Shannon’s idea. sert c to get d. If it happens that d is

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equal to a, then we say that a has period had written about it at the turn of the three. In a similar way, a number might 20th century—it came as a shock to have period four, five, or any number. many scientists. Storm conditions to- What Yorke and Li proved, assuming day, Lorenz suggested, might have continuity, is that if some number has been caused several weeks ago by a period three, then one can find num- butterfly flapping its wings in Brazil. bers of any period one chooses. Butterfly effect was the term he coined Yorke and Li also showed that many to reinforce the metaphor. numbers have successive outputs that If a mathematical term is to catch never return to their starting value. fire with general readers, it must More surprisingly, pairs of such non- spark their imagination. A powerful periodic numbers can be found as image helps. In the case of chaos, Lo- close together as desired, yet having renz himself had supplied it. It was successive outputs that move apart. It a bundle of curves, today called the is an example of sensitive dependence Lorenz attractor, suggesting the infinite on initial conditions. The situation is, number of solution curves to a system well, chaotic. of three differential equations. And it Had Yorke and Li published their resembled the two wings of a butterfly. paper in a specialists’ journal in their Start at any point of one of its solu- field of dynamical systems, it is likely tion curves and follow around, and that chaos would never have caught the you visit the two wings successively in public’s imagination. Few people know Claude Shannon of Bell Telephone Laborato- some infinite pattern. Start at a nearby that the word had already appeared ries in 1948 borrowed the term entropy from point on a different curve and the pat- with another meaning in the wonder- statistical mechanics to name his algebraic tern might become wildly different fully oxymoronic title “The Homoge- expression for the amount of uncertainty in after some time. The Lorenz attractor neous Chaos.” The author was Norbert an information source. His term has attracted became the emblem of a new and last- widespread attention. Today some consider the Weiner, the creator of cybernetics. ing field, chaos theory. statistical mechanical notion to be a special case Weiner published his article in the of Shannon’s entropy. (Photograph courtesy of 1938 volume of the research-oriented Tekniska museet/Flickr cc.) Choosing Words, Sometimes with Care American Journal of Mathematics. Instead Poorly chosen words and phrases can Yorke and Li published in the American tion? Within 10 years, James Gleick’s interfere with the progress of mathe- Mathematical Monthly, an expository Chaos: Making a New Science would matics. René Descartes showed us how. journal published by the Mathematical become a bestseller. The book, which While pondering solutions to alge- Association of America, intended for a marks its 30th anniversary this year, braic equations, Descartes was com- broad readership from college students celebrated its subject, beginning with pelled to consider the possibility that to researchers. When biologist Robert the ideas of mathematician and me- some numbers when multiplied by May read the article and wrote about teorologist Edward Lorenz. In 1961 themselves could give a negative re- its implications for population models Lorenz had noticed that over extended sult. Certainly no “real numbers,” that a year later in the journal Nature, the periods of time, his model of weather is, no numbers on the familiar number word chaos appeared on top of the first patterns behaved differently when line, behave that way. Descartes called page. According to Yorke, that is when its initial conditions were varied only the numbers imaginaire (imaginary). In the term took off. slightly. Although such a phenomenon La Géométrie, his effort in 1637 to unify How long does it take a mathemati- was not new to mathematicians—the geometry and algebra, he explained cal word to seize the public imagina- French mathematician Henri Poincaré that “true or false roots can be real or imaginary.” Although mathematicians sometimes joke about the terms they try to introduce, some agonize The expression imaginary number over the words that they invent, and others wonder whether neologisms cause confusion. caught on. Carl Friedrich Gauss, one

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The Lorenz attractor is a bundle of curves plotting the solutions to a system of three differential time. During the 1800s rigorous and equations. It resembles the wings of a butterfly, and became an emblem for the subject of chaos. effective definitions, those of limit Some of its infinitely many curves are colored to distinguish them. (Image by Paul Bourke.) and derivative, were finally developed without the mention of time, and of the greatest mathematicians of all some students that complex numbers mathematicians stopped using New- time, despised it. In 1831 Gauss wrote: are more than imaginary, having sig- ton’s f-words. “If this subject... [has been] enveloped nificant applications throughout the British mathematicians of the 19th in mystery and surrounded by dark- sciences. century loved inventing new words ness, it is largely an unsuitable termi- In 1670 Isaac Newton contributed and phrases for mathematical con- nology which should be blamed.” the intensely bothersome words flu- cepts. Unfortunately, they got off to a Gauss preferred the less censori- ents, fluxions, and even ffluxions. They rather bad start. ous term complex numbers, which in- were intended to describe the path In 1801 a book by Cambridge pro- cludes both ordinary (real) numbers and velocity of fluid in motion, but fessor John Colson, who held the Lu- and imaginary numbers appearing defining them rigorously proved too casian chair of Mathematics (earlier held by Newton and later by Stephen Hawking) was published as an English Leibniz was so smitten with symbols that translation of Instituzioni analitiche ad uso della gioventú italiana [Foundations he dreamed of a purely symbolic language, of Analysis for the Use of Italian Youth], a textbook about calculus written by Maria Agnesi in 1748. It is a pity that one with which nations might someday Colson didn’t know much Italian. He learned just enough to follow the path settle arguments, using computation rather of translation, dropping a hazardous rock onto the road along the way. than swords and cannon. In her book Agnesi had described a particular curve, referring to it as “la curva... dicesi la Versiera.” The word together in a single expression, such difficult even for the Cambridge ge- versiera was an adaptation by another — as 2 + √–3. Regrettably, Descartes’s nius. For more than a century math- Italian author, Guido Grandi, from the coinage remains in circulation, add- ematicians tried and failed to clarify Latin word versoria, meaning “a rope ing to the handicap that mathematics the meanings of these words with that turns a sail.” It was a helpful im- teachers endure as they try to convince their implied metaphysical notions of age. Colson could not find Agnesi’s

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“la versiera,” because it was not in any birth, so to speak, to a square matrix nus sign that we use for subtraction. In dictionary. He used the closest word by striking out unwanted rows or col- medieval Europe the operation of sub- that he could find, l’avversiera. umns, matrix, with its suggestion of traction was written out; we find it re- In Italian l’avversiera means “the fertility, seemed appropriate. corded as minus (Latin), moins (French), witch” or “the she-devil.” Colson The word matrix lives on in math- or meno (Italian). However, by the 15th wrote: “...the equation of the curve to ematics at all levels. And like chaos, century, the word had been syncopated, be described, which is vulgarly called it has captured popular imagination. shortened to m–. The symbol – began the Witch.” Today’s calculus textbooks Sylvester would have been delighted to replace m– as early as 1489, the year continue to use the term Witch of Agne- to know that at the end of the 20th cen- that Johannes Widmann published a si, and students continue to stare at the tury both a Hollywood science-fiction book of commercial arithmetic with the curve and wonder what demonic forces film and a compact car would carry phrase (in translation): “What – is, that shaped it. It is ironic that Agnesi was a the name. is less, and the + is more.” devout woman who spent most of her No matter what their origin, sym- adult life aiding the poor. A Picture Worth 1,000 Symbols bols have been a source of mystery for No British mathematician was a The symbols of mathematics appear to mathematicians. They do more than greater wordsmith than James Joseph be separate from the words alongside merely stand in for words. Gottfried Sylvester. Born in London in 1814, he them. In fact, they have evolved from Wilhelm Leibniz, who shares with attended Cambridge University but words. The 19th-century German phi- Newton credit for discovering calcu- could not be awarded a degree be- lologist and historian Heinrich Nes- lus, believed it. Leibniz was so smitten cause, as a Jew, he did not subscribe selmann was the first to recognize this by symbols that he dreamed of a pure- to the Thirty-Nine Articles of Religion concept. He identified three stages of ly symbolic language, one with which of the Anglican Church. He managed their evolution: rhetorical, syncopated, nations might someday settle argu- to support himself by teaching at the and symbolic. ments, using computation rather than secular University College London An illustration of Nesselmann’s swords and cannon. He imagined an and working as an actuary. Finally, in theory is furnished by the humble mi- alphabet of ideas. 1876, Sylvester’s career reached its full promise when he was appointed to a Maria Gaetana Agnesi (left) authored a professorship at the new Johns Hop- mathematics textbook in Italian in 1748. kins University in Baltimore, Mary- In the volume she describes a particular curve (below), calling it la versiera, land. There he began the United States' and adaption from the Latin word ver- first mathematics research department soria, meaning a rope that turns a sail. and its first mathematics research jour- But when her textbook was translated nal, the aforementioned American Jour- into English by Cambridge mathemati- nal of Mathematics. cian John Colson and published in 1801, Sylvester loved language almost as he mistook the word for another that much as mathematics. He composed means “the witch.” The mistranslated unappreciated poetry, and in 1870 he moniker still sticks with the curve in proudly self-published a slim vol- modern textbooks, which call it Witch of ume, The Laws of Verse, in which he Agnesi, to the confusion of students who are not told of the reasons for any su- proposed rules for effective versifica- pernatural connections. The story dem- tion. Not surprisingly, Sylvester coined onstrates the importance of choosing many mathematical words. At the potential mathematical terms with care. end of his article, “On a Theory of the Syzygetic Relations of Two Rational Integral Functions,” published in 1853, he attached a glossary of “New or unusual Terms, used in a new or unusual sense in the preceding Memoir.” It began with allotrious, apocopated, bezoutic, sprinkled monotheme, perimetrical, rhi- zoristic along the way, and finished up with umbral, weight, and zeta. Most of Sylvester’s words have been forgotten, but some have survived. Perhaps his most notable contribu- tion to mathematic’s lexicon is matrix, a square or rectangular arrangement

of terms in rows and columns. It is a Wikimedia Commons Latin word that means womb. Sylves- ter was most interested in the case of a square matrix, one for which the numbers of rows and columns are equal. Because a rectangular matrix can give

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stretched not only argument. Beginning in the late 19th across its pages but up century, intuition-defying examples and down them as well. from the expanding subject of topolo- Today Frege’s work gy reinforced doubts about our spatial is regarded by many intuition and proofs that rely on them. as the most important Giusseppe Peano’s space-filling curve single work in logic. was one such example: Try to imagine However, in its day, an unbroken curve inside a square that the book was derided. does not miss a single point. Few can, Logician John Venn but Peano could. He constructed such (remembered today a curve using an infinite recursive pro- for his eponymous cess. No picture can fully describe it. diagrams) described (More about Peano can be found in Begriffsschrift as “cum- “Crinkly Curves,” Computing Science, bersome and inconve- May–June 2013.) nient.” Another influ- Mathematicians’ reluctance to ac- ential logician, Ernst cept images in place of words has Schröder, called it a softened but not vanished. It is a com- “monstrous waste of mon and uncomfortable experience space” and complained for someone presenting a pictorial ar- that it “indulges in the gument to hear a skeptic ask, “Is that Japanese custom of really a proof?” Predrag Cvitanovi° writing vertically.” of Georgia Institute of Technology Frege faced resis- knows the experience. He recalls the tance not just from taunt of a colleague staring at the pic- readers. His two- tograms that he had left on a black- dimensional formu- board: “What are these birdtracks?” las and other exotic Cvitanovi° liked the ornithological symbols precipitated term so much that he decided to adopt

Chris Hellier / Science Source complaints from his it for the name of his new notation. typesetter. “After all, So what are these birdtracks? Brief- James Joseph Sylvester, who taught mathematics at Johns the convenience of the ly, they are combinations of dots, lines, Hopkins University in the late 1800s, invented a host of mathematical terms, but the most enduring one is matrix. Sylvester typesetter is certainly boxes, arrows, and other symbols, let- borrowed the term from the Late Latin word for womb, likely not the summum bonum ters of a diagrammatic language for to imply how a rectangular arrangement of terms in rows and [highest good],” Frege a type of algebra. They were inspired columns can “give birth” to a square one. argued some years by the famous paper about QED, later. Costs associated written in 1948 by physicist Richard Leibniz never found his univer- with typesetting, once a bane for Feynmann, and also later articles by sal language, but others have had mathematicians, have disappeared mathematical physicist Roger Penrose. success searching for ideographic today thanks to effective software As Cvitanovi° explained in his 1984 languages with more specialized that enables authors to create cam- book Group Theory: Birdtracks, Lie’s, and functions. The German mathemati- era-ready manuscripts for journals Exceptional Groups, the diagrams rep- cian and philosopher Gottlob Frege and periodicals. Nevertheless, the resent an evolution of language. They thought that he had found a way to mathematical community’s reluc- are not merely mnemonic devices or an aid for computation. Rather, they are “everything—unlike Feynman dia- It is a common and uncomfortable grams, here all calculations are carried out in terms of birdtracks, from start to finish.” Could one perform the cal- experience for someone presenting a culations without them? Yes, but as Cvitanovi° warns the reader, it would pictorial argument to hear a skeptic ask, be like speaking Italian without using your hands. “Is that really a proof?” Birdtracks are not the only picture- language game in town. Others have been, and are being, invented for dif- communicate with just symbols. tance to adopt pictorial arguments ferent purposes. Louis H. Kauffman, In 1879 he published Begriffsschrift, has slowed their acceptance. a mathematician at the University of an 88-page booklet in which the quan- Pictures have accompanied math- Illinois at Chicago and one of the most tifiers of formal logic first appeared. ematical proofs since the days of Eu- inventive and influential topologists Frege described his work as “a for- clid. But a picture can mislead us by of our time, uses a variety of new dia- mula language, modeled on that of suggesting that the special case it il- grammatic languages for the study of arithmetic, of pure thought.” Diagrams lustrates is sufficiently general for our knots. An algebraist familiar with bird-

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cause mathematics is not just another = language.” Simply put, mathematics is more general than any language that tries to express it. = Traditional methods of learning mathematics are discursive, demanding a sequential, step-by-step understanding. Assuming that a lesson succeeds, = = there is a moment of “aha!” when lights F2 F2 turn on and the room is illuminated for us. One day it might become possible to flip on the light switch as soon as we enter the room. Philosopher and logician Susanne K. Langer once called = for a revolution in our modes of communication, moving beyond our “tiny, grammar-bound island.” Our journey

Wikipedia from words to symbols to picture language is bringing Langer’s revolution Attempts at purely symbolic mathematical languages have taken on a range of formats. One just a bit closer. diagram from the work of Gottlob Frege in 1879 asserts that: “If b implies a, then the negation of a implies the negation of b” (top left). Louis Kauffman used picture-language to argue that a References certain quantity for a knot does not depend on how the knot is drawn (top, middle). The quon Cvitanovi°, P. 2008. Group Theory: Birdtracks, language is used at top right to express the properties of a pair of expressions in Frobenius Lie’s, and Exceptional Groups. Princeton, NJ: algebra. Disks called planar tangles are used to express properties in planar algebra (bottom). Princeton University Press. Feynman, R. 1965. The Character of Physical tracks would recognize much but not much in common with the languages Law. London: Cox and Wyman Ltd. all of what she might read in Kauff- of Cvitanovi° and Kauffman. Gleick, J. 1987. Chaos: Making a New Science. man’s book Formal Knot Theory, much According to its inventors, the quon New York: Penguin Books. as a traveler might understand spoken language can do more than aid in the Hadamard, J. 1945. The Psychology of Inven- tion in the Mathematical Field. Princeton, NJ: cognates of a foreign tongue. study of quantum information. It is also Princeton University Press. Planar algebras are another signifi- a language for algebra and topology, Jones, V. F. R. 1999. Planar algebras, I. cant picture language. Jones (the one with the ability to prove theorems in arXiv:math/9909027v1. with the big black dot mentioned ear- both subjects. In an interview with the Kauffman, L. H. 1991. Knots and Physics. Singa- lier) introduced them in 1999, and they Harvard Gazette, Jaffe remarked, “So this pore: World Scientific Publishing Co. provide a general setting for important pictorial language for mathematics can Langer, S. K. 1942. Philosophy in a New Key. quantities in the study of knots. The give you insights and a way of thinking Cambridge, MA: Harvard University Press. basic pictures of the language are pla- that you don’t see in the usual, algebra- Sylvester, J. J. 1853. On a theory of the syzy- nar tangles—disks with smaller disks ic way of approaching mathematics.” getic relations of two rational integral func- inside them—connected by line seg- He added that “It turns out one picture tions. Philosophical Transactions of the Royal ments and decorated with stars and is worth 1,000 symbols.” Society of London 143:407–548. shading. Planar tangles can be com- Li, T-Y. L., and J. A. Yorke. 1975. Period three implies chaos. The American Mathematical bined to form new characters. The Not Just Another Language Monthly 82:985–992. properties they exhibit mirror those Something strange is indeed happen- Liu, Z., A. Wozniakowski, and A. M. Jaffe. of different algebraic and topological ing in mathematics seminar rooms 2017. Quon 3D language for quantum in- structures that are already familiar to today, but it amounts to more than formation. Proceedings of the National Acad- researchers. Consequently, planar al- amusing sights and sounds. Mathema- emy of Sciences of the U.S.A. 114:2447–2502. gebras have a variety of applications. ticians are attempting to break through Birdtracks and planar algebras are the barriers of traditional language picture-languages that draw their in order to think more deeply about initial inspiration from physics. Yet fundamental questions. Their strange another is quon language, first intro- words and images are attracting atten- duced in December 2016 on arXiv. tion, motivating all of us to learn more org, a repository of online research- about them. For relevant Web links, consult this paper preprints that is used by scien- In a series of lectures at Cornell Uni- issue of American Scientist Online: tists throughout the world. Quon lan- versity in 1965, Richard Feynman con- guage, created by Harvard University templated the effectiveness of math- www.amsci.org/magazine/issues/2017/ mathematicians Zhengwei Liu, Alex ematics in science. He sympathized november-december Wozniakowski, and Arthur M. Jaffe, is with the lay reader who asked why derived from three-dimensional picto- it was not possible to explain math- rial representations of particlelike exci- ematical ideas with ordinary language. tations and transformations that act on Correcting Gibbs, who started our dis- them. An earlier, simpler version has cussion, Feynman replied that it is “be-

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The Persistence and Peril of Misinformation

Defining what truth means and deciphering how human brains verify information are some of the challenges to battling widespread falsehoods.

Brian G. Southwell, Emily A. Thorson, and Laura Sheble

isinformation—both de- would if they were correctly informed, disinformation is more problematic, liberately promoted and as suggested by the research teams of as it involves deliberate alienation or accidentally shared—is Stephan Lewandowsky of the Univer- disempowerment of other people. Le- perhaps an inevitable sity of Bristol in the United Kingdom wandowsky and his colleagues have Mpart of the world in which we live, but and Elizabeth Marsh of Duke Univer- carried forward this definition of dis- it is not a new problem. People likely sity, among others. In other words, we information as intentionally incorrect have lied to one another for roughly worry that misinformation (or false information. as long as verbal communication has information) might lead people to hold From a critical theory perspective, existed. Deceiving others can offer an misperceptions (or false beliefs) and we might worry about the impossibil- apparent opportunity to gain strategic that these misperceptions, especially ity of proving that any information is advantage, to motivate others to ac- when they occur among large groups objectively true, a concern that com- tion, or even to protect interpersonal of people, may have downstream con- plicates any distinction of misinforma- bonds. Moreover, people inadvertently sequences for health, social harmony, tion from information on the basis of have been sharing inaccurate informa- and political life. the former being false and the latter tion with one another for thousands being true. Nonetheless, we respect- of years. However, we currently live Concern about fully reject a worldview in which no in an era in which technology enables degree of consensus among people— information to reach large audiences proving that any agreement as to what is true—is pos- distributed across the globe, and thus sible. If we allow that a claim acknowl- the potential for immediate and wide- information is edged by consensus to be true is valid, spread effects from misinformation objectively true we then can position misinformation now looms larger than in the past. Yet as a category of claims for which there the means to correct misinformation can complicate is at least substantial disagreement (or over time might be found in those same even a consensus for rejection) when patterns of mass communication and the distinction of their truthfulness is judged by the wid- of the facilitated spread of information. misinformation est feasible range of observers. That approach would include disinforma- Misinformation vs. Disinformation from information. tion as a special type of misinformation Misinformation is concerning because distinguished by the promoter’s intent. of its potential to unduly influence at- Does misinformation require inten- From an ethical perspective, many titudes and behavior, leading people tional deceit on the part of the pre- people worry most about active pro- to think and act differently than they senter? Philosopher Jürgen Habermas, motion of disinformation. We think who taught at institutions such as it is best, however, to continue to use Goethe University Frankfurt and the the word misinformation, because we Brian G. Southwell is director of the Science in Max Planck Institute in Germany until should acknowledge that false infor- the Public Sphere Program at RTI International formally retiring in the 1990s, focuses mation can mislead people even if un- in North Carolina and a faculty member at Duke on a speaker’s intent to deceive to dis- intentionally promoted or mistakenly University and the University of North Carolina tinguish between misinformation and endorsed as the truth. This approach at Chapel Hill. Emily A. Thorson is an assistant disinformation. Habermas views truth opens the door for certain claims to professor of political science at Syracuse Uni- as only possible collectively among evolve from accepted information to versity. Laura Sheble is an assistant professor of people as a product of consensus; one’s become misinformation, and vice ver- information science at Wayne State University in Michigan. Adapted, with permission, from Mis- collegial participation in such collective sa, as a function of a society’s chang- information and Mass Audiences, edited by understanding also matters. Misinfor- ing consensus. (And, of course, such Brian G. Southwell, Emily A. Thorson, and Laura mation from such a perspective, then, evolution of evidence can be useful.) Sheble; © 2018 by the University of Texas Press. is contentious information reflecting We can define misinformation as claims Email for Southwell: [email protected]. disagreement among people, whereas that do not enjoy universal or near-

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Michele Rosenthal Although the practice of purposeful deception, or unintentional spreading of falsehoods, is teams of Erik Asp of the University of not new, the recent, rapid growth of mobile devices and social media have greatly expanded Chicago and Daniel Gilbert at Harvard the conduit for both information and misinformation to rapidly reach a large, global audience. University, among others, has supported Spinoza’s account: People appear universal consensus as being true at a timating the potential for subsequent to encode all new information as if it particular moment in time on the basis problems. Although individuals gen- were true, even if only momentarily, of evidence. erally have considerable routine expe- and later tag the information as be- rience encountering information now ing either true or false, a pattern that Why Misinformation is Problematic considered to be false, the question of seems consistent with the observation At least three observations related to exactly how—and when—we mental- that mental resources for skepticism misinformation in the contemporary ly label information as true or false has physically reside in a different part of mass-media environment warrant the garnered philosophical debate. the brain than the resources used in attention of researchers, policy mak- The dilemma is neatly summarized perceiving and encoding. ers, and really everyone who watch- by a contrast between how the phi- We also know from work by one of es television, listens to the radio, or losophers René Descartes and Baruch us (Southwell) and others that people reads information online. First of all, Spinoza described human information judge source credibility as a cue in de- people who encounter misinforma- engagement centuries ago, with con- termining message acceptability and tion tend to believe it, at least initially. flicting predictions that only recently will turn to others for confirmation Secondly, media systems often do not have been empirically tested in robust of the truth of a claim. If the people block or censor many types of misin- ways. Descartes argued that a person surrounding someone tend to initially formation before it appears in content only accepts or rejects information af- believe misinformation, then the spec- available to large audiences. Thirdly, ter considering its truth or falsehood; ter of network reinforcement is raised, countering misinformation once it Spinoza argued that people accept all meaning that the false claim becomes has enjoyed wide exposure can be a encountered information (or misin- more difficult to debunk as it is be- resource-intensive effort. formation) by default and then sub- lieved by more people. Knowing what happens when peo- sequently verify or reject it through a What about our claim that misinfor- ple initially encounter misinformation separate process. In recent decades, mation often can appear in electronic holds tremendous importance for es- empirical evidence from the research or print media without being preemp-

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The FDA oversees direct-to-consumer prescription drug advertising, for example, and has developed mechanisms such as the “Bad Ad” program, through which people can report advertising in apparent violation of FDA guidelines on drug risks and benefits presentation. People appear to encode all new information as if it were true, even if only momentarily, and later tag the information as being either true or false. Such programs, although laudable and useful, do not guarantee that false

photo Gage Skidmore/Flickr cc photo Gage Skidmore/Flickr advertising never appears on the air- The phenomenon of fake news has become commonplace on the Internet. Some sites waves and, moreover, do not prevent disguise themselves as legitimate news outlets and release false stories, such as a 2016 false news stories from appearing. In hoax about actor Sylvester Stallone’s death. Although other sites, such as the one in the addition, as shown by one of us (Thor- screen shot here, quickly counter the stories, hoaxes are often shared widely before being son), even misinformation that is suc- disproven—and, ironically, repeating the falsehood can further engrain belief in it. cessfully corrected can continue to affect attitudes. tively blocked? One might consider Federal Trade Commission, the Federal Following on this last point, counter- the nature of regulatory structures in Election Commission, and the Food ing misinformation with new informa- countries such as the United States: and Drug Administration (FDA) offer tion requires effort not only to develop Regulatory agencies tend to focus on considerable monitoring and notifica- new content that is understandable but post hoc detection of broadcast infor- tion functions, but these roles typically also to ensure adequate message ex- mation. Organizations such as the U.S. do not involve preemptive censoring. posure. As Robert Hornik of the Uni- versity of Pennsylvania has argued, a communication campaign can succeed or fail, at least in part, as a function of exposure or lack thereof. A campaign to correct misinformation, even if rhe- torically compelling, requires resources and planning to accomplish necessary reach and frequency. For corrective information to be persuasive, audiences need to be able to comprehend it, which requires either effort to frame messages in ways that are understandable or effort to educate and sensitize audiences to the possibility of misinformation. That audiences might not be aware of the potential for misinformation also sug- Wikimedia Commons gests the potential utility of How the brain encodes information and when it judges it to be true or false has been a subject of philo- media literacy efforts as early sophical debate for centuries. René Descartes (left) argued that people would consider the truthfulness as elementary school. Even or falsity of information before accepting or rejecting it. Baruch Spinoza (right) argued that people accept with journalists, pundits, and all information by default, then verify or reject it through a separate process. scholars pointing to the phe-

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In Kano, Nigeria, the polio virus thrives in sewage-contaminated water. Misinforma- tion, however, caused many residents to re- fuse the polio vaccine, leading to the disease’s reemergence a few years ago, after it was nearly eradicated.

nomenon of “fake news,” people often do not distinguish between demon- strably false stories and those based in fact when scanning and processing

information. ZUMA Press, Inc./Alamy Stock Photo We live at a time when widespread misinformation is common. Yet at this time many people also are passion- ately developing potential solutions and remedies. The journey forward undoubtedly will be a long one. The way in which media systems have developed in many democratic societies inherently calls for both vulnerability to occasional misinformation and robust systems to detect and address it. Future remedies will require not only continued theoretical consideration but also the development and maintenance of consistent monitoring tools and a willingness among neigh- bors and fellow members of society to agree that some claims that find prominence on shared airwaves and in widely available media content are insufficiently based in scientific consensus and social reality and should be countered. Misinformation arises as a function of systems structure, human fallibility, and human information needs. To overcome the worst effects of the phenomenon, we will need coordinated efforts over time, rather than any singular, one-time panacea we could hope to offer.

Bibliography Aikin, K. J., et al. 2015. Correction of overstate- ment and omission in direct-to-consumer prescription drug advertising. Journal of Communication 65:596–618. Asp, E. W., and D. Tranel. 2012. False tagging theory: Toward a unitary account of pre- frontal cortex function. In D. T. Stuss and R. T. Knight, eds. Principles of frontal lobe function. New York, NY: Oxford University Press, pp. 383–416. Gilbert, D., R. Tafarodi, and P. Malone. 1993.

You can’t not believe everything you read. Everett Collection Journal of Personality and Social Psychology 65:221–233. Lewandowsky, S., U. K. H. Ecker, C. M. Seifert, N. Schwarz, and J. Cook. 2012. Misinforma- tion and its correction: Continued influence and successful debiasing. Psychological Sci- ence in the Public Interest 13:106–131. In 1938, actor Orson Welles rehearses for a radio broadcast of H. G. Wells’s The War of the Worlds. Thorson, E. 2016. Belief echoes: The persistent Some Americans panicked when they believed the radio drama—and then newspapers sensation- effects of corrected misinformation. Political alized the panic to demonize their radio competitors. Such incidents demonstrate that misinforma- Communication 33:460–480. tion can be mistakenly spread as fact whether or not the originator had that intention.

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Scientists’ E`^_kjkXe[

egant mechanics of the acoustic era to the intricate circuitry threading The Scientists’ Nightstand, Sumptuous through digital devices. (One patent American Scientist’s books Science illustration, submitted by the Victor section, offers reviews, review Talking Machine Company in 1927, essays, brief excerpts, and more. ot so long ago, when digital depicts an instructional tag that offers For additional books coverage, books were ascendent, avid a suggestion that remains refreshingly please see our Science Culture N readers would speculate useful: “Read your Instruction Book blog channel, which explores from time to time about the future of carefully—it will save you expense how science intersects with other print books. As the number of readers and trouble.”) Each chapter opens areas of knowledge, entertain- browsing print copies of newspapers with a timeline that anchors its topic ment, and society: and magazines dwindled, it seemed and is followed by a lucid essay by americanscientist.org/blogs plausible that book readers might mi- Burrows, an author who specializes grate en masse as well. in music history, that discusses the de- ______/science-culture . More recently digital book sales velopments of that era and effectively have been declining and, for a multi- contextualizes the images to follow. ALSO IN THIS ISSUE tude of reasons, print books don’t ap- These images—delightful, varied, and pear to be destined for the endangered attentively captioned—make up the THE RISE OF BIG DATA POLIC- species list anytime soon. For this, as a bulk of each chapter, and rightfully so. ING: Surveillance, Race, and the reader, reviewer, editor, and certified The real stars are Simon Pask’s copi- Future of Law Enforcement. book addict, I am grateful. Although ous photographs, which manage to By Andrew Guthrie Ferguson. there’s nothing handier than being be both luscious and crisp, of items page 378 able to carry the equivalent of a book- from the EMI archives. From a 1902 case full of titles on a device the size of gramophone that played discs made ONLINE a paperback, it remains true that some of chocolate, to a 1940 U.S. Army– books are best experienced on paper. issued wind-up record player for use Upcoming on our And in a few cases, the full wonder of in war zones, to a shiny array of Sony Science Culture blog: a title may be otherwise lost. Minidisc Walkman devices from the americanscientist.org/blogs Such is the case for an impres- 1990s through the early 2000s, these ______/science-culture sive clutch of recent releases. Each artifacts transfix. I’d encourage any- will richly reward readers who leaf technology CLIMATE CHANGE AND THE one who suspects that and through their pages, linger over their beauty HEALTH OF NATIONS: Famines, are antithetical terms to spend images, and launch into the text. Fevers, and the Fate of Popula- time immersed in these pages. Moreover, each demonstrates how Instead of sound, Keely Orgeman tions. By Anthony J. McMichael. vibrant and gorgeous science-related lavishes attention on light in Lumia: We Choose to Go: A Conversa- titles can be. Thomas Wilfred and the Art of Light tion with Apollo 8 Author Jef- The experience of reading Terry (Yale University Art Gallery and Yale frey Kluger Burrows’s The Art of Sound: A Visu- University Press, 2017). The book’s real History for Audiophiles (Thames lease coincided with the opening of and Hudson, 2017) is akin to strolling an exhibition of Wilfred’s work earlier through a thoughtfully staged mu- this year at the Yale University Art Gal- seum exhibit on the history of sound lery, where Orgeman curates American recording and playback—one that artwork. Lumia is the first book devot- presents technology matter-of-factly ed to Wilfred’s work in 40 years, and it while also dipping into pop culture. aims to introduce the artist to new gen- The book is divided into chapters erations. Enthusiasts familiar with con- representing four eras of audio evolu- temporary artists such as James Turrell tion: acoustic, electric, magnetic, and (who contributes the book’s foreword), digital. Sections of patent drawings Jenny Holzer, and Olafur Eliasson, punctuate the transitions between whose light-based installations are chapters, and it’s easy to lose your- well-known and widely exhibited, From Lumia. self in their details as you take in the may never have heard of Thomas Wil- change over the decades from the el- fred, who pioneered the art form. (His

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Courtesy of the Peabody Museum of Natural History, Yale University Rudolf Zallinger’s 1943 tempura study for his masterwork, Age of Reptiles, prepared him for ing group of volumes is Paleoart: Vi- the daunting task of painting the 110-foot-long mural at Yale’s Peabody Museum of Natural sions of the Prehistoric Past (Taschen, History. This detail shows a few of the creatures depicted in the mural, specimens spanning 2017), by Zoe Lescaze, a writer whose from the Devonian to the Cretaceous periods, based on paleontologists’ understanding at the background includes art history and time. From Paleoart. archaeological illustration. Paging name for the medium, lumia, never of the work, but also its significance through it is like taking a time- and caught on.) His experiments with main the context of technology and phys- space-bending, multicentury glob- nipulating light into art began in 1919, ics at the time. “Broadly speaking, al tour of natural history museums which meant that it was necessary for Wilfred’s precise light-bending tech- and amusement venues and getting him to invent many of the technologies nique mimicked that of physicists’ to compare what scientists and art- that made his work possible. Early in laboratory experiments,” Keely notes, ists from era to era believed prehis- his career, he focused on producing “which often used angled mirrors toric creatures must have looked like. vibrant, abstract performance artworks to test the velocity of light when its The experience begins before you’ve comprised of vividly hued, sinuous path was redirected by reflection. The even opened the book. The cover’s light forms that would flicker, swell, sophistication that the artist demon- pebbly, reptilian surface may take a and diminish on a projection screen strated in his technical work shows his few minutes to discover, as its jacket for audiences who would watch the deep understanding of the behaviors has been designed to stop readers in complex interplay of colors. The effect of light—how it traveled and how it their tracks. There, front and center, is somewhat resembled the aurora borea- interacted with other elements in its a grotesquely beautiful painting of an lis, a look that remained his signature environment.” Essays contributed Inostrancevia shown in profile, its hide style throughout his career. Wilfred by a historian, a curator-conservator flecked with coppery foil that lends invented a device, which he dubbed pair, and a media studies scholar, fo- its tawny folds dimension. Crimson a clavilux, for these performances; it cusing, respectively, on Wilfred’s art viscera dangles from its fangs like a resembles modern soundboards, and in a postwar context, on the process holiday garland. Its amber eye gives he’d play it somewhat like an organ- of conserving the works’ mechanical the impression of regarding the view- ist. Although the performances were structures, and on the artist’s legacy, er with cool contemplation. Painter silent, he thought of them as orches- make for fascinating reading as well. Alexei Petrovich Bystrow has empha- tral, and he named his work in the The still images of Wilfred’s works sized the mammal-like appearance of style of symphonic music, a practice do not disappoint, and photos of the the saber-toothed reptile and his cre- he continued after moving on to cre- equipment he developed and some of ation seems to exist, powerfully and ate installations that played automati- his conceptual drawings are helpful unnervingly, in an interstitial world. cally, many of which were designed to and revealing. Incidentally, the Wilfred Its body plan caught between the rep- project a flow of spontaneously gener- exhibition shown at Yale has traveled tilian and the mammalian, the Bys- ated light forms (that is, they didn’t to the Smithsonian American Art Mu- trow’s Inostrancevia appears to inhabit repeat) and a few that were designed seum, where it will be on display until a time that is at once ours and its own. to be enjoyed in the home. These later January 8, 2018. Seeing these works In fact, that visual collapsing of time— works, which began appearing around in all their performative glory could whereby ancient creatures appear to 1930, prefigured the television, yet the well be worth a trip to the capital— have traveled forward in time—is a devices somewhat resemble cabinet there are some things even the most hallmark of Paleoart. Across its pages, TVs if they’d been made by modern- beautiful book can’t capture. readers may certainly track the ad- ists. Lumia makes it clear why Wilfred That doesn’t mean that authors vance of paleontological knowledge, deserves a spot in the 20th-century and publishers won’t try, though, and but they can also take in the effect of canon, and Keely does a terrific job sometimes the effect is downright different modes and fashions of paint- discussing not only the artistic merits dazzling. The juggernaut of this fetch- ing. Some of these modes make for

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The 1967 Telefunken Mag- weight, which is nearly 20 pounds. A netophone CC Alpha (top) strong bookshelf is a must for these was among a crop of battery- volumes, but the yield will be hours of operated devices that imple- enlightening enjoyment. mented new compact cassette technology to make recorded Dianne Timblin is book review editor for American music affordably portable. Scientist. More than 40 years earlier, design innovations had enabled manufacturers to offer smaller gramophones. A tin children’s model made by Nirona #FZPOE%BUB%SJWFO around 1925 (below) features a small bell-shaped horn that 1PMJDJOH could emit sound at a high volume despite its compact Andrew Guthrie Ferguson size. From The Art of Sound. Top: Interfoto/Alamy Stock Photo, Bottom: EMI Archive Trust Archive Interfoto/Alamy Stock Photo, Bottom: EMI Top: Big data is undeniably a big deal. The process of computationally analyzing huge stunning paleoart. Works by mid- volumes of data to uncover patterns and 20th-century English artist Maurice associations has become a mainstay in Wilson, who had an affinity for Jap- fields as diverse as finance and health care. anese and Chinese painting tech- In his book The Rise of Big Data Polic- niques, exhibit rare warmth and ing: Surveillance, Race, and the Future delicacy. Lescaze points out that of Law Enforcement, Andrew Guthrie Wilson was known for “eschewing Ferguson, a law professor specializing in three-dimensional illusionism alto- predictive policing, big data surveillance, gether,” rendering stylized scenes and the Fourth Amendment, examines that draw and hold the viewer’s the good, the bad, and the ugly of law en- eye. His watercolor of an archae- forcement’s increasing reliance on big data opteryx, depicted in russet and analysis and its driving algorithms. Fer- golden hues, perched on a branch gatefolds!) and in stature. Many books guson provides in-depth discussion of the with its wings spread wide, is sim- about prehistoric life cross my desk in often troubling ethics involved, particular- ply breathtaking. Lescaze proves an a given year, but I’ve never seen any- ly injustices stemming from implicit racial intrepid guide through the scientific thing like this. bias that all too easily becomes encoded in and artistic eras, and her lovely writ- The measure of a book is usually the algorithms. (For more on ethics and ing and good humor make the text a tallied by page count, binding style, or algorithms, see “A Peek at Proprietary pleasure to read. This is a huge book— physical dimensions. For these three Algorithms” on page 326 of this issue.) In in size (oh, the stunning pullouts and titles, I offer instead their combined this passage, Ferguson takes a step back to consider how different municipalities and their police forces intervene to try to prevent violent crime and protect potential victims after these individuals have been flagged as being at risk.

knock on an apartment door. A man gives the prognosis to A a worried mother. Your son might die. He is at grave risk. Others he knows have already succumbed. An algorithm has identified the most likely to be stricken. He is one of a few thousand young men who may die. In Chicago, Illinois, this scene has played out hundreds of times at hundreds of doors. The danger, however, is not some blood-borne pathogen. This is not a doctor giving a cancer diagnosis but a police detective giving a life diagnosis. Violence is contagious, and Photo courtesy of Yale University Art Gallery you are exposed. As a young man in Thomas Wilfred’s 1959 work Study in Depth, Op. 152 was commissioned by Clairol, which Chicago, due to your friends, associ- displayed the luminous, continually moving artwork on a cinema-size screen in the lobby of ates, and prior connection to violence, its headquarters building in New York. From Lumia. you have been predicted to be the

378 American Scientist, Volume 105

victim or perpetrator of a shooting. greater the risk of being a victim or and potential sentencing outcomes Your name is on the “Strategic Sus- perpetrator of gun violence. Who gets for future criminal acts.” These cus- pects List,” also known as the “heat shot? The algorithm knows. And the tom notification letters symbolize for- list,” and a detective is at your door heat-list algorithm has been tragically mal messages of deterrence written with a social worker and a community accurate. On a violent Mother’s Day in black and white. Mess up and you representative to tell you the future is weekend in 2016, 80 percent of the 51 will be prosecuted to the fullest extent not only dark but deadly. A vaccine people shot over two days had been of the law. The message is also quite exists, but it means turning your life correctly identified on Chicago’s heat personal. You—the person named in around now. list. On Memorial Day 2016, 78 percent the letter—are known by police and of the 64 people shot were on the list. are being watched. Data and Its Limitations Using the heat list, police have pri- But the hard reality is that violence Only a tiny percentage of people com- oritized youth violence to intervene in in Chicago has only increased. In fact, mit violent crime. Police tend to know the lives of the most at-risk men. 2016 has seen a heartbreaking uptick the people who commit those crimes, The algorithm remains a police se- in violent shootings, leading to pub- but the difficulty has always been get- cret, but reportedly the factors include lic criticism of the model. Questions ting “the criminals” to know that the past criminal history, arrests, parole remain about the program’s effective- police know they are committing the status, and whether the target has ness and in particular whether enough crimes. Enter “focused deterrence”—a been identified as part of a gang. As has been done to remedy the social theory that seeks to understand and described by the Chicago Police De- and economic risks identified. For ex- dismantle the networks of criminal ac- partment, “The software is generated ample, there exists the open question tors that drive violent crime. Focused based on empirical data that lists at- of whether the algorithm adequately deterrence involves a targeted and ex- tributes of a person’s criminal record, distinguishes between targets who plicit message to a narrow slice of the including the record of violence among are “high risk” (those who might get population that police, prosecutors, criminal associates, the degree to which shot) and those who are “high threat” and the community know who is en- his criminal activities are on the rise, (those who might shoot). Intensive gaged in violence and that the killings and the types of intensity of criminal surveillance and police intervention must end. Person-based predictive policing involves the use of data to identify and investigate potential suspects or Without targeted social service victims. Part public health approach to violence and part social network interventions, the algorithm just became approach to risk assessment, big data can visualize how violence spreads a targeting mechanism for police. like a virus among communities. The same data also can predict the most likely victims of violence. Police data history.” The algorithm ranks these for those who might be victims may is shaping who gets targeted and fore- variables to come up with a predictive not be as important as targeting those casting who gets shot. score of how “hot” individuals might who might engage in violence. But if While these predictive technologies be in terms of their risk of violence. the heat-list formula counts the risk are excitingly new, the concerns under- Selection to the heat list can be ac- and threat equally, police resources lying them remain frustratingly old- companied by a “custom notification may be misdirected. fashioned. Fears of racial bias, a lack of visit.” As described at the beginning of Stepping back, two important in- transparency, data error, and the distor- this chapter, it involves a home visit, sights arise from the heat-list experi- tions of constitutional protections offer usually by a senior police officer, a so- ment. First, the public health approach serious challenges to the development cial worker, and a member of the com- of mapping social networks of vio- of workable person-based predictive munity (perhaps a football coach or lence may successfully identify those strategies. Yet person-based policing pastor). During the visit, police hand who might be involved in violence. systems are being used now, and peo- deliver a “custom notification letter” Second, studying the data to forecast ple are being targeted detailing what the police know about who might be engaged in violence the individual’s criminal past, as well does not automatically end the vio- The Chicago Way as a warning about the future. As de- lence. Custom notifications, while well In Chicago, 1,400 young men have scribed in another police department meaning, may not have the intended been identified through big data tech- document, “The Custom Notification effect if not implemented with a fo- niques as targets for a roster called the Letter will be used to inform individu- cus on addressing underlying social heat list. Software generates a rank- als of the arrest, prosecution, and sen- needs. The second step of providing order list of potential victims and sub- tencing consequences they may face if interventions, resources, and redirec- jects with the greatest risk of violence. they choose to or continue to engage tion must also accompany the risk Based on an algorithm designed by in public violence. The letter will be identification. Without targeted (and Miles Wernick of the Illinois Institute specific to the identified individual funded) social service interventions, of Technology, the heat list uses 11 and incorporate those factors known the algorithm just became a targeting variables to create risk scores from 1 about the individual inclusive of prior mechanism for police. Plainly stated, to 500. The higher the score means the arrests, impact of known associates, mapping the social network of vio-

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of these localized interventions came from the same data set that mapped crime, governmental services, and public infrastructure. Building from the data, the city launched a holistic strategy to address violence reduction focused on those who were identified as being most at risk. Some focused-deterrence policies were implemented with call-ins, “stop the shooting meetings,” and police targeting of suspected offend- ers. Since 2013, a multiagency gang unit has indicted 110 targeted gang members. But a host of other, non-law- enforcement social-services programs also were enacted (and funded). These programs included violence-reduction measures involving mediators, violence interrupters, community first re- Fotan/Alamy Stock Photo sponders, and other individuals who It doesn’t take an algorithm for New Orleans officers to know that the French Quarter regu- worked to defuse conflict and thus larly requires a police presence. To predict and prevent violence more generally, the city works prevent retaliatory shootings. City of- with a technology partner to analyze large volumes of data. Crucially, law enforcement, com- ficials also improved social-services munity organizations, and social service agencies work together on interventions. programs addressing family violence, mentoring, fatherhood classes, behav- lence may be easier than ending the including the location of schools, hos- ioral interventions, and other mental violence. Data identifies the disease pitals, libraries, parks, police districts, and physical health concerns for those but offers no cure. liquor stores, and even streetlights. who were at risk. Programs focused Using crime-mapping software, on redirecting tension in public school Big Data Meets the Big Easy particular violent hot spots were iden- by addressing trauma and on building An example of a more successful, ho- tified. Using social network analysis, restorative justice principles into disci- listic approach to reducing violence particular individuals were identified pline systems. All told, New Orleans can be found in New Orleans, Loui- as being most likely to be victims of adopted 29 different programs focus- siana, once the murder capital of the violent crime. As in Chicago, New ing on family, school, job training, re- United States. In 2013, the Big Easy Orleans analysts could identify par- entry, and community and economic averaged 1.46 shootings a day, and ticular individuals at risk for violence. development. The goal of all of the Mayor Mitch Landrieu turned to data Analysts predicted they could iden- changes was to target those individu- to get a handle on the societal prob- tify between 35 percent and 50 percent als most at risk of committing violence lems driving violence in the city. Pri- of the likely shooting victims from a and then to provide alternatives, sup- vate technology company Palantir has subpopulation of 3,900 high-risk indi- port, and an opportunity to change. partnered with the mayor’s office to viduals. In addition, linkages between From 2011 to 2014, New Orleans identify the 1 percent of violent crime these individuals in terms of rivalries, saw a 21.9 percent reduction in ho- drivers in the city. The city’s ambitious retaliations, and relationships could micide, a better statistic than could be public health approach to violence has explain why these men were in dan- found in similar big cities such as Bal- relied on these insights, as they illumi- ger. Analysts using Palantir systems timore, St. Louis, Newark, or Detroit. nated largely hidden relationships in identified 2,916 individuals from the More impressively, the city saw a 55 already-existing city databases. general New Orleans population of percent reduction in group or gang- Mayor Landrieu’s project—NOLA 378,750 (the 2013 city estimate) most involved murders. for Life—began with data. Because the likely to be the victim of homicide. New Orleans’s holistic approach data sources included large-scale city The data insights, however, contin- to predictive policing did much more systems with continuously generat- ued beyond people. On the basis of the than identify the high-risk people in ing records, Palantir engineers had Palantir analysis, the Fire Department a community. By using public data to to carefully integrate existing police increased its presence around partic- address factors that created an envi- and public-safety data into the system. ular schools, and the Department of ronment for crime, the New Orleans This data included police calls for ser- Public Works repaired missing street- project looked to widen the lens of vice, electronic police reports, proba- lights. The Health Department targeted big data technologies. Funding public tion and parole records, sheriff’s office high-risk schools for violence preven- resources to respond to the underly- arrest and booking records, gang da- tion, and police mapped gang territory ing economic and social problems ap- tabases, field information cards, bal- to identify areas of tension. Alcoholic- peared to offer more long-term solu- listics, and the current case-manage- beverage enforcement targeted liquor- tions. Big data alone cannot stop the ment system. The analysts also added store violations, and neighborhoods shooting without resources to address community and infrastructure details, were targeted for street cleanup. All the underlying causes of violence.

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Nov.–Dec. 2017 Volume 26 Number 6 Sigma Xi Today A NEWSLETTER OF SIGMA XI, THE SCIENTIFIC RESEARCH HONOR SOCIETY

Q & A with Fenella From the President Saunders Fenella Saunders is the new editor- Who is Responsible? in-chief of American Scientist and director of science communications and I would like to reflect on some of the core elements of publications for Sigma Xi. Sigma Xi’s reason for being and what members bring to the table. The Society was formed more than a Are there changes to American Scientist century ago as a means to celebrate accomplishments that readers can expect under your in research as well as to promote collaboration and leadership? companionship throughout the various disciplines. American Scientist remains a premier Sigma Xi is an honor society, meaning that peers and publication for longform narrative sto- mentors nominate members, who must be approved ries about all areas of science, as told by for induction by a well-defined process at the local the researchers themselves. We will con- chapter level or by the Committee on Qualifications President Stuart L. tinue to work with scientists to bring and Membership. It is expected that members will Cooper their process of discovery to a wider hold to the highest standards of research ethics and audience. In recent years the magazine promote the public understanding of science and technology. staff have worked hard to offer our Many of these values are emphasized at Sigma Xi headquarters. An ex- readers articles that convey researchers’ ample of this involves our leadership giving voice to concerns of the scientific unique voices, vividly tell their stories, community in terms of the health and funding of science and technology and and feature dynamic layouts with great the need for research to underpin governmental policy issues. Our involve- custom graphics. We’ll continue to cus- ment in the March for Science this past April exemplified these goals. Other tomize our content to bring readers the important goals, such as promoting public understanding of the importance best experience possible in print, while of research and encouraging youth toward careers in science and engineer- also expanding online blogs, features, ing, are driven forward by the joint actions of our headquarters and our local and multimedia. Watch for more pod- chapters. Finally, after all is said and done by our organizational and local casts, as well as live interviews and oth- chapter leadership, it is incumbent on individual members to have a role in er opportunities for readers to interact these endeavors. with scientists. What does this mean? Sigma Xi members have been elected to a scientific Where do you hope to focus your ef- research honor society and have assumed nontrivial responsibilities of mem- forts as director of science communica- bership in our Society. It is more than just a line on one’s resume. Foremost tions and publications? is a requirement that as long as one’s career has a research component that the member pursue new discoveries with the same drive and enthusiasm In addition to American Scientist, Sigma Xi that brought him or her to membership in Sigma Xi. Members should also publishes Chronicle of The New Researcher be active in nomination of the next generation of inductees and, if possible, (CTNR), a pioneering journal that gives participate in local chapter activities. budding researchers in high school the The future workforce needs to be well populated by individuals with opportunity to publish professionally re- science and engineering skills that are applied with diligence and integrity. viewed research. This cause is close to my Get involved wherever possible in K–12 activities, whether by visiting class- heart, because I started my own research rooms, judging at science fairs, mentoring, or supporting excellence and career in high school. So I hope to expand innovation in precollege science teaching. Engaging the public about the im- CTNR’s reach and impact. Sigma Xi has portance of research is something in which we can all participate and should a great history of involvement in science be willing to do. ethics and nonpartisan policy, and the So- Sigma Xi will continue to have a meaningful role as long as individual ciety has vast potential to contribute more members are active participants in that for which we stand. to these areas.

Sigma Xi Today is edited by Heather Thorstensen Stuart L. Cooper and designed by Justin Storms.

www.americanscientist.org 2017 November–December 381

EVENTS

Symposium Will Address Climate and Health

Symposium on Atmospheric Chemistry, Climate, and Health Featuring a Public Town Hall about Climate Change November 10, 2017 Student Research Conference November 11, 2017 Raleigh Convention Center Raleigh, North Carolina: www.______sigmaxi.org/fallsymposium-src

High school, undergraduate, and graduate students will compete for poster presentation awards at the Student Research Conference after Sigma Xi's symposium. (Image courtesy of Robb Cohen Photography and Video.) You are invited to Sigma Xi’s 2017 fall How did science-based policies of the Simulation and Forecast of Infec- symposium, a gathering of climate re- past lead to solutions for air quality tious Disease: Environmental Deter- searchers, Sigma Xi members, and the and climate? What are some potential minants and Transmission Dynamics public on November 11 in Raleigh, paths forward for current problems? How do scientists predict the spread, North Carolina, to discuss critical growth, and timing of disease issues facing our planet. Join us for The Ozone Hole: From Discovery to outbreaks? in-depth presentations and thought- Recovery provoking discussions about the ef- What science, policies, and actions Student Research Conference fects of climate change on human were successful in putting the ozone Science and engineering students are health and the environment. layer and ozone hole on the path to invited to the 17th Annual Student Re- The registration fee is $75 and in- recovery? search Conference on November 11 cludes lunch. Veterans and active mili- for a poster presentation competition, tary members receive a 50 percent dis- Air Pollution and Health: Scientific professional development workshops, count in honor of Veterans Day. and Public Policy Controversies networking, and a chance to connect The symposium will feature the fol- Does a safe threshold of pollution exist? with the world’s largest research hon- lowing sessions: or society. Humanity and Global Warming: Get the group discount! Groups of The Past Is Prologue: Lessons Learned Views from the Carbon Cycle 25 students or more from the same for Science-Based Policies to Address How will today’s energy decisions im- institution receive a 10 percent regis- Air Quality and Climate pact the future? tration discount.

Members Share Solar Eclipse Stories

Game Day…for Science! School and professor of physics and as- The College of Charleston in Charles- tronomy, College of Charleston ton, South Carolina, threw an eclipse party for 1,500 students, faculty, and We Drove 700 Miles staff members, and the party served My wife and I traveled some 700 miles as a staging area for NASA TV’s na- from Fort Lee, New Jersey, to Madi- tional total solar eclipse coverage. The sonville, Tennessee, to see the total excitement led Alicia Caudill, College solar eclipse. We now want to do the of Charleston executive vice president same thing again in 2024! —Dickson of student affairs, to say, “It looks like Despommier, emeritus professor of pub- game day…for science!” Astronomy lic and environmental health, Columbia faculty and students took the event University Brian C. Lee watched the total solar eclipse off campus to 16 locations, including on August 21 from his driveway in Corvallis, parks and retirement homes. —Jon Read more eclipse stories at ww____w. Oregon. Hakkila, associate dean of the Graduate sigmaxi.org/2017-eclipse.

382 Sigma Xi Today

SUPPORTING STUDENTS

Hiding Where There Is No Place to Hide

Sigma Xi awarded Bagge, a Society member who recently received her PhD in biology from Duke Univer- sity, funding from its Grants-in-Aid of Research program to support her study on seven species of transparent crustaceans called hyperiid amphipods. She published her research in Current Biology in 2016, and her work has been featured in the popular press, such as National Geographic. She found these crustaceans carry an antireflective optical coating that A hyperiid amphipod (Image courtesy of may be made of living bacteria. The Laura Bagge.) coating reduces surface reflections, Duke University PhD graduate Laura Most people never see one of Laura similar to the thin-film coatings that Bagge in the submersible Alvin. Bagge’s favorite animals, a crusta- can be applied to eyeglasses to re- Department of Chemical Engineering cean called Phronima that is nearly duce glare. It helps make the clear and Materials Science at University of transparent to hide itself from pred- crustaceans even harder for preda- California, Irvine, she will continue ators in the open sea. Bagge finds tors to find. her research on how ocean animals them by looking for the one part of Learning how organisms make use camouflage. their body they can’t camouflage— their bodies transparent is interdis- “I am most inspired and motivated the four tiny black dots of the ani- ciplinary work, requiring expertise by placing myself in the environment mals’ eyes. in biology, chemistry, physics, and where these animals live,” she said, “My colleagues often joke that I nanoengineering. Bagge hopes what “because it helps me understand the can’t be sure if I’ve actually caught she and others learn can be applied to pressures these animals face, such one of the clear crustaceans in a jar nanomedicine, the physics of imaging as trying to camouflage themselves because you can’t see anything in systems, and even military defense. in the open water where there is no- there,” she said. As a postdoctoral associate in the where to hide.”

New Partnership Will Support STEM Professionals and Students

Research Triangle Park (RTP), North from the N.C. Biotechnology Center, Carolina, and a US2020 city coali- Sigma Xi, and the Research Triangle tion site. Its mission is to unlock and Park Chapter of Sigma Xi, the Pizza share STEM knowledge and experi- Lunches are held in RTP. ences from local STEM companies Additionally, STEM in the Park will and higher education institutions become a consultant on Sigma Xi’s to K–12 students and educators in K–12 programming, which currently the Triangle region of central North includes a scientific journal for high Carolina. school research, an opportunity to “We are looking forward to working network with professional researchers with STEM in the Park to create new as a Sigma Xi Explorer, an in-person A new partnership between Sigma Xi outreach opportunities for our mem- research presentation competition, and STEM in the Park will work to- bers and to help increase diversity in and an online research presentation ward the goal of ensuring that every STEM,” said Jamie L. Vernon, execu- competition. science, technology, engineering, and tive director and CEO of Sigma Xi. STEM in the Park will also provide math (STEM) professional has career STEM in the Park will provide Sigma Xi’s members with new op- support and that every child is given meeting space and consult on pro- portunities to mentor and reach out in a fair opportunity to pursue a career gramming for American Scientist’s other ways to 5th- through 12th-grade in STEM. Pizza Lunches, monthly public pre- students, especially minority groups, STEM in the Park is a program of sentations about cutting-edge scien- girls, and students from low-income the Research Triangle Foundation in tific research. Made possible by funds backgrounds.

www.americanscientist.org 2017 November–December 383

MEMBER NEWS

New Quarterly Conversations Last quarter’s conversation was about the reproducible science issue; this quarter’s topic is open access

Sigma Xi launched an initiative in July r Start a Best Papers Club wherein Meeting. We encourage all members to to promote and cultivate quarterly membership requires excellence in gather together to discuss this impor- conversations about critical issues in scientific writing. tant topic. research. Executive Director and CEO Jamie L. Vernon prompted members to r 'JOEXBZTUPBEESFTTUIFQSPCMFN Q2 FY2018 Topic: Open Access discuss how Sigma Xi can contribute to that too many researchers are chas- The process of making scientific solving the reproducible science crisis, ing too little funding. results freely available to anyone in light of recent findings about the irre- could improve the dissemination and producibility of many published studies r Create a website that documents the use of scientific results, especially that have hurt the public perception of number of times a given result has for students, who often can’t afford science. been replicated. Provide attribution subscriptions to research publications, “Not only should Sigma Xi members to the researchers involved and the and for the public, who through be calling on all of their qualified stu- details of the replication process. taxes pay for much of the research dents and colleagues to take the Sigma conducted at universities and Xi pledge, but also we can take mean- r Educate the public about the chal- government laboratories. Publishers, ingful steps toward addressing the lenges and processes of scientific however, add infrastructure and problem of reproducibility,” he wrote in reproducibility, including scientific validity to the publishing process, his monthly Sigma Xi Speaks message. methods and analysis, so they under- which requires a viable business Members sent in their thoughts and stand why studies sometimes con- model. Should Sigma Xi promote open contributed in the online community, tradict one another or may fail to be access, and to what extent? What can The Lab: Members to Members. The reproduced. Sigma Xi do to help improve access ideas so far include taking the following to scientific results for the public steps toward a solution: Though some of these ideas draw and students? How should scientific from existing initiatives, they represent publishers be compensated for their r Create a certified reviewers group. Sigma Xi’s first foray into this area. We work in an open access system? As opposed to reviewing submis- will explore ways to put these recom- sions for publication, this group mendations into action, possibly as a Contribute to quarterly conversations in would write critiques of published report that could be shared with the Sigma Xi’s community, The Lab: Members papers, acting as a watchdog for the research community or as a conversa- to Members, at community.sigmaxi.org or research enterprise. tion during the 2018 Sigma Xi Annual email [email protected].______

Vote in the Sigma Xi 2017 Elections All active Sigma Xi members are en- bers with questions or concerns should gion, Northeast Region, Southwest couraged to vote in the Society’s 2017 contact the executive office by email- Region elections. Voting takes place online ing [email protected]______or calling r 3FQSFTFOUBUJWFTGPSUIF$PNNJUUFF and opens at 8 a.m. EST on Novem- (800) 243-6534. on Nominations: Area Groups, In- ber 8. Active members will receive an Open positions in this election are dustries, State, and Federal Labora- email from [email protected]______the following: tories Constituency; Baccalaureate that day with instructions on how to r 1SFTJEFOUFMFDU Colleges Constituency; Compre- vote. The polls will close at 11:59 p.m. r 5SFBTVSFS hensive Colleges and Universities EST on December 7. r %JSFDUPST#BDDBMBVSFBUF$PMMFHFT Constituency; Membership-at- Active members may vote for pres- Constituency, Canadian/Interna- Large Constituency; Mid-Atlantic ident-elect, treasurer, and other open tional Constituency, Northwest Re- Region; Northeast Region; North- positions in the region and constituency gion, Southeast Region west Region assigned to their chapter. Members-at- r "TTPDJBUF%JSFDUPST#BDDBMBVSFBUF large will vote for open positions in the Colleges Constituency, Member- Membership-at-Large Constituency. ship-at-Large Constituency, Re- Information about the candidates is The Society will announce the results search and Doctoral Universities available on the Sigma Xi website at www.____ on its website, www.sigmaxi.org. Mem- Constituency, North Central Re- sigmaxi.org/about/2017-society-elections.______

384 Sigma Xi Today

Your legacy will benefit generations.

Remember Sigma Xi in your will to help researchers and engineers solve the most pressing issues of our time.

To learn more, contact Sigma Xi at 1-800-243-6534 or

[email protected].______

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