SPS SPS Volume XLVI,Issue3 the O bserver

Fall 2012 The the SPSVolumume XLVI, Issue 3 Observer Fall 2012

Editor Devin Powell Failure in Physics...... 3 Assistant Editor Kendra Redmond My First Visit to a Job Fair...... 5 Editorial Assistants Galileoscopes in Classrooms...... 6 Elizabeth Hook Tracy M. Schwab Beyond Borders, with a BANG!...... 7 Copy Editor Special Feature: PhysCon 2012 Cynthia Freeman Students & Stardust: Experiencing the 2012 Quadrennial Physics Congress.... 8 Art Director Tracy M. Schwab Solving NASA's Problems...... 9 SPS President Biased Results...... 10 David Donnelly Texas State University The Physics of Physical Comedy...... 10 SPS/Sigma Pi Sigma Director Chandeliers and Space Gas...... 11 Toni Sauncy Photos and Quotes...... 12 SPS/Sigma Pi Sigma Assistant Director Reflections on the Sigma Pi Sigma 2012 Quadrennial Physics Congress...... 14 Thomas Olsen Experiencing Another Continent...... 15 Society of Physics Students Cool Stars in the Summertime...... 16 One Physics Ellipse College Park, MD 20740-3843 What’s Cooler than Being Cool? Ultracold Physics!...... 17 (301) 209-3007, Fax (301) 209-0839 www.spsnational.org Elegant Connections in Physics: Connecting Worlds Through Tides...... 19 PhysCon 2012: Stay Connected...... 24

The SPS Observer (ISSN 2160-1305) is the magazine of the Society of Physics Students. Published quarterly by the American Institute of Physics. Printed in the USA. Standard postage paid at Columbus, OH. POSTMASTER: Send address changes to The SPS Observer, One Physics Ellipse, College Park, MD 20740- 3841. About the Cover More than 120 schools were represented at the 2012 Quadrennial Physics Congress held in Or- The American Institute of Physics is an organization of 10 physical science societies, representing more than 135,000 lando, FL, November 8-10, 2012. See the special congress section beginning on page 8. scientists, engineers, and educators, and is one of the world’s Image credit: Ken Cole. largest publishers of scientific information in physics. AIP pursues innovation in electronic publishing of scholarly journals and offers full-solution publishing services for its Member Societies. AIP publishes 13 journals; two magazines, including its flagship publication Physics Today; and the AIP Conference Proceedings series. AIP also delivers valuable resources and expertise in education and student services, science communication, government relations, career services for science and engineering professionals, statistical research, industrial outreach, and the history of physics and other sciences.

AIP Member Societies: American Physical Society • The Optical Society • Acoustical Society of America • The Society of Rheology • American Association of Physics Teachers • American Crystallo- graphic Association • American Astronomical Society • American As- sociation of Physicists in Medicine • AVS: Science & Technology of Materials, Interfaces, and Processing • American Geophysical Union

Other Member Organizations: Sigma Pi Sigma, the Physics Honor Society • Society of Physics Students • AIP Corporate Associates

2 | The SPS Observer Fall 2012 Pathways Failure in Physics by John Mather of NASA's Goddard Space Flight Center, a speaker at the 2012 Physics Congress What a Nobel Laureate Learned from his Failed Thesis Project

ailure is the essence of progress, in a particular way; if we never fail, then f we just aren’t trying very hard. But "failure" isn't real, like a proton is. It's only a label. And it seems a little un- necessary for a physicist to decide that a certain subset of all the possible configu- rations of the natural universe qualifies for that label. Abstraction aside, though, the failure of my thesis project on its first flight was pretty darned important to me. The project was conceived by my adviser, Paul Richards, and I worked on it at “...failure is an the University of California, essential part Berkeley, along of research.” with two other grad students: David Woody and Norman Nishioka. It was a balloon-borne, far-in- frared spectrometer designed to measure the spectrum of the cosmic microwave background radiation (CMBR), and it was quite ingenious. The CMBR was predicted in 1948 and would become the strongest proof yet that the expanding universe theory is correct. (The name “big bang” implies to most people that there was a time before time, which is linguistically meaning- less and not implied by the observa- tions.) But to know that the CMBR is a predicted remnant of the big bang, Top: Dr. John Mather delivers his plenary talk, "The James Webb Space Telescope: Science we needed to confirm that it has the Opportunities and Mission Progress," at the 2012 Quadrennial Physics Congress, November right spectrum and that it comes almost 9, 2012. Bottom: Dr. Mather answers questions from students following his plenary talk. Image equally from all directions, not from a credits: Ken Cole. local source. The CMBR had been discovered in interferometer immersed in liquid helium from Berkeley and the balloon base, we 1965, but its status as evidence of the to suppress thermal emission from the in- prepared it for launch. The launch was early universe was a little uncertain, strument and enable sensitive detections. successful. The payload went up and up, since a number of faulty measurements After working on the project for what and then let down 2,000 feet of unrolled had already disagreed dramatically with seemed like forever, in the fall of 1973 we cable that should have allowed the the predicted 3 kelvin blackbody spec- decided that it was time to try a launch, payload to observe the sky, not just the trum. Our payload was to rise above 99 which our team had never done before. balloon overhead. percent of the Earth's atmosphere to get David and I drove the payload to the Imagine our chagrin when the instru- a look between the atmospheric emis- balloon base in Palestine, TX. With help ment did not work. There was nothing sion lines using a polarizing Michelson from Paul and professional engineers we could do except sit in the control

Fall 2012 The SPS Observer | 3 room and watch the data come in. The because the detector preamplifier was motor that was to move the interfer- too cold. David, Paul, and Norm fixed ometer did not turn, and the detector the problems with better electronics and reported an oscillating signal that should better protection for the motor, flew the not have been there. payload again, and it worked that time. As I recall, we were all too tired to Later, they upgraded the instrument display a lot of emotion; the job at hand with liquid helium-3 cooling for the de- was now to retrieve the payload and tectors and flew it two more times. The figure out what happened so we could fly instrument now resides in the Smithson- again. Paul was very generous and let me ian National Air and Space Museum in write a thesis about the instrument that Washington, DC, not far from an over- More than three decades after his botched did not work (and about a ground-based head model of the Cosmic Background thesis project, John Mather would have cause instrument that did work). I hurried off Explorer (COBE) satellite. to smile when he received the Nobel Prize in to my upcoming postdoctoral position What did I learn? Number one, if Physics for his studies of cosmic microwave with Pat Thaddeus at the NASA God- you do not test something, it will not background radiation. Image credit: NASA. dard Institute for Space Studies in New work. Some people think it's worth a try York City, convinced that this CMBR anyway, but I think it's not a matter of work was much too hard for a young chance at all. Nature knows when we are found some faults and fixed them. person. trying to cheat, and Murphy was an opti- One was particularly important and Meanwhile, David Woody conceived mist. Even if you are tired (or broke), was found with a test I might have of an inexpensive environmental test you should not skip the testing. skipped. The moving calibrator body for chamber (made of plywood and Sty- This came back to me much later the space version of my thesis experiment rofoam and filled with dry ice) for the when my luck had turned and I was did not work properly and would have payload and quickly discovered what our working at NASA's Goddard Space wrecked the mission. I thank my lucky problems were. The motor didn't turn Flight Center with a huge team of scien- stars every day for (a) my experience of because it had rusted on the ground in tists, engineers, and technicians, prepar- failure with my thesis project and (b) my the moisture of Texas and because its ing the COBE for launch. The COBE brilliant colleagues at NASA who knew control electronics wouldn't work cold. carried a new and greatly improved quite well why we had to test, and didn't The oscillating signal likewise appeared version of the balloon-borne instrument, give up. Just about 33 years after that along with two balloon payload failure, I got a call from other instruments Stockholm, as did my colleague George built to examine Smoot, for our work on the COBE. the early universe. Part of the point of this story is that Over and over I failure is an essential part of research. had to resist the My friend and noted astrophysicist temptation to Harvey Moseley grew up on a farm and think that I really describes life there as endlessly fixing knew that some- broken things. On a farm, you're pretty thing was okay to much on your own. There is no instruc- launch. tion book and no handy stockroom of With a big spare parts. He says scientific research budget at stake, is much the same, always fixing broken the temptation to things without an instruction book. capitulate to man- I like to think that we are puzzling agement pressure out the giant crossword puzzle of the to launch on time universe, putting in letters and getting was pretty strong. them wrong and finding out and fixing Conversely, after them. I imagine the general public thinks all the expendi- our lives are quite different, as brilliant ture of personal scientists who must know so much. But time and public on the cutting edge of research, we are money, we owed it always looking for things that don't fit, to the taxpayers and the minute we understand some- to get it right and thing, we go on to the next thing we not take chances don't understand. It takes a certain with their funds. degree of nerve to do it, considering This diagram from John Mather's PhD thesis details the anatomy of a So we tested ad- how little we know. But if you like it, balloon-borne spectrometer that failed to collect accurate data after equately, and we welcome to a thrilling life in science! l being exposed to moisture and chilled high in the atmosphere. Image credit: John Mather.

4 | The SPS Observer Fall 2012 Pathways

My First Visit to a Job Fair Reflections from a Novice Job Fair Attendee

by Shouvik K. Bhattacharya of Minnesota State University Moorhead, a 2012 SPS Summer Intern who explored how physics departments can help Shouvik K. Bhattacharya. Image their students be better prepared to enter the workforce upon graduation. credit: Tracy M. Schwab.

take a deep breath and step inside the a positive attitude toward learning new city life motivates employees to perform fair pavilion at the Ronald Reagan things are essential to an employee’s job better. He also tells me that it never hurts I Building in Washington, DC. There are security. I realize that all the representa- to be ambitious. A representative from about 30 small booths occupied by pro- tives at the job fair are actually there the Defense Intelligence Agency asks me spective employers at this summer career to help applicants, and I feel confident why I have not highlighted in my resume expo sponsored by the magazine Equal thereafter. the electronics courses that I have taken. Opportunity, and already four of them Then I stop by the job booth of the The resume I had handed him focuses on are crowded. The University of Virginia US Nuclear Regulatory Commission, my research background in observational booth looks less crowded, so I decide to where I am handed a job list. This gov- astronomy. I realize that having a few visit it first. ernment agency definitely hires physics different versions of my resume would be An officialelcomes w me with a warm undergraduates. The representative asks beneficial. smile and gives me a pen with the univer- me to share this information with anyone In the beginning, I felt a little over- sity’s name printed on it. She says that who would be interested in applying for whelmed, but I soon realized that all of the human resources department recruits the entry-level openings. Job titles include the representatives are there to help and applicants from diverse academic back- general engineer and scientist, both of answer questions. Looking back at it now, grounds, including physics. An applicant which require a minimum cumulative I know what I have to do when I attend with a STEM (science, technology, engi- GPA of 2.8 overall and 3.4 in the appli- my next job fair. The role I played at neering, and mathematics) background is cant’s major. The job descriptions include this fair might be considered that of a expected to have the ability writing, critical thinking, decision making, surveyor, rather than that of a potential to effectively coordinate inspection, and conformity research as the job seeker. I didn't prepare different ver- “I know and collaborate with others. integral duties that employees would have sions of my resume, highlighting differ- what I These are valuable skills to perform. I get a little excited seeing ent skill sets. That is the first thing one that employers care about. all these details. So far this has to be my should do before attending a fair, as the have to She shares her contact in- best experience of the job fair, as I get to resume serves the role of a conversation formation and also requests see an example of how a physics major starter. Wearing business clothes is also do when my resume in turn. can start working after a successful degree a must, because it shows how interested I attend I wander off for a bit completion. and serious one is about finding a job. I and then enter the US The US Air Force posts its jobs on made a few new connections at the job my next Bureau of Labor Statistics the USAJOBS website, which I learn fair, and I’ve now sent follow-up emails to booth. Many who complete at its booth. The representative at the each, conveying my thanks for spending job fair.” bachelor’s degrees in physics Internal Revenue Service booth tells me time with me. The job fair visit was an have taken some statistics that living in a big city can seem tough absolutely amazing learning experience courses, and that is what motivates me and challenging, but ultimately it often for me. l to stop by this particular booth. But the turns out to be beneficial, as dynamic representative informs me that a phys- ics major should apply only if he or she SPS Jobs has a strong mathematics and statistics Remember to make SPS Jobs, the official online job site of the Society of Physics Students background. and Sigma Pi Sigma, an essential part of your career planning! The next representative I speak with, at the Boeing Company's booth, sounds Job Search: jobs.spsnational.org/jobs very positive and enthusiastic. She tells Getting Started: jobs.spsnational.org/jobseekers/profile/ me that the company has many entry- level openings. She advises me to create a profile on Boeing’s career website and SPS Internships: Application Deadline Feb. 1, 2013 to prepare a resume based on the jobs Spend the summer in DC working in outreach, policy, or research. that are available. She emphasizes that Learn more: jobs.spsnational.org/jobs/5023593 being flexible about relocation and having

Fall 2012 The SPS Observer | 5 Interactions

Worldwide, Galileoscopes have had great impact. Here’s a picture of a group of children in Tanzania using a Galileoscope brought by Chuck Ruehle (left), a pas- tor from Racine, WI. Image credit: Chuck Ruehle.

education organizations in the country. The three of us, all Carthage physics students and SPS members, worked with Prof. Arion and spent the summer in New Hampshire, helping out with programs that included solar observations, night sky observations, and public lectures at AMC lodges and high mountain huts. It’s fun to hike telescopes up into the Galileoscopes in Classrooms mountains and show people the sky from Exciting Kids about Astronomy and Physics dark, beautiful sites. In the first year by Coty Tatge, KelliAnn Anderson, and Zach Troyer, Carthage College we talked about the sky with more than 2,000 visitors! In addition to using larger, commercial our hundred years after Galileo’s first Telescopes 4 Teachers (T4T, www. telescopes to do sky shows, we also used telescope observations, the year 2009 telescopes4teachers.org) lets people make Galileoscopes in workshops with scout f was celebrated as the International tax-deductible donations through Astro- groups, camp groups, and kids of all ages, Year of Astronomy (IYA). Several big, sphere New Media, a nonprofit astronomy promoting T4T to as wide an audience as worldwide initiatives were launched to outreach group. The donations pay for possible. Guests have been surprised at engage people with astronomy. Ranking Galileoscopes to be sent to teachers or how well the Galileoscopes work, especial- among the largest was the Galileoscope schools designated by the donors. ly given how inexpensive the devices are. Project (http://galileoscope.org). One T4T isn’t the first such donation We’re hoping that the visitors have great of our physics professors, Doug Arion, program. During the IYA more than 7,000 experiences at our workshops, continue helped start Galileoscope, which is still Galileoscopes were put into use in devel- to be interested in astronomy, and maybe going strong three years later. oping nations. An observatory in South purchase a Galileoscope (or two!) so they You may be familiar with the inex- Africa distributed the donated telescopes. have a great tool with which to observe pensive telescopes sold in stores. They’re But other requests came in from people the sky. often difficult to use and don’t give good who wanted to send telescopes to schools. It has been a great experience working viewing. That’s the kind of experience T4T is the best way to make that happen. with the public, especially with kids, and that won’t turn anyone on to astronomy. The T4T program isn't the only way getting people excited about the sky. SPS Well, the Galileoscope team realized how we’ve been working with Galileoscopes to chapters can get involved by using Galil- big a problem this is and developed a new help improve science education. A new as- eoscopes for their own outreach programs telescope to get people excited—one that tronomy education and outreach program and fund-raisers, and by promoting the has high optical and mechanical quality, partners Carthage College and the Appa- T4T program. The telescopes make great comes with an educational kit, and is very lachian Mountain Club (AMC), one of the Christmas gifts, too! l inexpensive so that people all over the largest and oldest outdoors and nature world can afford it. There are now more than 200,000 Galileoscopes in use in more than 100 Right: Authors KelliAnn countries! Members of our SPS chap- Anderson '14, Coty Tatge ter used the telescopes for astronomy '12, and Zach Troyer '14 outreach programs this summer, and it were 2012 summer astron- was great to hear people looking through omy interns working with Galileoscopes exclaim, “Wow, I really can the Appalachian Mountain see Saturn’s rings!” Club. Here they are near Galileoscope continues today as a the summit of Mount Wash- legacy project of the IYA, manufacturing ington above the Lakes of and distributing telescopes for individu- the Clouds Hut after doing als, schools, and other science education an astronomy program for organizations. One new project called the nearly 100 hut guests. Image credit: Doug Arion. 6 | The SPS Observer Fall 2012 Interactions

Beyond Borders, with a BANG! Above: Water and packing peanuts erupt from a trash can during a Peer Pressure Team Helps Bring Physics to All Peer Pressure demonstration, the "nitrogen trash can blast," at one of the many elementary schools visited by Angelo State University SPS by Blake McCracken, Angelo State University members during their annual road trip. Image credit: Hardin Dunham.

ur time at Yeso Elementary ceive from our exciting demonstrations is to answer all of the questions in the time School in Artesia, NM, was welcomed, especially when they learn that we have. Some students are so interested O almost over. Standing in front our program comes at no cost to them. and inquisitive that they get back to class of a group of 3rd and 4th graders, we got This past year, in conjunction with late. ready to close our physics demo show the national SPS theme “Science Beyond SPS volunteers have noticed the with a bang . . . literally! The students Borders: Physics for All,” we decided to children’s eyes, glued with anticipation to were silent in anticipation, as were we. take our road trip out of Texas and into the presenter, just waiting for the climax Then, all of a sudden, a loud boom New Mexico. At 7:30 in the morning on of the demonstration. The soft and long from a rubber trash can broke the silence. Monday, May 14, our 700-mile journey “woooooow” that follows, spoken by the Water, packing peanuts, and a white haze began. We visited three schools in Texas students in unison, gives us an immedi- shot into the air. As the excited students on the way to New Mexico. Then, on ate satisfaction born from the impact yelled, screamed, and clapped, a confused Wednesday morning, the ASU SPS Peer we are having on these children. We also and distraught teacher bolted out of a Pressure Team made its out-of-state receive hundreds of thank you letters from nearby building to see what all the ruckus debut in eastern rural New Mexico. Five students saying they want to be scientists was about—only to find teachers, admin- elementary schools welcomed us with ex- just like us when they grow up. This is istrators, and 200 students enthusiasti- cited groups of students and teachers. The extremely rewarding, and we anticipate cally applauding for some college students students filed into gymnasiums, cafeterias, that ASU physics will find a way to con- from Texas. and libraries, where our team of 13 college tinue these annual outings. The value of Memorable events such as this one are students and two physics faculty members introducing children all across the state, why SPS members in the Angelo State from Texas was ready and waiting to wow and even the nation, to the wonderful University (ASU) Peer Pressure Team the kids with both familiar and unfamiliar world of physics is well worth the trip. l continue the Physics Road Tour year after equipment. year. The tradition began in 2003 and has During our shows, physics concepts continued to be a great success every year such as pressure, light, sound, and since. During the week after university temperature were explored using marsh- classes end, we spend hours driving from mallows, fire, liquid nitrogen, lasers, and school to school. Each day is booked with other props. Our team created a custom at least two shows. laser light show for each school, much to The continuous hustle and bustle is the delight of the children. We finished well worth it. By targeting schools with each show with one of our more boister- significant populations of underprivileged ous demonstrations, either a nitrogen students, we can make a meaningful im- trash-can blast or a nitrogen thunder pact on students who might not otherwise cloud. be exposed to the possibilities of phys- We always make sure to provide ics. Usually, the schools we visit lack the students with some time to ask questions. SPS members in Angelo State University’s Peer Pres- funds and resources needed to provide That's the time we value most, because sure Team prepare to cross into New Mexico during their students with a robust science cur- that's when the true interest of the their annual Physics Road Trip. Image credit: Hardin riculum. The enrichment the schools re- students shows. Oftentimes we're unable Dunham.

Fall 2012 The SPS Observer | 7 Special Feature: PhysCon 2012 Students and Stardust Experiencing the 2012 Quadrennial Physics Congress

by Lily Udumukwu, University of Miami

More than 800 students, alumni, and professors participated in the 2012 Quadrennial Physics Congress. Image credit: Liz Dart Caron.

n November 8, 2012, there’s something electric dotes of immeasurable value. or her esteemed contributions the University of about the human drama of It was enthralling. Strangers to the world of physics. O Miami’s SPS chapter the island, a treasured piece of only the night before engaged Dialogue took place over arrived at the Sigma Pi Sigma history he’s been a part of for in constructive debates over buttered bagels. Earnest and 2012 Quadrennial Physics Con- many years. the importance of science to eager students discussed the gress (PhysCon)—just in time It was not the numbers— public policy, in workshops secrets of the universe with for what would be a once-in-a- more than 800 students, that highlighted science's practicing scientists during lifetime affair for many of the faculty, alumni, and profes- potential to improve our ever- “Breakfast with the Scientists.” participating students. sionals who traveled from as changing society. Omnipresent Confident handshakes brought Held in Orlando, FL, the far away as China—that made was the murmur of excite- together admissions person- conference brought together the most profound impression ment and intrigue, as a sea of nel from top-tier universities people of different backgrounds at the congress. Instead, it was hundreds broke into resounding and prospective candidates and social circles, linked by the gravity of the attendees' applause at the conclusion of presenting their exceptional one common interest: a passion accomplishments, imparted in yet another anticipated guest resumes at the exhibit hall. for physics. The diverse menu a series of inspirational anec- speaker’s talk highlighting his In one corner, professors and of world-class speakers at the professionals huddled around event included a Nobel laure- a poster presentation. Off- ate, an astronaut, a sitcom con- the-cuff conversations with tributor, and a Fellow from the students ensued. US Department of State. All Reverberating throughout were luminaries in physics. All the days of this unique and in- were an honor to experience. credible meeting was the theme Some students at the con- of “Connections.” Transcending gress embarked on a “behind- expertise, school, region, and the-scenes look” at the NASA even language, we were united. Kennedy Space Center on At the close of this event, the Merritt Island. The tours were physics students of UM left specially arranged by Space as a community with newly Center staff, and ours was formed intangible connections, hosted by a comical (yet com- fueled by Nobel laureate John mitted) retired NASA firefight- Mather’s parting words: “We er. Though he didn't major Quadrennial Physics Congress attendees tour NASA's Kennedy Space are all made of stars.” l in science, our host admitted Center. Image credit: Ken Cole.

8 | The SPS Observer Fall 2012 Special Feature: PhysCon 2012 Solving NASA's Problems A Behind-the-Scenes Look at NASA's Kennedy Space Center by Kevin Rhine, Idaho State University, who joined dozens of other SPS reporters for a special tour of NASA's laboratories and launch pads. All Congress attendees were treated to a general tour.

s a child, I fre- quently heard Moon Makers A about the achieve- ments of our impressive space At NASA many different program but found it difficult fields of science are being to imagine what really goes on utilized to further human at NASA—aside from sending space exploration. I noticed rockets beyond our atmosphere. lots of effort going into After seeing for myself during cutting the costs of and a behind-the-scenes tour of the increasing the efficiency of Kennedy Space Center, it all space travel, specifically by seems quite clear now. NASA is extracting oxygen, hydro- a place for problem solvers. gen, and other elements This organization reaches from regolith (lunar soil) to not only into the sky, but use as fuel, water, and air deep into the general physics for the next leg of the jour- community. Bob Youngquist, ney into space. The first lab a NASA scientist who gave us we went to was the Regolith an extremely enjoyable and NASA's Bob Youngquist demos a device for detecting leaks. and Environment Science Image Credit: Michael Harrington. informative demonstration, and Oxygen and Lunar has for decades found solutions Volatile Extraction (RE- to problems for which other pulses to disperse the pesky All weight goes into the drill- SOLVE) lunar rover develop- NASA departments are not particles. This approach would ing process, rather than just a ment lab. There, the focus specialized. One such prob- be especially useful for cleaning fraction. Interestingly, due to was on combining robotics and chemistry to extract, lem stemmed from the need the camera of a rover explor- buoyancy, underwater robotic analyze, and produce to closely examine the space ing a planet that has little or drilling can result in some of water from regolith. Another shuttle, liquid fuel tank, and no atmosphere, where dust the same problems as in the lab we visited develops solid rocket boosters prelaunch. interacts with other matter in lunar situation. automated and remote-con- Measuring the size and severity ways it doesn’t here on Earth. I came away from this trip trolled mining techniques of blemishes from the ground is With more progress, this may to NASA with a renewed sense for missions to the Moon difficult. So NASA scientists ar- be a technology we will begin of clarity and a new motiva- and to Mars. Much effort ranged two laser pointers with seeing in terrestrial vehicles tion for tackling the problems I is also going into testing to parallel beams a fixed distance and eyewear. sometimes face in my own life. determine the best material apart in a portable box. This Another endeavor under- During the final night of the to build launch and landing box could be mounted on a way at NASA is the pursuit conference, a friend and I found pads on low-gravity bodies. camera, allowing a photogra- of efficient lunar mining. The ourselves stuck in the sand in In the last lab we visited, pher to document any faults low-gravity environment of the a rented jeep that lacked four- projects varied from the from the ground with two Moon makes a normal dozer wheel drive. After several hours detection of minerals while pinpoint laser dots providing a or drill design impractical. On of digging, lifting, and experi- a rover is in motion to the sizing scale. This simple device Earth we can make tractors menting with various makeshift effects of LED light color has been used not only to fur- as big and heavy as needed in wooden ramps and levers, we temperatures on the sleep ther space exploration, but to order to perform in whatever might have lost morale. But we cycles of astronauts. improve crime scene investiga- environment they are designed worked with the determination tions. for. But this brute-force ap- and deliberate thoughtfulness by Michael Harrington, During another presenta- proach isn't cost effective on of the NASA scientists who Appalachian State University tion, we learned of a technology the moon, since lifting the spoke to us. We resolved our being developed to clear sand extra pounds into space is very problem. and dust from a glass pane expensive. The solution being To many, the technologies concepts and applications we without the use of mechani- developed is a lunar tractor that come out of the NASA already understand, construct- cal wipers. Nearly invisible that lowers counter-rotary drill- space program are indistin- ed by people not much different electrodes embedded in the ing buckets at both of its ends, guishable from magic. To me, from myself, and held together glass create electromagnetic lifting up the entire machine. they are simply outgrowths of by ingenuity. l

Fall 2012 The SPS Observer | 9 Special Feature: PhysCon 2012

Biased Results Stith illustrated this con- (students and faculty) should Prejudice Damages Academia, James Stith Warns cept using a story told by one take to ensure their environ- by Jennifer Rehm, Georgia State University of the great civil rights leaders, ment is growing toward a Desmond Tutu. Archbishop diverse perspective. “There he subject of race and Ratings of verbal skills were Tutu boarded a plane in Jo- should be at least one person gender is systematic lower when evaluators were hannesburg one day and, upon in every department to whom "Tin our community,” told an African American noticing that both of his pilots reports of discrimination can said James Stith, Vice Presi- wrote a piece of text as op- were black, felt so proud to see be made; this should be known dent Emeritus of the American posed to a white person. In the day in which this equity by everyone,” said Stith. Those Institute of Physics. He opened another study, employers were was possible. When the plane in positions of power who have the November 8 workshop more likely to hire an applicant later hit turbulence, he found nothing to lose professionally “Connecting Diverse Perspec- if the name on a real woman’s himself wishing that his pilots should speak up and empower tives in Science” with astonish- CV was changed to that of a were white. “At that point he those that feel powerless. Said ing findings from studies of man. Every study showed a realized how damaged he was,” Stith: “Not saying something unconscious bias. During blind, significant bias due to race or said Stith. is a way of condoning the randomized trials, evaluators gender, but most interestingly, In a later interview, Stith behavior. We need to create a assigned the exact same job the race and gender of the emphasized the importance culture of openness. Students performance a lesser score if evaluator from which the bias of discussing diversity among and faculty need to have these told it was completed by a came did not play a significant colleagues and the steps all conversations.” l woman rather than a man. role. members of a department The Physics of Physical Comedy David Saltzberg on Science Outreach Via The Big Bang Theory by Jeni Hackett and Elana Urbach, The College of William and Mary

okes that mention non- Saltzberg found himself him. This breadth exposes the have to like the characters,” inertial reference frames working as a science consultant audience to a wide variety of Saltzberg reiterated through- J were once relegated by chance, through a friend of scientific terms and experi- out his talk and our interview. to laboratory lunches and a friend. “The writers are big ments. What viewers choose Penny, the girl next door, also meetings between undergradu- geeks,” says Saltzberg. They to do with this exposure is plays an important role. “Every ate science majors. Complex want, first and foremost, to up to them. One fan actually science show has that one char- mathematical formulas tended make the show entertaining performed the calculations to acter that isn’t a scientist, so to be feared by the general but also strive to do it right, to fact check a joke. When she [the scientists] can turn to that public. References to cutting- never let bad science slip in, he got a different answer than the character to explain what’s edge science were for science says. one in the show, she struck up going on.” The physicists fiction. But now, millions tune Listening to his talk, I real- a conversation with Saltzberg have to learn to communicate in weekly to watch the exploits ized just how much effort is about it! with Penny, and in so doing of four scientists on the sitcom put into making the sitcom not The fact that The Big they gradually expose her to The Big Bang Theory, in which only scientifically accurate, but Bang Theory has become such scientific ideas. By explaining all of the above occur regularly full of background nods to the a hit indicates a shift in the science to her, they explain sci- and, more impressively, accu- scientific community. White- perception of scientists in the ence to the audience. rately. Suddenly, physicists are boards covered in equations are popular media. They’re no “It’s pretty clear what I’ll in the spotlight, as entertainers just the tip of the referential longer relegated to lab coats be remembered for at this rather than educators. iceberg. According to Saltz- (Saltzberg took the writers on point,” says Saltzberg. He says Ensuring the soundness of berg, if you send in a research a tour of UCLA, where they he doesn’t find that frustrating. the science in The Big Bang poster, it could be used in the saw that none of the physicists By being involved in the show Theory is David Saltzberg, a background of a scene. We did wore lab coats) and no longer he helps spread awareness in a high-energy physicist who stud- spot him picking up some Phy- background characters, but are subtle way. Anything that gets ies the particles that rain down sCon fliers, and PhysCon did instead brought to the forefront the general public captivated on Antarctica from space. He host a poster session… material as main characters. with (or even just a little bit doesn’t write the jokes or have for the university set’s message The characters provide an more understanding of) science a hand in shaping the show's board, perhaps? accessible point of reference is something that we welcome characters. Instead, he links “We’re broad but not very for the general audience as to in a prime-time sitcom spot. l the writers to the scientific deep,” Saltzberg explained what a physicist is. “For people community. during our interview with to tune into a sitcom, they

10 | The SPS Observer Fall 2012 Special Feature: PhysCon 2012

Chandeliers and Space Gas Mercedes Richards Sees the Universe in 3D by Katrina Hanson and Theodore McDonough, University of Wisconsin–River Falls

hat do chan- has adapted and deliers and advanced this W extraterres- natural sur- trial bodies have in common? vival skill into Both are objects of interest a relevant and for Mercedes Richards, whose useful imaging childhood fascination with her method. neighbor’s illuminated fixtures The intrinsic was a mere antecedent to her value of tomog- now-preeminent knowledge of raphy is being binary star systems and the realized through gas flows between those stars. major applica- The Penn State Department of tions in the Physics and Astronomy profes- fields of medi- sor joined us in Orlando, FL, cine, oceanogra- as one of PhysCon’s notewor- phy, geophysics, thy plenary speakers. archaeology, As Richards presented her and even art. talk, “The Incredible Tomog- The healthcare Group photo of several UWRF students with Richards immediately after her presentation. raphy Imaging Technique,” it industry relies From left to right: Wesley Barnes, Tyler Capek, Katrina Hanson, Mercedes Richards, Alesha became evident that both her on tomographic Radke, Samantha Oswald, and Philip Middlemiss. Image credit: Ken Cole. topic and the woman herself technology every truly embody the 2012 congress time a CAT (computed axial considered an early applica- angles and superimpose these theme: “Connecting Worlds.” tomography) or MRI (magnetic tion of tomography. Neverthe- projections into a representa- A Jamaican native, Richards resonance imaging) scan is less, astronomy is considered tive figure. Richards initiated completed her undergraduate ordered. Similarly, artist Louis to be one of the last scientific the use of this technique when work at the University of the Tiffany incorporates layers of disciplines to realize the imag- she collaborated with Russian West Indies. She then traveled stained glass into his pieces ing technique’s full modern scientists to produce the first to England to earn her mas- to create a three-dimensional usefulness. Despite its belated three-dimensional velocity im- ter’s degree from York Uni- effect. Seismic tomography introduction, tomography has ages of magnetically threaded versity, before completing her applies tomography to primary now become a staple within gas streams. This application doctoral requirements at the and secondary waves moving astrophysics’ technological of tomography is truly incred- University of Toronto. She is a through Earth to scan the cen- arsenal. ible, as the name of her plenary living example of the impor- ter of the planet which cannot Richards uses Doppler talk suggests. tance of promoting diversity in be reached. Radar (radio detec- tomographical imaging to After Richards' presenta- science. tion and ranging) and Sonar study binary stars. About 70 tion, we shared a meal with Her technique of choice, (sound navigation and ranging) percent of stars that appear to her. She was very accommodat- tomography, is itself a tool for are critical imaging techniques be single are actually binary ing in our requests for material, connecting and communicat- that provide the means for or multiple star systems. Stars and her willingness to work ing. This approach to imaging using tomography to map geo- in such systems transfer gas with students was encouraging. pieces together two-dimensional logical and oceanic Earth and from one to the other, typically The conference brimmed with projections to create 3D imag- even led to the rediscovery of forming rings of gas around inspiring moments and learning es. Humans already use a form the sunken Titanic. recipient stars. opportunities, but it was Rich- of tomography in their every- Now Richards and other When white-dwarf stars lose ards who truly embodied the day lives, Richards pointed out. scientists are applying the their ring of gas, tomography heart of PhysCon’s motto. Not When we see the shadow of a far-reaching abilities of can produce three-dimensional only does she connect worlds, wolf on a tent wall while camp- tomography to yet another images of the gas. The orbital she gives the next generation of ing, our brains conjure up the field: astrophysics. Aristotle’s motion of the stars leads to scientists the courage to be fas- animal’s real-space stature. We rationalization of Earth’s cyclic Doppler shifts in their cinated with its own personal immediately identify the flat spherical shape, based on the spectra. This characteristic al- “chandeliers.” l shadow as a projection of the projection of its curved shadow lows scientists to obtain views fully fleshed-out being. Science on the moon’s surface, can be of a star from a vast range of

Fall 2012 The SPS Observer | 11 Special Feature: PhysCon 2012

Yashashree Jadhav (right) learns more about GradSchoolShopper from Exhibitor Daniel SPS Zone 9 Associate Zone Councilor Brandon Clary (left) inducts Greenberg. Freeman Dyson (right) as an honorary member of Sigma Pi Sigma.

I loved that many of the speakers stayed around for the entirety of the conference so we were able to talk with them in a smaller group setting. – Grove City College

Participants in the "Connecting Physics and the Public" workshop explore the theme "Connecting Worlds."

Students from Southeast University in China enjoy the Kennedy Space Center Visitor Complex.

"Connecting Academia and Industry" workshop leader Shelly Arnold (center) engages with students at the Breakfast with the Scientist event.

It was surprising to see the diversity of Attendees engaged in discussions at various workshops, while moderators groups at the Confer- known as "Workshop Wizards" wandered around facilitating discussions. ence. Freeman Dyson himself even noted that there were nearly We would be lying if we said we 50 percent women! weren’t geeking out in the extreme as our bus drove up to the famous – University of shuttle launch countdown clock. Central Florida – The College of William and Mary

Filling in the famous countdown clock during their tour of NASA’s Kennedy Space Center are (left to right), former SPS Associate Zone Councilor (AZC) Chris Faesi, Zone 11 AZC Audrey Burkart, Zone 15 Dayton Syme, Zone 4 AZC Mary Clare Roche, former Zone 10 AZC Jenna Smith, and Zone 18 AZC Chad Garrison.

12 | The SPS Observer Fall 2012 Special Feature: PhysCon 2012

Poster presenter Adetogun Adeyemo received an Honor- Yashashree Jadhav (right) learns more about able Mention for the Outstanding Student Poster Award, GradSchoolShopper from Exhibitor Daniel sponsored by the Optical Society (OSA). Greenberg. Much of what we experienced will help us in the future whether we wish to enter directly into the Sarah Reiff and Sylwia Ptasinska from the workforce or pursue further learn- University of Notre Dame speak with a ing in graduate school. student in the Exhibit Hall. – The College of Wooster

We hope that those that come after us will follow in our foot- steps and be part of the 2016 PhysCon in San Jose. – Roberts Wesleyan University For more information & PhysCon photos, visit: www.spscongress.org

Attending the Students from Southeast University in China enjoy the Kennedy conference for us Space Center Visitor Complex. was like meeting a long lost family. The love, support Throughout the conference, and friends that one theme surfaced repeat- we made during edly in almost every lecture the conference and workshop. Outreach to will last with us the public is crucial for the forever. advancement of physics. – St. Peter’s College – Marquette University

Students take advantage of some time to socialize between sessions.

I for one was very surprised and impressed at the turnout and dance skills of an all physicist dance party. – Michael Harrington, Appalachian State

The dance floor at the "Club Congress" party sponsored by the American Physical Society was packed all evening.

Image credits: Ken Cole. Fall 2012 The SPS Observer | 13 Special Feature: PhysCon 2012

Reflections on the Sigma Pi Sigma 2012 Congress An Old-Timer's Perspective

by Dwight E. Neuenschwander, Southern Nazarene University

have been privileged to David Mosher, director of the attend every Quadren- National Security Division of I nial Congress of Sigma Pi the Congressional Budget Of- Sigma since the first one of the fice, tested the physics students "modern era," which took place with a model exercise that in Dayton, OH, in 1992. What bridged science and society. He a ride it has been! I recall how asked groups to decide how to the organizing committee of cut more than $80 billion of the 1996 Congress worried spending from federally funded whether even 100 people would science programs. As you know, show up. Several members of physics students are always up that committee were present at to a challenge! But the sober- the 2012 Congress, which drew ing exercise made everyone more than 600 students and realize the difficulty of such a another 200 faculty members task, ponder the consequences and alumni to Orlando, FL. of different choices, and con- Much has changed. Our hearts sider how science interacts with were glad. politics—which can be just as Sigma Pi Sigma has made complex as physics itself. a place for itself in the wider Revolutions are almost physics community. This year's always started by young people congress overflowed with not who eagerly want to change only a passion for physics and Dwight E. Neuenschwander (right), a former director of SPS and the the world. Those with physics- a spirit of sheer joy, but also at large member of the SPS Executive Committee, is pictured at the trained habits of mind are with a combination of activ- 2012 Quadrennial Physics Congress with another former SPS director, especially well equipped to ism and a willingness to serve George Miner. Image credit: Ken Cole. enact those changes responsibly the larger society. Yes, a good and sensibly. Both the phys- time was had by all. But more another. Let us keep that ball Most of the congress attend- ics enterprise and society at importantly, Sigma Pi Sigma, rolling! ees were young. The youthful large would be well served by in partnership with the Society Relationships hold com- exuberance that filled this incorporating those who have of Physics Students and other munities together. For large congress revitalized us old-tim- a passion for physics and are organizations, is now poised to communities to remain stable ers, reminding us of the values willing to strive earnestly for make an indelible contribution and authentically alive for long and passions that drew us competence. That is where Sig- to the culture of physics. timescales, those relationships into physics in the first place. ma Pi Sigma and the Society of The proactive enthusiasm must be based on openness, Conversely, the advice and Physics Students come in. As exhibited during the congress diversity, and respect. Over the wisdom of senior physicists was in baseball or in music, physics and the broad range of support decades physicists have some- clearly valued and appreciated will always have its legendary it enjoyed from institutional times appeared to be rather by the young. It was heart- superstars. But physics needs cosponsors suggest that the exclusive. Agendas within the warming to see the likes of a deep bench, a broad base of physics community may be community deemed worthy of Jocelyn Bell Burnell and John informed appreciators. ready to encourage not only respect have often been quite Mather surrounded by crowds The 2012 Congress showed those who invest their lives in narrow, dictated by esoteric of young people. Freeman Dy- how young people who carry research, but also those who problems in elite laboratories. son was particularly amazing. this tremendous reservoir of en- want to use a physics education But physics is too important Eighty-eight years old, he stood thusiasm, talent, willingness to to reduce poverty, ignorance, and too powerful and too patiently for three days, facing serve, and passion for physics— and despair. Critically placed beautiful to be owned by a long lines of people waiting all spiced with a joyful love of in the landscape of physics small number of experts talking to shake his hand, turning no life—can find one another and society meetings, the congress mostly with each other. The one away. He was essentially work creatively in the interest provides an effective venue for Sigma Pi Sigma Congresses can the last congress participant to of improving the well-being a wider democracy in physics, revitalize how the physics com- leave on Saturday night. of civilization and life on our by helping such people find one munity sees itself. A workshop coordinated by planet. l

14 | The SPS Observer Fall 2012 Meeting Notes

immediately upon entering their universi- Experiencing Another Continent ties, which made me slightly jealous; their demanding high school curricula made fur- A Shared Love of Physics Breaks Down Barriers ther general education in college unneces- sary. Such a system lets students progress by Christopher Frye, University of Central Florida, reporting on the International quickly to explore quite advanced material Conference of Physics Students (ICPS), August 4–10, 2012, Utrecht and Enschede, the Netherlands by the third year. However, I do prefer the American system's approach of absorbing the master's degree into the PhD pro- gram. This allows students to build strong relationships with professors at their universities and provides undergraduate research opportunities quite uncommon throughout Europe. The opening night of the conference began with a welcome lecture by the Dutch physicist-turned-politician Jan Terlouw. Speaking in a cathedral built shortly after the turn of the first millen- nium, he described his love for the beauty of physics and the search for truth, and stressed the responsibility all physicists hold as citizens. He emphasized that those who quantitatively understand the laws of nature must admonish their leaders and their peers when policies seem doomed for failure. Terlouw warned the audience that current economic models, upon which governments base decisions, assume infi- nite growth can be achieved; however, we live on Earth, which is essentially a closed Dormitories at Utrecht University campus in the Netherlands. Image credit: Christopher Frye. system once one includes the Sun. Because infinite growth cannot occur in a finite system, he fears society may soon collapse pon arriving overseas for the the previous day on the bus. A shared love and calls on scientists to spread the word. 2012 International Conference of physics quickly broke down the barriers In a fascinating two-hour lecture, U of Physics Students (ICPS) in between students of different cultures. Hitoshi Murayama of the University of the Netherlands, I immediately encoun- Learning about other countries' ap- California, Berkeley, spoke about neutri- tered a language barrier. It would be a proaches to studying physics forced me to nos and why they might be the reason constant reminder during my stay that analyze my own opinions about the US that stars, planets, and humans are all I was a visitor in a foreign country and education system. Many of the students made of matter. He discussed theories that culture. I developed an envy of European I met last summer specialized in physics combine ideas about antineutrinos, extra students proficient in two, three, or even four languages, having spent their lives in More Information multicultural environments. The event fell at the end of my sum- Christopher Frye received an all-expenses paid trip to ICPS as a winner of the 2012 SPS mer studentship at CERN in Geneva, Outstanding Student Award for Undergraduate Research, along with fellow winner Rachel Switzerland, so I had already enjoyed nine Ward from Utah State University. Read their research abstracts and full meeting reports at weeks immersed in a European environ- www.spsnational.org/programs/awards/2012/osa.htm. Interested in applying for the 2013 ment. But at ICPS I met students coming Outstanding Student Award? Visit www.spsnational.org/programs/awards/student.htm. from an especially diverse collection of Applications are due March 15, 2013. countries. Some had just entered uni- versity. Others were nearly finished with doctorates. The friendliness with which all Next up attendees treated one another took me by surprise. Each encounter with a new group Heriot-Watt The next ICPS will take place of students gave me the impression that August 15–21, 2013 they had all come from the same univer- {ICPS} Edinburgh, Scotland sity, even though they had often just met 2013 www.iaps.info/icps/scotland-2013

Fall 2012 The SPS Observer | 15 Meeting Notes

dimensions, and asymmetries between matter and antimatter. These theories Cool Stars in the Summertime attempt to explain why shortly after the big bang, the universe consisted by Stephanie Douglas, Franklin & Marshall College, reporting from Cool Stars 17, The mostly of matter instead of antimatter. Cambridge Workshop on Cool Stars, Stellar Systems and the Sun, June 24–29, 2012, Bill Unruh of the University of British Barcelona, Spain Columbia, Vancouver, spent the major- ity of his lecture explaining an illumi- nating analogy between photons travel- ing near a black hole and water waves traveling on the surface of a stream with varying current speeds. It sur- prised me to discover that experiments done with water waves have provided insights into black hole thermodynam- ics. During the conference, I also en- joyed hearing about the research proj- ects of the new friends I made during the student lecture sessions. I especially enjoyed talks about knot theory and the foundations of quantum mechan- ics. During the poster session, I had an illuminating discussion with a student studying tachyons, hypothetical par- ticles that travel faster than light. I also had the privilege of giving a talk about my latest research at the Stephanie Douglas (left) poses in front of the poster she presented at Cool Stars 17, joined by Christine Wilson (right). Image credit: Stephanie Douglas. European laboratory CERN—a new method for beam splitting in a machine called the Proton Synchrotron. With uring his talk at Cool Stars, Todd meetings of the American Astronomical 20 minutes allotted for my presenta- Henry of Georgia State Univer- Society (AAS), but Cool Stars was smaller, tion, I went into detail, describing the Dsity had the entire audience stand more focused, and much more international. theory and the calculations behind my up and participate in an exoplanet dance. The conference is held every two years, work. I enjoyed the challenge of making It was, quite possibly, the funniest moment alternating between the United States and the talk understandable to those in the of the conference. Europe. This year 433 attendees gathered in room with a knowledge of only elemen- Astronomers were told to perform differ- Barcelona to discuss pretty much any star- tary physics. ent motions depending on what exoplanet like object that astronomers consider "cool" All together, ICPS was a wonderful search method each was most involved in. . . . everything from recently discovered learning opportunity. Not only did I Those participating in the Kepler mission room-temperature Y dwarfs, to old giant gain experience in presenting a lecture and other transit searches, which wait stars that measure a toasty 6,000 Kelvins. on my own research and finding out for planets to pass in front of stars and The coolest hydrogen-burning stars, M about neutrinos in the early universe, block the starlight, stood with their hands dwarfs, are gaining a lot of attention. Bár- but I also came to appreciate the rich clasped behind their backs. Those using bara Rojas-Ayala of the American Museum diversity of cultures and perspectives radial velocity searches, which look for the of Natural History explained to me that the exemplified by the new friends I made gravitational wobble of a star induced by details of M dwarfs were largely ignored for from around the world. l a planetary companion, moved their heads a long time. The stars were thought of as back forth in “what we in America call 'the small, boring, and unimportant. But they funky chicken,'” said Henry. The remaining are ideal hosts for detectable planets, and members of the audience were instructed as Caltech's Kaspar von Braun stated dur- to move side to side and shake their heads ing his talk, “You understand the exoplanet back and forth while twisting their arms only as well as you understand the parent around in a circle to represent all the star.” In light of this, the entire last day of effects that could show up in a third, lesser- the conference was dedicated to M dwarfs known method for finding planets around as exoplanet hosts. M dwarfs make good nearby stars: astrometry, or the precise hosts for detectable exoplanets because measurement of stellar positions. they are relatively dim compared to Sun- Cool Stars 17 provided a new meeting like stars. A planet transiting the face of a Utrecht, the Netherlands. experience for me, and not just because of dimmer star will block a higher percentage Image credit: Christopher Frye. the dancing. I had been to the large winter of the starlight, making it easier to detect.

16 | The SPS Observer Fall 2012 cused on biosignatures that might signify together at many events throughout the life, as well as the effects of the host star’s week. The lack of other undergraduates spectrum and magnetic activity on habit- made the meeting slightly more intimidat- ability. She cautioned that we can only be ing than the AAS winter meeting, where sure that a planet is inhabited if we detect undergraduates make up a significant modulated electromagnetic signals coming fraction of attendees. There were a good from it; otherwise, we can only determine number of graduate students, however, the probability that the planet hosts life. and each of the three splinter sessions I Another area of interest at Cool Stars attended included a graduate student talk. was the transition from M dwarfs down Outside of the conference, there was through the different classes of less mas- plenty to see in Barcelona. The city is host sive brown dwarfs. Brown dwarfs have the to a myriad of buildings designed by the same composition as stars but don't have architect Antoni Gaudí. Christine and I, enough mass to ignite hydrogen fusion. along with City University of New York Due to their cool temperatures, brown graduate student Kay Hiranaka, spent an dwarfs have cloudy atmospheres. Atmo- afternoon exploring two of Gaudí’s works: spheric models usually assume a uniform La Sagrada Familia and Park Güell. atmosphere, but that's probably not the Between the city, the astronomy, and case for many brown dwarfs. Several as- the dancing, I had a great time at Cool tronomers presented evidence that brown Stars. l dwarfs vary over time as the objects rotate, indicating that, like Jupiter, brown Antoni Gaudí designed this unusual structure dwarfs may have nonuniform bands or in Barcelona's Park Güell, not too far from the Next up site of the Cool Stars meeting. Image credit: patches of clouds. Stephanie Douglas. Very few undergraduates attended The next Cool Stars meeting Cool Stars. I met only one other! Chris- will take place Victoria Meadows of the University of tine Wilson, from Saint Mary’s University June 8–14, 2014 Washington spoke about the habitability in Halifax, Nova Scotia, presented her Flagstaff, Arizona of exoplanets and explained that there research on the supergiant star Epsilon www2.lowell.edu/ are a huge number of factors that affect a Aurigae. We met because we were both workshops/coolstars18/ planet’s ability to harbor life. Her talk fo- staying in the same hostel, and we stuck What’s Cooler than Being Cool? Ultracold Physics! by Patrick Donnan, Auburn University, reporting on the 43rd Annual Meeting of the American Physical Society (APS) Division of Atomic, Molecular, and Optical Physics (DAMOP), June 4–8, 2012, Orange County, CA

On the last night of this year's DAMOP DAMOP is a conference largely conference, the speaker came from beyond composed of younger scientists and has a the grave. In a recording made before he tutorial on the first day to orient gradu- passed away last year, Norman Ramsey ate students new to the field. The confer- talked about his interactions with famous ence was very lively; there were always scientists such as Rutherford, Thompson, physicists gathered in the lobby, discussing Rabi, and Dirac. It was fascinating to hear their research and the talks they had at- about the personalities and quirks of scien- tended or were planning to attend. tists whose names often remain associated Philip Burke of Queen’s University with concepts in textbooks but never quite Belfast gave a talk about R-matrix colli- come to life. Ramsey, a Nobel laureate, was no slouch himself. His work contrib- uted to the development of MRI machines Next up and GPS systems. He had his share of The next DAMOP conference quirks as well and was a very entertaining will take place lecturer. The previous night had featured June 3–7, 2013 a session commemorating his contribu- Quebec City, Quebec, Canada tions to AMO physics, and it was great to Author Patrick Donnan gives his talk during www.aps.org/units/ the undergraduate session at DAMOP. Image see the community honor the passing of damop/meetings/annual/ credit: Patrick Donnan. one of its greatest.

Fall 2012 The SPS Observer | 17 sion calculations that was particularly of note; he could not attend due to health issues and instead presented a recorded talk. I emailed him during the conference to thank him for going the extra mile to present, and he responded within a day, sending me a long list of papers about the R-matrix method. Gestures like this help make DAMOP much less imposing for younger students, especially when a lot of the material is going right over your head! Other talks I enjoyed included those of Charles Adams, Ian Spielman, and Rudi Grimm. Charles Adams from Durham University spoke about electromagneti- cally induced transparency in frozen Ryd- berg gases, a phenomenon that has great potential for use in quantum information science. Ian Spielman of the Joint Quan- DAMOP attendees peruse one of the meeting's three poster sessions. Image credit: Patrick Donnan. tum Institute, the National Institute of Standards and Technology, and the Uni- versity of Maryland talked about recent are selected to give talks that are slightly post-talk question session! The DAMOP breakthroughs in spin-orbit coupling in longer than contributed conference talks. community supports its undergrad speak- ultracold atomic systems. These systems This year’s undergraduate session was ers; quite a few people came up to me provide a great way to test condensed incredibly diverse. It opened with one of afterward with complimentary remarks. matter theories in the highly control- last year’s LeRoy Apker Award win- A lunch social was also provided for the lable environment of atomic ensembles. ners, Bethany Jochim. She gave a great presenters. Comparing this experience to Lastly, Rudi Grimm of the University of invited prize talk on the dissociation of other experiences I've had at universities Innsbruck discussed universality and its the molecule NO2+. I was very excited to across the United States, I learned that relation to his work in ultracold cesium. be presenting my work on calculations of universality isn’t restricted to atoms! Universality is a fascinating phenomenon antihydrogen spectroscopy in this session There is lots of exciting research going that allows you to work out certain prop- with other undergrad researchers in my on in AMO physics today. I’d highly rec- erties of how few-body systems behave, field. The work I presented was part of a ommend that undergrads trying to figure regardless of what the actual bodies are. larger effort by the Antihydrogen Laser out what subfield of physics they want to You just need to know if they are bosons Physics Apparatus (ALPHA) Collabora- enter give AMO a look. The community is or fermions. tion that resulted in the first measure- lively and highly receptive, and the excite- Of particular note to undergrads is the ments of the antihydrogen spectrum. I ment is infectious. Personally, I hope to be special undergraduate session at DAMOP. made it through my talk, and, perhaps attending DAMOP meetings for years to Undergraduates apply to speak, and six more importantly, I wasn’t drilled in the come. l

Upcoming Physics Meetings

American Association of Physics Teachers 2013 Winter Meeting January 5-9, 2013, New Orleans, LA, www.aapt.org/conferences/wm2013 Be an

2013 Annual Meeting of the American Association for the Advancement of Science SPS Reporter! February 14-18, 2013, Boston, MA, www.aaas.org/meetings SPS provides $200 stipends for SPS chapters or individual students who report on international or March Meeting of the American Physical Society national physics meetings for SPS publications. March 18-22, 2013, Baltimore, MD, www.aps.org/meetings/march For details, visit: April Meeting of the American Physical Society www.spsnational.org/programs/awards/reporter.htm April 13-16, 2013, Denver, CO, www.aps.org/meetings/april

222nd Meeting of the American Astronomical Society June 2-6, 2013, Indianapolis, IN, aas.org/meetings/aas222

18 | The SPS Observer Fall 2012 Elegant Connections in Physics

Connectin� Worlds �rou�� Tides

by Dwight E. Neuenschwander

“It is not unlikely that the first remark of many who see my titleThe tides and kindred phenomena in the solar system will be that so small a subject as the Tides cannot demand a whole volume; but, in fact, the subject branches out in so many directions that the difficulty has been to attain to the requi- site compression of my matter… The problems involved in the origin and history of the solar and of other celestial systems have little bearing upon our life on the Earth, yet these questions can hardly fail to be of interest to all those whose minds are in any degree permeated by the scientific spirit.” —George Darwin (1898)

Quepos, Costa Rica. Image credit: Dwight E. Neuenschwander.

ur obligation to the Sun as the source of energy for life to elementary but quantitative physics. Let’s have a go at it. on this planet needs no elaboration. Should our appre- To get at the essentials of the tidal mechanism and the ap- ciation also extend to the Moon? A journalist once said, pearance of two tidal bulges, we will begin with an oversimplified “We live with the Moon, but not by it.”[1] That may model of the Earth. Then we will add realistic complications, be true of our attitudes toward our Moon and our awareness of including friction created by the Earth’s crust rotating beneath Oit, but if the Moon did not exist, how different would life on this the oceans. The friction acts like a brake applied to Earth’s spin planet be?[2] and slightly displaces the bulges from the Earth–Moon axis. This Astronomical bodies are connected by gravitation, which holds offset allows Earth and the Moon to exert torques on one another. satellites in their orbits about stars and planets. To understand The consequences include Earth’s day gradually getting longer as the orbits themselves we initially model these bodies as point the Moon slowly recedes from Earth. masses. But planets and moons have finite sizes. Gravitational Geological and paleontological evidence has long supported forces vary with distance, and gradients in the field produced by the hypothesis that the days were shorter in the distant past. one body generate internal stresses in other bodies. For instance, To clinch the the torque-coupling hypothesis, confirmation was the Moon’s gravity is slightly stronger on the Moon-facing side needed that the Moon’s orbit is receding. This became possible in of Earth than on the opposite side, producing strains through- 1969, when the Apollo 12 astronauts left reflectors on the lunar out Earth, the “tidal forces.” The distortions produced by these surface, enabling the distance between Earth and the Moon to be stresses show up most dramatically in the oceans, forming two measured to millimeter precision with pulsed lasers. bulges of water on opposite sides of the planet. The bulges lie approximately on the line connecting the centers of the Earth and the Moon. A Simple Model of Tidal Forces and Bulges The bulge on the side of the Earth facing the Moon makes intuitive sense, but why is there a bulge on the opposite side? Let us start with an isolated, smooth, spherically symmetric, non- The authors of one introductory astronomy textbook write that rotating Earth with a rocky core covered by a global ocean. Such the second bulge exists “because the Moon pulls more strongly on an Earth is necessarily spherical because gravity is an inverse- the Earth’s center than on the far side. Thus the Moon pulls the square central force.[5] Earth away from the oceans, which flow into a bulge away from Now bring the Moon into the game. Assume it to be a spheri- the Moon....”[3] Other authors write that “the high tide on the far cally symmetric body. So long as Earth and the Moon can each be side of the Earth from the Moon occurs because the water there modeled as a single particle, tides do not enter into the picture. is ‘left behind’ as the Moon pulls the solid center of the Earth Each body orbits the system’s center of mass, following Kepler’s toward it.”[4] Such explanations were written for nonmathematical laws; equivalently, the system behaves like a “reduced mass” mM/ audiences, so the authors had to resort to plausibility arguments. (m+M) orbiting in a central field.[6] “Elegant Connections” readers may prefer discussions linked directly

Fall 2012 The SPS Observer | 19 and squeezing inward in cross sections perpendicular to the axis

(Fig. 2). At a point on Earth’s surface along the z axis, |geff| = 1.1×10-6 m/s2, about 10-7 of Earth’s own gravitational field.[8] This difference and the planet’s plasticity allows its material to bend or flow in response to stresses. A bulge forms facing the moon, and another bulge exists on the opposite side. If tidal forces exceed a body’s self-gravitation and internal cohesive forces, the tides rip the body apart. The closest orbital radius about which one body can orbit another without disinte- grating is called the “Roche limit.” I will return to this below. As Earth spins under the Moon, a wave of flexing a few centi- meters in amplitude runs through the lithosphere. We who are on land bob up and down as we are carried along. The oceans have Fig. 1. Coordinate system for calculating tidal forces. The origin lies at a more noticeable response, exhibiting pronounced tidal bulges. Earth’s center, with the Moon located distance r from it. From where we sit on the seashore, we see the tide “come in” until high tide, then “go out” toward low tide. About 12½ hours later our For now, let’s ignore the effects of the other planets and piece of coastline passes through the second high-tidal bulge (two the Sun. Once we understand how one body produces tides on per day, the “diurnal” tides).[9] Why 12½ and not 12 hours? Earth another, we can include the tidal effects of additional bodies by spins west to east, so the Moon appears to rise in the east and superposition. We will also pretend for now that the Moon orbits set in the west. However, it rises about 52 minutes later each day, directly over Earth’s equator. because it orbits eastward about 12° daily. Following the Moon, The Moon exerts a gravitational force on Earth. To a first ap- proximation the Moon can be considered a point source of a gravi- tational fieldg . We need to map this g across Earth. As observers riding on Earth, let us fix our coordinates to it. Let the unperturbed spherical Earth have mass M and radius

ro, label the Moon’s mass m, and denote the distance between the centers of the bodies r. Place the origin of an xyz coordinate system at the center of Earth. The displacement from the Moon’s center to an arbitrary point within Earth’s volume is described by vector R (Fig. 1) [7]:

R = x i + y j + (z+r)k. (1) Fig. 3. Tidal bulges. The Moon’s gravitational field at that point isg (x,y,z) = the tidal bulges creep eastward across Earth’s surface. −GmR/R3. Since r ≈ 60r , to first order in ratios such as x/r we o We can calculate the shape of an idealized ocean surface with

can use the binomial theorem to write

tidal bulges (neglecting Earth’s rotation, solar tides, and coastline effects). Think ofg as the negativeΔ gradient of a potential φ. The eff potential that yields g = − φ is (2) eff

so that φ

(5)

. (3)

We must also note that Earth accelerates toward the Earth–Moon where, on the surface, r 2 = x2 + y2 + z2 and z = r cosθ (Fig. 3). system’s center of mass. Whenever we do physics in a reference o o A sailboat of mass m' floating on the ocean surface “feels” not only frame that accelerates with acceleration a relative to an inertial o Earth’s own gravitation, but also the potential energy of φ. At frame, we must subtract a from the acceleration a that is due to o an elevation of h+r above Earth’s center, the sailboat’s potential the “real” forces. Without the tides or Earth’s rotation, every point o energy, for h << r , is in the planet would fall freely toward the Moon with an accelera- o tion equal to the Moon’s gravitational field at Earth’s center, a o U = m'g h + m' φ, (6) = (Gm/r2)(−k). Therefore, the effective lunar gravitational field o – acting on Earth, geff= g ao, becomes 2 with go = GM/ ro denoting the magnitude of Earth’s own gravita- tional field at r .[8] An ideal ocean in equilibrium has an equipo- . (4) o tential surface with an axially symmetric but oblong shape, A map of g throughout Earth’s volume resembles a quadrupole, eff (7) pushing Earth outward along the Earth–Moon axis (our z axis) High tides occur at θ = 0° and 180°, along the line connecting the terrestrial and lunar centers. Low tides occur at θ = ± 90°. The maximum and minimum heights differ by

(8)

Δ For the lunar tides induced on Earth, h ≈ 53 cm.

Fig. 2. Tidal stresses on the Earth due to the Moon. 20 | The SPS Observer Fall 2012 Fig. 5. Model of the Earth–Moon system for studying the torques on the Earth.

Interaction between water and land also has long-term, po- tentially ominous global effects. Earth’s crust rotates about the planet’s axis (~400 m/s at the equator) much faster than the Fig. 4. The diurnal tides. The relative amplitudes of successive high tides speed at which a tidal bulge propagates as a wave.[12] Therefore depend on the latitudes of the observer and the Moon. the rocky bulk of the planet spins beneath the oceans. Since water has a nonzero viscosity, the oceans sliding over the seafloor act like The Sun is about 300 million times more massive than the a brake on Earth’s crust. This friction pulls on the tidal bulges. Moon, but it is also about 400 times more distant. Thus, for solar- Since Earth spins faster than the Moon orbits, the tides lead the Δ induced tides on Earth, h is about 24 cm, less than half the lunar Earth-to-Moon axis by a small amount, presently about 10° and tide. Solar tidal bulges lie along the line connecting the centers denoted λ in the equations to follow. This offset has consequences. of Earth and Sun. They add to the lunar tide to produce the net The mass M' carried by each bulge gives the Moon’s gravitation tide. (Tides on Earth due to Jupiter and other planets are neg- a “lever arm” by which it torques Earth. Operating in the same ligible.) When the Sun–Earth–Moon system is colinear during a direction, tidal friction and lunar gravitational torques slowly new Moon or a full Moon, the solar and lunar tides add construc- decrease Earth’s spin. tively to produce maximum high tides, the “spring tides.” During By Newton’s third law, Earth’s tidal bulges also exert forces the lunar first- or third-quarter phases, the high tides fall to their on the Moon. Each of those forces has a component tangent to the minimums, the “neap tides.”[10] lunar orbit that exerts a torque on the Moon, changing its angular The Earth’s equator tips about 23° relative to the ecliptic, and momentum and making the Moon recede from Earth. George the Moon’s orbit tips 5° from the ecliptic. Tidal bulge peaks can Darwin articulated this effect in 1897.[13] Let us model it. therefore appear at different latitudes within 28° of the equator. As a result, successive high tides at a given location may have different depths. Depending on the latitude, an observer might Frictional and Lunar Torques on Earth pass through a bulge’s maximum during one high tide but be off the bulge’s peak when passing through the opposite one 12½ hours later (Fig. 4). Here we will lay out the implications of torques on Earth produced by (a) tidal friction as the rotating Earth crust slides beneath its ocean load and (b) the Moon’s gravity acting on Earth’s tidal Interaction of Tides with Land Masses bulges. For now we neglect the Sun’s torque on the Earth. The spinning Earth tugs at the water above the ocean floor, while the bulge wants to stay pointed at the Moon. Thus the So far our calculations have conceptualized a simple model that magnitude of the tidal friction depends on the difference in the reveals the essentials of tidal dynamics. But the tide–land interac- angular velocities of Earth’s spin and the lunar orbit. Let denote tions introduce significant complications. If your boat can make it the angular velocity of Earth’s spin ( ≈ 2π/24 hr presently), and into the bay only at high tide, a lot rides on having an accurate let the Moon’s orbital angular velocity above Earth be denotedε ̇ prediction! When sailing into Half Moon Bay in Auckland, New (≈ 2π/27 days). The tidal frictionalε torque ̇ will be a function of Zealand, for instance, the equilibrium tidal bulge model must be ( − ). To first order we may write the frictional torque as supplemented with local statistics. Only then can those who live ̇ θ−b( − ), where b is some constant. by the tide reliably predict its timing and depth. ̇ ε ̇ Toθ represent the Moon’s gravitational torque on Earth’s tidal As Earth’s rotation carries a coastline into a tidal bulge, the ̇ bulges,ε ̇ weθ can model Earth as a sphere of radius r and treat the tide appears to advance in a relentless wave. In some locations, o bulges as two point masses, each of mass M', lying on the planet’s the shape and dimensions of a bay may introduce tidal resonances surface along a line inclined at angle λ from the Earth–Moon axis with astonishingly large amplitudes. At the Bay of Fundy between (Fig. 5). New Brunswick and Nova Scotia, high and low tides can differ The rotational version of Newton’s second law says the net by some 12 meters! As with musical instruments, such resonances torque acting on Earth equals the rate of change of the planet’s occur whenever the length of the “tube” closed on one end is ¼ the angular momentum. When the system is viewed from above wavelength.[11]

Fall 2012 The SPS Observer | 21 Earth’s northern pole, with counterclockwise rotations assigned Moon phase locked to Earth early in its history. Thus the Moon the positive sign, Newton’s second law in terms of torque gives keeps only one face toward Earth today, with its spin and orbital periods equal. The now-frozen lunar tidal bulges, aligned along the , (9) Earth–Moon axis, offer no lever arm for Earth to exert torque on the Moon. where the double overdot denotes the second derivative with However, Earth’s tidal bulges are not yet aligned along that respect to time, I represents Earth’s moment of inertia about its axis, so they exert a torque on the Moon relative to Earth’s cen-

spin axis, and the forces F1 and F2 are the lunar gravitational ter. To analyze those torques, let’s reuse Fig. 5, invoke Newton’s forces on the near and far bulge, respectively, with lever arms third law, and evaluate the torques with respect to Earth’s center.

of lengths h1 and h2. From Fig. 5 the force magnitudes are F1 = The net torque changes the lunar angular momentum, which can 2 2 GM'm/s1 and F2 = GM'm/s2 . A lever arm distance can be writ- be partitioned into the orbital angular momentum of the Moon’s

ten h1 = r sinβ1, and with the law of sines and small angles, sinβ1 ≈ center of mass revolving about Earth, plus the lunar spin angular

β1 ≈ roλ/s1; similar expressions hold for h2. To a good approxima- momentum about the Moon’s center of mass.[16] Newton’s second – tion s1 ≈ r ro and s2 ≈ r+ro. Equation (9) then becomes approxi- law, written in terms of torque, now says mation, , (12) , (10) where we have invoked the equality of the Moon’s orbital and giving a clockwise torque; hence the angular acceleration is nega- spin angular velocities, and i denotes the lunar moment of inertia tive and decreases with time. Earth’s day is presently shrinking about its spin axis. The torque computations are similar to our by about 0.0023 seconds every century, about 2 hours every 300 previous case but with a crucial change of sign, leaving million years.ε̇ Assuming this rate to be constant (which it isn’t, but the assumption nonetheless offers an order-of-magnitude long- (13) term estimate), 900 million years ago the day would have been about 18 hours long, a conclusion consistent with fossil records This time the term in square brackets is positive, which implies from that era.[14] At this deceleration rate, 3 billion years ago the day would (14) have been about 6 hours long! Prevailing winds of 100 mph or more would have been normal. With the smaller solar-induced The Moon’s orbit about Earth is well described by Kepler’s 2 3 tides and violent wind-driven wave action on shores, the transition third law, which says that ~.. 1/r . Differentiating this with of life from the sea to the land would have faced extra challenges! respect to time means that 2 − 3ṙ/r4. Using Kepler’s third ̇ ~ Had the Moon never come into existence, life on this planet would law again to substitute r forθ , we find that − 1/r5/2. For large ̇ ~ be very different.[2] We owe the Moon some profound apprecia- r and short times (astronomicallyθθ speaking), the lunar angular ̇ ̇ tion. We may live with it and not by it, but our physiology and acceleration is very small and θthe orbital angularθ velocity approxi- routines of life have adapted to its rhythms. mately constant. Thus it seems safe to say that 2mrṙ > 0, which As a player in tidal friction, the tidal bulge offset angle λ means that, in our era, ṙ cannot be zero or negative. Thus ̇ depends on the difference between Earth’s spin frequency and the ṙ > 0, which means the Moon recedes from Earth. θ Moon’s orbital frequency. If Earth’s spin period were the same as Only after the Apollo 12 astronauts left reflectors on the Moon the lunar orbital period (with the Moon in geosynchronous orbit), capable of reversing the direction of a laser beam could the value the Earth–Moon system would rotate as if it were a rigid body, of ṙ be measured. It turns out to be about 3.8 cm/yr.[17] with the tidal bulges aligned along the Earth–Moon axis. Should the Moon somehow orbit faster than Earth spins ( < ), the tidal bulges would lag the Earth–Moon axis, changing the sign of ̇ Long-Term Future λ. The Moon would appear from Earth to rise in theε ̇ westθ and set in the east. Evidently, λ is a function of ( − ). Earth’s spin will continue to slow down, with λ decreasing For the foreseeable future the Earth will keep rotating as the ̇ all the while, until → and λ → 0. Whenε ̇ θ = one of the Moon revolves around it. As the Moon recedes, its orbital period Earth’s hemispheres will face the Moon all the time, an effect will slowly lengthen, and Earth’s spin will gradually slow down. ̇ ̇ called “tidal phase locking.”ε ̇ θ Then λ = 0 and theε ̇ lunarθ torque Those effects will continue, with the phase-locking mechanism exerted on Earth will vanish. making continual adjustments, until Earth’s rotation period Now let’s switch perspectives and think about the tidal forces matches the Moon’s orbital period. The Moon and Earth will exerted by Earth on the Moon. The Moon is already phase locked then be mutually phased-locked to each other. The Moon will not to Earth; the satellite’s spin period equals its orbital period, so be visible from half of Earth’s surface! The tidal bulges will still the Moon always presents the same face to us. It was not always be there, but they will lie along the Earth–Moon axis. At a fixed this way. Early in the history of the Earth–Moon system, a Moon latitude, high and low tides will no longer occur. Earth’s day will newly formed by accretion would have been hot and relatively be about 50 times longer than it is today, and the Moon’s orbital fluid. Using Eq. (8), the max-to-min tides on the Moon (due to radius will be about 1.4 times its present value.[18] For those on Earth) compared to those on Earth (due to the Moon) would have Earth who can see it, the Moon will subtend an angle about 70 been percent of its present angular diameter in the sky. Solar eclipses will be annular, not total. , (11) However, the Sun will continue exerting tidal forces on Earth, causing tidal stresses, tidal bulges, and tidal friction, though diminished from the lunar-induced case. With the solar-induced where ρ denotes the lunar radius. Because M ≈ 100m and ρ ≈ tidal friction operating, Earth’s spin will continue to slow after the Moon and Earth become mutually phase locked. If the Moon ¼ro, Earth would produce tidal bulges about 40 times larger on the Moon than those the Moon produces on Earth. Thanks to could be dismissed, Earth and the Sun would eventually become large tidal torques [15] and the small lunar moment of inertia, the phase locked. With the Moon still in action, the solar-induced

22 | The SPS Observer Fall 2012 torque will slow Earth’s spin below the value at which the planet [6] See John C. Taylor, Classical Mechanics (University Science Books, phase locked to the Moon. Then the Earth will spin more slowly Sausalito, CA, 2005), p. 296; Jerry B. Marion and Stephen T. Thornton, th than the Moon orbits, and the Moon will appear from Earth to Classical Dynamics of Particles and Systems, 5 ed. (Thornson Brooks/ rise in the west and set in the east. Lunar tides will reappear with Cole, Belmont, CA, 2004), pp. 287–289. torques opposite from those of our era. Those future lunar-induced [7] See Hans C. Ohanian, Gravitation and Spacetime (W.W. Norton, New York, 1976), pp. 26–32; Taylor (Ref. 6), pp. 330–336; Marion and Thorn- tidal bulges will lag instead of lead the Earth–Moon axis. Instead ton (Ref. 6), pp. 198–204. of receding, the Moon will approach the Earth. The closer the [8] Another noninertial acceleration comes from Earth’s spin, which satellite gets, the stronger the tides, until the Moon comes within carries angular velocity ω = 2π rad/day = 7.3×10−5 rad/s. A point on the Roche limit. 2 Earth’s equator gets carried around the spin axis with the acceleration roω To estimate the upper bound for the orbital radius at which −8 2 ≈ 4×10 m/s (~25 times smaller than tidal forces ), directed toward the tidal forces break the Moon apart, neglect the chemical bonds that local vertical. See “When ‘F’ does not Equal ‘ma,’” SPS Observer (Spring/ hold the rocks together and imagine the Moon is held together Summer 2001), pp. 10–14. only by its self-gravitation.[19] Return to Eq. (4) after interchang- [9] The word “diurnal” may seem less strange if we compare it to the more ing the roles of Earth and the Moon, and look at the stress along familiar “nocturnal.” the Moon’s z axis. When the lunar self-gravitation becomes less [10] The “spring” tide’s name is not seasonal but comes from the notion of than the z component of the tidal force, the Moon will disinte- the tide “springing up” higher than usual. According to Webster’s Diction- grate; that is, when ary, “neap” comes from the Middle English neep or the Anglo-Saxon nep, which meant “scarcely touching.” [11] One might ask how a pulse of water, such as an incoming tide, can (15) have “a wavelength.” A wave pulse can be built by a superposition of harmonic waves. 1/3 6 or r <(2M/m) ρ. Since M ≈ 100m and ρ ≈ 1.74×10 m, the [12] Left to itself, the tidal bulge, as a heap of water, would form a wave 7 Moon would come apart when r < 10 m ~ 10ro. Perhaps Earth pulse, a superposition of waves. In deep water the phase velocity of a sur- will then have a Saturnian ring system! The actual Roche limit face wave is √( gλ/2π) for wavelength λ. Everyday waves have wavelengths is smaller than this crude estimate because the Moon’s rocks are on the order of 100 m or less, giving speeds on the order of 10 m/s or less. held together by internal forces. The Moon presently orbits at In contrast, tsunamis can travel over 500 mph, with wavelengths on the order of 100 km. See, e.g., http://walrus.wr.usgs.gov/tsunami/basics.html. about 60ro, well outside our pessimistic Roche limit. All of this would take billions of years, much longer than the [13] George Howard Darwin, The Tides and Kindred Phenomena in the lifetime of the Sun.[20] Four to five billion years from now, the Solar System (Houghton, Mifflin and Co., Boston, MA, 1898), Chs. XVI Sun will deplete the hydrogen in its core. Nuclear collisions fusing and XVII, “Tidal Friction” and “Tidal Friction (continued).” This book hydrogen to helium today will be quenched. Gravity will squeeze was adapted from Darwin’s Lowell Lectures at the Lowell Observatory in Boston in 1897. George Darwin (1845–1912) was a highly decorated the solar core tighter, raising its temperature. Before the core astronomer, professor at Cambridge University, President of the Royal temperature hits the 100 MK or so necessary to fuse helium to Society, and (in case you are wondering) the son of Charles Darwin. carbon, the layers around the core will reach the 15 MK or so nec- [14] Seeds and Backman (Ref. 3), p. 70. 900 million years ago the only essary to start hydrogen fusing to helium. Shells of fusion working life on Earth was algae and bacteria, and they were sparsely distributed; their way through the star will swell it into a red giant that will see, e.g., Bill Frio, Geology of the Great Basin (University of Nevada-Reno engulf the Earth–Moon system. Press, Reno, NV, 1986), p. 32. However, this planet, moonlight walks, sunrises and sunsets, [15] The strong tidal torquing of the early Moon would keep its interior and the starry sky are no less beautiful for their being temporary. hotter for a time longer than otherwise; a similar thermodynamics seems Get out there and enjoy them! Appreciate what we have, and be to be operating on Jupiter’s moon Europa today, which has a deep-water aware of what it means. We are part of nature, not a spectator on ocean beneath its frozen crust, despite the intense cold of the Jovian the sidelines. Connect with the many worlds around us! l region. Radioactivity also provides a long-lasting heat engine for planetary structures. [16] See any introductory physics textbook, or “Angular Momentum and ‘Spin,’” SPS Observer (Fall 2000), pp. 10–14. The theorem follows because Acknowledgments angular momentum is additive. [17] It is an elementary exercise in geometrical optics to design a set of mirrors that will return a light ray back along its incident direction. The I am grateful to Thomas Olsen and Mark Winslow for reviewing a arrays of reflectors built into automotive taillights use the same geometry. draft version of this article. [18] Robert B. Gordon, Physics of the Earth (Holt, Rinehart, and Win- ston, New York, 1972), p. 69. [19] Bradley W. Carroll and Dale A. Astlie, An Introduction to Modern As- References trophysics (Addison-Wesley, Reading, MA, 1996), pp. 766–767. [20] Longer than the Sun’s lifetime follows from a back-of-the-envelope [1] Statement by Charles Kuralt in the CBS Documentary “The Moon estimate. For the Earth to become phase locked to the Moon, assuming Above, The Earth Below” (1989), broadcast on the 20th anniversary of the nothing else changes, the Earth would have to lose about 26 hours. If the flight of Apollo 11. spin slow-down rate would stay at 0.0023 s/century for all time, this would [2] Neil F. Comins and William J. Kaufmann III, Discovering the Uni- take only 280 billion years! Of course, as the Moon recedes, its orbital verse, 5th ed. (W.H. Freeman, New York, NY, 2000). See the provocative period changes, so the coupled situation gets rather dynamic. But the essay on p. 146, “What if the Moon Didn’t Exist?” See also Comins’ essay point is, for large bodies the phase-locking timescale may be comparable to by the same title on a website of the Astronomical Society of the Pacific, a star’s lifetime. However, many planetary satellites besides our Moon are http://www.astrosociety.org/education/publications/tnl/33/33.html. already phase locked to their planets. Pluto and its satellite Charon are [3] Michael Seeds and Dana Backman, Horizons: Exploring the Universe, already mutually phase locked. 12th ed. (Brooks-Cole, Boston, MA, 2012), p. 68. [4] Comins and Kaufmann (Ref. 2), p. 140. [5] Because fields from a point source go as inverse distance squared, the point-sphere equivalence theorem for gravitation (Newton’s law of uni- versal gravitation) and electrostatics (Coulomb’s law) holds. This can be shown with integration or by Gauss’ law. See any calculus-based introduc- tory physics text with chapters on gravity, Coulomb’s law, and Gauss’ law.

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PhysCon 2012: Stay Connected

hysCon 2012 may be over, but the excitement, inspiration, and new connections that were formed will have a lasting impact on SPS and its members for years to come. It’s impossible to capture the spirit and highlights P of the meeting in just these few pages—so look for more coming in the next few issues of The SPS Observer and on the PhysCon website. And whether you attended PhysCon in person or are experiencing it through these pages for the first time, here are some ways that you can continue “Connecting Worlds through Science and Service”:

Be inspired by the words of Freeman Dyson, John Mather, Jocelyn Bell Burnell, and the other PhysCon plenary speakers by listening to or viewing their talks. www.spscongress.org/physconprogram/speakers

Explore the workshop topics in more detail using the resources on the PhysCon Media List. www.spscongress.org/resources/reading-list

Check out the coverage of PhysCon in the press and blogosphere. www.spscongress.org/about/press

Browse meeting photos and upload your own. www.spscongress.org/about/#photo