PWFeb10cover 25/1/10 17:21 Page 1

physicsworld.com Volume 23 No 2 February 2010

Complex affairs Challenges in network science

Measures of success Your favourite units revealed Courting trouble Are colliders breaking the law? Quantum wonderland Alice through the double slits Capture the Concept TM

With Comsol Multiphysics® you are empowered to build the simulations that accurately replicate the important View Multiphysics applications at: characteristics of your designs. The key is the ability to comsol.com/multiphysics include all physical effects that exist in the real world. This multiphysics approach delivers results—tangible results that save precious development time and spark innovation.

© 2010 COMSOL, INC. 2010. COMSOL, COMSOL MULTIPHYSICS, COMSOL REACTION ENGINEERING LAB, AND FEMLAB ARE REGISTERED TRADEMARKS OF COMSOL AB. physicsworld.com Contents: February 2010

Quanta 3

D Brockmann Frontiers 4 Alien spectrum revealed ● Seeing with electrons and light ● Gobbling up the galaxy ● Neutrons on the slide ● Colour-changing skins News & Analysis 6 Controversy surrounds murdered Iranian physicist ● Africa launches physical society ● Fraud in China revealed ● Heidelberg opens heavy-ion cancer centre ● First product for Cambridge spin-off ● Budget relief for physicists in Japan ● Reforms called for at UK funding council ● Spy agency shares climate data ● Standards lab funds new centres ● France’s grandes écoles accused of elitism ● Law and the Large Hadron Collider Comment 15 Complexity made simple Critical Point 17 Paper trail – proxy-data networks 31–34 Your favourite units Robert P Crease Feedback 20 Learn to lecture, science and the Royal Society, plus comments from physicsworld.com Photolibrary Features Complexity A networked world 22 An unusual 1998 paper that considered a worm’s neural system, the US electrical grid and Hollywood actors triggered a surge of interest in network science. Mark Buchanan and Guido Caldarelli explain why the field has become so popular Weights and measures – beyond SI 17–19 The flu fighters 26 The spread of infectious diseases like the H1N1 swine-flu pandemic can be far faster On the cover now than they could before air travel became so common. Vittoria Colizza and Challenges in network science Alessandro Vespignani explain how techniques from statistical mechanics and (B Goncalves et al., Indiana University) 22–38 Your favourite units revealed 17–19 complex networks can follow a virus’s progress in real time Are colliders breaking the law? 12–13 Quantum wonderland 52 Following the money 31 Web-based tools that can track the movement of banknotes and the location of mobile phones can reveal patterns in how people travel that may even, as Dirk Brockmann explains, be governed by basic physical laws Simplicity and complexity 36 Not everyone agrees about what complexity is or even what its researchers are trying to achieve. James Crutchfield and Karoline Wiesner outline future directions and wonder if a road map for the field is needed Reviews 40 Complexity for beginners ● A turbulent tale ● Web life: ComplexityBlog.com Physics World is published monthly as 12 issues per annual volume by IOP Publishing Ltd, Dirac House, Temple Back, Bristol BS1 6BE, UK Careers 44 United States Postal Identification Statement Life on the borders Edward Barry ● Once a physicist: David Roy Physics World (ISSN 0953-8585) is published monthly by IOP Publishing Ltd, Dirac House, Temple Back, Bristol BS1 6BE, UK. Annual subscription price is US $585. Air freight and mailing Recruitment 47 in the USA by Publications Expediting, Inc., 200 Meacham Ave, Elmont NY 11003. Periodicals postage at Jamaica NY 11431. US Postmaster: send address changes to Physics World, American Institute of Physics, Suite 1NO1, Lateral Thoughts 52 2 Huntington Quadrangle, Melville, NY 11747-4502 Alice through the double slits G G Davies 1 Physics World February 2010 Glassman Physics World Feb 10 15/1/10 12:04 pm Page 1

Fully Floating Technology

Giving you the Power to Perform

The new FL series from Glassman is available with fully ‘floating outputs’ of up to 1500Vdc.

Standard operating features include automatic crossover from constant voltage to constant current mode, a universal ac input voltage range of 90Vac – 264Vac and integral RS232,

RS485 and USB digital programming facilities, together with 0-5Vdc/0-10Vdc selectable analogue programming.

The FL series boasts 1.5kW of continuous operating power from a lightweight 1U rack mountable chassis, full RoHs and CE accreditation and a 3 year parts and labour warranty.

GLASSMAN EUROPE Tel: +44 (0) 1256 883007 Fax: +44 (0) 1256 883017 GLASSMAN USA Tel: (908) 638-3800 Fax: (908) 638-3700

GLASSMAN JAPAN Tel: (045) 902-9988 Fax: (045) 902-2268 www.glassmaneurope.co.uk physicsworld.com Quanta

For the record Seen and heard It’s absurd to believe that the Royal Institution can survive without a 24 and 34, who are based in London, who have a university education and are strong director physically attractive, he found that there Martin Rees from Cambridge University quoted in were 26 women in total who fitted his bill.

The Times Elle Starkma, PPPL Backus calculates that on an average night Last month the Royal Institution (RI) abolished the out there would then be only a 1 in 285 000 job of director, which was held by neuroscientist chance of meeting any of them. Rather Susan Greenfield, as it could no longer afford to amazingly, the Australian website support the position. It will now be led by business news.au.com reports that Backus has found graduate Chris Rofe, who is the RI’s chief executive. a girlfriend and that they have already been dating for six months. “She meets all my If ever there were a technical project criteria,” Backus claims. that humanity should invest in, this is it Right on track Staff at the Princeton Plasma Physics Own your own Higgs Physicist Chris Rapley, director of the Laboratory have come up with an Finding the Higgs boson at the Science Museum, quoted in The Times ingenious, low-cost solution to a tricky Large Hadron Collider might not be worth When asked what the next decade in science could problem by building a circular train track anything like the 710bn that has already bring, Rapley highlighted “artificial trees” that could inside the lab’s National Spherical Torus been spent on it at the CERN lab. That is suck carbon dioxide out of the atmosphere. Experiment to help calibrate the reactor’s after a Higgs boson was sold on eBay last neutron detectors. Doug Darrow month for a paltry £21.00 (plus £2.95 for There is nothing in science that isn’t and colleagues placed a piece of postage and packaging). After being not so worth being excited about californium-252 on top of a train, which hotly contested for seven days, the Higgs, then travelled in a circle allowing the which is thought to give other particle their Writer Bill Bryson quoted in New Scientist detectors to pick up the emitted neutrons mass, only received 10 bids in total. Bryson, author of the bestselling popular-science as it travelled round. The neutrons from The seller, who goes under the name of book A Short History of Nearly Everything, says the radioactive element have an energy sahbman and is based in Glasgow in the that the place where you would expect to find similar to that of deuterium–deuterium UK, promised the highest bidder a excitement about science is in schools, but that fusion neutrons. According to Darrow, certificate of authenticity, the Higgs in a these days that often does not ring true. having a moving piece of californium was matchbox secured with a piece of Blu-Tack must better than just placing the sample in as well as, er, “potential mastery of reality”. A real crunch is coming the centre of the tokamak. Indeed, Unfortunately for the eventual buyer, researchers recorded a calibration however, no returns are accepted. Consultant Jack Lifton quoted in the Independent improvement of 10% using the moving With mines in China accounting for nearly 97% of source. Whether any toy train track will Space sushi global supplies of rare-earth elements, Lifton says feature in an updated design blueprint for When you think about that the UK and the US should secure the supply of the ITER project remains to be seen. astronauts eating in space, rare-earths from sources outside China otherwise the first thing that there could be shortages due to export cuts that Are you out there? probably springs to mind

could hit battery and motor manufacturers. Most physicists will be familiar with the iStockphoto.com/vasko is liquidized food being Drake equation used to estimate the sucked out of vacuum- I am hanging a lot of sex and music number of possible civilizations in the packed plastic bags with a straw. But now and philosophy on it universe. Formulated by the US the International Space Station (ISS) is set astronomer Frank Drake in 1960, it for a finer dining experience as sushi is Nobel laureate Frank Wilczek quoted in the suggests that there could be as many as apparently going on the menu. Late last New York Times 10 000 civilizations living in the universe. December, Japanese astronaut Soichi Wilczek is writing a novel, The Attraction of However, economics PhD student Noguchi brought raw fish to the station as Darkness, about four physicists who discover what Peter Backus from the University of he, together with Russian cosmonaut dark matter is – only for one of them to mysteriously Warwick in the UK has now adapted the Oleg Kotov and US astronaut Timothy die before they are awarded a Nobel prize. equation to calculate another hard-to- Creamer, blasted off from the Baikonur predict phenomenon: the probability of Cosmodrome in Kazakhstan to carry out a I first liked ginger peach. Then I finding a partner. Backus, who states he is a series of maintenance operations. “We had discovered there is lemon zinger heterosexual male and was only looking for training in Japan and I trained [the other a girlfriend, replaced all six original astronauts] to be sushi lovers,” Noguchi Cosmologist George Smoot from University of parameters in the equation with similar told a press conference before the launch. California, Berkeley quoted in the San Francisco ones to suit his search. For example, he “So I am going to make a couple of varieties Chronicle replaced fi, the fraction of Earth-like of sushi.” Creamer and Noguchi have been Smoot, who shared the 2006 Nobel Prize for planets supporting life of any kind, with fw, providing regular Twitter updates on their Physics with John Mather for discovering the the fraction of people in the UK who are mission, but as Physics World went to press anisotropy of the cosmic microwave background, women. Not being too choosy, and after there was no mention yet of any fishy reveals a passion for specialty teas. taking into account that he would only like dishes. Perhaps they decided to stick to the to date people who are aged between mushroom soup. 3 Physics World February 2010 physicsworld.com Frontiers In brief Honing in on habitable planets Pulsar bursts are ‘faster’ than light Astrophysicists in the US have observed radio icals, such as water vapour and methane, but pulses emitted by a pulsar – a rapidly spinning measurements are difficult to make because neutron star – that appear to be travelling faster the exoplanet’s spectrum tends to be dwarfed

than the speed of light. Although Einstein’s special ESO/M Janson by light from the star. What is more, this theory of relativity says that information cannot method can only be used on those few exo- travel beyond this limit, pulses of light can be planets that happen to have just the right warped to make it appear that they have arrived at orbital inclination relative to the Earth’s line a destination faster than unaffected light would. of sight. This process of “anomalous dispersion”, which Now, Markus Janson of the University of previously had only ever been seen in the lab, has Toronto and colleagues are the first to obtain now been observed in radio pulses emerging from Alien lights The spectrum of the exoplanet HR 8799c. the spectrum of an exoplanet directly. The the pulsar PSR B1937+21 that have been key to isolating the planet’s chemical signa- dispersed by interactions with neutral hydrogen Astronomers in Canada and Germany have ture from that of its parent star was to focus and plasma in the interstellar medium. The directly measured the atmospheric spectrum on the planet for more than five hours using researchers believe that these observations could of a planet existing outside our solar system an infrared camera installed at the European help us to gain a better understanding of the for the first time. The exoplanet in question, Very Large Telescope in Chile. The resolu- regions between stars, for example the properties HR 8799c, is a gaseous giant some 10 times tion was further enhanced using an adoptive- of neutral hydrogen clouds in our galaxy more massive than Jupiter and is one of optics system. (arXiv:0909.2445v2). three planets orbiting a star 130 light-years The researchers were surprised by the re - from Earth. The researchers say that meas- sults, which suggest that the giant planet may Quantum computing hydrogen energy uring HR 8799c’s spectrum is an important be more like the Earth than a star. “There is The hydrogen molecule may be the simplest of all step forward in the search for life elsewhere less methane than expected in the upper at- the two-atom systems, but chemists have needed in the universe. mosphere, which implies that the carbon is to work hard to calculate its properties from first The first discovery of a planet orbiting mostly locked up in carbon monoxide in- principles using quantum mechanics. Now, another star was made in 1992, and today stead,” says Janson. This means that the however, a team of physicists and chemists in the more than 400 of these exoplanets have been planet may be enriched in heavy elements US and Australia has for the first time calculated catalogued. A key aim of this research is to compared with its parent star (Astrophys. J. the molecule’s energy levels using a primitive study the chemical composition of exoplan- at press). quantum computer that consists of a pair of etary atmospheres, as this can give us clues Meanwhile, scientists working on NASA’s entangled photons, in which one photon as to how a planet formed and evolved – and Kepler mission have unveiled the first five represents the molecule and the other its energy. might also reveal their signatures of life. exoplanets discovered by the space telescope Using an iterative phase-estimation algorithm, the Astronomers have already glimpsed exo- since it was launched last March. Although team obtained an energy-versus-separation curve planetary atmospheres by studying what hap- these bodies are nothing like the Earth, their that agrees exactly with that obtained by a pens when a planet disappears behind its rapid discovery suggests that Kepler is on classical computer. Quantum chemistry is one parent star. This technique has revealed the track to discover a habitable exoplanet with- field that could benefit from larger-scale quantum existence of a number of atmospheric chem- in its initial run of three years. computers, as the required computing power increases exponentially with the number of atoms in a molecule (Nature Chemistry 10.1038/ Evanescent waves light up nanotechnology nchem.483). Researchers at the California Institute of of electrons that travel at 70% of the speed Ancient Mars wetter than we thought Technology in the US have invented a new of light at the nanostructure. Whenever an Early Martian history may have involved more type of imaging technique that incorporates electron interacts with the evanescent wave water on the planet’s surface than was previously the best qualities of both electron and light at the surface, it is accelerated by the inter- thought, according to researchers in the UK who microscopy. The hybrid technique, dubbed action. The researchers are able to construct have spotted a series of channels resembling the “photon-induced near-field electron micro- an image of the nanosurface by locating the thermokarst landscapes in Siberia and Alaska. scopy”, can image nano-objects with femto- points at which these electrons are acceler- They say that the channels could only have been second time resolutions. It could be used to ated. The resulting imaging technique com- formed by running liquid. Spotted in high- directly visualize ultrafast events that occur bines the nanoscale spatial resolution of resolution images captured by NASA’s Mars on the nanoscale. electron microscopy with the femtosecond Reconnaissance mission, the channels are The technique, developed by Ahmed Ze- time resolution of ultrafast light pulses. believed to be about three billion years old. wail and colleagues, involves illuminating One snag with the new technique is that the Scientists had previously believed that Mars had a carbon nanotube, silver nanowire or other electrons only spend a fraction of a femto- become a frozen wasteland by this period in its nanostructure to be imaged to create an second near the surface of the sample, given history, which is known as the Hesparian epoch “evanescent wave” on the surface of the sam- the high speeds at which they are travelling. (Geology 38 71). ple. Unlike ordinary, free light, evanescent To increase the electron–light interactions at waves exist only near the surface of a ma - such short time intervals, the researchers Read these articles in full and sign up for free terial and so they interact efficiently with need to magnify the light fields. They do this e-mail news alerts at physicsworld.com electrons at the sample’s surface. Zewail’s by using two synchronized femtosecond light team exploits this effect by also firing a pulse pulses (Nature 462 902). 4 Physics World February 2010 physicsworld.com Frontiers

Innovation Philips produces colour electronic paper

NASA/CXC/MIT/F Baganoff et al. Researchers at Philips, the Dutch electronics giant, have designed a novel type of electronic paper that does not require backlighting and that can change colour at the flick of a switch. Philips says that its colour “e-paper” could be used for digital signs, enabling shop displays to be changed rapidly and then maintained without consuming too much energy. The firm is also considering colour- changing “skins” for products like mobile phones and hand-held games consoles. Electronic paper looks like conventional paper but because it reflects ambient light, it does not need to be backlit like conventional liquid-crystal displays. The technology is already found in electronic book readers, such as Amazon’s Kindle, which have a matt appearance that resembles the Black hole struggles to swallow its Milky Way pages of a paperback. Such devices typically Supermassive black holes are some of the most amazing objects in the universe and are believed to exist consist of electrically charged nanoparticles at the centre of most, if not all, galaxies. They can be billions of times heavier than the Sun and expand by encapsulated between two electrodes. The feeding on dust that is blown off massive young stars just outside their event horizon – the zone beyond particles are located at pixel sites that can be which not even light can escape. In the Milky Way, these neighbouring stars are located a relatively large controlled by applying an external electric field, distance away from the supermassive black hole, which is believed to exist in the region of Sagittarius A* – in a process called electrophoresis. a bright radio source at the centre of the galaxy. For this reason, scientists had calculated that In a standard book reader, the colour of each Sagittarius A* should be consuming only 1% of the available dust. But now a team of astronomers, pixel can be alternated between two colours of including Roman Shcherbakov of Harvard University, claims that it could have an even smaller appetite choice – usually black and white – by flipping the than we thought. The researchers reached this conclusion by studying this image, which was constructed polarity of the pixel with an applied electric field. from a series of observations captured by NASA’s Chandra X-ray Observatory over a period of almost two In this way, the pattern of black pixels on a screen weeks. The long exposure time gave the researchers a clear view of the gas surrounding the event horizon, forming the words of a book can be altered by revealing a series of gaseous lobes stretching in various directions. Shcherbakov and his colleagues say pressing a button whenever a reader “turns” a page. that collisions between particles leads to heat transfer by conduction from an inner region, near the The Philips researchers instead apply a voltage black hole’s event horizon to an outer region that includes the black hole’s fuel source. This process creates across the plane of the e-paper, rather than an outward pressure that acts to counter the gravitational pull of the black hole and leads to 99.99% of the “into” the display as in conventional “top-down” incoming star dust being blown away. These findings were presented at the 215th annual meeting of the electrophoresis. This “in-plane” electrophoresis American Astronomical Society (AAS), in Washington, DC, last month. means that it is possible to combine different- coloured pigments in each pixel and use a third electrode to control how these particles spread Newton’s idea spotted in neutrons across the display, which in turn dictates the saturation or shade of the colour. In the Philips An optical effect first proposed in the 17th Netherlands, has demonstrated the so-called design, the four different-coloured pigments – century by Isaac Newton has now been ob- Goos–Hänchen effect with neutrons. The cyan, magenta, yellow and black – can be served to affect matter as well, thus providing team exploited the fact that a neutron pos- stacked in the corner of each pixel site to leave a yet further affirmation of wave-particle du - sesses a magnetic moment that can be rep- transparent display. “It boils down to: where ality. Newton predicted that a beam of light resented by a wavefunction that comprises can we hide the coloured particles?” explains reflected at a glass–vacuum surface should both up-spin and down-spin components. Kars-Michiel Lenssen, who is leading the Philips undergo a minuscule lateral shift. He thought Theorists have calculated that the Goos– team developing these devices. that wavefronts, having reached the vacuum, Hänchen shift should affect the up and down Lenssen’s team created a 10 μm-thick display should “slide” a short distance along the in- wavefunctions to differing extents, meaning filled with magenta pigment to demonstrate the terface before re-emerging and reflecting that, during reflection, the up and down spin principle of the new technology. It reflects 80% of back into the glass. Given the tiny scale of this states should be split in space and time. incoming light in the transparent state, when the effect, however, it was not until 1947 that it Using a new instrument at ISIS that can pigment is “hidden” in the corner. When the was first observed experimentally by the phy - detect subtle differences in polarization over pigment is spread out, it reflects about 10% of the sicists F Goos and H Hänchen. a tiny area, the researchers recorded a spa- incoming light at a wavelength of 570 nm. Now, a group of researchers, including tial “splitting” of the neutron wavefunctions Importantly, the device has a contrast of 25:1, Sean Langridge at the ISIS neutron facility of up to 100 nm, which also corresponds to a whereas previous e-papers have only managed near Oxford in the UK and Victor de Haan time delay of the order of 0.1 µs (Phys. Rev. about 8:1 (J. Soc. Information Display 18 1). from Delft University of Technology in the Lett. 104 010401). 5 Physics World February 2010 physicsworld.com News & Analysis Murdered physicist leaves Iran reeling

The murder of the Iranian physicist was not a political figure, the physicist Masoud Alimohammadi last month was one of 420 academics who signed has left the country’s academic com- a letter supporting the reformist can- munity in a state of shock. Alimoham - Getty Images didate Mir Hossein Mousavi in last madi, a 50-year-old physics professor June’s presidential elections. at the University of Tehran, was killed The murder of Alimohammadi has on 12 January by a remote-controlled left academics in Tehran in what Man- bomb attached to the side of a motor- souri calls “an atmosphere of fear”. cycle outside his home. The bomb was Najib Ghadbian, a political scientist detonated as he left for work, but the at the University of Arkansas and reason for the murder remained un- author of Democratization and the clear as Physics World went to press. Islamist Challenge in the Arab World, Reports by the Iranian state media adds that the overall situation in Iran blamed the US and Israel for the at- has been “very tense” since President tack – a claim that the US later des - Mahmoud Ahmadinejad was re- cribed as “absurd”. elected last June. “The rhetoric of the Alimohammadi was not an applied Angry reaction built specifically to bring together sci- authorities in relation to the West is nuclear physicist, as has been widely Mourners carry the entists from across the Middle East. getting more hard-line and I am cer- reported, but a mathematical physi- Iranian-flag-covered Having done a PhD at Sharif Uni- tainly very concerned for independ- cist working in quantum mechanics body of murdered versity of Technology in Tehran, Ali- ently minded academics,” he says. and field theory. He had published physicist Masoud mo hammadi was one of the first four Ghadbian also believes that the more than 50 papers and had recently Alimohammadi. physicists to complete his doctorate threat of further UN sanctions if Iran specialized in theories of dark energy. entirely within Iran, as the nation did does not end its nuclear ambitions “None of his work has anything re - not run PhD programmes before the only strengthens the anti-Western motely to do with nuclear weapons, so 1979 Islamic revolution. He had been rhetoric of the Ahmadinejad regime I wonder why they are calling him a offered a place by Reza Mansouri, a and makes life even more perilous nuclear scientist and suggesting that cosmologist at Sharif and a former for academics in Iran. “What politi- the US or Israel may have bumped deputy science minister, who told cians in the West fail to understand is him off,” says Subir Sarkar, a theoret- Physics World that “Alimohammadi that support for a nuclear programme ical physicist at the University of Ox - was a practising Muslim and was en- is widespread in Iran, even among ford in the UK. Alimohammadi was gaged in activities linked to the [Ira - those who do not support the presi- also on the council of the SESAME nian] cultural revolution”. Although ding regime,” he says. synchrotron in Jordan, which is being Mansouri added that Alimohammadi James Dacey International Africa launches continent-wide physics society

A new cross-continent society to rep- densed-matter physicist from Ghana The AfPS will more sensitive than any other radio resent all physicists in Africa was who is interim president of the AfPS. endeavour telescope (Physics World June 2009 launched at a meeting in the Se ne - He says the AfPS was set up partly p7). A joint bid from Australia and galese capital Dakar last month. The because no African nation features to increase New Zealand is also in the running to African Physical Society (AfPS) will in the top 20 countries for physics, as the resource host the array. support the work of existing physical measured by the average number of for physics The AfPS replaces the Society of societies in the continent and help citations given to papers by physicists. training and African Physicists and Mathe ma ti - those physicists in African countries However, every country that is in cians, which was founded in 1984. Na - that do not have their own society. the top 20 does have national and re - research in tional physics societies across the The AfPS, which is expected to ini- gional structures for supporting phys - Africa and continent will be members of the AfPS. tially have about a 1000 individual ics and astronomy. [its] economic The new society has also launched an members, will also encourage physi- The AfPS will also play a lobbying African Association of Physics Stu - cists across Africa to collaborate. and support role for new projects that and social dents, of which all student members “As an advocate for physics across could be hosted in Africa. The AfPS, development of the AfPS will become a part. In ad- the continent, the AfPS will endeav- for example, has already endorsed the dition, plans are afoot for an African our to increase the resource for phys - siting of the $1.5bn Square Kilometre Astronomical Society and an Optics ics training and research in Africa Array in South Africa. This is a set of and Photonics Society of Africa. and [its] economic and social devel- radio antennas spreading out to a dis- Michael Banks opment,” says Francis Allotey, a con- tance of 3000 km that will be 50 times ● africanphysicalsociety.org 6 Physics World February 2010 physicsworld.com News & Analysis

Research misconduct “Applying for research funding, promotion, salary and bonus mainly depend on how many papers have Chinese duo fired for scientific fraud been published, so a few people do choose the misconduct path,” says Huang Ruiwang, a physicist working A major case of academic fraud in Under a cloud at the State Key Lab of Cog nitive China has led to calls for the country Two researchers Neuroscience and Learning at Beijing to adopt a new system of academic have been sacked Normal University. “Jinggangshan evaluation that steers away from by Jinggangshan University has given a bad name to heavily supporting scientists who pub- University for researchers in China, but at least it falsifying scientific lish the most papers. The calls have Jinggangshan University has now said it will look into modify- been made after some 70 papers pub- papers. ing its current evaluation system.” lished by Chinese scientists in Acta Another problem is the high level Crystallographica Section E were re- of bureaucracy, with only the govern- tracted from the journal late last year. ment deciding how funding is dis - The authors acknowledged that their correctly determined”. However, the tributed to scientists. “They are not analysis had been fabricated. authors then replaced one or two of very clear about how science research According to a statement from the the atoms to create what looked like works,” says Li Daguang, director of journal’s publishers Wiley-Blackwell, new structures. “The worst example the Science Communication Center the 70 papers were mostly published generated no fewer than 18 suppo - at the Chinese Academy of Sciences. in 2007. It added that the number sedly original structures from a single Biophysicist Stephen Roper from of falsified articles was likely to “rise common set of data,” the statement the University of Miami in the US, further” as they investigate more said. Zhong wrote 41 of the papers who has visited China and is seeking publications by the two correspond- and Liu authored 29. greater ties with Chinese scientists, ing authors, Zhong Hua and Liu Tao, Some think that this case of fraud says combating misconduct in Chi- who are both at Jinggangshan Uni - has happened because Chinese uni- nese institutions must start with the versity in Jiang Xi province in south- versities are operating more like careful oversight of graduate students east China. Zhong and Liu were both business corporations than research and postdocs to help them un der - fired by the university as a result of organizations. “Professors are treated stand how serious plagiarism, falsifi- the fraud. like white-collar workers,” says Fang cation and fabrication of data are. The papers concerned the crystal Shimin, a former biochemist who “They tend to feed on themselves, structures of a number of organic started the “new threads” website in grow and become habit-forming,” compounds. The statement from 1994, which reports other cases of says Roper. Despite numerous at - Wiley-Blackwell noted that the falsi- plagiarism and academic fraud in tempts, Physics World could not reach fied structures came with a “bona fide China. “Their work is evaluated and Zhong and Liu for comment. set of intensity data, usually on a com- awarded just by simply counting the Li Jiao pound whose structure had been number of publications,” he says. Beijing Medical physics New German ion-therapy centre treats its first patients

Patients have started undergoing “gantry” system that allows the ion beam treatment at a new ion-therapy centre at to be aimed at the tumour at any angle to Heidelberg University in Germany. vastly improve the treatment. Costing 7170m, the Heidelberg Ion- As the beams can be used to irradiate Beam Therapy Center (HIT) is expected to patients with millimetre accuracy, they treat over 1300 patients a year by hit the tumour while leaving the accelerating a beam of ions that can be surrounding healthy tissue unaffected. used to irradiate cancerous tumours. The “We estimate that about 10–15% of the HIT, which opened last November is the patients currently treated using first combined proton- and ion-therapy Heidelberg Ion-Beam Therapy Center chemotherapy or surgery will receive facility in Europe. improved treatments using our scanning HIT has grown out of research ion-beam method with protons or carbon performed at the GSI heavy-ion laboratory Every angle covered The new facility is operated by ions,” says Thomas Haberer, scientific in Darmstadt, which carries out research The “gantry” system Heidelberg University Hospital and technical director of HIT. However, he into nuclear physics. It opened a pilot ion- at the new Heidelberg includes a 5 m linear accelerator and a adds that HIT is not a facility being therapy centre in 1997 and has treated Ion-Beam Therapy 20 m diameter synchrotron, which is used optimized for patient throughput. “It has over 400 patients using carbon-ion beams Center allows the ion to accelerate either protons or carbon been designed to find out what kind of to irradiate tumours. Some clinical beams to be aimed at ions. The centre has three separate particle and treatment protocols best studies have shown that the facility had a patients’ tumours at beamlines to deliver accelerated ions to benefit which kind of patients,” he says. cure rate of up to 90%. any angle. patients, of which one is a unique Michael Banks 7 Physics World February 2010 News & Analysis physicsworld.com

Industry Flexible electronics enters the e-reader market

A company that was spun off from the they could print transistors – made physics department at the University from an organic semiconductor – of Cambridge in the UK 10 years ago onto a plastic substrate. As there is no released its first product last month. Plastic Logic glass, Plastic Logic’s 27 cm shatter- Plastic Logic, founded by Henning proof display does not break if bent Sirringhaus and Richard Friend, or dropped. “Flexible-electronics de- launched an electronic reader that vices are an emerging technology,” can display books, magazines and says Sirringhaus. “We think that this newspapers on a flexible, lightweight un derlying technology can be used to plastic display. The reader commer- make many display products and not cializes pioneering work first started just e-readers.” over 20 years ago at the lab by the two The Que is not cheap. Plastic Logic physicists, who are based in the de - have released two models in the US – partment’s optoelectronics group. a 4GB reader costing $649 and 8GB Plastic Logic, founded in 2000, un- model priced at $799. However, Sir- veiled the Que reader at the Con- ring haus says that anyone should be sumer Electronics Show in Las Vegas use amorphous silicon as a transistor At your fingertips able to find uses for it. “As a scientist, I last month. The Que is an “e-reader” that is deposited onto a glass sub- Plastic Logic’s Que read many PDFs of research articles that can display text on a screen, strate. This layer is then laminated reader will be able to that I really do not want to carry round which, the company says, is easier to with a sheet filled with microcapsules display thousands all the time in paper form. So aca - read than on laptops and most containing a dye that turns black or of documents. demia is a perfect market – physicists portable electronic devices because white depending on the voltage ap- are people who need to read a lot.” it does not have any glass. The Que, plied. The pixels then reveal the text Sirringhaus says that the story of which is about the size of an A4 sheet on the screen. Using a glass substrate, Plastic Logic, which has about 300 of paper, can be used to store thou- however, means the device is heavy staff, is a prime example of basic re- sands of documents and can be easily and prone to damage. search that has turned into a high-tech transported as it has a mass of less Plastic Logic says its device offers product. He notes that the Que also than 500 g. the most realistic feel of ink and paper appeals to students, who can be shown Conventional e-readers, such as yet. Que is based on research carried that physics can be used for “real- Amazon’s paperback-sized Kindle out at Cambridge in the 1980s when world” applications. device that was first released in 2007, Friend and Sirringhaus found that Michael Banks

Funding Japanese science saved, but worries linger

Scientists in Japan have breathed a funding, while the operating budget of Tokyo. “The cut amounts to about sigh of relief after the government for Japanese universities has not been ¥50m (about 7400 000) and that backed away from slashing this year’s cut either. However, there have been trans lates to a loss of about six post- science budget. In late December the some casualties: for example the GX docs, which hurts, but we’ve avoided a government announced it would cut rocket – a satellite launcher being de- potential disaster to lay off scientists.” the budget by only 3.3% to ¥1 332bn veloped by the Japanese space agency However, Murayama is worried (about 710.5bn) – a much smaller re - (JAXA) and Japanese industry – has that Japan’s credibility has been hurt, duction than had previously been had its funding terminated. and says he may find it hard to recruit feared. The current administration, One programme that was expecting people who could question whether led by Prime Minister Yukio Hato- Saving face a cut of up to 50% is the World Pre m - the country’s spending on science in yama, has stated, however, that sci - Japan’s Prime Minister ier International Research Centre stable. “A longer-term ramification is entists may well have to defend their Yukio Hatoyama has Initiative (WPI), which led to the cre- the loss of trust in international part- programmes against possible cuts dur- stated that scientists ation in 2007 of five institutes to attract ners to realize big projects,” he says. ing public hearings again next year. may have to defend researchers from abroad to work in “We’ve not come quite to that, but it Researchers had feared the worst their budgets again Japan. Its budget will now be cut by is heading in that direction.” after working groups re-evaluated next year. just 22%, which means that the five Worse still, the Japanese govern- about 400 research projects through institutes have got away relatively un - ment openly announced after the public hearings held in November to scathed, although the initiative will budget that it plans to evaluate pro- identify cuts for the 2010 budget, be unable to set up a further three jects every year through similar pub- which begins in April. Some projects institutes it had planned. “I am very lic hearings. “The cat is out of the bag were expected to get as little as half relieved,” says Hitoshi Mu rayama, and can’t be put back in,” says Mura - the money they needed, while others head of the WPI’s Institute for the yama. “We have to fear for the worst faced the axe completely. Most of the Physics and Mathematics of the Uni- every autumn I’m afraid.” projects have now been given full verse (IMPU) based at the University Michael Banks 8 Physics World February 2010 physicsworld.com News & Analysis Questions raised over future of UK research council Physicists have called for reform of one of the UK’s main funding agencies after its decision to pull out of some 25 international projects. Michael Banks reports

Five senior physicists have written to the budget cuts to safeguard the UK’s the UK science minister, Lord Dray- international reputation, ensure the son, about the “dismal future” for country can attracts the best overseas researchers in the country in the wake researchers, and carry out work that of a £40m shortfall in the budget of helps support the UK economy. the Science and Technology Facilities The STFC has already indicated it Council (STFC). The physicists, who will be unable to participate in an up- chair the STFC’s five advisory panels, UK Dark Matter Collaboration grade to the LHCb detector at CERN, have also called for structural reforms research into a Super-B factory that to be made to the council. They warn seeks to produce copious amounts of that unless the government takes B mesons, and an upgrade to the neut- action to reverse the situation, the rino experiment at the new J-PARC UK will be “perceived as an untrust- facility in Japan. Burrows, who leads a worthy partner in global projects” and team of five PhD students and two predict that a brain drain of the best postdocs that carry out research into UK scientists to positions overseas linear colliders, currently has funding will ensue. until 2011 but will now have to start The STFC announced the cuts in winding down the work they do. “As mid-December in a document enti- Dark days ahead science programme and domestic fa - things stand, we will have to look for tled “Investing in the Future 2010– Work at the Boulby cilities that are used primarily by opportunities in other areas,” he says. 15”, which revealed that the UK will mine in Cleveland scientists funded by other research be forced to withdraw from more than has been hit by councils”. The STFC was formed in Structural problems 25 leading international projects in the cuts. 2007 through a merger between the The Institute of Physics, which pub- astronomy, nuclear physics, particle Particle Physics and Astronomy Re - lishes Physics World, released a state- physics and space science. The cuts search Council, which awarded ment last month that included a list of would also lead to a 25% reduction in grants, and the Central Laboratory of recommendations for the STFC. It the number of STFC studentships and the Research Councils, which ran the called for a “national laboratory” to fellowships over the next five years, UK’s main central facilities. be formed to support big facilities as well as a 10% drop in support for such as the Diamond synchrotron and “future exploitation grants”. Among Facing trouble the ISIS neutron-scattering centre the projects affected are the UK’s par- The cuts will see support end for five that are used by scientists across many ticipation in the ALICE heavy-ion astronomy projects including the disciplines. The Institute’s statement experiment at CERN’s Large Hadron Auger telescope in Argentina and also said that central government Collider and research into dark mat- the UK Infra-Red Telescope, as well should bear the risk for changes in the ter at the Boulby mine in Cleveland. as nine projects in particle physics, exchange rate in subscriptions for “We are throwing in the towel with including the UK’s contribution to the international projects. regard to investing in future forefront CDF and D0 experiments at Fermilab In a separate statement from the science projects without getting any and plans for a UK neutrino factory. Royal Astronomical Society, it called return on this investment,” says Philip In nuclear physics, the STFC will for the STFC’s responsibility for Burrows from Oxford University, who phase out its support for the AGATA “science exploitation” and facilities is chair of the STFC’s particle-physics and PANDA experiments at the GSI provision to be split, at least finan- advisory panel and project manager of heavy-ion laboratory in Darmstadt, cially. “The STFC would greatly the UK’s involvement in a next-gen- while the UK will pull out of five space benefit from a more transparent divi- eration linear collider. The other four missions – Cassini, Cluster, the Solar sion be tween science and multidisci- authors are Michele Doug herty from and Heliospheric Observatory, Venus plinary national facilities via separate Imperial College London, who chairs Express and XMM-Newton. boards,” the statement says. “[This] the near-universe advisory panel, We are The “managed withdrawal” from would avoid the direct tensioning be- Martin Freer from the Univer sity of these projects is expected to save the tween national facilities and the [par- Birmingham (nuclear physics), Philip throwing in STFC a total of about £115m over ticle physics, astronomy and nuclear Mauskopf from Cardiff University the towel with the next five years. The council has physics] community.” (particle astrophysics) and Bob Nichol regard to also zeroed out funding for research Lord Drayson and Michael Sterling, from the University of Portsmouth investing in and development into new acceler - chair of the STFC, will be looking to (far universe). ator and detector technology that, address the council’s structure, with In the letter, the authors say that future forefront for example, could affect the UK’s in- an announcement expected by the end the STFC “cannot continue to stag- science volvement in the International Linear of this month. The Institute has also ger between financial crises on an projects Collider (ILC) – the next big particle- written to Drayson, welcoming his re- almost annual basis”, and warn that without getting physics experiment after the Large view, highlighting in particular the the funding council is “structurally Hadron Collider at CERN. In their long-term viability of nuclear physics incapable of managing both an in- any return on letter, Burrows and colleagues call on and warning of the potential impact of ternationally leading fundamental- this investment the government to take action against the cuts on young researchers. 9 Physics World February 2010 News & Analysis physicsworld.com

Environment Spy agency shares data on climate change

The Obama Administration has re - provide support for US policymakers ESA surrected a collaborative programme when they are negotiating and imple- that gives climate scientists access to menting international agreements on data obtained by Earth-monitoring environmental issues. satellites owned by the Central Intel - “Decision-makers need informa- ligence Agency (CIA). The initiative tion and analysis on the effects climate will allow climate scientists to gather change can have on security,” CIA data on remote regions of the Earth director Leon Panetta said at a press without needing to launch their own conference announcing the climate satellites and with much greater pre- change centre. “The CIA is well posi- cision than is otherwise possible. tioned to deliver that intelligence.” The programme, dubbed the Meas- However, there have been complaints urement of Earth Data for Environ- about the new centre. John Barrasso, a mental Analysis (Medea), involves Republican senator in Wyoming, com- about 60 academic, industrial and plained that the agency should not be government scientists who each have “spying on sea lions”. security clearance. They will work The CIA insists that its environ- under the guidance of the National mental information gathering does Academy of Sciences. According to Bleak outlook during the Bush Administration. not prejudice its overall security mis- atmospheric scientist Norbert Unter - The Measurement of Although the reasons for the with- sion. Medea, the agency states, will steiner from the University of Wash- Earth Data for drawal remain unclear, the adminis- use images and other resources that ington, the CIA images are particularly Environmental tration was known to be sceptical of it has already gathered. It adds that valuable for assessing changes in the Analysis will use CIA any link between human activity and such a programme offers the agency ice coverage of the Arctic Ocean that satellites to monitor global warming. Medea’s resumption the advantage of maintaining contact could offer clues to the dynamics of ice coverage in the late last year followed by a CIA an - with academic departments and think global warming. Arctic Ocean. nouncement in September that it tanks that are also tackling the issue Medea started in 1992 following had opened the Center on Climate of environmental change. Scientists discussions between Senator Al Gore Change and National Security at its are now analysing images obtained by and Robert Gates, then head of the headquarters in Langley, Virginia. Its satellites in the 1990s to suggest new CIA and now defence secretary in the opening provided official recognition tasks for the programme. Obama Administration. However, of the security implications of en- Peter Gwynne the programme was cancelled in 2001 vironmental issues. The centre will Boston, MA

CERN collisions light up Copenhagen

Anyone passing by the Niels Bohr Institute in Copenhagen, Denmark, might be startled by some strange moving lights on the facade of the institute’s main building. In fact, the dancing beams show, almost in real time, collisions from the ATLAS experiment at CERN’s Large Hadron Collider (LHC). Dubbed the Colliderscope, the display contains nearly a hundred diode lamps and was created by artists Christian Skeel and Morten Skriver with help from physicists Clive Ellegaard and Troels Peterson at the institute. The Colliderscope lights up whenever ATLAS’s “transition radiation tracker detector” – designed by researchers at the institute – picks up a signal as a charged particle passes through it. The particle’s track is then displayed onto the facade. Set to run until 2011, the project began last month and has been supported by the Danish Arts Agency, the Velux Foundation, which provides funding for scientific, cultural, artistic and social projects, and the Niels Bohr Institute. Michael Banks ● colliderscope.nbi.dk

10 Physics World February 2010 FEATURING 4 STANDARD INPUTS & OUTPUTS

Phone: (614) 891-2244 Fax: (614) 818-1600 [email protected] www.lakeshore.com 125 x 91mm NEW CATALOUGE.pdf 25/7/08 11:36:34

7+(3+<6,&$/&(// ,QVHDUFKRIWKHGHVLJQSULQFLSOHVRIOLIH

WK-XQH Extended range of Photomultiplier




 8QLYHUVLW\&ROOHJH/RQGRQ Tubes from ET Enterprises 7KHPHHWLQJZLOOEULQJWRJHWKHUNH\FHOOELRORJLVWVDQGELRSK\VLFLVWVWRGLVFXVVWKH SK\VLFDOEDVLVRIPDQ\FHOOXODUSURFHVVHV,WZLOOFRQFHQWUDWHRQPRGHOV\VWHPV ET Enterprises has extended its LQ ZKLFK D FRPELQDWLRQ RI H[SHULPHQWDO VWXGLHV DQG SK\VLFDO PRGHOOLQJ KDV VLJQL¿FDQWO\HQKDQFHGRXUXQGHUVWDQGLQJRIDZLGHYDULHW\RIOLYLQJFHOOVDQGWKHLU range of photomultipliers to FRPPRQGHVLJQSULQFLSOHV7KHPHHWLQJZLOOEHRUJDQL]HGDURXQGWKHWKHPHVRI include types for use in the following applications areas: ‡6SDFHDQG7LPH ‡6\PPHWULHV ‡*URZWKDQG)RUP s5LTRA HIGHTEMPERATURE ‡&KDQFHDQG&RQWURO s5LTRA LOWTEMPERATURE ‡(YROXWLRQ s6IBRATIONANDSHOCK 3DUWLFLSDWLRQ RI VWXGHQWV DQG \RXQJ UHVHDUFKHUV LV VWURQJO\ HQFRXUDJHG %XUVDULHV DUH DYDLODEOH s6ACUUM 56 VISIBLEANDNEAR )2 IRU SDUWLFLSDQWV IURP (XURSHDQ DQG GHYHORSLQJ FRXQWULHV DSSOLFDWLRQ GHDGOLQH VW 0DUFK  2EQUESTACOPYOFOUR.%7PHOTOMULTIPLIER 63($.(56 %HFKDUD.DFKDU86$ -|UJ$OEHUW8. .DUVWHQ.UXVH*HUPDQ\ CATALOGUEVIAOUR.%7WEBSITEWWWET ENTERPRISESCOM 5REHUW$XVWLQ86$ 6WDQLVODV/HLEOHU86$ ORE MAILSALES ET ENTERPRISESCOM !LSOONOURWEBSITE -RKQ%HFKKRHIHU&DQDGD /0DKDGHYDQ86$ THEREISANEWSEARCHFACILITYWHICHACCESSESTHEWHOLERANGE 'DPLDQ%UXQQHU*HUPDQ\ 7LPRWK\0LWFKLVRQ86$ 0LFKDHO(ORZLW]86$ %HOD0XOGHU1HWKHUODQGV  OF%4%NTERPRISESPHOTOMULTIPLIERSBYANYCOMBINATION (UZLQ)UH\*HUPDQ\ $QGUHZ0XUUD\86$  OFTHEMAINPERFORMANCEPARAMETERS 'DUUHQ*LOPRXU*HUPDQ\ 9LFWRU6RXUMLN*HUPDQ\  0DUWLQ+RZDUG8. 3KRQJ7UDQ)UDQFH /RYOUCANCALLUSIFYOUWOULDLIKETODISCUSSYOURAPPLICATION -HDQ)UDQoRLV-RDQQ\)UDQFH 6WHYH:LOVRQ8. )UDQN-OLFKHU*HUPDQ\  -HQQLIHU=DOOHQ86$ ET%4%NTERPRISES,IMITED "URY3TREET Enterprises Limited, Riverside Way, 25*$1,=,1*&200,77(( Uxbridge,2UISLIP -IDDX (!4! 5+ UB8 2YF, UK $QGUHD-LPpQH]'DOPDURQL,PSHULDO&ROOHJH/RQGRQ Tel:0HONE   +44 (0) 1895 200880 *XLOODXPH&KDUUDV8QLYHUVLW\&ROOHJH/RQGRQ Fax:&AX   +44 (0) 1895 270873 5HJLVWUDWLRQ DEVWUDFWVXEPLVVLRQ [email protected] ET ENTERPRISESCOM %X]]%DXP8QLYHUVLW\&ROOHJH/RQGRQ  GHDGOLQHVW0DUFK 7KRPDV'XNH8QLYHUVLW\&ROOHJH/RQGRQ %LECTRON4UBES &ORGE7AY -RQDWKDQ$VKPRUH8QLYHUVLW\&ROOHJH/RQGRQ ZZZXFODFXN3K\V&HOO 5NIT& 2OCKAWAY .* 53! 0HONE  &AX  SALES ELECTRONTUBESCOM www.electrontubes.com

Untitled-7 1 19/1/10 14:42:05 ETAd withOct advert.inddnew wording 1 May09.indd 1 22/4/097/10/09 09:47:0611:24:29 physicsworld.com News & Analysis

Education Sidebands France’s grandes écoles accused of elitism

Physicists in France have backed It is self-evident “diversification” of admission procedures government plans to open up the that the to widen the social basis of students country’s elite grandes écoles to more admitted to the grandes écoles. Many students from poorer backgrounds. The grandes écoles critics say that students from lower-

government wants to allow up to 30% of should look income families are discriminated ESO/NAOJ/NRAO/W Garnier students to be given free scholarships in for the best against by the exacting entrance exams, an attempt to broaden the social mix of students, but which test not only knowledge of a the student body. The physicists say this specific field but also the general cultural ALMA sharpens its vision would not lead to a lowering of standards. some flexibility knowledge of candidates. The first three antennas belonging to the There are about 200 grandes écoles in in exams will Jean Dalibard, a condensed-matter Atacama Large Millimeter/submillimeter France, which are private bodies that not result in physicist at the Ecole Normale Supérieure Array (ALMA) based in northern Chile have exist outside the mainstream public (ENS) in Paris, says that it is self-evident been linked together for the first time, university system. They educate pupils to a lowering that the grandes écoles should look for the allowing astronomers to begin taking degree level, although the number of of standards best students, but that some flexibility in high-resolution images of the universe. scholarship students has fallen from entrance exams will not result in a When fully complete in 2012, ALMA will about 29% in 1950 to just 15% now. lowering of standards. He cites the Ecole consist of 66 antennas, each 12 m in However, the Conférence des Grandes Polytechnique, an engineering school in diameter, which will be built at an altitude Ecoles (CGE) – an association that Paris where he teaches, as an example of of 5000 m in the Chilean Andes. ALMA will represents about 70% of the grandes écoles what can be achieved. “A big effort has provide unprecedented sensitivity and – said in December last year that it been made to enlist foreign students, and resolution at millimetre and submillimetre disapproved of formal quotas and called the exams are different than those for wavelengths that will allow astronomers to for the entrance exams to continue to be French students,” he says. “The Ecole study a range of phenomena, including the same for everyone. Polytechnique now admits 100 foreign planetary and star formation, the French president Nicolas Sarkozy has students per year. It is an enrichment to emergence of early galaxies and galaxy since declared that the government has have these 100 foreign students, and clusters, and the creation of organic no intention of imposing quotas for nobody protests.” molecules in space. admission, but that he would like to see a Alexander Hellemans Moroccan solar-thermal plant planned Funding Morocco has confirmed plans to create a 2 GW solar-thermal energy project by 2020. The project will involve building five US standards lab funds new research centres separate plants around the country, each of which will consist of an array of mirrors A dozen US research institutions to focus sunlight onto a heating element. have won grants totalling $123m from The hot element will then boil water to the National Institute of Standards power steam-driven electricity-generating and Technology (NIST) to build new HDR/CUH2A turbines. Morocco hopes that the plant will laboratories or extend existing re- account for about 40% of the country’s search facilities. The funds, from the electricity needs by 2020, and the American Recovery and Reinvest - government estimates that it will cost ment Act, will be used to develop new some $9bn. It claims that the solar-energy measurement technologies as well as project will mean it can decrease oil improve environmental-monitoring imports by about 12% a year, saving the techniques. The institutions – 11 uni- country $500m. The project will add to versities and one non-profit organ- Morocco's other renewable-energy ization – beat off competition from Up to standard quantum information and quantum projects, which include two 140 MW and 155 other institutions for the funds. The Laboratory for computation,” says Rolston. 300 MW wind farms. One winner is the Laboratory for Advanced Quantum Meanwhile, the University of Pitts- Advanced Quantum Science at the Science at the burgh will receive $15m to help it Thailand plans ‘science city’ University of Maryland, which gets University of build 13 new experimental-physics The Thai government has announced plans $10.3m towards a total budget of Maryland will get laboratories for research into new to build a $150m “science city”. The city $15.6m to create environmental con- $10.3m to provide nanoscale measurement technologies will be based in the southern state of trols for clean air, low vibration and better measurement and novel electronic and telecommu- Chon Buri, about 100 km south-east of electromagnetic interference. “This standards. nication devices. Other winners in - Bangkok, and built on a former industrial new laboratory will be part of a larger clude the University of Nebraska, estate. Kanlaya Sophonphanit, Thailand’s physical-science complex,” says Mary- which qualifies for half the $13.8m science minister, says that the science city land physicist Steve Rolston, who is cost of a nanoscience-metrology fa- will be the country’s main centre for also co-director of the NIST/Mary - cility, and Georgetown University in science and technology education, and be land Joint Quantum Institute whose Washington, DC, which gains $6.9m the focus for the nation’s R&D. The work the new lab will support. “We’re towards the cost of the Institute of government is expected to appoint an trying to explore how to use quantum Soft Matter Synthesis and Metrology. advisor soon to set the scope and possible mechanics to do more for measure- Peter Gwynne industry connections for the project. ments in terms of better sensors, Boston, MA 11 Physics World February 2010 News & Analysis physicsworld.com

between particle theorist Frank Wil- czek, who was then at the Institute for Law and the end of the world Advanced Study in Princeton, and reader Walter Wagner about colli- A US lawyer believes the courts must step in if required to halt sions of gold ions at the Relativistic experiments like CERN’s Large Hadron Collider, which pose a hypothetical Heavy Ion Collider (RHIC) at the Brookhaven National Laboratory in risk of global destruction. Edwin Cartlidge examines his case the US. Wagner feared that the col - lisions might produce the dreaded Before the Large Hadron Collider strange-quark containing strangelets.

(LHC) was switched on at CERN in CERN Brookhaven’s then director John September 2008, stories abounded Marburger appointed a committee of that the machine might destroy the scientists led by Robert Jaffe of the planet. The fear was that the 76.3bn Massachusetts Institute of Technol - LHC, which will collide protons to - ogy (MIT) to examine the matter be- gether at energies of up to 14 TeV, fore RHIC started up in 2000. The would be powerful enough to create committee, which included Wilczek, mini black holes that could consume concluded that strangelets posed no the Earth – or that it might produce threat, partly because stable strange hypothetical “strangelet” particles matter has never been observed any- that could convert the planet into a where else in the universe. It also saw lump of ultra-dense “strange” matter. no risk of RHIC producing Earth- These stories certainly left their mark, devouring microscopic black holes with people telephoning the Geneva be cause the collider would not be lab in tears imploring researchers not powerful enough to generate the gra- to switch on the accelerator. vitational forces required. Those at CERN never had any Unconvinced, Wagner, who was doubts that the LHC was safe. Safety one of the two plaintiffs in the Ha - reviews published in 2003 and 2008 waiian case against the LHC, filed a both concluded that there was no dan- lawsuit in California in May 1999 to ger that the particle collisions would have RHIC stopped. It was eventually lead to devastation. These reviews dismissed because the Californian ultimately rested on the simple obser- courts said they had no jurisdiction vation that higher-energy versions of over what takes place in New York, these collisions take place billions where the Brookhaven lab is located. of times each second in nature when Judgement call has published a 90-page paper in the A separate suit, filed by Wagner in cosmic rays smash into every object CERN physicists may Tennessee Law Review (2009 76 819) New York in 2000, was also thrown in the universe – bombardments that be convinced that the arguing that the courts must use their out, because the Californian case was leave the Earth and all else intact. In- Large Hadron Collider power to halt hypothetically cataclys - being actively pursued at the time. deed, since the collider restarted last is safe, but would mic experiments such as the LHC if Although RHIC started up without Novem ber, it has generated record- their view hold up they are called upon to do so, and he incident, fears over the safety of breaking proton–proton collisions of in court? puts forward the criteria by which the colliders did not end there. In 2002 2.36 TeV without incident. courts could pass meaningful judge- Steven Giddings, a string theorist at Some people, however, remain un- ments in such cases (see also arXiv: the University of California, Santa convinced and have tried to halt the 0912.5480v2). Barbara, suggested that the argument LHC through the courts. Plaintiffs Johnson claims that he has no in- in the Jaffe report might not apply have filed lawsuits in Switzerland, tent or desire to shut down the LHC – if space has more than the familiar Germany, Hawaii and the European or to “engender fear” – but believes three dimensions, just as string theory Court of Human Rights. However, to that there are grounds for question- proposes (Phys. Rev. D 65 056010). date, no action has resulted in a de - ing CERN’s safety case. He acknow- The idea is that gravity appears much cision on the merits of the case. The ledges that the courts risk being weaker than the other fundamental Swiss lawsuit was dismissed because manipulated by “frivolous objectors” forces because it leaks into these tiny, CERN straddles the Franco-Swiss if they simply decide it is better to be extra dimensions. Accessing these tiny border and the lab’s treaties with safe than sorry when confronted with length scales, which would be within France and Switzerland guarantee it requests for injunctions against ex- the reach of the LHC, might then pro- immunity from legal process in both tremely complex experiments like the vide the strength of gravity needed to countries. The Hawaii suit was thrown LHC. But he believes that the courts produce microscopic black holes. out because the judge handling the must not shirk responsibility. “If the Seeking to head off similarly neg- claim ruled that US funding and par- judiciary refuses to involve itself in ative reaction to the LHC, the then ticipation in the LHC did not provide such disputes, then the rule of law is director-general of CERN Luciano the Hawaii court with sufficient juris- lost,” he writes. Maiani set up a committee to look diction under the environmental law If the judiciary into the new collider’s safety. Re - invoked by the plaintiffs. refuses to Courting trouble porting in 2003, it acknowledged that However, Eric E Johnson, a lawyer involve itself in The LHC is not the first accelerator black holes could potentially be pro- at the University of North Dakota in such disputes, to spark fears about possible cata- duced by the collider, but that they the US, believes that such jurisdic- strophes. Similar concerns arose fol- would evaporate before doing any tional problems should not prevent then the rule lowing an exchange of letters in the damage. However, some physicists justice from being done. Johnson of law is lost July 1999 issue of Scientific American continued to speculate that black 12 Physics World February 2010 physicsworld.com News & Analysis holes might not necessarily evaporate One LSAG panel member – CERN and in 2007 CERN set up another theorist John Ellis – is highly critical safety panel – the LHC Safety Assess- of Johnson’s paper, saying it reads like ment Group (LSAG). “the prosecution in a Perry Mason Its safety case was based on a re- trial, with every phrase unfriendly to fined version of the cosmic-ray argu- the particle physicist”. Specifically, he ment contained in a detailed paper points out that Johnson mistakenly

by Giddings and Michelangelo Man - Brookhaven National Laboratory states that the LHC is designed to gano of CERN (Phys. Rev. D 78 “create particles that have not existed 035009). It had been suggested that since the time of the Big Bang”, the continued existence of the Earth whereas the LHC will only produce might not prove the LHC was safe particles already generated in cosmic- because the mini black holes created ray collisions. Moreover, as Fermilab by cosmic rays would pass straight particle physicist Don Lincoln points through the planet at high speed, out, physicists have close control over whereas those made in the Geneva these collisions. “The type of science lab would linger inside the detectors we are doing is not nearly as unusual (since the colliding protons meet each as you might think,” says Lincoln, who other head on). But Giddings and is also a member of the CMS colla - Mangano showed that certain kinds boration at CERN. of white-dwarf star would be dense Johnson believes that his formula enough to trap mini black holes, if for handling the black-hole case they existed. The fact that we observe son acknow ledges that second guess- False alarm? could also be applied to other poten- these white dwarfs, the pair argued, ing the assumptions of an incredibly Collisions of gold ions tially apocalyptic branches of science, proves that such black holes either do detailed scientific analysis such as at the Relativistic such as nanotechnology, genetic en- not exist or do no damage. that carried out by Giddings and Heavy Ion Collider gineering and artificial intelligence. LSAG also concluded that the Mangano would be hard work; but he at the Brookhaven Lincoln, however, remains cautious, LHC, operating in heavy-ion mode, points out that Cambridge University National Laboratory arguing that the adversarial US legal would be less likely to generate quantum phy sicist Adrian Kent have been taking system is not well suited to assessing strange lets than RHIC, which – a claims to have identified flaws in both place for a decade scientific cases because it can give decade after firing up – has still not the Jaffe report and in a separate re- without incident. unjustified weight to arguments not produced any strangelets. “There is port on the safety of heavy-ion colli- supported by the science. He also be- no basis for any conceivable threat sions by Arnon Dar and two other lieves that judges or jurors reviewing from the LHC,” said the LSAG re- colleagues at CERN. such cases would have to fully under- port, which was subsequently en - In his paper, Johnson also discusses stand the science being reviewed. “I dorsed by CERN’s scientific-policy how psychology and sociology could would hate to see the fate of any sci- committee. “Indeed, experimental be utilized in the courtroom. He entific project rest on a silver tongue and theoretical developments since points out that scientists may be pre- instead of a scientific fact,” he adds. 2003 have reinforced this conclusion.” disposed not to believe that one of Ellis, too, does not see how a court their experiments could wreak havoc, can avoid the question of whether the Unearthing flaws particularly when billions of dollars science is right, adding that “the job In his legal analysis, Johnson acknow- and years of work have been invested of the court is to get at the truth”. In ledges that neither he nor any other in it. Johnson also discusses the poten- any case, he believes the case against non-physicist can hope to thoroughly tial for “groupthink” – the idea, devel- the LHC has been closed for some evaluate the scientific substance of oped by psychologist Irving Janis, that time. “Every time someone comes up CERN’s safety case. But he believes striving for unanimity can override with a new theoretical speculation there are plenty of “human factors” individual critical thinking. In addi- about accelerator safety, it is interest- that would allow a court to sensibly tion, he believes that CERN’s safety ing to see why that speculation does pass judgement on this and other sim- reviews have been weakened by a sig- not constitute risk, but it always comes ilar cases. Among these are the extent nificant conflict of interest: while all back to the cosmic-ray argument,” he to which the theories underlying the but one of the members of the 2003 says. So does that mean these safety safety case have become well estab- LHC Safety Study Group were from reviews are nothing more than a lished or are still the subject of debate outside CERN, there was only one curiosity? “Correct. There is no sci- between scientists. He regards the outsider on the LSAG panel. entific motivation for these reviews. understanding of black holes to be in They are a foregone conclusion, even the latter category. Rigorously reviewed though the community has the right Even if such basic theory appears In response to Johnson, CERN com- to expect CERN to demonstrate the sound, Johnson also believes that munications chief James Gillies says validity of the safety arguments.” courts could identify the potential for that the lab’s safety analyses have un- Kent disagrees. He would prefer smaller-scale errors of modelling, cal- dergone rigorous review. He points an experiment to be risk-assessed by culation or observation. He points out that all of CERN’s operations independent experts before it is built out that such errors have occurred must be endorsed by the lab’s gov- – rather than by ad hoc panels set up before, such as when physicists at erning council, which consists of rep- in response to media interest – and to Los Alamos overlooked the effects of resentatives of the lab’s 20 member only go ahead if the risk is less than lithium-7 within the “Castle Bravo” states. He also says that the scientific- what scientists deem acceptable. But H-bomb test of 1954, which led to the policy committee is made up of non- whether this approach is necessary – bomb’s explosive yield being under- CERN scientists and that the LSAG and indeed practicable – remains an estimated by a factor of three. John- study underwent peer review. open question. 13 Physics World February 2010 physicsworld.com Comment Complexity made simple Physics World Dirac House, Temple Back, Bristol BS1 6BE, UK Tel: +44 (0)117 929 7481 This special issue examines some of the key topics in complexity and network science Fax: +44 (0)117 925 1942 With their passion for analysing the world by breaking it down into ever-smaller E-mail: [email protected] Web: physicsworld.com pieces, most physicists are “reductionists” at heart. Whether through tradition or instinct, our natural inclination is to reduce matter first to molecules and then to Editor Matin Durrani Associate Editor Dens Milne atoms and on to nuclei, nucleons, quarks and beyond. But this approach, while News Editor Michael Banks astonishingly successful in terms of understanding the Reviews and Careers Editor Margaret Harris fundamental particles and forces of nature, does not Features Editor Louise Mayor Web Editor Hamish Johnston always work. In other words, the whole can often be Web Reporter James Dacey more than the sum of the parts. Advisory Panel John Ellis CERN, Peter Knight The classic fly in the ointment is the three-body prob- Imperial College London, Martin Rees University lem, in which, say, the Moon is orbiting the Earth, which of Cambridge itself orbits the Sun. As Henri Poincaré pointed out Publisher Jo Allen over a century ago, it is simply impossible to calculate Marketing and circulation Angela Gage B Goncalves et al. , Indiana University how the three bodies will move. Or consider the beau- Display Advertisement Sales Edward Jost Recruitment Advertisement Sales Chris Thomas tiful patterns created by large flocks of birds flying in the sky, which cannot be Advertisement Production Mark Trimnell explained by understanding in ever greater detail the physiology of those birds. Art Director Andrew Giaquinto Diagram Artist Alison Tovey It is the interactions between the birds that are the key: the patterns form if each individual simply keeps a steady gap between it and its neighbours and flies in Subscription information 2010 volume their average direction. The subscription rates for institutions are £310/7460/$585 per annum. Single issues are This month we look at the science of “complex systems”, which, loosely speaking, £25.00/736.00/$47.00. Orders to: IOP Circulation are those containing lots of individual elements that interact in some way – be it Centre, Optima Data Intelligence Ltd, 12/13 Cranleigh Gardens Industrial Estate, Southall, Middlesex UB1 2DB, traders striking deals in the City, car drivers moving along a motorway, or com- UK (tel: +44 (0)845 4561511; fax: +44 (0)870 4420055; puters linking to form the Internet. Complexity science is a vast, interdisciplinary e-mail: [email protected]). Physics World is available field that brings together not just physicists but also biologists, mathematicians on an individual basis, worldwide, through membership of the Institute of Physics and computer scientists. Indeed, the field is flourishing because computers now have the power to calculate by brute force how a complex system evolves with time. Copyright © 2010 by IOP Publishing Ltd and individual contributors. All rights reserved. IOP Publishing Ltd permits One active area of complexity, where physicists are making much of the running, single photocopying of single articles for private study or is network science. Mark Buchanan and Guido Caldarelli (p22) kick off the issue research, irrespective of where the copying is done. by charting the rise of the field, which involves studying any system with proper- Multiple copying of contents or parts thereof without permission is in breach of copyright, except in the UK ties that lie not in the behaviour of the individual components of the network but under the terms of the agreement between the CVCP and in the nature and structure of the connections between them. It is important to the CLA. Authorization of photocopy items for internal or personal use, or the internal or personal use of specific note that while networks are complex systems, not all complex systems are net- clients, is granted by IOP Publishing Ltd for libraries and works. A colony of ants, for example, might co-operate to build a nest that each other users registered with the Copyright Clearance Center (CCC) Transactional Reporting Service, provided that ant alone could not do, but their connections are not formalized in any way. A net- the base fee of $2.50 per copy is paid directly to work of traders, computers or phones, in contrast, do have such links. CCC, 27 Congress Street, Salem, MA 01970, USA Much of the fascination of network science lies in its roots in everyday life. On Bibliographic codes ISSN: 0953-8585 page 26, Vittoria Colizza and Alessandro Vespignani describe how tools from CODEN: PHWOEW statistical mechanics and network science can be used to model how infectious Printed in the UK by Warners (Midlands) plc, The Maltings, West Street, Bourne, Lincolnshire PE10 9PH diseases, such as the H1N1 swine-flu pandemic, spread in real time. Meanwhile, Dirk Brockmann (p31) shows how information garnered from the geographical movement of banknotes and the location of mobile phones can reveal patterns in how people travel – and even that human mobility follows fundamental laws. The Institute of Physics Some physicists, though, might wonder what researchers involved in complexity 76 Portland Place, London W1B 1NT, UK Tel: +44 (0)20 7470 4800 science are actually trying to achieve. James Crutchfield and Karoline Wiesner Fax: +44 (0)20 7470 4848 round off this issue by tackling this tricky question, even daring to suggest that a E-mail: [email protected] road map staking out future directions is needed (p36). For them, the future lies in Web: iop.org applying ideas from complex systems to the social sciences – a brave notion, but one that may make hard-core reductionists shudder.

The contents of this magazine, including the views expressed above, are the responsibility of the Editor. They do not represent the views or policies of the Institute of Physics, except where explicitly stated. 15 Physics World February 2010 1 Standard 18 Hydrogen METALSALS & ALLOYS& ALLOYS Helium 1 H Catalogue Items 2 He 1.0079 June 2006 4.0026 0.090 June 2006 0.177 -252.87 2 13 14 15 16 17 -268.93 Element Name Lithium Beryllium Element Name Boron Carbon Nitrogen Oxygen Fluorine Neon Atomic 3 4 Atomic No. Symbol 5 6 7 8 9 10 Li Be No. Symbol B C N O F Ne

6.941 9.0122 Atomic weight 10.811 12.011 14.007 15.999 18.998 20.180

0.54 1.85 Atomic weight � 2.46 2.27 1.251 1.429 1.696 0.900

� 3 ADVENT

180.5 1287 Density Solids & (g/cm ) Gases(g/l) 2076 3900 -195.79 -182.95 -188.12 -246.08

� Liquids3 ADVENT Density Solids & (g/cm ) Gases(g/l) M.pt./B.pt.(˚C)� Liquids Sodium Magnesium Melting point (Solids & Liquids) • Boiling point (Gases) Aluminium Silicon Phosphorus Sulphur Chlorine Argon M.pt./B.pt.(˚C) Melting point (Solids & ) • Boiling point (Gases) 11 Na 12 Mg Liquids 13 14 15 16 17 18 22.990 24.305 26.982Al 28.086Si 30.974P 32.065S 35.453Cl 39.948Ar 0.97 1.74 2.70 2.33 1.82 1.96 3.214 1.784 97.7 650 3456789101112660.3 1414 44.2 115.2 -34.04 -185.85 Potassium Calcium Scandium Titanium Vanadium Chromium Manganese Iron Cobalt Nickel Copper Zinc Gallium Germanium Arsenic Selenium Bromine Krypton 19 K 20 Ca 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 39.098 40.078 44.956Sc 47.867Ti 50.942V 51.996Cr 54.938Mn 55.845Fe 58.933Co 58.693Ni 63.546Cu 65.39Zn 69.723Ga 72.64Ge 74.922As 78.96Se 79.904Br 83.80Kr 0.86 1.55 2.99 4.51 6.11 7.14 7.47 7.87 8.90 8.91 8.92 7.14 5.90 5.32 5.73 4.82 3.12 3.733 63.4 842 1541 1668 1910 1907 1246 1538 1495 1455 1084.6 419.5 29.8 938.3 816.9 221 -7.3 -153.22 Rubidium Strontium Yttrium Zirconium Niobium Molybdenum Technetium Ruthenium Rhodium Palladium Silver Cadmium Indium Tin Antimony Tellurium Iodine Xenon 37 Rb 38 Sr 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 85.468 87.62 88.906Y 91.224Zr 92.906Nb 95.94Mo [98]Tc 101.07Ru 102.91Rh 106.42Pd 107.87Ag 112.41Cd 114.82In 118.71Sn 121.76Sb 127.60Te 126.90I 131.29Xe 1.53 2.63 4.47 6.51 8.57 10.28 11.5 12.37 12.45 12.02 10.49 8.65 7.31 7.31 6.70 6.24 4.94 5.887 39.3 777 1526 1855 2477 2623 2157 2334 1964 1554.9 961.8 321.1 156.6 231.9 630.6 449.5 113.7 -108.05

Caesium Barium Lutetium Hafnium Tantalum Tungsten Rhenium Osmium Iridium Platinum Gold Mercury Thallium Lead Bismuth Polonium Astatine 0Radon 55 56 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 Cs Ba 57-70 132.91 137.33 174.97Lu 178.49Hf 180.95Ta 183.84W 186.21Re 190.23Os 192.22Ir 195.08Pt 196.97Au 200.59Hg 204.38Tl 207.2Pb 208.98Bi [209]Po [210]At [222]Rn 1.88 3.51 9.84 13.31 16.65 19.25 21.02 22.61 22.65 21.09 19.30 13.55 11.85 11.34 9.78 9.20 – 9.73 28.4 727 * 1652 2233 3017 3422 3186 3033 2466 1768.3 1064.2 -38.83 304 327.5 271.3 254 302 -61.85 Francium Radium Lawrencium Rutherfordium Dubnium Seaborgium Bohrium Hassium Meitnerium Darmstadtium Unununium Ununbium Ununtrium Ununquadium Ununpentium Ununhexium 87 Fr 88 Ra 89-102 103 Lr 104 Rf 105 Db 106 Sg 107 Bh 108 Hs 109 Mt 110 Ds 111 Uuu 112Uub 113 Uut 114 Uuq 115 Uup 116 Uuh [223] [226] [262] [262] [262] [266] [264] [277] [268] [281] [272] [285] [284] [289] [288] [292] – 5.0 ** – – – – – – – – – – – – – – – 700 1627 – – – – – – – – – – – – –

Order on line Visit our website for www.advent-rm.com latest Catalogue prices Advent Research Materials Ltd • Eynsham • Oxford • England OX29 4JA £ • � • Sfr • US$ + new stock lines Lanthanum Cerium Praseodymium Neodymium Promethium Samarium Europium Gadolinium Terbium Dysprosium Holmium Erbium Thulium Ytterbium 57 58 59 60 61 62 63 64 65 66 67 68 69 70 138.91La 140.12Ce 140.91Pr 144.24Nd [145]Pm 150.36Sm 151.96Eu 157.25Gd 158.93Tb 162.50Dy 164.93Ho 167.26Er 168.93Tm 173.04Yb 6.146 6.689 6.64 6.80 7.264 7.353 5.244 7.901 8.219 8.551 8.795 9.066 9.321 6.57 *Lanthanoids 920 795 935 1024 1100 1072 826 1312 1356 1407 1461 1497 1545 824 Actinium Thorium Protactinium Uranium Neptunium Plutonium Americium Curium Berkelium Californium Einsteinium Fermium Mendelevium Nobelium 89 90 91 92 93 94 95 96 97 98 99 100 101 102 [227]Ac 232.04Th 231.04Pa 238.03U [237]Np [244]Pu [243]Am [247]Cm [247]Bk [251]Cf [252]Es [257]Fm [258]Md [259]No **Actinoids 10.07 11.72 15.37 19.05 20.45 19.816 – 13.51 14.78 15.1 – – – – 1050 1842 1568 1132 637 639 1176 1340 986 900 860 1527 827 827

METALS & ALLOYS • Foils • Sheets • Plates • Wires • Insulated wires • Wires straight cut lengths • Woven wire meshes • Rods • Tubes Pellets • Lumps • Ingots • Polymers • for Research/Development & Industry • Small quantities • Competitive prices • Fast shipment Tel + 44 1865 884440 Fax + 44 1865 884460 [email protected]

For the best careers ^ce]nh^Xh k^h^iWg^\]igZXgj^ih#Xdb

OLE_3rd_193x83mm_Numbers.qx7:Electro Optics 28/5/08 19:35 Page 1

M PW AD 1109 Spaceman 193x36.indd 1 19/1/10 14:23:00 Products: Services • Interlock systems • UKAS accredited Safety, in numbers • Illuminated warning testing to EN60825-1 signs • Training • Labelling • Consultancy • Laser safety software • FDA registration • Shutters • Laser protection • Protective eyewear adviser service • Protective curtains and •Risk assessment screens • Laser safety audit • Filter windows • Power meter • Power meters calibration All your quality laser safety equipment and • Enclosures / cabins compliance services from the world leaders. Lasermet for design, supply and install.

Tel +44 (0)1202 770740 [email protected] www.lasermet.com physicsworld.com Comment: Robert P Crease Critical Point Your favourite units Deluged by responses to his ing per week) is enough to give a farmer self- BIPM sufficiency for his family. request for your favourite units, Other respondents liked the “chain”, that Robert P Crease discovers that once-indispensable surveying tool invented in the 17th century. Equal to 22 yards, the non-SI units persist, and are chain has left its mark on everything from the cricket pitch (1 chain) and the definition sometimes even popular, of the acre (10 × 10 chains) to the length of among the physics community countless city blocks. David Brandon from the Technion in Israel, meanwhile, was fond Units are among the most intriguing features of the “firkin” – a wooden barrel that could of science. They are the “bridges” between hold nine imperial gallons, which just hap- the empirical world of physical phenomena pened to be the quantity of beer needed and the non-empirical abstract world of to fuel parties back in his undergraduate mathematics, allowing us to traffic back and days at Cambridge University. “Think forth. Once upon a time, many bridges of about it: nine gallons or 72 pints [was] just different varieties existed independently of about enough to keep 20 students happy each other. Over the years, the International until they were thrown out of college at mid- Bureau of Weights and Measures (BIPM) night,” he explained. has consolidated them into a single network, the “International System of Units” (SI). SI and SI hybrids SI is an elaborate convention consisting of Setting the standard The kilogram may be one of the Some readers, however, questioned the seven base units – the metre, kilogram, sec- bedrocks of the SI system, but non-SI units endure. SI system itself. Indeed, as Jim Bogan, a ond, ampere, kelvin, candela and mole – and retired physicist living near Eugene, Ore- numerous derived units, such as the hertz, few people in his area own so much land, and gon, poin ted out, units based on the CGS volt, newton, coulomb, tesla and ohm, with it seems likely that 1000 acres in the west of (centimetre–gram–second) system are still still other units “accepted for use” within it, Ireland, despite all its bogs and rocky hills, standard in astrophysics; stellar masses, such as the tonne (103 kg) and day (86 400 s). would be more than enough to serve the for example, are often measured in grams. These are all fully ingrained in the scientific average cow. Nevertheless, his point is that How ever, Bogan is no fan of CGS: it means world, yet some pre- and non-SI units persist a collop-measure cuts the neighbour’s boast that the Earth–Sun distance (1 astronomical outside and even inside the scientific world. down to size. “The devil be from me! But the unit or AU) is a ridiculous 15 000 giga-centi- In September 2009, I asked you to submit people in the old days had sense.” metres or 15 tera-centimetres, which re - your favourite examples, and I received hun- The old Irish also had a superior way of quires two Greek prefixes. It would be more dreds of replies. reckoning time, the basic unit of which was aesthetic, he proposed, to use the MGS the lifespan of a rail, a type of small bird. The (metre– gram– second) system, in which Pre-SI units tailor then translates a list of units based on 1 AU is 150 giga-metres. Many pre-SI units arose directly out of it: a hound outlives three rails; a horse out- The MGS system would leave the Planck everyday life. Consider those mentioned in lives three hounds; a jock outlives three and gravitational constants unaffected – Eric Cross’s novel The Tailor and Ansty, a horses; a deer outlives three jocks; an eagle h=6.625–31 g m2 s–1, and G=6.673–14 m3 g–1 s–2 book that gave such precise voice to Irish wit outlives three deer; a yew tree outlives three – changing only in order of magnitude. and poetry that it was banned the year after it eagles; and an old ridge in the ground out- Electromagnetic units would also be unaf - was published in 1942. The book concerns lives three yew trees. There is no need to go fected in the MGS system, although electro- a country tailor who is fond of relating the further, for three times the age of the ridge dynamic units, like the Planck length, mass wisdom of the old Irish, that is, before “the is the age of the universe. and time, would have to be rescaled. The people got too bloodyful smart and edu- The tailor is wildly off (small surprise) in plus of the MGS system is that it would unite cated, and let the government or anyone else his estimate of the age of the universe, which the CGS and the MKS (metre–kilogram– do their thinking for them”. Some of this is unlikely to be (lifetime of the rail) × 38. second) system, which “has been a headache wisdom involved units. Still, his point is well made that the old Irish for physicists and their students for over a Land, the tailor announces, used to be unit system may possess certain superiorities century”. But Bogan is not holding out much reckoned in “collops”. The collop, based to ours in that it was “reckoned on the things hope for things changing any time soon, be- on the “carrying power” of land, “told you a man could see about him, so that, wherever cause of what he dubs a “rigid adherence” the value of a farm, not the size of it. An acre he was, he had an almanac”. to the SI force standard of the newton. “Try- might be an acre of rock, but you know where Physics World respondents gave numer- ing to change this is like battling city hall,” you are with a collop”. One collop, for exam- ous examples of similar pre-SI units derived he complained. ple, was the area needed to graze “one sow from the world’s almanac. John Blake, a re- I posed this to Richard Davis, head of the or two yearling heifers or six sheep or twelve tired physicist and patent attorney living in BIPM’s mass section and a man wise in the goats or six geese and a gander”, while three Winchester in the UK, who spends several ways of SI (and whose favourite non-SI unit collops were needed to graze a horse. The months a year in Spain, reported that the is the perch for sentimental reasons; the tailor complains of a neighbour’s boast of dia de buy (or “ox-day”) is still used in rural deed to his former home in Washington, DC, owning 4000 acres – which sounds like a parts of Asturias in northern Spain. It refers gave the dimensions of the property in those plantation, but the area only has “enough to the amount of land a farmer can plough units). Davis’s two-part answer explains why real land to graze four cows”. The tailor is using an ox, which depends on soil and crop; nearly all suggested improvements to SI are surely exaggerating here (small surprise), for a 50 ox-day plot of land (one day’s plough- never quite as good as they seem. Part one is 17 Physics World February 2010 Comment: Robert P Crease physicsworld.com Photolibrary

Measure for measure Ox-days, firkins, litres, gnat’s whiskers and Nelson’s Column – some of the many and varied non-standard units that you chose as your favourites. historical: the SI system was built on the one.) Indeed, Yeung measures his car’s petrol reduce the intensity of light to 1/1000th part legacy of the decimal metric system in an consumption in miles per litre, preferring it of its incident value”. attempt to maintain historical continuity as to the old miles per gallon because fuel in John Hearle, an emeritus professor of much as possible. Recognizing the formid - the UK is now usually priced by the litre. “I textile technology at the University of Man- able difficulty of changing measuring habits, know it combines imperial and metric units,” chester, liked the N/tex, a unit for specific SI took into account units that were in wide Yeung explained, “but it’s easily understood stress, and claims in an appendix to the scientific use while tying up loose ends. This (more miles per litre is better, fewer is worse). fourth edition of his book Physical Properties is the reason why one of the base units – the [It also] allows drivers to gauge how much of Textile Fibres that it deserves a special kilogram – contains a prefix, which other- fuel they need in litres to make a specific jour- name apart from its strict SI sibling, N m kg–1, wise does not seem to make much sense, ney in miles, and has a sensible scale, with or its other names, psi/(gm/cc) and BTU/lb. though allowing this unit as an exception normal cars having a value between 5 and Many physicists liked “the barn” (10–28 m2), seems harmless. 10.” The European measure of litres per which is used widely in nuclear and high- The other part of the answer, Davis said, 100 km, in contrast, indicates better efficiency energy physics to express the likelihood of involves “coherence”, in the special mean- with a lower number. one particle scattering off another and with ing given this term by the “SI brochure”. “If But the Physics World community also its amusing origin during the Second World you take any equation of physics, you can includes several die-hard and principled SI War to apply to the cross-section of uranium plug in SI values for all quantities and it enthusiasts. Peter Main, an emeritus pro- nuclei (“as big as a barn!”) that is a well- automatically works as it should; that is, in fessor of physics at the University of York in known part of physics lore. Its cousin is “the a coherent system like SI, there is never a the UK, told me that his son Andrew is an shed” (10–24 barn). Bryan Lovitz pointed out need to tack on additional constants that absolute SI fundamentalist who refuses to that the yoctometer, the smallest SI area were not originally in the equation,” he said. observe normal birthdays and instead meas- unit, is 10 000 sheds. The MGS system is not coherent, in Davis’s ures his age in megaseconds. Andrew (a Another class of non-SI units names the eyes. “Take everybody’s favourite equation: software engineer) admits that although the “least amount”. Andy Taylor, a retired in - E = mc2,” he explained. “If, on the right- second is an astronomical accident – ori- strument engineer, said that a “midge” was hand side, I plug in mass in kilograms and ginally related to the rotational behaviour “the smallest amount of linear or rotational the speed of light in metres per second, my of the Earth – at least it is SI and is now movement achievable at the output of a result automatically appears in joules. But defined without reference to the solar sys- given mechanical or electrical device, within in the MGS, the Einstein relation would tem. His father has taken on the spirit, if not the constraints of static friction, the adjust- become E = km mc2, where m is in grams, c the letter, of his son’s position by informing ment mechanisms provided by the designer is in metres per second, E is in joules and km students that the length of each lecture is and the dexterity of the operator”. Paul is a conversion factor equal to 10–3 kg g –1. a “microcentury”, which corresponds to Wilby, a teacher in the East Midlands, liked Many of the bright ideas for reforming SI 52 minutes and 36 seconds. the “gnat’s whisker” – a subdivision of that would lead to incoherence in this way.” The somewhat larger, well-known unit that, requirement of coherence, Davis added, Off SI because Physics World is a family magazine, helped guide the way in which additional Many non-SI units have, however, survived. I’ll call a “gnat’s testicle”. Kevin Meyer, a base units, such as the ampere and the Gary Harper, an engineer stationed with the physicist and software engineer from South kelvin, were introduced into SI. City hall has US military in Okinawa, Japan, cites the mil Africa, explained the technical terms used its reasons. – an angular measure used worldwide – as an to capture signals: a “tweak” is a fine-tune, a Thomas Yeung, from Suffolk in the UK, example of a non-SI unit that persists due to “twiddle” a gross manipulation and a “frob” was one respondent who espoused the merits sheer practicality. Artillery personnel find an aimless manipulation. of the litre (10–3 m3) – another example of a it useful because a mil at a thousand yards non-SI unit that is “accepted for use”. (The or metres is about a yard or metre, “which Off-off SI coherent SI unit of volume is the m3, which makes it easy to adjust artillery fire”. Gil Yet another category of unit is light-hearted has no special name. The litre is not a coher- Ross liked the “nebule” – a unit minted in and of no practical value except for satir- ent SI unit because 1 l = 10–3 m3 – an equation 1938 to measure visibility at night. It is a unit izing, spoofing or symbolizing the process of containing an extra factor that does not equal of obscuring power “such that 100 units unit-making itself. The classic example of a 18 Physics World February 2010 physicsworld.com Comment: Robert P Crease Pssst! Need a low-noise amplifier? Go to www.femto.de to learn more about …

… Low-Noise Voltage Amplifier – Series DLPVA-100

n Input Noise down to 400 pV/3Hz n Variable Gain up to 100 dB (x 100,000) n Input Impedance up to 1 T1 n Manual and Remote Control unit used ostensibly to measure an entirely Theatre cushion” as a unit of absorption. The subjective property, for instance, is the teacher had in mind the story of how the US … High Speed Current Amplifier – “helen”, named after the line in Christopher physicist Wallace Sabine, a pioneer of archi- Series HCA Marlowe’s Doctor Faustus referring to tectural acoustics, came up with a formula Helen of Troy’s face as having “launch’d a relating reverberation time to absorption, thousand ships”, implying the “millihelen” volume and surface area by experimenting as the amount needed to launch one. Niki with the seat cushions from Harvard Uni- Walton insisted that the amount of breath versity’s Sanders Theatre. Imprecise, per- needed to blow out candles on a child’s haps, but it worked. Other improvised units birthday cake is measured in “ant-farts”, used for estimation include the “Nelson’s while Tony Yule’s favourite units were the Column” (for height), the “Sydney Harbour” “cows” and “dogs” that his A-level physics (for volume) and Physics World’s own bête n Bandwidth DC up to 400 MHz, Rise-Time teacher wrote on his graphs as axis titles noir the “football field”, to describe the area down to 1ns when he had omitted them. of everything from solar power plants to tele- n Optimized Models for Large Source The classic example of an improvised unit scope arrays, which last year drew criticism Capacitances up to 2 nF named for a person is the “smoot”, after from certain readers. n Ideal for Fast and Large Area Photodiodes Oliver Smoot, a freshman at the Massa chu - setts Institute of Technology whose height The critical point was used to measure the length of the Given that SI was designed to serve the Massa chusetts Avenue Bridge in 1958. But needs of the scientific community (and, as … 19” Lock-In Amplifier Board – Physics World readers knew of others. At the much as possible, those of ordinary life) why Series LIA-BV(D)-150 annual sailing event of Bill Clay’s company, do so many non-SI units continue to be 0.01 knots is called a “rick” after an em - used? SI is, after all, carefully supervised, ployee who is particularly adept at setting maintained and continually improved, the sails to optimize the yacht’s perform - which makes it somewhat odd that some ance. Alison Lees (née Procter) recalled an non-SI units seem so actively to resist SI. A-level biology class in which her class- The reason, as the above contributions de- mates were using uncalibrated electronic monstrate, is that units serve human needs, sensors to measure some quantity. Her and the needs of everyday life are diverse protest against marking outputs in “arbi- and continually changing. trary units” provoked a discussion on the Even satirical and silly units have a valu- nature of units – and the recording of the able function, for they bring to light the con- n Working Frequency up to 120 kHz outputs in “proctors”. ventional character of units without forcing n Phase Independent Output Matthew Evans, meanwhile, claimed that us through the trauma of a breakdown or n Manual and Remote Control his brother, who, like him, has a degree in transition. All this seems to confirm Gary n For Low Cost, Multi-Channel and OEM physics from the University of Southamp - Harper’s suspicion that, after having wit- Applications ton, concocted a set of units based entirely nessed decades of changes in SI and non-SI on cruelty to moles: a mole of gas is the units, the strongest human instinct does not amount that can fill a mole before it ex- involve survival, procreation or protection plodes, a mole of length is the distance a of the young, but “the desire to modify the deflating fully-inflated mole propels itself, current measurement system”. No doubt a mole of area is how thinly you can spread a Physics World readers will continue to want single SI-standard mole, and so on. “Purely to make their own changes. FEMTO® Messtechnik GmbH theoretical,” Evans insists, lest the animal- Berlin / Germany rights organization PETA adds unit deter- Robert P Crease is chairman of the Department mination to its agenda. of Philosophy, Stony Brook University, and historian [email protected] n www.femto.de As for Nigel Branson, he recalled how his at the Brookhaven National Laboratory, US, physics teacher used to use the “Sanders e-mail [email protected] 19 Physics World February 2010 physicsworld.com

(December 2009 pp16–17) is an might want to take action on the matter. illustration of why some university Even if there had been a growing popular lecturers do need to be educated about opposition to the facts revealed, it would Feedback education. His argument that we should have been settled by some years of use lectures because students like them further research. Letters to the Editor can be sent to Physics World, ignores the large body of educational The current situation is different. Dirac House, Temple Back, Bristol BS1 6BE, UK, research stating that this is the least Governments need to take urgent action or to [email protected]. Please include your address and effective form of education. It might, as and they need advice. It makes sense to ask a telephone number. Letters should be no more than the well-known aphorism states, be a for opinions from the most informed 500 words and may be edited. Comments on articles successful means of transferring the notes scientists, and if there is a majority opinion, from physicsworld.com can be posted on the website; of the lecturer to the notes of the students then the learned societies should spell it an edited selection appears here without going through the minds of either, out. Be that as it may, I fully endorse but the evidence shows that only 10% of David Tolfree’s comments in the same students learn material in this way. Rather, issue. The sustainable-energy challenge all the educational literature points to the very closely overlaps that of climate Promoting education fact that interactive, discursive methods change; and if we can solve the latter, then are much more likely to produce learning we can feel that we have responded as best from the bottom up with understanding. we can to both issues. Students “like” lectures because they are Roy Danson I am not an academic, just a foot soldier: intellectually undemanding. To accede to Chapel-en-le-Frith, Derbyshire, UK I help out with the Children’s University students’ natural disinclination to use their [email protected] and as a Schools Science Ambassador, brains is to fail to educate and challenge giving talks and demonstrations in physics. them; instead, lecturers are simply Ridley reminds us that it was Newton, not The recent £40m cuts in the budget of the transmitting a body of information. And if the Royal Society who gave the world its UK’s Science and Technology Facilities this is actually their intent, why bother with first account of gravity. But in the same Council (January p6) have created quite a lectures? Indeed, one could argue that this vein, it was the Swedish scientist Svante stir in the academic community, with talk is something that more astute students Arrhenius (1859–1927) who first identified of a “brain drain”. Those in the penthouse have known for many years, particularly and modelled the greenhouse-gas effect of should come down to the basement, where when they can download better carbon dioxide – even predicting rates of they would see just how thin and fragile the explanations from YouTube. temperature change from the burning of scientific foundation is. Where Magueijo is right is in attacking fossil fuels. The big difference between It is widely recognized that in developed the view that the necessary competence gravity and greenhouse gases is that the countries, young people have become and skills to become a good educator are Earth’s gravitational pull is not affected by increasingly disinterested in the sciences – measured by the acquisition of credentials. human economic activities, whereas its a phenomenon known in Japan, where I Whether such courses have appropriate climate is. lived and worked for several years, as goals and whether the methods used lead I fully support our scientific institutions Rika-banare, or science-shunning. In the to this achievement is an appropriate making statements on the risks (not the UK we have a plethora of organizations question. What is not is the implicit certainties) associated with the continued purporting to combat this “shunning”, all premise that lecturers do not need to learn growth of greenhouse-gas emissions. It is with good intentions. However, their some of the knowledge that has been clear, as the scientists involved in the effectiveness tends to diminish the closer acquired about effective education. Intergovernmental Panel on Climate one gets to the front line. There needs to be Contrary to the common myth, good Change have said, that the level of risk is more effort, involvement and, of course, education is a highly complex act and it too high to continue our business-as- money invested in the foundations, or the takes many years of practice to become an usual emission trajectories. Given the whole will topple. accomplished practitioner – something disappointing outcome of the Copenhagen In Japan, in contrast, children at that any of the teachers who read this summit, it is even more important that the elementary school (aged 6–11 years) know magazine would corroborate. rational and collective voice of science is more about radioactivity than most adults Jonathan Osborne heard loud and clear by politicians. in the UK. They are introduced to the Shriram Family Professor of Science Education, Chris Tuppen subject when they are each given a Stanford University, US Colchester, UK radiation monitor for a week. The children [email protected] [email protected] call it a Hakaru-kun, meaning “measuring friend”, and they also get an opportunity to Your readers are right to raise questions see a cloud chamber in action. All this is at about climate-change models. In the no expense to the school. More views on climate current media frenzy the question of the Perhaps a small portion of the £40m I hesitate to take issue with a fellow of the accuracy of output forecasts, which shaved off the UK budget might be Royal Society, but there is a flaw in depends on the accuracy and reliability of invested in refurbishing the basement. Brian Ridley’s argument (January p21) the input data, has been lost. But the Martin Page that it and other scientific societies should complexity of climate science means that Ashford, Kent, UK not take a stance on issues such as climate simplifications and assumptions have to be [email protected] change. Ridley rightly notes that it was made to make the calculations Isaac Newton who gave the account of manageable. An independent appraisal of gravity to the world, not the Royal Society, the margins of error in the output would but the theory of gravitation had no enable more sensible decisions to be made Lecturing the lecturers immediate consequences for the life and about the risks and allocation of resources. João Magueijo’s article “Cargo-cult death of civilization. Learned scientists Ashley Catterall training” about the failings of compulsory were free to debate the new theory Ross on Wye, UK educational training for lecturers without any thought that governments [email protected]

20 Physics World February 2010 physicsworld.com Feedback

Comments from physicsworld.com The UK’s Science and Technology Facilities have nothing to do with “real science”; it’s where their next funding cheque is coming from! Council (STFC) has been plagued by problems ultimately about the STFC and the UK government. mwdb66, Canada since December 2007, when it revealed an £80m nick.evanson, UK shortfall in its 2008–2011 operating budget. A I believe these cuts are good for science. Necessity period of belt-tightening and government loans I’ve got a real sense of foreboding about all is the mother of invention. Maybe the increased reduced this deficit by almost half, but in late this. Money is thrown at offshore windmills, competition resulting from smaller budgets will 2009 officials filled the remaining £40m gap by Prime Minister Gordon Brown promises hundreds of filter out the worthless career-PhD types and give scrapping support for more than 25 international millions of extra cash to make himself look like a those with real passion a chance to shine. projects in astronomy, nuclear and particle world statesman, and yet the fundamental science sorinis, US physics, and space science. Unsurprisingly, that might solve our problems can go to hell in a the decision, which was covered both online handcart. I would urge people to make the This is really bonkers. The STFC’s original £80m and in print (“UK physics hit by savage cuts” connection and join the dots while they’ve still got budget deficit is a mere 0.007% of the £1.2 trillion 16 December 2009; January p6) did not go down jobs in physics. that was just handed over to the bankers – not well with most of the physics community. John Duffield, UK even enough to cover the zinc plating on the wheelbarrows. How are we going to have a future The Liverpool Telescope provides schoolchildren As in Canada, politics and a the lack of public economy without physics R&D? with unprecedented access to a professional understanding drive such decisions. Given the captainbonkers, UK observatory: not just looking at the images it excellent physics talent that the UK has, I think it’s a produces but actually using the telescope. Will shame that a few short-sighted people are making Liverpool John Moores University be able to such a decision. Perhaps a little less spending on continue to provide the same level of access free of items that will improve Mr Brown’s re-election bid charge, or will it be forced to reduce the availability and more on these projects might help keep more Read these comments in full and add your own at (or, worse still, initiate an access fee)? These cuts UK physicists focused on their research and not on physicsworld.com

scientists, we have a duty to carry out our thought suggest that spouts need a lip that Jump-starting the work responsibly. curves downward at the tip. Conforming It may be true that natural events spouts in my kitchen supply only one drip fusion revolution involving particle collisions with similar per lip, no dribbles. This works a treat with and higher energies than those used in the liquids that do not defy gravity; pouring a Your article “Laser fusion shifts into LHC have been observed in the cup of helium might be different. HiPER drive” (fusion supplement, atmosphere, but the difference is that Andrew Cleare December 2009 p7) states that “Igniting nature has the capacity to take the many Axminster, Devon, UK the fuel will require a laser capable of catastrophic events of its making in its [email protected] delivering a few petawatts (1015 W) of stride. While reading Gillies’ article, I power – more than 10 000 times the entire could not help but recall the apprehension Is the standard of scientific enquiry capacity of the UK National Grid – in less and concern among those scientists who dropping such that we should be startled than a picosecond.” While any physicist were closely involved in the first atomic by physicists in France who have been would be able to make sense of this claim, detonation – as well as the fact that they studying dripping teapot spouts? They I think this wording is dangerous and went ahead with it anyway. announce as completely unexpected could be seriously misinterpreted by As a physicist, I welcome the opening of the fact that the surface of the spout non-scientists, who might envisage huge new doors to knowledge and innovation, affects the flow of the liquid as it is numbers of power stations labouring for and I shall await with undeniable travelling. Have they never put the back of months or years just to get the laser-fusion excitement – although probably with a spoon under a tap? Or was something system jump-started. I would have fingers tightly crossed – the results from the lost in translation? suggested “...but only for less than a LHC experiments, with the hope that any John Chapman picosecond” as a less misleading surprises that nature has up its sleeve will North Perth, Australia conclusion to this sentence. inspire and benefit us all. Meanwhile, [email protected] Phil James perhaps we should bear in mind, with Liverpool John Moores University, UK humility, our small place in this vast Quiz results [email protected] universe, and realize that much of the knowledge within its bounds will Congratulations to Cristina Lazzeroni of undoubtedly remain beyond our grasp. Birmingham University in the UK, who won the In conclusion, should I ever meet James Quiz of the year 2009 (December 2009 p52). See you in Narnia in Narnia, I shall expect him to buy me a Answers Having read James Gillies’ Lateral very large drink! A. Petrified wood B. Peter Terren C. 500 m D. 53 Thoughts article on “The perilous world Peter Wright 1. Johannes Kepler 2. World Wide Web 3. Austria of the wardrobe” (January p52), I could London, UK 4. Lisa Raitt 5. Gordon Brown 6. Stephen Hawking not appreciate his comparison of the [email protected] 7. E (Lawrence Krauss) 8. D (Miyuki Hatoyama) experiments at the Large Hadron Collider 9. A (Buzz Aldrin) 10. B (Alan Boss) (LHC) with the opening of a wardrobe 11. F (Colin Pillinger) 12. C (Catherine Cesarsky) door, albeit tongue in cheek. It is absolutely 13. Antibacterial underwear 14. Cillit Bang and understandable that scientists should wish Spouting off Mr Muscle 15. Copernicium 16. Apollo 11 to support and justify their work, but With reference to your article “Tackling 17. Abraham Lincoln 18. 410 19. 17 however much scorn Gillies pours on those trickling teapots” (December 2009 p3), a 20. Seedlings grew faster with opposing views, the fact is that, as drop of the Coanda˘ effect and a hap’orth of 21 Physics World February 2010 Complexity: Network science physicsworld.com A networked world Mark Buchanan and Guido Caldarelli chart the remarkable rise of network science, examine why it has become so popular, and predict what its future may bring

Mark Buchanan Just over a decade ago, in June 1998, a curious three- the major conceptual revolutions of physics and engin- is a science writer page paper appeared in Nature. In it, the authors – two eering in the latter part of the 20th century. Even so, based in the UK and applied mathematicians – reported a link between the neither this nor similar founding papers in areas such Guido Caldarelli structure of the US electrical grid and the wiring of a as spin glasses or self-organized criticality – both key is a physicist at the nematode worm’s neural system. They also noted that sub-fields within the broader category of “complexity Centre for Statistical these patterns were strikingly similar in their structure science” – have come close to matching the citation Mechanics and to the social networks of Hollywood actors, one of the popularity of these papers on networks. Complexity at the University of Rome few such networks for which the authors could find “La Sapienza”, Italy, extensive data. It is hard to imagine a more bizarre A social-network world and the London melding of topics in one study. It could be, of course, that this explosion is the scien- Institute for Yet this strange paper (Nature 393 440) by Duncan tific equivalent of a financial bubble. Science has its Mathematical Watts and Steve Strogatz – then both at Cornell Uni - fashions like any social activity, as researchers decide Sciences, UK, versity – initiated an explosion of further research. In what to study in part by seeing what other people are e-mail guido. “Collective dynamics of small-world networks” the pair working on. Moreover, the availability of cheap and caldarelli@ showed that a new type of mathematical network – nei- powerful computers has made it relatively easy to col- roma1.infn.it ther fully random, nor fully ordered like a regular lat- lect and analyse data on real-world networks. Once the tice – could be an exceptionally useful tool for describing low-hanging fruit is picked, runs the argument, the real-world networks. The paper has since garnered flood of papers in network science might fade to a thousands of citations and launched an entirely new trickle and slip into history alongside earlier fashions quantitative science of disordered networks, with appli- such as catastrophe theory or general systems theory. cations in fields from epidemiology and public transport But another, more likely, possibility is that the sur- to genetic regulation, linguistics and economics. ging interest in networks reflects the action of forces This is itself an extraordinary accomplishment, but bigger than science, and a resonance between the ideas the speed at which this new field has gathered momen- of this field and recent developments in human cul- tum is perhaps even more remarkable. The citation his- ture. After all, these landmark network papers ap- tory (see figure on page 24) shows that the Watts and peared at a time of rapidly growing awareness of Strogatz paper – like other key papers in this area, such globalization, as people became increasingly inter- as one by Albert-László Barabási and Réka Albert in connected thanks to cheap air travel and the advance 1999 on the World Wide Web (Science 286 509) – has of modern telecommunications. The explosive growth accrued citations at a rate faster even than a number of in network science may simply reflect a phase trans- famous papers that launched previous scientific mini- ition in human culture between the years of about 1990 revolutions. One example is Edward Lorenz’s land- up to the present. Arguably, our move towards a more mark 1963 paper “Deterministic non-periodic flow”, networked existence has amplified the importance of which demonstrated how fully deterministic equations network science. in a model of atmospheric dynamics could give rise to For example, the term “globalization” only gained highly irregular and essentially unpredictable beha- prominence in the mid-1990s, as social scientists, politi- viour. It became one of a handful of seminal works in cians and business leaders began noting the increasingly the theory of deterministic chaos, which was one of decentralized nature of human movements and enter- prises. Although the Internet has existed since the early 1970s, it too emerged as a global force in the 1990s, and The surging interest in networks soon spawned the greatest repository of information in human history in the shape of the World Wide Web. The reflects the action of forces Internet search company Google was formally founded in September 1998, just three months after the Watts bigger than science, and a and Strogatz paper appeared. The “open source” soft- ware movement took off that same year, as the Linux resonance between the ideas of operating system demonstrated how the Internet and Web could act as organizing infrastructures for a power- ful collective or network intelligence. this field and recent developments Not all these societal developments were benign, of course. The terrorist attacks of 2001 helped bring the in human culture dark side of networks into the public mind, with talk of “sleeper cells” working within decentralized, extended 22 Physics World February 2010 physicsworld.com Complexity: Network science 11150 104 Proc. Natl Acad. Sci USA 2007 S Carmi et al.

and hard-to-defeat networks of malign individuals. Yet their dense webs of interactions. In areas ranging from Only connect even the unpleasant aspects of networks helped thrust materials and climate science to ecology and anthro- This image shows the the idea into prominence at many levels simultaneously, pology, scientists have recognized that many of their hierarchical structure as part of a “perfect storm” of globalization. most pressing problems can no longer be solved simply of the Internet, by breaking systems into parts and understanding those the rise of which has paralleled Scientific feedback parts. Understanding the behaviour of electrons within the increasing Overall, it is probably fair to say that the explosive a single atom, for example, is not nearly enough to importance of growth of network awareness has carried network sci- allow physicists to grasp the complex collective organ- network science. ence along with it. But looming issues within science ization underlying superconductivity, or even the also reinforced this network-centric transformation. abrupt transformation of water from liquid to ice at When biologists released a complete draft of the 0 °C. Rather, it is the synthesis that matters the most – human genome in 2003, it was both a landmark understanding the network of interactions among the achievement and a demonstration of the limitations parts and how those interactions lead to properties of a traditional way of doing science. The Human such as solidity or electrical conduction, or, in other set- Genome Project found that human beings have tings, adaptability, robustness in the face of challenges, roughly 30 000 genes, far fewer than the 100 000 or intelligence. expected. In contrast, some species of rice do have In some sense, the ideas of network science can be about 100 000 genes, suggesting that it is not the raw likened to calculus. Much as calculus can be applied to number of genes that makes for our complexity but radio communications or to the swimming motion of a the way these genes interact. In other words, the key bacterium, network science is providing the general issue is the subtle organization of the genetic network. concepts and perspective needed to address problems Many, if not most, diseases and functions in organisms typical of a wide range of complex systems. It provides can only be understood by thinking in terms of a dense a theoretical framework for analysing the Web and the web of interactions and feedback. Internet, the web of interactions in a social group, the Of course, this problem of feedback is not specific to network of molecular interactions underlying cellular biology, and it lies behind the recent growth of com- metabolism, correlations in the stock prices of many plexity science – a broad field that aims to understand organizations, and so on. the more holistic properties of systems by penetrating Remarkably, and despite their differences, these sys- 23 Physics World February 2010 Complexity: Network science physicsworld.com

800 chaos spin-glass renormalization group diffusion-limited aggregation high-temperature superconductivity 600 neural networks self-organized criticality small-world networks scale-free networks

400 number of yearly citations

200

0 1960 1970 1980 1990 2000 2010

Networks take off This graph of the number of citations garnered by a handful of groundbreaking physics papers shows that even within this elite group, the popularity of papers on networks has been unprecedented.

tems show strong similarities in their architecture. In It will be interesting to see how long this explosive almost all cases, real-world networks have a “small growth of network science lasts. However, recent de- world” character, meaning that it takes only a handful velopments – for example, the highly influential of steps to move between any two points in the network, PageRank algorithm in computer science, which vastly even one that includes many millions of elements. Like- improved the results of Web searches – suggest a rich wise, most (though not all) real-world networks show future. Some researchers, such as biologist Carl Woese an enormous variance in the way links get shared out and physicist Nigel Goldenfeld, have recently sug- between the network elements; typically, a small few gested that evolutionary biology is due for a network have an enormous number of links, while most have revolution of its own. They believe that as biologists very few. absorb the fact that bacteria and viruses are always exchanging genetic material “horizontally” – shuttling Where do we go from here? it between individuals in ways that have little to do with One thing that is still missing from this picture is a com- traditional mechanisms of evolution – biology at a fun- plete theory of why nature is so fond of networks. Such damental level will need to focus on the network con- a theory would need to explain why the natural world, nections between individuals in a way it has not done whether in physics or biology, has so often settled on in the past. particular, archetypal network structures, and why our Similarly, in the social sciences, modern techniques human-engineered structures so often recreate similar for gathering data have stimulated a renewed interest designs. On a more practical level, it would offer useful in human interactions, which has led some researchers guidance for anyone wishing to design a network – an to suggest that a lot of human intelligence is not based electrical grid, say – with desirable properties like infor- in the individual at all, but instead resides in the rela- mation-processing efficiency or resilient performance. tionships and connections within groups of individuals. Yet even without such a complete theory, the tools If true, this might imply that we have a form of “collec- of this new science have already become indispensable tive” intelligence – that humans can be ant-like as well to a world of new network-based businesses, which are as ape-like. the main drivers of our freshly network-centric world. If this kind of broad transformation into network One thing that The software algorithms underpinning the popular thinking is the real explanation for the fast growth of is still missing social-networking website Facebook, for example, network science, then this exciting new field should is a complete count the number of common friends a person has in continue to grow apace for some time. Network science theory of order to identify new people he or she may want to may be explosive science because it is very general sci- meet. Similarly, the software used by the online re - ence; it is busy building up the basic physics and ma- why nature is tailer Amazon keeps a record of items bought by vari- thematics needed to understand, or at least speak so fond ous users to recommend new interests in books, films, intelligently about, webs of interactions among all kinds of networks electronics etc. of things. 24 Physics World February 2010 FUNCTIONAL MATERIALS ENERGY MATERIALS A Amorphous and Polycrystalline Thin-Film Silicon W Diagnostics and Characterization of Energy Materials with Synchrotron Science and Technology and Neutron Radiation B Silicon Carbide—Materials, Processing, and Devices Y Computational Approaches to Materials for Energy C Solution Processing of Inorganic and Hybrid Materials Z Actinides V—Basic Science, Applications, and Technology for Electronics and Photonics AA Scientific Basis for Nuclear Waste Management XXXIV D Plasmonic Materials and Metamaterials BB Materials for Nuclear Applications and Extreme Environments E Chemical Mechanical Planarization as a Semiconductor CC Solid-State Batteries Technology Enabler DD Thermoelectric Materials—Growth, Properties, Novel Characterization F Materials, Processes, Integration, and Reliability Methods, and Applications in Advanced Interconnects for Micro- and Nanoelectronics EE Defects in Inorganic Photovoltaic Materials G Materials and Physics of Nonvolatile Memories FF Polymer Materials and Membranes for Energy Devices Advancing materials. Improving the quality of life. H Phase-Change Materials for Memory and Reconfigurable GG Nanoscale Charge Transport in Excitonic Solar Cells Electronics Applications HH Organic Photovoltaic Science and Technology I Materials for End-of-Roadmap Scaling of CMOS Devices J Materials and Devices for Beyond CMOS Scaling SOFT/BIOMATERIALS K Functional Materials and Nanostructures for Chemical II Materials Science and Charge Transport in Organic Electronics and Biochemical Sensing JJ Stretchable Electronics and Conformal Biointerfaces L Recent Advances and New Discoveries KK Micro- and Nanofluidic Systems for Material Synthesis, Device in High-Temperature Superconductivity Assembly, and Bioanalysis M Structure-Function Relations at Perovskite Surfaces LL Directed Assembly and Self Assembly—From Synthesis and Interfaces to Device Applications MM Evaporative Self Assembly of Polymers, Nanoparticles, NANOMATERIALS and DNA N Functional Oxide Nanostructures and Heterostructures NN Materials Exploiting Peptide and Protein Self Assembly— O Multifunctional Nanoparticle Systems—Coupled Behavior Toward Design Rules and Applications OO Hierarchical Self Assembly of Functional Materials—From Nanoscopic P Semiconductor Nanowires—Growth, Physics, Devices, to Mesoscopic Length Scales and Applications PP Interfacing Biomolecules and Functional (Nano) Materials Q Template-Based Nanofabrication—Nanowires, Nanotubes, QQ Biological Materials and Structures in Physiologically Extreme and Associated Heteronanostructures Conditions and Disease R Carbon Nanotubes and Related Low-Dimensional Materials GENERAL S Graphene Materials and Devices T Photovoltaics and Optoelectronics from Nanoparticles X Frontiers of Materials Research U Scanning Probe Microscopy—Frontiers in NanoBio Science MATERIALS RESEARCH SOCIETY V In Situ Transmission Electron Microscopy and Spectroscopy www.mrs.org/spring2010

The Exact Lens you need, the Expert Support you want From Prototype to Production Universe Kogaku Designs Lens Assemblies for Every Application Medical Imaging Lenses UV Quartz Lenses Microscope Objectives CCD & CMOS Lenses Photographic Lenses CCTV Lenses Lens Mounting Accessories Diode Laser Lenses Lens Filters and Accessories High Res Lenses Image and Barcode Lenses Your Custom Lens Custom Lens Manufacturer Thousands of Lens Sizes in Stock Most Lenses Ship Same Day www.UKAoptics.com In USA: 516-624-2444 Email: [email protected] © 2010 Universe Kogaku (America) Inc. Complexity: Modelling epidemics physicsworld.com The flu fighters Quick and easy global air travel aids the spread of infectious diseases like the current H1N1 flu pandemic, and makes modelling them a complicated task. But as Vittoria Colizza and Alessandro Vespignani explain, physicists and computer scientists are at the forefront of such studies, using tools developed from fields such as statistical mechanics and complex networks

Vittoria Colizza is a The Black Death was one of the most devastating pan- predecessors. These include not only significant research scientist at demics in history. Beginning in 1347, the plague took progress in medical science, but also a powerful new the Computational just three years to spread from Constantinople in west- epidemic-fighting weapon: computational models Epidemiology ern Turkey to Italy and then on to the rest of Europe, derived from network science, mathematical epi- Laboratory, Institute leaving nearly a quarter of the continent’s population demiology and the statistical physics of reaction-dif- for Scientific dead in its wake. Historical studies confirm that the dis- fusion processes. In the words of evolutionary biologist Interchange, Turin, Italy. Alessandro ease diffused smoothly, generating an epidemic front Andrew Dobson, models are now “as crucial in the Vespignani is a that travelled through the continent as a continuous study of infectious diseases as are microscopes, stetho- physicist in the wave at a rate of about 200–400 miles per year. scopes and the tools of molecular diagnosis”. School of Informatics In 14th-century Europe few means of transport were Models can be used to assess the impact of epidemics and Computing, available and travellers could cover only relatively short and pandemics on human health, and to predict the Indiana University, distances in a day. The advent of modern transporta- geographical spread of a disease, the expected number US, e-mail alexv@ tion has dramatically altered this picture, speeding up of cases and the timing of an epidemic’s peak. Nu - indiana.edu disease transmission significantly. For example, the merical results from these models can help alert health influenza pandemic of 1918 took just one year to spread officials, guide planning for social-distancing measures from its US or European source to isolated Pacific like school closures, and suggest strategies for the de - islands, while the 1957 flu virus swept the globe in about velopment, production and administration of vaccines. six months. They can also allow public-health experts to assess the On 11 June 2009 the World Health Organization impact that all these interventions might have in miti- (WHO) declared that a new virus, known as H1N1 gating the pandemic. influenza or “swine flu”, had become the first pandemic of the 21st century. This time, only two months passed The role of physics between the first international alert and the WHO’s Physicists have long used computational approaches announcement. From a scientific and public-health to solve problems involving a large number of degrees perspective, such rapid transmission posed an unprece- of freedom, and can now simulate material processes dented challenge: we and other groups working at the and physical phenomena on a wide range of scales. It interface between physics, epidemiology and compu- is now almost routine to study, say, fracturing processes tational science needed to track the evolution of the in materials by simulating over a billion atoms or to pandemic in real time. Under these circumstances, solve evolution equations for six billion finite elements there is a large degree of uncertainty in what will hap- in plasma fluids. Furthermore, the advent of ab initio, pen. How fast will the virus spread to new countries? Monte Carlo and other simulation techniques in areas What will be the impact on the population? How dan- such as quantum chemistry, molecular dynamics and gerous is it? And, most importantly, what weapons do materials science has made it possible to calculate the we have to fight it? behaviour of single atoms or aggregate states of mat- As an interconnected, mobile society, we face a ter from first principles. number of disadvantages in combating pandemics. Given these successes, it is natural to wonder why Fortu nately, we also have some advantages over our we are at a far more primitive stage in the quantitative forecasting of how newly detected emerging diseases At a Glance: Modelling epidemics (or even seasonal influenza) will evolve. The basic dif- ference is that even though the simulation of six billion ● Modern pandemics spread more quickly and less uniformly than in the past, human beings is in principle computationally feasible, thanks to the global air-transportation network and the complex and the models used in epidemic and contagion processes interconnected nature of our society have to include social and behavioural factors, not just ● Modelling the spread of new infectious diseases requires theoretical and the (comparatively simple) physical laws governing computational models that take into account physical and biological principles fluids or atomic motion. So, while the theoretical foun- plus social and behavioural factors dation required to approach the spread of diseases ● A range of new tools for simulating influenza-like illnesses has been developed in computationally has been in place for a long time, recent years, allowing researchers to predict how events like the current H1N1 flu progress has been hindered by a lack of data on how pandemic will evolve people interact, travel and behave – as well as on how communities are structured, and how they react to 26 Physics World February 2010 physicsworld.com Complexity: Modelling epidemics B Goncalves et al. , Indiana University

environmental, political, technological and cultural As a result of this data revolution and increased com- When Europe factors. All these layers – from the single individual to puter-processing power, researchers are now begin- sneezes the global society and its surrounding environment – ning to integrate large-scale datasets into models of Layers of data on interact at multiple scales, thereby increasing the com- mathematical epidemiology. This means that we are transportation plexity of the phenomena to be modelled and creating finally in a position to move from analysing the “social networks – including formidable obstacles to the development of predictive atom”, or small social groups, to analysing “social both air- and land-based travel – computational approaches. aggregate states” made up of millions of people. But in make up the The last decade has, however, witnessed a sharp in- making this transition – which is equivalent to the shift backbone of disease- crease in our capacity to gather these data. This is from atomic and molecular physics to the physics of immunization models. mostly because the boundaries between real-world bulk matter – we must confront the complexity of the social behaviour and the cyberworld have started to system that emerges from the collective behaviour of disappear. Devices like mobile phones and personal a large network of interacting units. digital assistants produce detailed traces of our daily Networks that trace the activities of individuals, activities. Websites have sprung up to record data, such social patterns, transportation fluxes and population as the dispersal of banknotes that can be used to infer movements all exhibit large-scale non-uniformity that human interactions and mobility, as shown by Dirk emerges spontaneously as the system evolves. The sta- Brockmann and co-workers (see article on page 31). tistical distributions characterizing the fluctuations in This huge mass of data is changing our understanding these networks are generally “heavy-tailed”, meaning of a wide range of phenomena by producing quantita- that their standard deviations are extremely large – tive descriptions of large-scale social systems. there are no “typical” values for many of the quantities 27 Physics World February 2010 Complexity: Modelling epidemics physicsworld.com

1 Speed of epidemic propagation

Dec 1350

June 1350

Dec 1349

June 1349

Dec 1348 before 31 March 1–15 April

time 16–30 April June 1348 Dec 1347 1–15 May June 1347

Epidemic spreading patterns changed dramatically after the development of modern transportation systems. In pre-industrial times, the spread of diseases was mainly a spatial-diffusion phenomenon. When the Black Death was spreading through 14th-century Europe, only a few means of travel were available and typical trips were limited to relatively short distances, lasting about a day. Historical studies confirm that the disease diffused smoothly, generating an epidemic front that passed as a continuous wave through the continent at about 200–400 miles per year (left). The speed and pattern of the 2009 H1N1 “swine-flu” pandemic, in contrast, were radically different. The swine-flu outbreak was declared the first pandemic of this century just two months after an international alert at the end of April 2009. The rapid spreading and the patchy propagation pattern are shaped by human-mobility networks that allow infected people to travel across continents in one day or less (right).

of interest. For example, the distribution that defines simply described in terms of diffusive phenomena but the probability that each node in the system (repre- must explicitly incorporate the spatial structure and senting anything from an individual to a country, de- deep interconnectedness of today’s modern society. pending on the model) is connected to k neighbouring In recent years, two major classes of models have nodes is often approximated by a power-law decay. emerged that are particularly useful for simulating This indicates that there is an appreciable probability influenza-like illnesses (figure 2). The first, known that some nodes may have orders of magnitude more as the agent-based approach, keeps track of each indi- connections than the “average” value of k for the sys- vidual in a population in an extremely detailed way. tem. A similar pattern is also observed for the intensity Agent-based models typically take into account the of the flow between connecting links, transport flows fact that infection can spread among individuals by and other basic statistical quantities characterizing the contacts between household members, school and network structure. workplace colleagues, and by random contacts in the Our ability to deal with such systems – where the general population. One key feature of such models is behaviour at any scale is the outcome of a complicated that they characterize the network of contacts among interplay among processes that occur on very different individuals based on the socio-demographic structure time and length scales – places an important constraint of the population. on efforts to model emerging infectious diseases. For - The second scheme relies on meta-population mod- tunately, some of these same difficulties have already els that consider the long-range mobility of people at been addressed in physical systems that feature phe- an inter-population level, while using coarse-grained nomena such as turbulence or critical behaviour (“tip- techniques at the level of individual interactions. In ping points”). Tools that were developed for these such models, the world is divided into geographical problems, including renormalization-group tech- regions that define a sub-population network. Connec - niques, timescale-separation approaches and homog- tions among each sub-population represent the fluxes enization methods are therefore viable candidates for of individual humans due to the transportation infra- addressing the new challenge of pandemic modelling. structure. Infections evolve inside each urban area, and this process is described by schemes in which the dis- Network-based models crete, stochastic dynamics of the individuals in different The network perspective itself is also creating new compartments depends on the specific causes and ori- mathematical tools and approaches. Both physicists gins of the disease and any containment interventions. and epidemiologists have recognized the importance Of these two techniques, agent-based models pro- of network structure in the spreading of diseases in a vide a large amount of data, but their computational globalized world and have developed models that cost and – most importantly – the need for very detailed explicitly integrate multiscale mobility networks into input data has, to date, limited their use to a few coun- the description of emerging diseases. For example, al- try-level scenarios. The structured meta-population though the spread of the Black Death can be adequately models, in contrast, are fairly scalable and can be con- described mathematically using continuous differen- veniently used to provide worldwide scenarios and pat- tial equations with diffusive terms, in modern times terns. Although the level of information that can be the spread of epidemics is mainly determined by the extracted is less detailed than in agent-based models, human-mobility networks that allow infected people to the spatial and temporal ranges, and the number of travel across continents in less than a day (see figure 1). realizations that can be computationally analysed, are The current swine-flu pandemic, therefore, cannot be all much larger. 28 Physics World February 2010 physicsworld.com Complexity: Modelling epidemics

2 Model approaches

susceptible infectious recovered

hospital

household

workplace

school These schematic diagrams illustrate the assumptions made in several different approaches to modelling the spread of infectious diseases. Circles represent individual people, while their colours correspond to specific stages of the disease. If a susceptible person (yellow) comes into contact with an infectious individual (red), they may contract the disease and thus become able to transmit the infection to others. At the end of the infectious period, the individual recovers from the disease (grey circles) and becomes immune to it. From left to right: homogeneous mixing, in which individuals are assumed to uniformly interact with each other at random; social structure, where people are classified according to social/demographic information (e.g. age and gender) that suggest how likely they are to interact; contact-network models, in which the detailed network of social interactions between individuals is explicitly considered, providing the possible virus-propagation paths; multilayer models, which consider sub-populations coupled by movements of individuals, while assuming homogeneous mixing on the lower scale; and agent-based models, which recreate the movements and interactions of individuals on very detailed spatial and temporal scales.

Modelling a pandemic in progress Using the mobility-network approach, we can instead While the recent growth of computational epidemiol- calculate transmissibility using data on the first handful ogy laid the foundations for a first-principles approach of cases detected in newly affected countries. These to modelling epidemics, the swine-flu pandemic rep- data tend to be more accurate. This new approach is resents the first time that such computational methods possible because the chronology of the infection of new have been used to model the spread of an infectious countries is determined by two factors: the number of disease in real time. So far, the results have been ex- cases generated by the epidemic in the originating coun- tremely encouraging: state-of-the-art, large-scale com- try; and the mobility of people from this country to the putational approaches have been able to capture the rest of the world. The mobility-network data are defined spatio-temporal pattern of the unfolding epidemic from the outset with great accuracy, and we can there- quite accurately, making projections up to three weeks fore determine the parameters of the disease by calcu- in advance. In particular, it has proved possible to anti- lating which values best fit the computational-model cipate which urban areas or countries will observe results for the chronology of infection in new countries. the first local cases of the disease, and thus become This strategy has already been used by the WHO Rapid “hotspots” of the epidemic. Remarkably, different Pandemic Assessment Collaboration, Harvard Uni - methodologies – including the Northwestern Univer - versity epidemiologist Marc Lipsitch and co-workers, sity group’s proxy networks and our own approach, and by our own group to provide independent early esti- which is based on the integration of real transportation mates of the transmissibility of the swine-flu pandemic and mobility data (figure 3) – provide very similar pat- virus and the cumulative incidence in Mexico. terns and results. This indicates that the basic elements Another notable success for this strategy was that we considered in the models – population distribution and were able to predict several months in advance that the human-mobility networks – are able to capture the swine-flu pandemic in the US and the Northern hemi- main features of the epidemic’s evolution. sphere would peak between late October and late The integration of large-scale mobility networks into November 2009. Being able to anticipate such peaks epidemic models is also providing new ways to esti- is crucial for testing possible vaccination scenarios, mate the virus’ transmissibility and other basic param - since the effectiveness of mass-vaccination campaigns We were able eters of the epidemic. Disease transmissibility, for depends on having vaccines available at the right time to predict example, is usually indicated by the mean number of and and in the right place. In this context, data-driven several months secondary cases that a typical infected individual gen- computational models can shed light on the fuzzy pan- in advance that erates in a population with no immunity. This quan- demic future, and serve as in silico experiments on the the swine-flu tity is often estimated using temporal data on the effectiveness of mitigation strategies. pandemic in number of cases detected in each country. However, the accuracy of these data depends on whether cases More to be done the US and are spotted and properly reported to health author- The swine-flu pandemic has shown that computational the Northern ities, and as a result they sometimes give a very mis- tools can be used successfully and considered as a sup- hemisphere leading picture of an evolving epidemic. For example, port tool in the complicated decision-making process would peak several studies indicated that the official number of of public-health policies. Yet even before the current between late swine-flu cases reported by the authorities in Mexico, pandemic started, simulation results had already fun- where the virus was first identified in April 2009, had damentally altered our understanding of the interplay October and underestimated the actual impact of the epidemic by a between social behaviour, infrastructures and the bio- late November factor of 100–1000. logical processes of infectious diseases. Thanks to 2009 29 Physics World February 2010 Complexity: Modelling epidemics physicsworld.com

3 The GLEaM model

demographic commuting air travel

The Global Epidemic and Mobility model (GLEaM) that we use in our computational studies of epidemics is based on a meta-population approach in which the world is divided into geographical census areas. These areas are connected by human-travel fluxes that correspond to transportation infrastructures and mobility patterns, and that together form a network of interactions. The model is based on a highly detailed population database containing demographic data in census cells that cover the entire Earth’s surface in a grid of 15 × 15 minute squares. To this, we add information on the long-range airline fluxes of people travelling to and from the airports listed in the International Air Transport Authority (IATA) database, which account for more than 99% of commercial air traffic worldwide. We can then subdivide the world population into a pattern of geographical areas centred on each IATA airport location, using a process known technically as a Voronoi decomposition. In addition to long-range air travel, GLEaM also incorporates short-range mobility patterns that correspond to ground movements and commuting patterns, based on data from more than 30 countries on five continents. These patterns can then be used to calculate the effective interactions between sub-populations in neighbouring areas (termed Voronoi tessels). Within each sub-population, the model assumes homogeneous mixing, with a compartmentalization that depends on the specific disease under study. The figures above show an extract of GLEaM layers centred on the UK and Ireland. More information can be found at www.gleamviz.org.

analysis performed by Deirdre Hollingsworth, Neil the epidemic that is transmitted via a variety of media Ferguson and Roy Anderson at Imperial College Lon- sources – could affect the choices people make, like don; the computational approaches of Ben Cooper deciding to travel less. This social adaptation to the and Joshua Epstein (based at the UK Health Pro - available information is part of the dynamic of the sys- tection Agency and the Brookings Institute, respect - tem. Paradoxically, the model’s reliability produces, ively); and our own analytical and simulation work, by through its predictions, a feedback on the model itself. 2006 researchers knew that travel restrictions alone This issue is still uncharted territory. Current mod- would do little to contain or even slow down a global els focus largely on situations where steady-state data epidemic. Using reaction-diffusion techniques, we are used to study the system under normal conditions, were able to show that the topology of the air-trans- in which the social behaviour is not altered or dis- portation network and the traffic flow through it rupted. The next challenge is to develop formal models meant that unless traffic restrictions were more than that can deal with the prediction–adaptation feedback 90% effective, they would not delay the peak of a loop and the possibility of their validation. This is some- pandemic by more than two to three weeks. And, of thing that goes beyond the physics of fluids, gases and course, such a drastic reduction in air travel would particles, or the “physics” of non-adapting social atoms. quickly lead to social and economic disruption. And it is where a truly interdisciplinary collaboration The same interconnectedness that makes draconian among physicists, epidemiologists, computer and social travel restrictions impractical also reduces the effect - scientists is inevitably needed. iveness of any containment or mitigation strategies that ■ are limited to a single country. A traditional strategy for epidemic control assumes that drugs will be used in More about Modelling epidemics the very few countries in the world capable of amass- D Balcan et al. 2009 Seasonal transmission potential and ing stockpiles, but in a highly connected world such activity peaks of the new influenza A(H1N1) BMC Medicine localized mitigation is not as effective as a coordinated 7 45 global strategy. If wealthy countries are willing to share B S Cooper et al. 2006 Delaying the international spread of a very small fraction of their stockpiles of antiviral pandemic influenza PLoS Med. 3 e12 drugs with developing countries, in contrast, this would J M Epstein et al. 2007 Controlling pandemic flu: the value of hugely mitigate the impact of a pandemic. international air travel restrictions PLoS ONE 2 e401 In some ways, computational approaches to the M C Gonzalez, C A Hidalgo and A-L Barabási 2009 spread of epidemics are remarkably similar to the so- Understanding individual human mobility patterns Nature phisticated simulation methods used in physics. In both 453 779–782 cases the “social atoms” interact, move and react in M E Halloran et al. 2008 Modeling targeted layered constrained spaces. The final aggregate state (the social containment of an influenza pandemic in the United States system and its epidemiology) is the outcome of the prin- Proc. Natl Acad. Sci. USA 105 4639–4644 ciples governing these microscopic processes. However, T D Hollingsworth, N M Ferguson and R M Anderson 2006 Will a major difference has to be factored in. Unlike a phys- travel restrictions control the international spread of pandemic ical system, the unfolding of the epidemic is going to influenza? Natl Med. 12 497–499 affect the individual’s behaviour. Indeed, even the M Lipsitch et al. 2009 Use of cumulative incidence of novel model predictions themselves – along with news about influenza A/H1N1 in foreign travelers to estimate lower bounds 30 Physics World February 2010 physicsworld.com Complexity: Proxy data

Following the money Tracking dollar bills and hunting for hidden treasures may seem like unusual pastimes for a physicist. Yet as Dirk Brockmann describes, data derived from such pursuits can reveal fascinating patterns in how people travel – and even hint that human mobility could be governed by fundamental physical laws

In 1271 a 17-year-old boy called Marco Polo embarked However, long-distance air travel reflects only a tiny Dirk Brockmann is a on an adventure that took him from his hometown of percentage of human mobility. Our world is also cov- theoretical physicist Venice, across Europe, the Middle East and Asia, all ered by a dense network of roads and highways, fre- in the Department of the way to Beijing. He returned home 24 years later, quently operating at their maximum capacity. Given Engineering Sciences having travelled over 24 000 km. A trip of this mag- the sheer complexity of human-mobility patterns and and Applied Mathematics at nitude was unprecedented in Polo’s time; almost transportation networks, it may seem bold to suggest Northwestern 750 years later, he is rightly remembered for it. But that there may be basic underlying principles that gov- University in what was an exception in medieval Italy is today an ern how such networks evolve, that mobility as a whole Evanston, Illinois, US, everyday occurrence: our 21st-century world is on the may follow fundamental laws, and that some regular- e-mail brockmann@ move. Every year, more than three billion passengers ities are hidden within the complex way we travel. Yet northwestern.edu use the international air-transportation network, fly- addressing these questions is of fundamental import- ing on a complex web of routes that connects more than ance, as increasing human mobility also facilitates the 3000 airports worldwide. This global connectivity has global spread of infectious diseases (see article on page made it possible for people to go from virtually any 26). Understanding human mobility is therefore not place on the planet to any other within a matter of days. just interesting, it can actually save lives. 31 Physics World February 2010 Complexity: Proxy data physicsworld.com

Where do you want Movement by proxy lation it can be reported again at another time and place to go today? But how can one possibly begin to analyse the multi- by some other person, thereby generating a trajectory The worldwide air- tude of traffic and transportation networks in a com- of the bill throughout the country. For each registered transportation prehensive way? The obvious option – monitoring bill one can monitor these movements and study the network. The red lines human movement directly – would be costly and inva- logs posted by individual finders. Forming an image of indicate routes with sive, as we cannot simply tag people with radio collars, millions of these dollar-bill journeys in my head, I was high traffic. as biologists do with migrating birds. But the task of convinced that analysing the data could reveal essential compiling mobility data for all possible means of trans- properties of human mobility – which is, after all, the portation into a massive dataset is not easy either. driving force behind the dispersal of banknotes. When my colleague Lars Hufnagel and I started think- After I returned from Vermont, Lars and I started ing about large-scale analysis of human-transportation extracting the data from the website. We began our networks in 2005, we knew our mission would be very analysis by asking a very simple question: what is the difficult at best, and impossible at worst. probability P(r) that a bill traverses a certain distance I was still wrapped up in these thoughts when, on my r in a short period of time? Common sense and every- way home from a physics conference in Montreal, day experience suggests that this probability ought to Canada, I decided to visit my old friend Dennis Derry - decrease with distance because long journeys are less berry, who lives in the green mountains of Vermont. likely than short ones. But the form of this expected One evening during this visit, Dennis asked “So Dirk, decrease turned out to be surprisingly simple. We what are you working on?”. I replied that I was inter- found that P(r) falls off with distance according to an ested in the patterns that underlie human travel, and I inverse power law: P(r) ~ 1/(r1 + μ) where the exponent described some of my efforts to better understand μ = 0.6 (see 2006 Nature 439 462). human mobility. “It’s just amazingly difficult to compile This simple mathematical regularity in the geo- all the data,” I concluded. Dennis paused a while and graphic circulation was not only a surprise to us, it then inquired “Do you know the website Wheresgeorge immediately implied important consequences. One [www.wheresgeorge.com]?”. I did not, but once he implication is that the successive geographical move- showed it to me it became clear that, in a flash, it could ments of bank notes are similar to a class of random solve a number of our most pressing problems. walks known as Lévy flights (see figure opposite). Un - Simply put, Wheresgeorge is an online game that tracks like ordinary diffusion processes, Lévy flights have a the geographic circulation of dollar bills, which carry self-similar structure. This means that, just like fractals, the face of US President George Washington. The way their trajectories look similar close up as they do from a it works is that individual bills are marked by a large distance. Lévy flights are more than just a ma the matical community of “Georgers” (the site has over four mil- peculiarity. They have been discovered in many com- lion registered users) throughout the country. When- plex systems ranging from the foraging movements of ever one of them gets hold of a marked bill, they visit animal species to the fluctuation of stock prices. the website and provide their current zip code and the The discovery that travelling banknotes exhibit a serial number of the bill. Once the bill is back in circu- Lévy-like pattern has another very important conse- 32 Physics World February 2010 physicsworld.com Complexity: Proxy data

1 Seattle

10–1

New York 10–2

Petaluma 10–3 P ( r )

10–4

10–5 Jacksonville

Houston 10–6 1 101 102 103 104 r (km)

Show us the money The trajectories of individual banknotes with initial entries in Seattle (blue), Petaluma (green), New York (purple), Houston (yellow) and Jacksonville (red) (top left). The lines connect the initial entry location and locations where bills were reported less than a week later. The probability P(r) of a bill traversing a distance r in a one-week period (top right). The dashed line is a power law as described in the text. The observed power-law relation in banknote dispersal indicates that their spatial trajectories are similar to Lévy flights – random walks that are statistically self-similar, shown here at three successive magnifications (bottom). quence: it indicates that modern patterns of human basic assumption in our analysis is that the more traffic movement are inconsistent with assumptions made for between two places, the more tightly they are coupled previous models for the spread of diseases. They as - and the less “distant” they effectively are. The entire sumed that infected individuals behaved like diffusing flux of banknotes can be quantified by a network made particles. In diffusion, position scales with time in a up of vertices (representing each US county) labelled 1/2 square-root fashion, X(t) ~ t . Lévy flights, in contrast, with an index i and connected by links wij that measure exhibit the scaling relation X(t) ~ t1/μ, where μ< 2. Such the number of banknotes travelling between vertices i behaviour is termed “superdiffusive” and the equations and j. To establish which geographic areas function as required to describe these processes are beyond those of “pseudo-countries”, one can group vertices into mod- ordinary calculus. In fact, the theory of fractional cal- ules such that the flux is large within the modules and culus is required to describe them properly. small between them. This is a non-trivial task for large- scale networks, but efficient network algorithms exist Ties that bind and divide that successfully solve it. By applying these to the multi - In addition to scaling laws, the circulation of money can scale mobility network derived from the flux of money, tell a story about the lines that separate us as a society. we recently extracted effective geographic borders that As communication and travel continue to bring people are implicitly encoded in human mobility. together on a global scale, it is interesting to investigate As the figure on page 34 shows, these effective mo- the significance of international, national and regional bility borders coincide with administrative borders only borders. Is it still appropriate to think in terms of the partially, and quite frequently borders exist in un - traditional geographical territorial patches that have expected places. The US state of Missouri, for exam- evolved over decades and centuries? How might these ple, is cut in half, with one half belonging to the city of legal borders differ from others that have no standing St Louis in the east and the other to the Kansas City in law but are more tightly coupled to the way we actu- area in the west. Further east, the Appalachian moun - ally behave – for instance to the way we travel? tain range makes up an effective boundary that bears It turns out that we can use the flux of several million only a loose relation to the various state borders that banknotes in the US to answer these questions. The intersect it. Knowing these effective boundaries may 33 Physics World February 2010 Complexity: Proxy data physicsworld.com

networks for each mobile phone in the dataset. This allowed the researchers to examine the underlying reasons why power-law relationships are observed in proxy mobility networks. To do this, they borrowed from physics the well-established concept of entropy, a measure for uncertainty in an unpredictable system, and found that in the mobile-phone mobility network, this quantity was much smaller than expected. This result implied that human mobility is more predictable than we might think. One additional limitation of the bill-tracking study is that, by definition, it deals only with mobility in the US, and thus is not able to show whether the observed sca- ling laws hold in other regions of the world. Might not Europeans, travelling over often smaller distances and on a very different transport network, exhibit mobility patterns that differed from those of Americans? Unseen boundaries Fortunately, the Internet is a great source of mobility The flux of banknotes data. In 2006 I read a column in a newspaper about a in the US between new type of online game known as “geocaching”. This 3109 counties. This is essentially a treasure hunt based on Global Posi tion - multiscale mobility ing System (GPS) technology. Players hide treasures, network encodes a or caches, at various physical locations and publish hidden structure of effective geographic the GPS co-ordinates on a website. Other players can borders in the US, then download these co-ordinates onto their own GPS shown as blue lines device and use this information to locate the cache. If on the map below. they are successful, they log their find and often ex- Within each blue- change toys and gifts at the cache site. bordered region, the This sounded fun to me, so in an effort to make my flux of banknotes is daughters Hannah and Lili (then aged eight and five) large, but the number New York spend more time outdoors, I bought a GPS device and of notes entering or Philadelphia introduced them to the game. They were excited and Pittsburgh leaving (the external Kansas City so we embarked on our first attempt to locate a cache in flux) is small. Thicker St Louis Washington the woods near where we live. In this cache we found lines indicate a what is known as a “travel bug”, or trackable item. higher degree of Cachers transport these dog-tagged items from one separation between Memphis cache to the next, logging the trace of their mobility pat- adjacent regions. terns online. As geocaching is an international game, in the future allow interdisciplinary scientists to address and millions of trackable items move between caches, a number of interesting questions – including to what I realized that aspects of human mobility in Europe extent these banknote barriers correlate with social and could be addressed by analysing the trajectories of cultural boundaries. these trackable items. After I contacted the people behind the geocaching Mobile phones and treasure hunts website, they provided their entire dataset for scientific Interesting as they are, banknote studies are by no analysis. Based on this data, I and a colleague Fabian means the only proxy for gathering data on human- Theis computed the multiscale mobility networks for mobility networks. Two years after my colleagues and I various European countries as well as the US. Contrary first studied the dispersal of dollar bills, Albert-László to our expectations, we found that all these networks Barabási and his research team at Northeastern Uni- are remarkably similar in their statistical properties. versity in Boston published an article analysing the For instance, the distribution of link strength, wij, fol- trajectories of individual mobile phones. Barabási’s lows the same mathe matical law – yet another indica- study made use of the fact that mobile-phone compan - tion that human mobility is governed by fundamental ies collect data on where individual phones connect to underlying laws. mobile-phone antennas. As these antennas make up a Studies of banknote circulation, games such as geo- fine geographic grid, the sequence of antennas that caching, or monitoring the movements of mobile individual phones connect to represents a geographic phones are all first steps in a new kind of science. The trajectory of these phones. amount of data on human behaviour that are currently The mobile-phone study confirmed the power-law collected online and that can serve as proxy data for relationship discovered in money circulation, but it was what we do is immense. Complexity research, complex also able to address important questions that the dol- network theory and concepts from statistical physics lar-bill study could not. The fact that people carry their will be one of the most promising scientific combi- own mobile phones – rather than passing them between nation of tools and methods to deal with these datasets. each other as they do banknotes – meant that Barabási Together, they form a new kind of science for the un- and his team were able to extract individual mobility derstanding of human behaviour at large. 34 Physics World February 2010 webinar series Green Energy Simulations JOIN US FOR THIS FREE WEBINAR Thursday 25 February 2010 10 a.m. BST (11 a.m. Central Europe, 5 a.m. East Coast US) This webinar will demonstrate some of the many applications where Green Energy Simulations are crucial to engineering success. Examples will cover solar-, wind- and hydro-power. You will see how to handle the coupled effects that are constantly present in Green Energy Simulations. Topics to be covered: • Producing biofuels • Manufacturing solar panels • Wind-loading on a solar array • Optimizing batteries and fuel cells

Register now at physicsworld.com/cws/go/webinar7 Complexity: Striving for simplicity physicsworld.com Simplicity and complexity

Research in complex systems can reveal the workings of everything from the human immune system and power grids to the social web. James Crutchfield and Karoline Wiesner wonder if there is a common theme to such work and ask where the field should go from here

James Crutchfield Is anything ever simple? When confronted with a com- plex systems – ensembles of dynamic, interacting ele- directs the plicated system, scientists typically strive to identify ments that exhibit robust collective properties – and Complexity Sciences underlying simplicity, which we articulate as natural the struggles to define complexity reveal a trend in the Center in the Physics laws and fundamental principles. This simplicity is what broader scientific community to become explicitly fo - Department, makes nature appear so organized. Atomic physics, for cused on how nature is organized. That trend is driven University of example, approached a solid theoretical foundation by an enthusiasm for finally building a conceptual California, Davis, US, and is a faculty when Niels Bohr uncovered the organization of elec- framework and experimental methods that directly member of the tronic energy levels, which only later were redescribed acknowledge nature’s diversity of form. Santa Fe Institute in as quantum wavefunctions. Charles Darwin’s revolu- New Mexico, US. tionary idea about the “origin” of species emerged by Defining complexity Karoline Wiesner mapping how species are organized and discovering The fact that nature exhibits robust organization is is in the Centre for why they came to be that way. And James Watson and a familiar one. From inanimate complex systems (such Complexity Sciences Francis Crick’s interpretation of DNA diffraction spec- as critical phenomena in condensed-matter systems) and School of tra was a discovery of the structural organization of to animate systems (such as the collective nest-build- Mathematics, genetic information – it was neither about the mole- ing of wasps) to the fragility of today’s engin eered University of cule’s disorder (thermodynamic entropy) nor about the systems (such as the “route-flapping” that plagued Bristol, UK, statistical randomness of its base-pair sequences. Internet bandwidth in the early 1990s), organized com- e-mail k.wiesner@ In 1948 the mathematician Warren Weaver, who was plex systems appear almost everywhere. bristol.ac.uk then director of the Rockefeller Foundation, wrote Yet although we know it when we see it, have we a famous essay entitled “Science and complexity” in made progress in defining organized complexity? Is which he rather boldly claimed that while “the 19th identifying simplicity with organization anything more century was the century of disorganized complex- than a tautology? More practically, do we understand ity…the 20th century must be that of organized com- these concepts well enough to measure their associated plexity”. Indeed, research on complex systems had properties? A quick review of the literature reveals that progressed on many fronts during the 1940s and 1950s, there is no shortage of answers. Indeed, the list of poss - which witnessed the temporary efflorescence of sys- ible ways of measuring complexity grows longer with tems science, cybernetics and theoretical biology. In every decade. These range from new proposals to hindsight, however, we know that Weaver glimpsed finally nail down the field’s earliest challenge – which only the beginning of a new era of science – what came boiled down to the question of how random is a coin to be known as the science of complex systems. Perhaps flip really? – to a plethora of ways to capture concepts Weaver, who died in 1978, would be disappointed of organization, such as “regularity”, “sophistication’’, to learn that, at the start of the second decade of the “hierarchy” and even “semantic content’’. Is this di - 21st century, the exact nature of organized complexity versity real and necessary or only apparent? remains the subject of ongoing debate. This seeming Tower of Babel is a liability, having led What remains prescient, however, is Weaver’s insight to criticism of the field both from within and outside. that organization plays a key role across the sciences. A closer look, though, reveals a good deal of pro gress. We think that the appearance of complex-systems sci- It turns out that some measures of complexity are bet- ence at the end of the 20th century was not an accident; ter defined than others, some are more revealing than rather, it was inevitable. The intense interest in com- others, while some are easier to estimate from data. One accepted milestone is that we already have well- The intense interest in complex defined (and closely related) measures of randomness, such as entropy (in the field of thermodynamics, meas- systems and the struggles to define uring degrees of disorder), Shannon information (in communication, measuring degrees of unpredictabil- ity) and Kolmogorov–Chaitin complexity (in compu- complexity reveal a trend in the tation, measuring the size of the minimal computer program required to produce an object). Weaver ac- broader scientific community knowledged this progress when coining the phrase “disorganized complexity’’. to become explicitly focused on how Thanks to these advances, when defining disorgan- ized complexity, we can now refer to it as “randomness”, nature is organized reserving the term “complexity’’ to mean structure, 36 Physics World February 2010 physicsworld.com Complexity: Striving for simplicity Fred Lyon/Science Photo Library

pattern and regularity. More to the point, a good meas- molecule can adopt – what is known as its “landscape” Disorganized ure of complexity captures kinds of organization. This is – using concepts from complex systems. The degeneracy complexity a necessary complement to understanding randomness, of structurally distinct physical states was resolved using Even deciding the as it enables us to ask questions like how much organ- network analysis and information theory. In particular, exact randomness of ization does a system use to produce its randomness? the researchers found that measuring the structural a coin flip is subtle. That organization and randomness are complementary complexity of a protein’s conformational fluctuations properties is familiar to computational physicists, who gave new insight into the memory that proteins store use pseudo-random number generators to emulate fair (2008 Proc. Natl Acad. Sci. USA 105 536). coin flips – ideal randomness. While giving similar Meanwhile, Dowman Varn of the Sante Fe Institute degrees of effective randomness, though, different in New Mexico and one of us (JC) discovered that generators can be very differently organized. That is, structure embedded in disordered solids can be ex- they are different algorithmic structures that use dif- tracted directly from experimental X-ray diffraction ferent amounts of memory organized in different ways. spectra of quasi-1D materials, called polytypes (2006 So, would Weaver be disappointed? Will “organized Acta Crystallogr. B 63 169). This “chaotic crystallog- complexity” forever evade understanding, as some sug- raphy” of noisy spectral data revealed that polytype gest? A number of recent experimental and theoretical structure consists of systematic mixtures of multiple, successes demonstrate otherwise: measures of com- competing crystal types and their faults. plexity can be calculated, estimated and interpreted in On the mathematical front, recent work by the ways that are meaningful to specific scientific problems. present authors and others has begun to show that For example, Chun-Biu Li and colleagues at the Uni- complexity measures fall under the umbrella of com- versity of Chicago recently mapped the number of dif- munication and computation theories. It turns out that ferent possible conformations that a long-chain protein various underappreciated aspects of Shannon’s ori - 37 Physics World February 2010 Complexity: Striving for simplicity physicsworld.com Photolibrary

Collective behaviour ginal information theory are key to breaking a system’s systems to gain quantitative and qualitative insights Pedestrian traffic organization into degrees of information storage and into collective group behaviour. Such work has even flows, such as those degrees of communication capacity, and to monitor- led to the development of strategies for controlling during the “hajj” ing the extent to which these are present but encrypted large numbers of people in panic situations, such as pilgrimage to in a system’s behaviour. during fires in crowded buildings, and in the annual Mecca, have been These results, and many others, suggest that organ- “hajj” pilgrimage to Mecca, where over two million successfully analysed using tools from ization – defined in terms of a system’s structure and faithful are in motion. the science of measurable using extensions of Shannon’s information Tracking the focus on organization through the re- complex systems. theory – is a unifying theme in the science of complex cent history of science, the field of complex systems systems. It is now not only desirable but possible and itself appears much more organized than at first sight. practical to develop a systematic and implementable We suspect that the field is ripe to take a substantial theory of organization. In addition to continuing ex- step forward, if its members are willing to identify com- perimental applications, the mathematical results sug- mon goals. Today, many scientific communities regu- gest a range of future conceptual developments that larly do just this – be it astroparticle physicists vying for delve more deeply into Shannon’s communication the- new facilities or semiconductor firms coordinating to ory and also his theory of secrecy systems. They will find develop ever-smaller and more powerful integrated important roles in analysing complex interacting net- circuits. The question is whether the complex-systems works, for example. community should attempt such a road map. This effort would not only put past advances in new light, but crys- Forced integration? tallize goals and ways to reach them. Reflecting on nature’s organization at different scales In July 1991 the Nobel-prize-winning condensed- – from fundamental particles to biochemical and matter physicist Philip Anderson wrote in Physics Today brain processes – is not such a new idea. Until recently, that “we complexity enthusiasts (perish the thought however, most work was focused on specific complex that we be called complexity scientists!) are talking, at systems, such as the Internet. But now that we can least for the most part, about specific, testable schemes quantitatively compare disparate complex systems – and specific mechanisms and concepts. Occasionally, thanks to recent work on complexity measures – we we find that these schemes and concepts bridge sub- are in a position to discover the mechanisms through jects, but if we value our integrity, we do not attempt to which low levels of organization successively give rise force the integration’’. to higher and higher levels – just as atoms form mole- Given the field’s progress since then, which suggests cules, molecules coordinate to form cells, and cells that we can identify common themes, and its rapidly cohere to form biological organisms. increasing diversity, which threatens to Balkanize We believe that the brave new frontier, however, is the field, it is time for us “complexity enthusiasts” to in applying complex-systems tools to the social sci- revisit Anderson’s concerns. We believe that an at- ences. There, complex-systems science may finally tempt now to integrate different schemes and con- overcome the long-appreciated limitations of adapt- cepts will not be forced at all, but will help researchers ing the physical sciences lock, stock and barrel to a to make progress. We are particularly hopeful about domain where observables are unclear and where the novel perspectives the field could lend to solving energy – the currency of physical theory – is not a uni- the daunting challenges that confront societies that versal fundamental. A notable example is work by construct ever-more complex socio-technical systems Dirk Helbing and colleagues at the ETH Zurich, who – systems with emergent properties, such as correlated have successfully analysed pedestrian traffic flow using risk, that we often do not anticipate, sometimes with mathematical and computational tools from complex disastrous effect. 38 Physics World February 2010 Untitled-1 1 12/10/09 11:21:56 physicsworld.com Reviews

Gordon Fraser Inside the complexity labyrinth

thor and complexity scientist Melanie Mitchell sets out to remedy this. Along the way we meet some of the person- alities from Gleick’s book, including Edward Lorenz, who in 1963 showed that initial conditions were the most influential factor in quantitative wea- ther forecasts; and Mitchell Feigen - baum, who discovered new constants of nature relating to the transition Mauro Fermariello/Science Photo Library from order to chaos. We come across some famous historical physics figures too, including the aforementioned Newton, Maxwell and Boltzmann, and some mathema ticians like Hilbert, Gödel and Turing. Mitchell is a deft guide, and there is plenty of fascinating stuff for read- ers to discover. In particular, she des - cribes how new developments in genetics – especially evolutionary de- velopment biology, or “evo-devo” – indicate that evolution itself is com- plex. Fresh insights in this field have begun to assign a role to the puzzling The way forward Although the world we live in is com- get to work among gas molecules. If “junk DNA” that previously appeared Complexity science plex, complexity as a science does not endowed with some capacity for to serve no purpose other than bur- could play a key role have a long history. For generations, judgement, he reasoned, such demons dening cells. Moreover, evo-devo can in unravelling the most physicists tried to understand would be able to make assemblies of make organized structure “evolve” in mysteries of everything in terms of interactions molecules behave in very different the dictionary sense of “appear”, evolutionary biology. between pairs of idealized “test par- ways. Talk of demons was anachronis- without evolution in the Darwinian ticles”. Then, about a 100 years ago, tic even in Maxwell’s time, but such sense of interplay between infinites - Complexity, Henri Poincaré pointed out that a new vocabulary often waits on devel- imal mutations and natural selection. A Guided Tour fully interacting three-body system opments in understanding. Until This can be a dilemma for evo-devo Melanie Mitchell was not just the sum of its three com- Newton adopted it, “gravity” was a proponents, who also feel obliged to 2009 Oxford ponent pairs. The famous “three- synonym of “solemnity”. Later, other defend classic Darwinian evolution University Press body problem” was born. words had to be commandeered to from attack by creationists. £14.99/$29.95hb At the time, few took any notice of con vey precise new meanings – inclu - Yet while we are skilfully guided 350pp this small cloud in the sunny sky of ding “field” and, latterly, “inflation”. through the labyrinth of complexity, reductionist simplification. Yet even One of the most recently rejigged we only see a part of it. In particular, before Poincaré – in fact, before the words is “complexity”. In science, this we are soon steered out of inanimate discovery of atoms – Maxwell and word means a lot more than its dic- physics and into artificial intelligence, Boltzmann had in some ways antici- tionary definition, and a number of evolution and genetics. Readers ex- pated the need for new approaches, books have already attempted to pecting to learn about complex sys- following their success in modelling define it for the general public. An tems in general, and physical ones in gases as disorganized swarms of elas- early (and still popular) one is James particular, will be disappointed. A tic molecules. While this method was Gleick’s magisterial Chaos, pub- classic case that is omitted is turbu- highly successful for gases, other sys- lished in 1988, which tracks how sci- lence, which caused even Wolfgang tems – from galaxies to crystals to entists discovered and tried to make Pauli to give up and turn to something flocks of birds – all showed structure sense of complex effects. But while easier. In 1900, when David Hilbert emerging from chaos. How, scientists the anecdotal illustrations and case produced his list of mathematical began to wonder, do such diverse studies in Gleick’s book are intri- problems to be solved in the coming constituents “get it together” and guing, most readers emerge breath- century, the Navier–Stokes equations, organize themselves? less with little appreciation of the which describe fluid motion, were Maxwell himself worried about science of complexity. one of them. A Guided Tour mentions “demons” that could surreptitiously In Complexity, A Guided Tour, au - other challenges on Hilbert’s list, but 40 Physics World February 2010 physicsworld.com Reviews

not this one. gine get only passing mentions. biology (see also Physics World’s spe- Mitchell sets out to show that sci- Still, any guide through complexity cial issue on physics and biology, July ence is done by people, but in her is welcome: a modern equivalent of 2009). Perhaps it could have been sub- account those people are, apparently, Ariadne’s mythical ball of thread, titled “A Guided Tour for Biologists”. mainly based in the US. Moreover, which helped the mighty Theseus to some of the major physics contributors find his way out of the Minotaur’s Gordon Fraser is the editor of New Physics for to the science of complexity – for ex- labyrinth. And, despite my few grum- the 21st Century, now reissued by Cambridge ample Lev Landau (who is in Gleick’s bles, this is an engaging book that University Press in paperback. He is currently book) and Roger Penrose – do not deals with some compelling science. writing a new book called Quantum Exodus – appear, while others like Per Bak, Indeed, it is particularly good at dis- Jewish Fugitives and Subatomic Science, Andrei Kolmogorov and Ilya Prigo- playing how physics ideas are useful in e-mail [email protected] Between the lines

Not rocket science enthusiast’s library. “how many people of splendid NASA Despite decades of development, ● 2009 Praxis Publishing intellect have pondered over this rocket-powered spaceflight remains £18.99/$29.95hb 215pp enigma – and yet how poorly…we a fairly crude phenomenon. Several understand its origin and nature”. astronauts have compared it to An unexplained visitor ● 2009 Springer £26.99/$29.95hb riding atop an exploding bomb, Comet, meteor, rogue black hole, 318pp adding that all of the “bomb’s” alien spacecraft, antimatter components were built by the lowest annihilation, “natural” hydrogen The everyday universe bidder. Rockets are expensive, too: bomb. These are just a handful of Sometime in the 19th century, the it currently costs about $15 000 to the hypotheses put forward to term “physics” began to replace Going up put 1 kg of cargo into Earth orbit, explain the events of 30 June 1908, “natural philosophy” in scientific Space elevators may and fuel accounts for much more when a massive explosion flattened circles. Although this linguistic be the transportation than 90% of a rocket’s lift-off mass. more than 2100 km2 of forest in the evolution had its advantages – did choice of the future. Small wonder, then, that the idea of Tunguska region of Siberia. As anyone ever study unnatural “space elevators” – long, thin cables The Tunguska Mystery explains, early philosophy? – the implied loss of stretching from a satellite in expeditions to the site observed a connection to the natural world is geostationary orbit down to the radial pattern in the fallen trees, nevertheless regrettable. In We Need Earth’s surface, traversed by climber suggesting a meteor impact. to Talk About Kelvin: What Everyday machines – has fired the imagination However, the more scientists Things Tell Us About the Universe, of space scientists and science- studied the event, the more they science writer Marcus Chown aims fiction writers alike. Yet as author found anomalies. If a meteor caused to rebuild that link by using familiar Michel van Pelt makes clear in this destruction, where was its phenomena as jumping-off points Space Tethers and Space Elevators, crater? And why was the event for discussions of modern physics. hauling loads into space on a cosmic preceded by peculiar lights in the One chapter, for example, describes conveyor belt is by no means the only night sky over Europe? In this how the electromagnetic force interesting thing that tether authoritative and engaging account, prevents people from falling through technology could do. Tethers could the Russian scientist and floors, even though both floors and also be used as a slingshot to boost philosopher Vladimir Rubtsov – a people are more than 99% empty satellites into interplanetary orbits, longtime participant in the Tunguska space. Seasoned readers of popular- improve astronauts’ health by debate – offers few definitive physics books will find little new supplying artificial gravity, and clean answers, for there are none. Instead, information in this first section of up space junk by using “tether he provides a compelling account of the book, which also covers topics terminators” to drag obsolete how the scientific complexity of the like the Pauli exclusion principle and satellites earthwards until they Tunguska problem has combined wave–particle duality. However, for burn up on re-entering the with various external difficulties – non-experts, Chown is an amiable if atmosphere. Van Pelt works for the including two world wars and sometimes over-excitable guide, and European Space Agency and is decades of Soviet dysfunction – to he rewards the patience of better- clearly keen on his chosen subject, create a riddle that still defies informed readers by venturing into but he is also realistic about the solution after more than a century of newer territory in book’s final obstacles of cost and difficulty. research. The book concludes with a section. A chapter on the connection Catching a satellite with a rotating plea for better cooperation between between randomness and tether and flinging it into space, he scientific disciplines. Too many complexity feels particularly novel, notes, “will be about as difficult as scientists, Rubtsov argues, have and Chown’s speculative essay on sitting in a rollercoaster and trying to “solved” the problem by taking into our chances of being alone in the catch an egg thrown up at you from a account only those facts about universe is genuinely thought- moving car”. Logical, thorough and Tunguska that relate to their specific provoking – for physicists and packed with fascinating information, field, while dismissing other “natural philosophers” alike. this slim volume would make a evidence as irrelevant. Perhaps the ● 2009 Faber and Faber £14.99hb valuable addition to any space real mystery is, as Rubtsov writes, 208pp 41 Physics World February 2010 Reviews physicsworld.com

Aaron Leonard couple together than they will ever be with him). Ryman, for his part, simply wants to be left alone to pursue his peace studies, but Meadows gradually inserts himself into his life. The unsettled heavens Anyone with a passing familiarity with contemporary history will be describe the disorientation this sets frustrated by the way that Foden loose, Foden gives us the wonderful makes D-Day seem like the pivotal Swahili word kizunguzungu – the spin- battle of the war. The Normandy ning dizziness to come. It is a clever invasion – while significant – was touch, as this word neatly captures the never the mythologized turning point trauma swirling around Meadows it is made out to be, especially in the throughout the story. context of the far larger war in the In advance of the D-Day invasion, East. Foden also stumbles in his re- Tek Image/Science Photo Library Meadows, a lowly meteorological as - latively uncurious treatment of Ry - sistant in the Met Office (closely integ- man’s politics. Unlike Meadows, who rated with the Royal Air Force during is given a complex emotional make the war), is tapped to pursue a reclu- up, Ryman comes off as cartoonish. sive scientist called Wallace Ryman. Given the prospect of nuclear annihi- Loosely based on the actual scientist lation that is the Second World War’s Lewis Fry Richardson, the character enduring legacy, Ry man’s “peace Ryman is a pacifist who developed a studies” would seem to merit a bit theory of weather prediction before more of a hearing than Foden offers. the war but who then abandoned Instead, Ryman is dismissed as a man these militarily-useful pursuits in who, though principled, was also ab- favour of something called “peace solutely naive to the danger presented studies”. Meadows is sent to Ryman’s by Hitler. Scot tish home on the pretence of That said, this is a novel, not history. monitoring weather conditions. How- There is something deeply sad in ever, his real mission is to befriend Foden’s tale, and this is what makes it Ryman and pry loose the “Ryman more than a run-of-the-mill “science number”: a quantity that Foden des- meets war” book. Its narrator is an old cribes as “a criterion by which the tur- man, someone who has lived through Set fair It takes a certain audacity to write a bulence of weather systems and other both the wonders of what the human Weather and war in a novel with a weatherman as its hero. flow can be measured”. imagination can apprehend and the fictionalized account Fortunately, audacity is something The Allies desperately want the horrors of what it can hand out. The of one man’s role in that author Giles Foden has in great Ryman number so that they can pre- events of Meadows’ life are inter- the D-Day landings. quantities, so perhaps it is not sur- dict the weather during the five-day twined with a broader study of the prising that the star of Foden’s new window that they need to make pressures asserting themselves in the Turbulence book Turbulence is a meteorologist “Operation Overlord” successful. heavens, much as physics and mete- Giles Foden – albeit one on the trail of a secret Meadows, too, is passionate about a orology are woven into Foden’s larger 2009 Faber and weather-predicting technique that subject that has become his life’s work. philosophical musings. It can be a fas- Faber £16.99hb could change the course of history. At one point – quoting Einstein – he cinating mix; as Meadows/Foden tells 368pp Like Foden’s first novel The Last remarks that “before I die, I hope us, “There are always scales and di- King of Scotland, which featured an someone will clarify quantum physics mension that are being ignored. And imaginary Scottish doctor and the all- for me. After I die, I hope God will this is dangerous because the whole too-real exploits of Uganda’s mur- explain turbulence to me”. But the point is that all these sizes of turbu- derous dictator Idi Amin, Turbulence weather is not Meadows’ only interest, lence are interconnected; they are mixes fact and fiction. As the book and at times he seems more concerned both separate and continuous; feed- begins, it is 1980 and the fictional pro- with smoking too much, drinking too ing energy from large to small then tagonist, Henry Meadows, is travel- much and fantasizing too much about back again...they don’t last long any- ling from Antarctica to Saudi Arabia two members of the Women’s Aux- way, these eddies, even if you do spot on a ship made of Pykrete, a futuris- iliary Air Force (who are more of a them. New information yes, but now tic-sounding but real amalgam of saw- it’s changing, now it’s gone – and what dust and ice that was invented during Physics and have you understood?” the Second World War. During his Anyone who reads Turbulence like a trip, Meadows passes the time by wri- textbook or journal article will come ting in his journal about the events meteorology are away quite unsatisfied. The science is leading up to the 1944 Allied invasion there, but like Meadows’ Pykrete ship, of Europe – the defining episode of woven into larger it is bound up with other substances. his life. Still, this novel with a factual bedrock Meadows is a son of imperial Brit - philosophical has a story to tell, and the sharp turns ain, born and raised in the African and sudden calamities make for a colonies. In a series of flashbacks to thoughtful and often wild ride. 1944, he tells a story full of humili- musings; it can be ation and self-doubt. Some fairly hor- Aaron Leonard is a freelance journalist based rible events hit him early on, and to a fascinating mix in New York, US, e-mail [email protected] 42 Physics World February 2010 physicsworld.com Reviews

Web life: ComplexityBlog.com anything worth thinking about can, potentially, fall complexity shop available on the Web today. There under its aegis. The blog section of the site have been other good sites in the past, notably celebrates this trait. In between “serious” posts on The Complexity and Artificial Life Research topics like game theory, cosmology and the Concept, but sadly, although www.calresco.org is methodology of agent-based models, you can also still active, it suffers from an outdated site design find oddities like an evolutionary theory of dating and multiple broken links. Only time (and its and a map of the popular (and notoriously authors’ future career paths) will determine complex) TV series Lost. The non-blog portion of the whether ComplexityBlog.com meets a similar fate, site features a short-but-helpful glossary of but for the moment, there is plenty of up-to-date, complexity-related terms, a list of popular books on fresh material here for experts and complexity complexity, and a host of useful links to academic neophytes alike. institutes and private companies involved in complexity research. Can you give me a sample quote? Bramson, while discussing whether complexity URL: complexityblog.com Who is behind it? science should have its own separate department The site began as a joint effort by two University of within universities, notes that “Complex systems is So what is the site about? Michigan PhD students, Aaron Bramson and still a young science; it suffers from conceptual The site’s homepage calls it “a repository of ideas Kenneth Zick, both of whom are interested in the immaturity and technical inability. It might appear and perspectives regarding the science, science of complexity. Bramson’s academic to be a backwards argument to claim that we ought engineering and philosophy of complexity”, and it background is in mathematics, economics and to establish a degree-granting institution so that pretty much does what it says on the tin. Part blog, philosophy, and a lot of his posts focus on the individuals can work to make the discipline part links archive, part library of modelling tips and social side of complexity theory. Zick, who left the credible. But we must recognize that pursuing a tricks, the site is chock full of information that project in late 2007, is a computer scientist and clearer understanding of the underlying comes under the general heading of “complexity”. engineer with a keen interest in topics like game mechanisms of phenomena…will simultaneously theory and evolutionary algorithms. enlarge [other] fields and ground complex What are some of the topics covered? systems. And by tying those mechanisms across One of the joys – or problems, depending on your Why should I visit? disciplines, we all gain a better understanding of perspective – of complexity science is that almost Because this is the nearest thing to a one-stop the individual applications.”

Next month NASA in Physics World Destination Mars Rovers like Curiosity and a planned mission to bring chunks of Mars back to Earth will yield fantastic insights into the red planet and set the stage for human exploration in the near future

The eerie silence Searches for extraterrestrial intelligence, which have now been under way for half a century, have so far yielded no rewards, but the net could be widened by looking for more than just radio signals

Playing dice with constants String theory’s failure to predict unique values for the physical constants may indicate that such quantities depend on where we are in the multiverse

Plus News & Analysis, Forum, Critical Point, Feedback, Reviews, Careers and much more physicsworld.com

43 Physics World February 2010 physicsworld.com Careers Life on the borders Edward Barry describes a career at the sharp end of interdisciplinary research, and how a virus from the New York City sewers is helping shape our understanding of nanoscale self-assembly

Interdisciplinary science has been a hot topic Come on in Many problems in biology could benefit from physicists’ input. for more than a decade, with increasing numbers of researchers working on projects the New York City sewer systems. The fd that a mutant virus, known as fdY21M, is that do not fit into neat departmental boxes virus has a long, thin shape, making it ideal four times as rigid as the wild-type virus, and like “physics” or “biology”. Yet despite this for studying hard, rod-like particles that in 2009 we published a paper where we increased activity, the structures in place to repel each other. Indeed, such “filamentous” showed that its phase transition is described support these interdisciplinary scientists – viruses have a long history of being used for quantitatively by the original Onsager the- including research grants and training for this purpose. For example, experiments with ory (see Soft Matter 5 2563). PhD students – have sometimes lagged the tobacco mosaic virus (TMV) inspired the behind. One programme that aims to help chemical physicist Lars Onsager to present What else can you do with these fill this gap for students of biomedical, phys- his seminal theory describing the way in biological systems? ical and computational sciences is the which suspensions of rod-like molecules can By adding a non-adsorbing polymer to sus- Interfaces Initiative, a joint project of the go from being randomly oriented to adopt- pensions of these rod-like particles we can Howard Hughes Medical Institute and the ing a more ordered state in which the long also change the interaction potential be - US National Institute of Biomedical Ima- axes of the rods, on average, align along a tween rods, thus allowing us to see how hard ging and Bioengineering. Physics World particular direction. Onsager’s work on this rods behave in the presence of some degree talked to a current Interfaces participant, isotropic-nematic liquid-crystalline phase of attraction. The polymer introduces an Edward Barry, who is finishing his PhD in transition laid the foundation for our under- attractive interaction between the rods via biology-related condensed-matter physics at standing of liquid crystals, which are now the depletion interaction. This occurs when Brandeis University in Massachusetts. common in the displays for TVs, computer the distance between the rods becomes less screens and other electronic devices. than the size of the polymer, such that the What attracted you to biophysics? In our fd system, we can obtain large quan- polymer can no longer fit between them. I became interested in biophysics-motivated tities of identical particles (1016) in a matter When this happens, an imbalance in os- research while working as a research as - of days – a significant advantage over the motic pressure forces the rods even closer sistant in Zvonimir Dogic’s complex-fluids TMV system, which takes months to grow. together. When we studied this process, we group at the Rowland Institute at Harvard In our system, we simply grow litres of bac- were surprised to observe the formation of University. I got plenty of hands-on experi- teria, infect them with the virus, and the next fluid-like 2D surfaces, known as monolayer ence in all of the projects the lab was work- day we have enough of the virus to do experi- membranes. These membranes have prop- ing on, as well as other research at the ments for weeks. erties identical to those of lipid bilayers, institute. This was a great learning experi- Due to the collective efforts of researchers which are the main constituents of the flat ence in general, and during invited talks over the past 20 years, the behaviour of sus- sheets that form a barrier around almost all at the institute and through collaborations pensions of the fd virus has now been char- living cells. In our system, the membranes can with visiting scientists and researches in the acterized in detail. These 880 nm long be quite large (hundreds of microns in di - Cambridge area, my interest in biological rod-like particles interact in suspension ameter) and their existence seems to suggest systems solidified. This interest carried on through hard-core repulsive interactions and a new unexplored and easily scalable mech- when we moved the lab to Brandeis Univer- undergo a phase transition into a “twisted” anism for the self-assembly of 2D materials. sity, where I began my PhD studies. nematic phase as their concentration in the Another system we have used in our re- suspension increases. This transition is only search uses bacterial flagella – the helical fil- What does your research involve? qualitatively described in the original On- aments that act as the rotor for bacterial We study physics using various biological sys- sager theory, as the viruses are not quite rigid movement. After removing the cell bodies, tems, including one particular virus, called rods but have a certain finite flexibility. we can isolate these helical particles and cre- the fd virus, that was originally discovered in However, we have been able to demonstrate ate suspensions of pure helical rods. We have 44 Physics World February 2010 physicsworld.com Careers

shown that these particles also undergo a tweezers, introducing improved methods in concentration-dependent, first-order phase One of the biggest microscopy, or even programming simula- transition into a chiral, or “handed”, liquid- tions – these are just a few examples of the crystalline state called the conical phase. hurdles in many opportunities for physicists and recent These liquid crystals have interesting bulk physics graduates. chiral properties that are determined by the Talk to researchers who are doing some- chirality of their constituent particles. interdisciplinary thing that you find interesting. You can send them an e-mail or go and speak to them at a What are some of the challenges of doing research stems conference if they sparked your interest. interdisciplinary research? One key thing to remember, though, is that One of the biggest hurdles stems from the from the different in the end, no-one is going to come looking different language that researchers use. It for you just because you have a degree in may seem trivial, but differences in scientific physics. However, your training as a physi- language, and understanding what different language that cist means you can offer different skills to scientific terms mean and imply, is really someone with a degree in biology or chem- important. This is most apparent at confer- researchers use istry, so use this to your advantage. ences or when attending scientific talks. On many occasions, a failure to understand cer- hour-long lectures to members of the quan- What do you plan to do next? tain biological terms and concepts has left titative-biology programme at Bran deis. I expect to finish my PhD in the very near me utterly and completely lost five minutes Preparing lectures that are engaging and future, and I have begun looking for post- into a talk that might otherwise have been useful for postgraduate students, postdocs doc opportunities. I have always wanted to very interesting and informative. and professors working in different fields teach undergraduates and postgraduates has certainly been a challenge, but oppor- while also conducting research in a univer- How has support and training from the tunities like this really help strengthen the sity setting. However, I am also considering Interfaces Initiative helped you? multidisciplinary dialogue. positions in industry. With a degree in quan- Above all else, it has enabled me to become titative biology and research experience at more versed in the methods of biological What advice do you have for physics students the interface between biological and phys- research. With unique opportunities, both interested in biology-related problems? ical science, I hope to find a position that is inside and outside of the classroom, this One of the most important things a physics not restricted to purely physical science, aspect of the programme, which is designed undergraduate student or a recent graduate such as working on solar energy or the de - to educate and train, has been by far the can do is get involved in research. Whether sign of photovoltaic systems. greatest assistance I have received. For ex- it is in a theory group or in the lab, many bio- ample, I recently won the Interfaces Scholar logical researchers can benefit from physi- Edward Barry is a PhD student at Brandeis University, Award, which means I get to deliver three cists’ input and training. Designing optical US, e-mail [email protected] Careers and people

Duo scoop astronomy prizes is recognized for her use of fluorescence Laboratory and Stanford University also Douglas Gough of the University of spectroscopy to study problems in cell won one of the $50 000 prizes for using Cambridge in the UK has won this year’s biology, such as the properties of individual angle-resolved photoemission to study gold medal for astronomy from the Royal protein molecules. Worth 72.5m each, the high-temperature superconductors and Astronomical Society (RAS). Gough is best Leibniz prizes are the country’s most other “highly correlated” systems. known for his work on stellar astrophysics, prestigious scientific awards. in particular for recognizing that Galactic gong for astrophysicist oscillations of the Sun’s surface could be US energy boss honours researchers Volker Springel from the Max Planck used to probe its interior. He then applied Steven Chu, the Nobel-prize-winning Institute for Astrophysics in Garching has the technique to other stars, coining the physicist who heads the US Department of won this year’s 7100 000 Klung Wilhelmy term “astroseismology”. Meanwhile, the Energy (DOE), has unveiled the six Weberbank prize for physics from the Otto RAS has awarded its gold medal for winners of the 2009 Ernest Orlando Klung Foundation at the Free University geophysics to John Woodhouse of the Lawrence awards, which are given to of Berlin and the Weberbank financial- University of Oxford. Woodhouse has researchers who have done the most to services firm. Springel’s research interests advanced our theoretical understanding of support the DOE’s work. They include lie in studying galaxy formation and using the Earth’s interior and helped to produce William Dorland of the University of numerical simulations to probe the nature some of the first reliable maps of it. The Maryland for his work on simulations of of dark matter and dark energy. medals and the society’s other awards will plasma turbulence in nuclear experiments, be presented at its national meeting in Omar Hurricane of the Lawrence Movers and shakers Glasgow on 12–16 April. Livermore National Laboratory for his Astronaut John Grunsfeld has been work on nuclear-weapons physics and appointed deputy director of the Biophysicist takes top German prize stewardship, and Wim Leemans of the Space Telescope Science Institute in Biophysicist Petra Schwille of the Lawrence Berkeley National Laboratory Baltimore, Maryland. Dresden University of Technology is one of for developing the technique of “laser- Thomas Roser is the new chair of the 10 winners of this year’s Leibniz prizes from wakefield acceleration”. Zhi-Xun Shen of collider-accelerator department at the the German Research Foundation. Schwille the SLAC National Accelerator Brookhaven National Laboratory. 45 Physics World February 2010 Careers physicsworld.com

Once a physicist: David Roy wheel will just keep accelerating until the spring is fully unwound – often creating quite a mess! So from a purely mechanical view, my sculptures are devices that regulate the unwinding of a spring. Over the years, I have invented quite a few different mechanisms to do this, starting with the concept of clock escapements and extending it to create longer, more active action cycles and random motion. I have two major advantages over clock designers: my works do not have to run for days and they do not have to keep time. Instead, my goal is to create interesting patterns of motion that keep moving (and entertaining) for hours.

What inspires your designs? David Roy is a sculptor who produces spring-driven My first goal was simply to create motion that moving artworks through his company Wood lasted for more than a few seconds. When I realized That Works that this could be done with interesting results, I started experimenting with ways to extend the run Why did you choose to study physics? time and increase the complexity of the motion. I My interest in science started very early, probably see my design development as fairly linear, with with science-fiction books like the Tom Swift series, one design leading to the next through evolutionary which are aimed at children. After brief stints in modifications as I learn about new materials and chemistry and engineering, I chose to study physics technologies. A list of the adaptations that at Boston University because I found it the most changed the course of my designs over the years challenging. I also had dreams of being an includes ball-bearings, constant-force springs, “inventor” and thought physics would give me an computer design, steel drive belts and (most understanding of how things worked. recently) computerized cutting of the wooden parts. There have been numerous other advancements How did you become interested in sculpture? over the years (the electric screwdriver was a Towards the end of my degree, I started spending godsend) and as I look back, each of these opened time at the Rhode Island School of Design, where up whole new avenues of exploration. my future (and present!) wife Marji was studying sculpture and art education. The world of art was What is the hardest part about making new to me, and I was particularly fascinated by these sculptures? some static wooden machine sculptures she had I enjoy both designing and building sculptures, and constructed. I kept suggesting that she make them I need to do both. Designing involves daydreaming, move but she was not interested and suggested I sketching and occasional intense periods on the try instead. After I graduated in 1974, I started computer, where I can lose hours or days. I love working as a computer programmer for an those periods but could not physically survive just insurance company. It was a tedious job that doing that – I need to work with my hands and see involved long periods of waiting, so during those real objects emerge. Long days of cutting, sanding, downtimes I started sketching ideas for small drilling and finishing are tasks that my hands do kinetic toys. I left the programming job after nine fairly automatically after years of practice. Most months and started Wood That Works by selling days I enjoy it, but it can get dusty and boring at these toys at local craft fairs. The toy designs times; then I look forward to more designing. evolved into the first kinetic wall sculptures. I had found a way to invent, but it was in an area I had How does your training in physics help? never dreamed of. It is essential to my career as a kinetic sculptor. Knowledge of basic mechanics is a necessity, but How are your sculptures constructed? the analytical study and problem-solving skills that All of my work is driven by constant-force springs, I developed as a physics student have been, if which use a two-spool set-up where a stainless- anything, far more important. The intense initial steel spring band is wound from one spool back design period when I was visualizing the concept of against its natural coil direction onto a second spring-driven kinetic sculptures felt very much like spool. As the spring fights to return to its original the long days and nights at university when I tried to form, it provides a fairly even torque over the full get my head round advanced physics concepts. length of the band. This mimics the torque provided ● www.woodthatworks.com by a traditional clock-weight drive, but in a more compact form. The concept of a constant-force spring confuses many people, because they think of it as a constant-velocity spring motor – something that will turn a wheel at a constant rotational speed. That is not the case: the torque or To make the most of your physics degree, visit force is constant, but the unregulated rotating www.brightrecruits.com

46 Physics World February 2010 physicsworld.com Recruitment Advertising Tel +44 (0)117 930 1264 www.brightrecruits.com Physics World Fax +44 (0)117 930 1178 IOP Publishing E-mail [email protected] Recruitment Dirac House, Temple Back Bristol BS1 6BE

The place for physicists and engineers to find Jobs, Studentships, Courses, Calls for Proposals and Announcements

PhD Scholarships

The International Max Planck Research School (IMPRS) for Quantum PhD studies at the University of Heidelberg, applicants should have a Master Dynamics in Physics, Chemistry and Biology is a graduate school offering a of Science degree (or equivalent). International applicants whose mother- doctoral degree program in these disciplines. The IMPRS is a joint initiative tongue is not English or German are advised to provide a proof of English of the Max Planck Institute for Nuclear Physics, Ruprecht-Karls University, proficiency. the German Cancer Research Center (DKFZ), the Max Planck Institute for Medical research (all in Heidelberg) and the Heavy Ion Research Center Applications for this round must be received by April 30, 2010. Each applicant (GSI) in Darmstadt. has to initiate his/her application by registering online at http://www.mpi- hd.mpg.de/imprs-qd/ and following the steps outlined there. In particular, Applications of students from all countries are welcome. To be eligible for applicants should not send any material until they are encouraged to do so.

Physics World February 2010 PWFeb10ClMaxPlanck6x4.indd 1 25/1/10 11:09:4647 Two Lectureships/Fellowships in Theoretical Condensed Matter Physics Salary will be in the range of £36,715 to £43,840 per annum plus £2,134 London Allowance. In a new initiative between the University of London (Royal Holloway, and University College/London Centre for Nanotechnology) and facilities on the Harwell Science and Innovation Campus, we wish to appoint two people to permanent Lectureships in Theoretical Condensed Matter Physics. The posts will be held at Royal Holloway University of London and initially they will involve relatively light teaching loads. We are particularly seeking individuals with a strong record of research in the theory of strongly correlated quantum matter. Possible areas of interest include strongly correlated electron systems (including dynamical mean field theory), quantum magnetism, superconductors and superfluids, topological quantum matter, new materials and nanostructures. A key mission of this new theory initiative will be strong interaction with scientists at Harwell, as well as with experimentalists in the University of London groups and elsewhere, to support an environment for world class research, from fundamental studies of model systems to the development of new functional materials. The Harwell Science and Innovation Campus hosts the largest scientific facilities in the UK, including the ISIS neutron spallation source, serving a wide international community of users. The new research activity will be supported by visiting Chair positions and we envisage an active international visitors’ programme. It will form part of the Thomas Young Centre, the London Centre for Theory and Simulation of Materials. Our Department is part of SEPnet, a wider regional consortium for teaching, outreach and research. Royal Holloway is one of the larger colleges of the University of London, situated on a pleasant campus about 25 km west of central London, close to the town of Windsor and to Heathrow Airport. For an informal discussion of the posts contact Professor John Saunders ([email protected]).

Further details and an application form are available to download at www.rhul.ac.uk/personnel/jobvacancies.htm or by contacting HR by email: [email protected] or tel: +44 (0)1784 414241. Please quote the reference: Z0110/5651. Closing date: Midday 30th April 2010.

We positively welcome applications from all sections of the community.

Icarus: Hybrid organic-inorganic nanostructures for photonics and optoelectronics

9 PhD Studentships and 3 PDRAs. We are pleased to announce the start of the EU-Funded FP7 Initial Training Network Icarus. Our network involves collaboration between industrial and academic partners in Crete, IBM Research -  Zurich, Imperial College, Milan, Munich, Pisa, Sheffield and  Southampton. Together with offering high-quality training at  postgraduate level, our aim is to develop the next generation  of optical, photonic and optoelectronic devices based on  combinations of organic and inorganic semiconductors. Our  network contains high-level experience in nanofabrication,   materials, spectroscopy and condensed-matter theory. Each      network partner seeks to recruit postgraduate students        and / or postdoctoral researchers who will all be employed           as Marie Curie Fellows. For more details on contributing         partners and positions vacant please see www.icarus.     group.shef.ac.uk/. Applicants can check their eligibility as  Early Stage Researchers or Experienced Researchers in   the document “Annex III (Initial Training Networks (multi-     beneficiary)” at http://cordis.europa.eu/fp7/calls-grant- agreement_en.html#people_ga.

48 Physics World February 2010 Dunedin, New Zealand Lecturer/Senior Lecturer/ Associate Professor (Confirmation Path) TheThe KarlsruheKarlsruhe InstituteInstitute ofof TechnologyTechnology (KIT)(KIT) isis thethe resultresult ofof thethe mergermerger ofof thethe UniversitätUniversität KarlsruheKarlsruhe (TH)(TH) andand thethe ForschungszentrumForschungszentrum Karlsruhe.Karlsruhe. ItIt isis aa uniqueunique Department of Physics institutioninstitution inin Germany,Germany, whichwhich combinescombines thethe missionmission ofof anan universityuniversity withwith thatthat ofof aa national research center of the Helmholtz Association. With 8000 employees KIT Opportunity to join a vibrant Physics Department and an internationally recognised national research center of the Helmholtz Association. With 8000 employees KIT isis oneone ofof thethe largestlargest researchresearch andand educationeducation institutionsinstitutions worldwide.worldwide. research group. Applications are invited for a permanent faculty position in the Department of Physics. We are TheThe PhysicsPhysics DepartmentDepartment atat KarlsruheKarlsruhe InstituteInstitute ofof TechnologyTechnology invitesinvites applicationsapplications for the position of a seeking a candidate who can drive an experimental research programme in either Ultra-cold for the position of a atoms or Photonics, and make a strong contribution to undergraduate and graduate teaching. The successful applicant will have a PhD in Physics and demonstrated research achievements in Ultra- ProfessorshipProfessorship (W3)(W3) ofof ExperimentalExperimental cold atoms or Photonics. They will become a member of the Jack Dodd Centre for Quantum Technology (www.physics.otago.ac.nz/research/jackdodd/), a well-established research group which Elementary-ParticleElementary-Particle PhysicsPhysics is closely linked to a similar group at Auckland University through the Dodd-Walls Centre at the Institut für Experimentelle Kernphysik (IEKP). The position has been (www.doddwalls.ac.nz). All areas within Photonics or Ultra-cold atoms will be considered, but at the Institut für Experimentelle Kernphysik (IEKP). The position has been establishedestablished inin thethe frameworkframework ofof thethe AusbauprogrammAusbauprogramm 20122012 ofof thethe statestate ofof there is an opportunity to take over a very well equipped laboratory in Ultra-cold atoms (details are Baden-WürttembergBaden-Württemberg whichwhich willwill taketake effecteffect asas ofof winterwinter 2010/2011.2010/2011. available on request). The successful candidate will contribute to scientific interactions within the wider group, and must be able to contribute strongly to the group’s research funding proposals. TheThe researchresearch focusfocus ofof thethe successfulsuccessful candidatecandidate shouldshould lielie inin thethe fieldfield ofof physicsphysics atat particle accelerators with emphasis on the search for dark matter or for other new The position is full-time and confirmation-path (similar to US tenure-track) and subject to a five particle accelerators with emphasis on the search for dark matter or for other new phenomenaphenomena andand shouldshould includeinclude thethe developmentdevelopment ofof newnew detectordetector technologies.technologies. year confirmation period. Specific enquiries may be directed to Professor Rob Ballagh, Head, Department of Physics, TheThe positionposition isis embeddedembedded inin anan excellentexcellent researchresearch environmentenvironment inin theoreticaltheoretical andand Tel 64 3 479 7793, Fax 64 3 479 0964, Email [email protected] experimentalexperimental elementaryelementary particleparticle physicsphysics andand astroparticleastroparticle physicsphysics carriedcarried outout inin severalseveral institutesinstitutes atat KIT.KIT. TheThe successfulsuccessful candidatecandidate isis expectedexpected toto supportsupport thethe Applications quoting reference number A10/03 close on Monday 15 March 2010. KIT-CenterKIT-Center ElementaryElementary ParticleParticle andand AstroparticleAstroparticle PhysicsPhysics (KCETA)(KCETA) andand toto participateparticipate atat currentcurrent andand futurefuture graduategraduate schoolsschools ofof KCETA.KCETA. APPLICATION INFORMATION Send applications to the Human Resources Division, Email [email protected], TeachingTeaching dutiesduties includeinclude appropriateappropriate participationparticipation inin thethe lecturelecture coursescourses forfor ourour Fax 64 3 479 8279. With each application, please include an application form, an EEO information basicbasic andand advancedadvanced programmesprogrammes inin physics,physics, bothboth forfor physicsphysics majorsmajors andand studentsstudents of other disciplins. Proficiency in German is expected. form, a covering letter and your curriculum vitae. The forms and a full job description are available of other disciplins. Proficiency in German is expected. at www.otago.ac.nz/jobs Alternatively, contact the Human Resources Division, ApplicantsApplicants mustmust havehave thethe degreedegree ofof HabilitationHabilitation oror demonstratedemonstrate equivalentequivalent Tel 64 3 479 8269, Email [email protected] scientificscientific qualificationqualification asas wellwell asas experienceexperience inin teaching.teaching. Equal opportunity in employment is University policy. KITKIT aimsaims toto increaseincrease thethe numbernumber ofof femalefemale professorsprofessors andand especiallyespecially welcomeswelcomes applicationsapplications fromfrom women.women. HandicappedHandicapped personspersons withwith equalequal qualificationsqualifications willwill bebe xxx/pubhp/bd/o{0kpct preferred.preferred. ApplicationsApplications withwith standardstandard documentation,documentation, includingincluding aa summarysummary ofof pastpast teaching,teaching, aa researchresearch planplan asas wellwell asas aa listlist ofof thethe fivefive mostmost importantimportant publications,publications, shouldshould bebe sentsent byby AprilApril 9th,9th, 20102010 to:to: DekanDekan derder FakultätFakultät fürfür Physik,Physik, KarlsruherKarlsruher InstitutInstitut fürfür TechnologieTechnologie (KIT),(KIT), CampusCampus Süd,Süd, 7612876128 Karlsruhe,Karlsruhe, GermanyGermany..

KITKIT – – University University of of the the State State of of Baden-Wuerttemberg Baden-Wuerttemberg and and National National Laboratory Laboratory of of the the Helmholtz Helmholtz 8VgZZgk^YZdhdc Association.Association.

XZgcXdjg^Zg#Xdb Fresh jobs higV^\]iidndjg^cWdm XZgcXdjg^Zg#XdbÉhWgVcY"cZlXVgZZgk^YZd Fresh jobs hZXi^dch]dlXVhZhXVgZZgdeedgijc^i^ZhVi H^\cjeidi]Z_dWhWnZ"bV^a `ZngZhZVgX]^chi^iji^dchVgdjcYi]ZldgaY# VaZgi[gdbWg^\]igZXgj^ih# higV^\]iidndjg^cWdm lll#Wg^\]igZXgj^ih#Xdb

Lighting the way. Optoelectronics Research Centre PhD in Photonics

Considering a career in lasers, optical communications, nanophotonics, biophotonics, fibre optics, integrated optics, or sensors? Come and work with some of the world’s leading photonics scientists in our brand new state of the art facilities! Fully funded places are available for UK students including tuition fees and a tax-free bursary up to £18,000. K^ZlLdg`^c\Vi?Z[[ZghdcAVWidYVnVi Fully funded places are also available for EU and International students; for XZgcXdjg^Zg#Xdb$Xlh$EV\Zh$_Z[[ZghdcaVWh#Yd details please visit our website.For the best careers ^ce]nh^Xh www.orc.soton.ac.uk/photonics_phd.html [email protected] H^\cjeidi]Z_dWhWnZ"bV^aVaZgi k^h^iWg^\]igZXgj^ihÄi]ZcZl_dWhlZWh^iZ[gdb Physics World February 2010 >DEEjWa^h]^c\#lll#Wg^\]igZXgj^ih#Xdb 49 [gdbWg^\]igZXgj^ih# lll#Wg^\]igZXgj^ih#Xdb 8VgZZgk^YZdhdc XZgcXdjg^Zg#Xdb XZgcXdjg^Zg#XdbÉhFresh jobsWgVcY"cZl XVgZZgk^YZdhZXi^dch]dlXVhZhhigV^\]iidndjg^cWdm XVgZZgdeedgijc^i^ZhVi`ZngZhZVgX] ^chi^iji^dchVgdjcYi]ZldgaY#H^\cjeidi]Z_dWhWnZ"bV^aVaZgi[gdbWg^\]igZXgj^ih#

I]Z[^ghi[ZVijgZYk^YZd^h[gdbI]ZI]dbVh?Z[[ZghdcCVi^dcValll#Wg^\]igZXgj^ih#Xdb 6XXZaZgVidg;VX^a^in?Z[[ZghdcAVW!JH#

?Z[[ZghdcAVW^hVjhZg[VX^a^in[dg^ciZgcVi^dcVahX^Zci^hih#>ih eg^bVgnb^hh^dc^hidXdcYjXiWVh^XgZhZVgX]d[i]ZVidbÉh cjXaZjhVii]ZfjVg`aZkZa#?Z[[ZghdcAVWgZVX]Zhdjiid]Zae ZYjXViZi]ZcZmi\ZcZgVi^dc^chX^ZcXZVcYiZX]cdad\n#

K^ZlLdg`^c\Vi?Z[[ZghdcAVWidYVnViXZgcXdjg^Zg#Xdb$Xlh$EV\Zh$_Z[[ZghdcaVWh#Yd

M CC AD 1109 Jefferson.indd 2 11/1/10 14:21:42

M PW AD 0609 Odd Size BrightRecruits.indd 2 26/1/10 08:52:13 LVciide^X`i]ZWZhiWgV^ch4Join tomorrow’s neutron stars JEDI KNIGHT OF NEW6YkZgi^hZ^ci]ZBVgX]

ESS_Nature_advert3.indd 1 23/12/09 09:56:11

13x2 Feb ad.indd 1 26/1/10 08:40:35 March Graduate Special L]Vil^aaWZdcndjg  b^cYi]^hBVgX]4

GZ\^hiZgViWg^\]igZXgj^ih#Xdb idgZXZ^kZi]Z_dWhl^gZ[ZVijg^c\ \gVYjViZedh^i^dch[gdbide ZbeadnZgh# Bleed full page template.indt 1 11/1/10 13:37:57 Wg^\]igZXgj^ih#Xdb$gZ\^hiZg

50 Physics World February 2010 We are looking for a
Project Coordinator Grid

About Us working in an international environment in the area between SWITCH is operating the Swiss education network with research, implementation and operation. As an open personality innovative IT services for Universities in Switzerland. In with good communicative skills you value the collaboration addition, SWITCH is operating the domain name registration with your customers. You are fluent in English and have the for domains ending in “.ch” and “.li“. Our offices are located in ability to express yourself in German. downtown Zurich, and the company has 90 employees. We Offer The Job Competitive employment conditions, very good social benefits, SWITCH is participating together with Swiss Universities in a flexible working hours as well as your continuing education are EU-funded project that coordinates a Grid infrastructure across important to us. Europe (“European Grid Initiative“ – EGI). SWITCH is acting as the leading institution for Switzerland within this project, for Contact which we have an open position for a project coordinator. The SWITCH, Human Resources, Gudrun Reheis, P.O. Box, 8021 job description comprises besides the coordination of the Swiss Zürich, participants, the reporting towards the overall project as well Tel. 044 253 98 22, [email protected] as participation in technical work. The latter consist of software development as well as operating grid services.
Your Profile You hold a higher degree in computer science or a related field and have in-depth knowledge of internet technologies, web services, object-oriented programming, PKI and software
engineering. Experience in grid computing is highly desirable; participation in EU funded projects is a definite plus. You have Werdstrasse 2, P.O. Box, CH-8021 Zürich gained experiences in project management and you enjoy Phone +41 44 268 15 15, www.switch.ch LVciide^X`i]ZWZhiWgV^ch4 6YkZgi^hZ^ci]ZBVgX]

Physics World February 2010 51 Lateral Thoughts: The White Rabbit physicsworld.com Alice through the double slits

Alice thought that she had simply followed the White Rabbit through one of the two slit-like holes, but felt strangely disturbed about whether she had “really” gone Photolibrary through just one hole, or had somehow passed through both holes simultaneously. The Rabbit, who was eating a turnip, was looking her over. “You must be one of those funny-looking things that thinks they know everything,” he said. “What are you? A lumpy wave or a wavy lump?” “I don’t feel like either,” said Alice, “so I must be some- thing entirely different.” The Rabbit snorted. “Well, at least you know that,” he said. “You might even be ready to learn more.” “How do you think you got here?” asked the Rabbit. “I’m not sure,” said Alice. “Did we come through one hole or two holes?” “You’re missing the point!” the Rabbit said scornfully. “Forget about whether you came through one hole or both holes.” He snorted again. “Listen! Are you aware that if lots of rabbits came through – even one at a time – you would still find us grouped along the field rows where the carrots grow?” “You mean you would all be What you field’s probabilities.” arranged in a wave-like interference pattern?” asked should be Alice opened her mouth to ask yet another question, Alice. “Oh!” said the Rabbit, with some surprise. He but he silenced her with a glare. “Although the individual feigned a courtly bow. “You know that much, then.” “Yes, doing is fields of individual rabbits are not identical,” he said, “they I have done some physics. What I don’t know is why it hap- looking for an are not dissimilar either, so the multiple outcomes from pens. No-one does,” said Alice. “What a bunch your kind explanation numerous rabbits build up to create the interference pat- must be!” said the Rabbit. “It’s doubtless because you’re that explains tern in the permitted areas. The link between the rabbits’ all looking for an explanation to fit your own mistaken energy on both sides of the holes is a non-local phenom- notion of what’s happening.” He waved the turnip at her. how what you enon.” “So now you know,” he said; and with that, he “What you should be doing is looking for an explanation see happening turned to hop away. “But there’s one thing you haven’t that explains how what you see happening can happen!” can happen mentioned,” said Alice. The Rabbit stopped, looking pos- He came closer. “If you’re a single particle,” he said, itively affronted. “And what’s that?” “You haven’t said why “the energy bound up in you gives you a dynamic, geo- the interference pattern disappears when someone tries metrically configured field of probability. The reason why to detect the rabbits at one hole or the other – and why this we end up grouped in rows once we arrive here – even if still happens even if they use delayed-choice detection we come through one at a time – is that our individual after they have passed through,” said Alice. probability fields extend geometrically through and “Well I must admit, for a funny-looking thing, you know beyond both holes, but with a momentary superior prob- quite a bit,” the Rabbit acknowledged, though still with ability at one hole, and a momentary inferior probability at the same air of impatience. “What the detector detects is the other.” Throwing the turnip away, he held his paws not the rabbit passing through, but rather the superior forward, with one higher than the other. “There’s the probability of its energy being at or beyond one hole. momentary superior probability; there’s the inferior one.” Although the probabilities at and beyond both holes are He changed their positions. “Now they are the other way part of the probability field of the energy bound up in the round.” He reversed the movement. “And so on.” Next, rabbit, the detector acts upon the momentary superior he began wiggling his paws around, repeatedly bringing probability, and by interacting with it, radically streng thens them close together in a series of sideways and up-and- its superiority.” “What does that do?” Alice asked. At this, down movements. “For each rabbit that comes through,” the Rabbit bristled. “It moves it from uncertainty to he said, “the probabilities within the field interfere with certainty , at the expense of the inferior probability and the each other.” probability field as a whole. The interaction of the detector “But why?” asked Alice. “Why do they interfere? Why with the probabilities of many rabbits is thus a series of must that happen?” The Rabbit easily dealt with this. “The localizing events incompatible with the uncertainty in- interference occurs because neither probability is a cer- herent in the probability fields of the rabbits’ energy.” tainty. The superior probability isn’t a positive certainty, “Satisfied now?” he asked, with the belligerent air of and the inferior probability isn’t a negative certainty. They a rabbit who wanted to finish the conversation. “Is it all are related characteristics of a single phenomenon – really that simple?” asked Alice. “Of course!” the Rabbit the dynamic probability field extending geometrically said, with more scorn. “The fewer assumptions, the bet- through and beyond the slits.” “So how does that make ter, as one of the Big People once said. This explanation the pattern form?” asked Alice. “Do you ever do anything requires only one – the probability field.” Then he had a except ask questions?” the Rabbit retorted. “It forms new, happier thought: “Preferably one with carrots in it.” because the energy bound up in each rabbit can register only in an area permitted by the dynamic geometry of its G G Davies is a freelance business and technical writer, e-mail reserve@ probability field, which has configurations of intensity and wwamwriters.co.uk. This article is an extract from “Alice through the direction that are affected by the interference between the double slits”, an as-yet-unpublished manuscript of about 25 000 words 52 Physics World February 2010 Download the latest news articles from physicsworld.com directly to your iPhone or iPod Touch.

Carrier 10:07 PM

ABOUT

Home Einstein dark matter

Supermassive black hole struggles to swallow Milky Way Jan 8, 2010 Gaseous lobes overcome the might of the black hole at the centre of our galaxy Best of the blog Dec 23, 2009 The bizzare stories from the world of physics this year

Breakthrough of the year Dec 21, 2009 NIST researchers demonstrate sustained quantum computing in trapped ions

Staying informed on the go has never been easier: • Browse headlines from the latest 25 news articles, which link through to the full stories. • Search terms to find relevant news articles. • Save your previous searches in a list for quick selection. • E-mail details of particular articles to access them from a desktop computer. More information on the app and how to download it is available at physicsworld.com/cws/pwnewsflash. High Vacuum Systems TURBOLAB 80 0.02.2010 BICOM_10483.02 ©

Compact turnkey vacuum solution - ready to operate. Our new TURBOLAB 80 plug and play high vacuum pump systems are based on well proven components. These table top units are available as basic or fully featured versions, eliminate the use of lubricating oils and can achieve 0.75 x 10-7 mbar vacuum. TURBOLAB 80 high vacuum systems are suited for use wherever a compact and most efficient vacuum solution is required. Get the details at oerlikon.com/leyboldvacuum

Oerlikon Leybold Vacuum GmbH Oerlikon Leybold Vacuum USA, Inc. Bonner Strasse 498 5700 Mellon Road D-50968 Köln Export, PA USA T +49 (0)221 347-0 T 1-800-764-5369 F +49 (0)221 347-1250 F 1-800-215-7782 [email protected] [email protected] www.oerlikon.com/leyboldvacuum

1001_TURBOLAB 80_EN_IOP.indd 1 25.01.2010 10:56:16 Uhr