Aspen Physics Turns 50 Michael S

COMMENT AWARDS Passion and punch-ups ECOLOGY A paean to decay EXHIBITION London show OBITUARY Akira Tonomura, in a chronicle of two contested charts the life that death celebrates Alan Turing’s imaging pioneer, Nobel prizes p.318 provides p.320 life and legacy p.321 remembered p.324 S. MAXWELL/ASPEN CENTER FOR PHYSICS S. MAXWELL/ASPEN CENTER FOR

Summer workshops at the Aspen Center for Physics give researchers respite from their academic duties. Aspen physics turns 50 Michael S. Turner reflects on how mountain serenity has bred big breakthroughs at the Aspen Center for Physics in Colorado.

heoretical physicists are an odd lot: 10,000 theoretical physicists, including 53 Victorian buildings and wonderful skiing. She bad communicators (Niels Bohr Nobel laureates, from 65 countries. The centre persuaded her husband, a devotee of German and Werner Heisenberg); brilliant can lay claim to the string-theory revolution, writer Johann Wolfgang von Goethe, to visit Tshowmen (Richard Feynman and George the birth of the arXiv preprint archive and in 1945. Seeing it as the ideal place to bring Gamow); the ‘strangest man’ (Paul Dirac); to setting the agenda for condensed-matter together the three aspects of life — economic, lots of Hungarians (Leó Szilárd, Edward physics. Its history is tied to the revival of a sil- cultural and physical — he invested millions Teller and Eugene Wigner); bad hair (Albert ver-mining town and the American entrepre- of dollars in rebuilding it. In 1946, he formed Einstein); and too few women. They don’t neurial spirit, and features a fascinating cast of the Aspen Skiing Corporation, which remains need fancy equipment — a pencil and paper characters, from philosopher Mortimer Adler the financial engine of the valley. will do. But they do like a serene environ- to journalist Hunter S. Thompson. Aspen’s cultural transformation came with ment, with blackboards and other people of The centre’s story cannot be separated from the 1949 Goethe bicentennial. Organized by their ilk, in which to come up with big ideas: that of the town. The 1893 repeal of the Sher- Walter Paepcke (with guidance from Adler among them relativity, the Big Bang, quan- man Silver Purchase Act demonetized silver and Robert Maynard Hutchins, then chan- tum mechanics and the atomic bomb. and almost overnight turned Aspen, with cellor of the University of Chicago in Illi- Over the past 50 years, the Aspen Center a population of about 15,000, into a ghost nois), the bicentennial aimed to rehabilitate for Physics (ACP), nestled in a beautiful valley town. Elizabeth Paepcke, wife of Chicago German culture and to revive humanism in at 2,400 metres above sea level in the Colo- industrialist Walter Paepcke, visited in 1939, the wake of the Second World War and the rado Rocky Mountains, has provided a ‘circle describing it as a place that “had slept since dawn of the atomic age. Around 2,000 peo- of serenity’ during the summer months for 1893”. She found 700 residents, decaying ple gathered in a tent designed by architect

Eero Saarinen for the 20-day celebration. handful of public phones. This put a limit on Contributions came from physicists, friends They included German–French theologian interruptions, but sometimes provided enter- in the Aspen community and the Smart Albert Schweitzer, pianist Artur Rubinstein, tainment. I once overheard particle physicist Family Foundation in Connecticut. philosopher José Ortega y Gasset and poet Murray Gell-Mann of the California Institute Three figures played a major part in estab- Stephen Spender. The event led to the for- of Technology quipping, “I don’t know the lishing the ACP in the theoretical commu- mation of the Aspen Music Festival (now English for it, but the Japanese is …”. nity: Philip Anderson of Princeton University, the Aspen Music Festival and School) and, An early attempt to bring together physi- Bethe and Gell-Mann. Coincidentally, they in 1950, of the Aspen Institute for Humanis- cists and philosophers failed because of all began coming to Aspen two years before tic Studies (now the Aspen Institute). Just as Adler’s insistence that they agree on “the pyra- receiving a Nobel prize. They set the agenda, Paepcke had imagined, today the town brings mid of knowledge”, which had physics at the served as scientific magnets and gave early together culture, wealth and athleticism — bottom and philosophy on top. Because of the legitimacy. Any high-energy theorist would and a touch of glitz. clash of cultures and egos, the centre did not kill to spend three weeks discussing physics stay tied to the Aspen Institute for long and with Gell-Mann; Bethe helped to get astro- BEGINNINGS became an independent entity in 1968. Since physics going at the ACP; and Anderson The ACP’s origins lie with physicist George then, the ACP has been run by physicists who shaped condensed-matter physics there for Stranahan, heir to the fortunes of the Cham- volunteer their time, helped by just two full- three decades. pion spark-plug company in California and time staff. More than 200 top theorists have Anderson set the tone for the condensed- a graduate student at the Carnegie Institute shaped and guided the centre — including matter field with his influential paper ‘More of Technology in Pittsburgh, Pennsylvania. five Nobel laureates and Stephen Hawking. is Different’ (P. W. Anderson Science 177, In the late 1950s, he decided that he would An early grant from the Sloan Founda- 393–396; 1972). Contrary to particle phys- rather do his physics during the summer tion was crucial, and Hans Bethe of Cornell ics, in which scientists pursue a reductionist months in the mountains of Colorado, University in New York donated part of his quest for simplicity at smaller and smaller where fishing and hiking provided a more 1967 Nobel prize money. Bethe Hall, built in scales, condensed-matter physics applies the enjoyable backdrop than did an office in 1978, was named in his honour. Robert Rath- basic rules to discover and study the often steamy Pittsburgh. After a few years, he real- bun Wilson, the first director and builder of unexpected, emergent phenomena that arise ized that theoretical physics was best done Fermilab in Batavia, Illinois, visited Aspen in large systems with complicated interac- with others, and set out to draw physicists in 1967 and convinced the US Department tions, such as superconductivity or biologi- to Aspen. When he later moved to Colorado, of Energy to build a large, temporary office cal systems. Today, biological physics has Stranahan became the landlord and close building there, where Fermilab’s facilities for emerged as a major activity at the ACP. friend of Thompson. particle-physics experiments were designed. Two other condensed-matter theorists Stranahan got things going with help from The construction of Hilbert Hall, named played a crucial part: David Pines of the Michael Cohen, a condensed-matter theorist after mathematician David Hilbert, almost University of Illinois at Urbana–Champaign at the University of Pennsylvania in Philadel- tripled the number of physicists that the cen- and Elihu Abrahams of Rutgers University phia, who was one of Feynman’s few PhD stu- tre could accommodate. in Piscataway, New Jersey. They pioneered dents, and Robert Craig, executive director workshops on the latest topics to attract a of the Aspen Institute. The Stranahan fam- SOLID FOUNDATIONS balance of researchers from universities and ily’s Needmor Fund paid for the first build- In 1972, the US National Science Foundation from industry (mostly Bell Labs). These ing, Stranahan Hall, designed by Bauhaus became the ACP’s main funder, with support workshops brought in young hotshots, keep- architect Herbert Bayer, who also planned from other US science agencies including ing the talent pool fresh. One area of scien- the Aspen Institute campus. Cohen found the Department of Energy and NASA. In tific focus, strongly correlated electrons in the physics talent, and Craig convinced the the mid-1990s, a $3-million fund-raising metals, laid the foundations for the current Aspen Institute to create a physics division. campaign led by astrophysicist David Sch- understanding of high-temperature and In spring 1962, a letter was sent out to the ramm of the University of Chicago financed other unconventional superconductors. physics community tentatively announcing the final and largest building, Smart Hall. In addition to Bethe’s presence, astro- “the possibility of a summer physics insti- physics at the ACP was jump-started by the tute”. The purpose was “to provide a place discovery in 1967 of pulsars and their identi- for physicists to work on their own problems fication as neutron stars. The exotic proper- during the summer, in a stimulating physics ties of pulsars — rapid rotation, superfluidity atmosphere, and in a location with pleasant and superconductivity — intrigued Pines surroundings and natural beauty”. That year, and other condensed-matter theorists. They 42 brave souls came to Aspen to “pursue brought in astrophysicists with expertise in their work with minimal distractions”. relativity and nuclear physics, and work The Aspen formula was — and still is — to done at the centre linked pulsar glitches to bring the best theorists together in an infor- superfluidity within neutron stars, advanc-

mal setting for weeks or months, free from ing both fields. In 1972, NASA started fund- PHYSICS S. MAXWELL/ASPEN CENTER FOR their usual responsibilities of students and ing an annual workshop, and astrophysics teaching, and isolated from distractions. had a foothold in Aspen. There, they could talk with one another, But it was cosmology that caused astro- think big thoughts and come up with game- physics to rise to the same level as particle changing ideas. Physicists were housed two physics and condensed matter. Around to an office and held discussions on a patio 1980, Schramm and others began to realize with a small blackboard, often accompanied that theories of unification in particle phys- by beautiful music from the town’s music tent. ics might revolutionize the sleepy field of Graduate students were excluded, differenti- cosmology, which had been the province of ating Aspen from teaching summer schools. George Stranahan, Michael Cohen and Robert astronomers since the time of Edwin Hub- For many years, the buildings had only a Craig (left to right): the centre’s three founders. ble. Aspen was the ideal incubator for this

fell to his death. A respected popularizer of physics as well as a brilliant theoretical physicist, Pagels’ name was given to the centre’s summer public lecture series. Schramm, my mentor, was also an expert climber. One summer, bad weather trapped him and his climbing partner on the face of Colorado’s Capitol Peak in freezing rain; they made it back to Aspen two days later, after many had given up hope. Sadly, in December 1997, Schramm died in a plane W. EUGENE SMITH/TIME & LIFE PICTURES/GETTY crash while flying his twin-engine turboprop from Denver to Aspen. THE FUTURE Today, the Aspen Center for Physics is thriv- ing on a 1.6-hectare campus, surrounded by a large ‘circle of serenity’ of open space on Aspen’s cultural shift started with big-top celebrations for Johann von Goethe’s bicentennial in 1949. the Aspen Meadows. The Aspen Institute, the Aspen Music Festival and School and the young, interdisciplinary field. Workshops good on this promise at the centre. In the ACP are recognized as the town’s three major brought together astronomers and physicists summer of 1984, their breakthrough came cultural institutions. to discuss the hot topics — Big Bang nucleo- with a historic paper that showed the Each summer, the ACP’s 16-week pro- synthesis, dark matter, inflation, large-scale mathematical consistency of string theory gramme and 10–15 workshops attract more structure, the cosmic microwave background (technically the cancellation of anomalies), than 500 leading theorists to work on the and cosmic strings. triggering the first string-theory revolution. most important problems in physics. With The Green–Schwarz discovery was delight, I note that about 20% of the attend- HIGH IMPACT announced immediately in grand fashion ees and members of the governing board are A staggering 10,000 or more papers are during a ‘physics cabaret’ at Aspen’s historic now women, and that the centre now has its attributed to visits to the ACP. But its real Hotel Jerome. In a skit, Schwarz, playing the first female president — progress for theo- impact is the big ideas that originated there. role of Gell-Mann, rushed onto the stage to retical physics. Discussions fill the offices, Much of today’s consensus cosmology, with announce that he had discovered the theory halls, alcoves and patios; spontaneous vol- its particle dark matter, inflationary origins of everything — and was eventually carried leyball games occur regularly. New ideas and and dark energy, can trace its roots to the off the stage by a man in a white coat. collaborations made in this informal envi- ACP. In his Nobel prize acceptance speech Another revolution, in physics publishing, ronment have launched the careers of hun- last December, Adam Riess of Johns Hop- traces its origin to a chance encounter on an dreds of young theorists (myself included) kins University described how his team, ACP bench in June 1991. Joanne Cohn, a and moved physics forwards. which co-discovered that the expansion of young theorist at the Institute for Advanced Will the Aspen formula continue to be as the Universe is speeding up, regularly met Study in Princeton, had been running an successful as it has been for the past 50 years? at the centre to chart its activities. informal preprint distribution service, Several theoretical-physics institutes now Whether or not string theory is the theory e-mailing papers to hundreds of string theo- exist — the Isaac Newton Institute in Cam- of everything, it has changed the course of rists who wanted to get the latest results as bridge, UK, and the Kavli Institutes in Santa physics. It began as a way to describe the quickly as possible. Paul Ginsparg, then at Barbara and Beijing. These have longer, more strong interactions between neutrons, pro- the Los Alamos National Laboratory, asked formal programmes, and lack the serenity of tons and related particles. Supersymmetry, her why she hadn’t automated the system. Aspen. The bigger challenge comes with the the symmetry between bosons and fermions By the next day, Ginsparg had written some change in the way science is done today. It and a hallmark of today’s string theory, traces scripts, and two months later the Los Alamos is more collaborative, more connected and its origins to theorist Pierre Ramond’s first arXiv (now residing at Cornell University) ‘more faster’. When the ACP was founded, summer in Aspen in 1970, where, as he put it, was opened for business. Today, more than collaboration required face-to-face inter- he “stopped calculating and started thinking”. 1 million articles are downloaded every week. action. Now, with e-mail and the Internet, When he got back to Fermilab, he prepared Physicists have always been attracted to many collaborators have never met in person. the paper that added supersymmetry to string mountains, to hike and to think. ACP co- Aspen continues to be a place to think, theory. This has become the pattern: think in founder Robert Craig was a world-class free from the constraints of everyday exist- Aspen, calculate and write at home. mountaineer who scaled some of the toughest ence — as Paepcke said, a place for “lifting us String theory was declared dead at a and tallest mountains, including K2 in Asia, out of our usual lives”. In today’s fast- paced 1974 Aspen workshop, having been beaten and many physicists who came to Aspen were world of science, the need for a circle of by quantum chromodynamics as the best serious climbers. A topographical map of the serenity is only more acute. ■ description of the strong (colour) interac- surrounding mountains is displayed promi- tions between the quark constituents of the nently in Stranahan Hall. Aspen’s combi- Michael S. Turner is director of the Kavli hadrons. But John Schwarz of the Califor- nation of challenging hikes, unpredictable Institute for Cosmological Physics at the nia Institute of Technology decided to be mountain weather and crumbling rock means University of Chicago, Illinois 60637, USA. bold and think bigger, touting strings as that tragedies are not uncommon. He is chair of the trustees of the Aspen Center the path to unifying the forces of the suba- In 1988, ACP trustee Heinz Pagels, execu- for Physics, which he has attended since 1979. tomic world with gravity. For the next ten tive director of the New York Academy of e-mail: [email protected] years, Schwarz, his collaborator Michael Sciences, slipped on a loose stone while For more on 50th anniversary events at the Aspen Green and a handful of others tried to make climbing on Pyramid Peak in Colorado and Center for Physics, see go.nature.com/lepwz8.