Aspen Physics Turns 50 Michael S

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

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Saarinen for the 20-day celebration. interruptions, but sometimes provided enter- in establishing the ACP in the theoretical They included German–French theologian tainment. I once overheard particle physicist community: Philip Anderson, Bethe and Albert Schweitzer, pianist Artur Rubinstein, Murray Gell-Mann quipping, “I don’t know Gell-Mann. Coincidentally, each began com- philosopher Jose Ortega y Gasset and poet the English for it, but the Japanese is …” ing to Aspen two years before he received a Stephen Spender. The event led to the for- An early attempt to engage physicists and Nobel prize. They set the agenda, served as mation of the Aspen Music Festival (now philosophers failed because of Adler’s insist- scientific magnets and gave early legitimacy. the Aspen Music Festival and School) and, ence that they first agree on “the pyramid of Any high-energy theorist would kill to spend in 1950, of the Aspen Institute for Human- knowledge”, which had physics at the bottom three weeks discussing physics with Gell- istic Studies (now the Aspen Institute). Just and philosophy on top. Because of the clash of Mann; Bethe helped to get astrophysics going as Paepcke had imagined, today the town cultures and egos, the centre did not stay tied at the ACP; and Anderson shaped condensed- brings together culture, wealth and athleti- to the Aspen Institute for long and became an matter physics there for three decades. cism — with a touch of glitz. independent entity in 1968. Since then, the Anderson set the tone for the condensed- ACP has been run by physicists who volun- matter field with his influential paper ‘More Beginnings teer their time, helped by just two full-time is Different’ (P. W. Anderson Science 177, The ACP’s origins lie with physicist George staff. More than 200 top theorists have shaped 393–396; 1972). Contrary to particle phys- Stranahan, heir to the fortunes of the Cham- and guided the centre — including five Nobel ics, in which scientists pursue a reductionist pion Spark Plug company and a graduate laureates and Stephen Hawking. quest for simplicity at smaller and smaller student at the Carnegie Institute of Tech- An early grant from the Sloan Foundation scales, condensed-matter physics applies nology in Pittsburgh. In the late 1950s, he was crucial, and Hans Bethe donated part the basic rules to discover and study the decided that he would rather do his physics of his 1967 Nobel prize money. Bethe Hall, often unexpected, emergent phenomena during the summer months in the moun- built in 1978, was named in his honour. Rob- that arise in large systems with complicated tains of Colorado, where fishing and hiking ert Rathbun Wilson, the first director and interactions, such as superconductivity or in provided a more enjoyable backdrop than builder of Fermilab, visited Aspen in 1967 biological systems. Today, biological physics an office in steamy Pittsburgh. After a few and convinced the US Department of Energy has emerged as a major activity at the ACP. years, he realized that theoretical physics is to build a large, temporary office building Two other condensed-matter theorists best done with others, and set out to draw there, where Fermilab’s facilities for particle- played a crucial part: David Pines of the physicists to Aspen. When he later moved physics experiments were designed. Hilbert University of Illinois at Urbana–Champaign to Colorado, Stranahan became the landlord Hall, named after mathematician David Hil- and Elihu Abrahams of Rutgers University and close friend of Thompson. bert, almost tripled the number of physicists in New Jersey. They pioneered workshops Stranahan got things going with help from that the centre could accommodate. on the latest topics to attract a balance of Michael Cohen, a condensed-matter theorist researchers from universities and from at the University of Pennsylvania in Philadel- Solid foundations industry (mostly Bell Labs). These work- phia, who was one of Feynman’s few PhD stu- In 1972, the US National Science Foundation shops brought in young hotshots, keeping dents, and Robert Craig, executive director became the ACP’s main funder, with support the talent pool fresh. One area of scientific of the Aspen Institute. The Stranahan fam- from other US science agencies including focus, strongly correlated electrons in met- ily’s Needmor Fund paid for the first build- the Department of Energy and NASA. In the als, laid the foundations for the current ing, Stranahan Hall, designed by Bauhaus mid-1990s, a $3-million fund-raising cam- understanding of high-temperature and architect Herbert Bayer, who also planned paign led by astrophysicist David Schramm other unconventional superconductors. the Aspen Institute campus. Cohen got the of the University of Chicago financed the In addition to Bethe’s presence, astrophysics talent, and Craig convinced the Aspen final and largest building, Smart Hall. Con- physics at the ACP was jump-started by the Institute to create a physics division. tributions came from physicists, friends in discovery of pulsars in 1967 and their iden- In spring 1962, a letter was sent out to the the Aspen community and the Smart Family tification with neutron stars. The exotic physics community tentatively announcing Foundation in Connecticut. properties of neutron stars — rapid rota- “the possibility of a summer physics insti- Three towering figures played a major part tion, superfluidity and superconductivity — tute”. The purpose was “to provide a place intrigued Pines and other condensed-matter for physicists to work on their own problems theorists. They brought in astrophysicists during the summer, in a stimulating physics with expertise in relativity and nuclear phys- atmosphere, and in a location with pleasant ics, and work done at the centre linked pul- surroundings and natural beauty”. That year, sar glitches to superfluidity within neutron 42 brave souls came to Aspen to “pursue stars, advancing both fields. In 1972, NASA their work with minimal distractions”. started funding an annual workshop, and The Aspen formula was — and still is — astrophysics had a foothold in Aspen. to bring the best theorists together in an But it was cosmology that caused astro- informal setting for weeks or months, free physics to rise to the same level as particle

from their usual responsibilities of students physics and condensed matter. Around P hy s i cs s . Maxwell/ As pen Center for and teaching and isolated from distractions. 1980, Schramm and others began to real- There, they could talk with one another, ize that theories of unification in particle think big thoughts and come up with game- physics might revolutionize the sleepy changing ideas. Physicists were housed two field of cosmology, which had been the to an office and held discussions on a patio province of astronomers since the time of with a small blackboard, often accompanied Edwin Hubble. Aspen was the ideal incu- by beautiful music from the town’s music tent. bator for this young, interdisciplinary field. Graduate students were excluded, differenti- Workshops brought together astronomers ating Aspen from teaching summer schools. and physicists to discuss the hot topics — For many years, the buildings had only a George Stranahan, Michael Cohen and Robert Big Bang nucleosynthesis, dark matter, handful of public phones. This put a limit on Craig (left to right): the centre’s driving forces. inflation, large-scale structure, the cosmic

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Pagels’ name was given to the centre’s summer public lecture series. s / G etty Schramm, my mentor, was an expert ture climber. One summer, bad weather trapped him and his climbing partner on the face of 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 was less fortunate, and died in a plane crash while flying his twin-engine tur- boprop from Denver to Aspen. W . E ugene S m ith/ T i e & L ife P c The Future Today, the Aspen Center for Physics is thriv- ing, made up of three buildings on a 1.6-hec- tare campus, surrounded by a large ‘circle of serenity’ of open space on the Aspen Mead- ows. Along with the Aspen Institute and the Aspen Music Festival and School, the ACP is Aspen’s cultural shift started with big-top celebrations for Johann von Goethe’s bicentennial in 1949. recognized as one of the town’s three major cultural institutions. microwave background and cosmic strings. the cancellation of anomalies), triggering the Each summer, its 16-week programme A staggering 10,000 or more papers are first string theory revolution. and 10–15 workshops attract more than 500 attributed to visits to the ACP. But its real The Green–Schwarz discovery was leading theorists to work on the most criti- impact is the big ideas that originated there. announced immediately in grand fashion cal problems in physics. With delight, I note Much of today’s consensus cosmology, with during a ‘physics cabaret’ at Aspen’s historic that about 20% of the attendees and members its particle dark matter, inflationary origins Hotel Jerome. In a skit in which Schwarz of the governing board are now women, and and dark energy, can trace its roots to the played the role of Gell-Mann, he rushed onto the centre now has its first female president ACP. In his Nobel prize acceptance speech the stage to announce that he had discovered — progress for theoretical physics. Discus- last December, Adam Riess described how his the theory of everything — eventually being sions fill the offices, halls, alcoves and patios; team, which co-discovered that the expansion carried off the stage by a man in a white coat. spontaneous volleyball games occur regu- of the Universe is speeding up, regularly met Another revolution, in physics publish- larly. New ideas and collaborations made in at the centre to chart their activities. ing, traces its origin to a chance encoun- this informal environment have launched the ter on an ACP bench in June 1991. Joanne careers of hundreds of young theorists (myself Stringing it together Cohn, a young theorist at the Institute for included) and moved physics forwards. Whether or not string theory is the theory Advanced Study in Princeton, had been run- Will the Aspen formula continue to of everything, it has changed the course ning an informal preprint distribution ser- be as successful as it has been for the past of physics. String theory began as a way to vice, e-mailing papers to hundreds of string 50 years? Several theoretical-physics insti- describe the strong interactions between theorists who wanted to get the latest results tutes now exist — the Isaac Newton Institute neutrons, protons and related particles. as quickly as possible. Paul Ginsparg, then at in Cambridge, UK, and the Kavli Institutes Supersymmetry, the symmetry between bos- Los Alamos, asked her why she hadn’t auto- in Santa Barbara and Beijing. These have ons and fermions and a hallmark of today’s mated the system. By the next day, Ginsparg longer, more formal programmes, and lack string theory, traces its origins to theorist had written some scripts, and two months the serenity of Aspen. The bigger challenge Pierre Ramond’s first summer in Aspen in later the Los Alamos arXiv (now residing comes with the change in the way science 1970, where, as he put it, he “stopped cal- at Cornell University) was open for busi- is done today. It is more collaborative, more culating and started thinking”. When he got ness. Today, more than 1 million articles are connected and ‘more faster’. When the ACP back to Fermilab, he prepared the paper that downloaded every week (P. Ginsparg Nature was founded, collaboration required face-to- added supersymmetry to string theory. This 476, 145–147; 2011). face interaction. Now, with e-mail and the has become the pattern: think in Aspen, cal- Physicists have always been attracted to Internet, many successful collaborators have culate and write at home. mountains, where they can hike and think. never met in person. String theory was declared dead at a ACP co-founder Robert Craig was a world- Aspen continues to be a place to think, 1974 Aspen workshop, having been beaten class mountaineer who scaled some of the free from the constraints of everyday exist- by quantum chromodynamics as the best toughest and tallest mountains, including ence — as Paepcke said, a place for “lifting us description of the strong (colour) interac- K2, and many physicists who came to Aspen out of our usual lives”. In today’s fast- paced tions between the quark constituents of the were serious climbers. A topographical map world of science, the need for a circle of hadrons. But John Schwarz of the Califor- of the surrounding mountains is displayed serenity is only more acute. ■ nia Institute of Technology decided to be prominently in Stranahan Hall. Aspen’s bold and think bigger, touting strings as the combination of challenging hikes, unpredict- Michael S. Turner is director of the Kavli path to unifying the forces of the subatomic able mountain weather and crumbling rock Institute for Cosmological Physics at the world with gravity. For the next ten years, means that tragedies are not uncommon. University of Chicago, Illinois 60637, USA. Schwarz, his collaborator Michael Green In 1988, ACP trustee Heinz Pagels, execu- He is chair of the trustees of the Aspen Center and a handful of others tried to make good tive director of the New York Academy of for Physics, which he has attended since 1979. on this promise at the centre. In the sum- Sciences, slipped on a loose stone while e-mail: [email protected] mer of 1984, their breakthrough came with climbing on Pyramid Peak and fell to his a historic paper that showed the mathemati- death. A respected popularizer of physics For more on 50th anniversary events at the Aspen cal consistency of string theory (technically as well as a brilliant theoretical physicist, Center for Physics, see go.nature.com/lepwz8.

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