50 Years of Mountain Serenity and Big Breakthroughs:
The Aspen Center for Physics celebrates its 50th Anniversary
Theoretical physicists are an odd lot -- bad communicators (Bohr and Heisenberg), strangest man (Dirac), brilliant showmen (Feynman and Gamow), lots of Hungarians (Szilard, Teller, Wigner, …), bad hair (Einstein), and too few women. They don't require big fancy equipment -- pencil and paper will do -- but they do require a serene environment with chalk boards and others of their ilk to come up with the big ideas that change the world -- relativity, the big bang, quantum mechanics and the atomic bomb to mention a few. For the past 50 years, the Aspen Center for Physics (ACP), nestled in a beautiful valley at 8000 feet in the Colorado Rocky Mountains, has provided a "Circle of Serenity" for 10,000 theoretical physicists (53 Nobel Laureates among them) from more than 65 countries during the summer months. The ACP lays claim to launching the string theory revolution, the birth of the arXiv, and the design of the Fermilab experimental facilities. The history of the Center is closely tied to the revival of a silver mining town and it involves the American cowboy style and a fascinating cast of characters, from Mortimer Adler to Margaret Thatcher.
It began when Champion Sparkplug heir and Carnegie Institute of Technology graduate student George Stranahan decided that he could do his physics during the summerin the mountains of Colorado, where fishing and hiking would provide a more enjoyable backdrop than a lonely office in steamy Pittsburgh. After a few years of going out to Aspen during the summer, he realized that theoretical physics is best done with others and set out to find a way to bring other physicists to Aspen.
With help from Michael Cohen, one of the few PhD students of Richard Feynman and a condensed matter theorist at the University of Pennsylvania, and Robert Craig, Executive Director of the Aspen Institute, Stranahan got things going. The Stranahan family foundation (Needmor) provided the funds for the first building thatwould housethe desired core of 20 theorists two to an office. Bauhaus architect Herbert Bayer, whose other Aspen work included the campus of the Aspen Institute and the Music Tent, designed Stranahan Hall. Michael Cohen worked to get the physics talent to Aspen, and Craig provided the connection to the Aspen Institute whichlent its imprimatur and sponsorship. [Craig went on to found the Keystone Center, whose interdisciplinary scientist-to-scientist program was featured in Nature, 376, 547 (1995).]
In 1962 the Physics Center began as a division of the Aspen Institute. A typewrittenletterwas mailed to the community in the spring of 1962, signed by Michel Baranger and Lincoln Wolfenstein (both at Carnegie) and Cohen and Stranahan. The letter began, “There is a definite possibility that a Summer Institute will be started in 1962 at Aspen, Colorado,” and continued with a statement of purpose, “To provide a place for physicists to work on their own problems during the summer, in a stimulating physics atmosphere, and in a location with pleasant surroundings and natural beauty.” Forty-two brave souls came that summer over the period of June 15 to September 15, to “pursue their work with minimal distractions.”
The Aspen idea.
The story of the Aspen Center for Physics cannot be told in isolation. The 1893 repeal of the Sherman Silver Purchase Act demonetized silver and almost overnight turned Aspen, then a silver-mining town of 15,000, into a ghost town. In 1939, Elizabeth Paepcke, the wife of Chicago industrialist Walter Paepcke, visited a town that in her words “had slept since 1893”, where she found700 residents, decaying Victorian buildings, andwonderful skiing. She convinced her husband to visit in 1945, and Paepcke, the son of a German immigrant and a Goethe devotee, saw Aspen has a the ideal place to bring together the three elements of life – economic, cultural/educational, and physical – a place for “lifting us out of our usual lives”. He invested millions of dollars in rebuilding Aspen and in 1946 formed the Aspen Skiing Corporation, which today is the financial engine of the valley.
However, the event that transformed Aspen and would make it different than other ski towns that would pop up all over Coloradowas the 1949 Goethe Bicentennial. Two thousand people gathered in a tent designed by Eero Saarinen for this 20-day celebration of the 200th anniversary of the birth of the great German humanist and polymath. The participants included Albert Schweitzer (his only visit to the U.S.), pianist Artur Rubinstein, writer Thomas Mann, philosopher Jose Ortega y Gasset, poet Stephen Spender and playwright Thornton Wilder. With guidance from two University of Chicago powerhouses, Professor and Great Books advocate Mortimer Adler and President Robert Maynard Hutchins, Paepcke staged this grand event to rehabilitate German culture and to revive humanism and in the wake of WWII and the dawn of the atomic age. The Goethe Bicentennial led to the formation of Aspen Institute for Humanistic Studiesin 1950 (now the Aspen Institute) and the Aspen Music Festival in 1949 (now the Aspen Music Festival and School, or AMFS), and set Aspen on its path to become the Mecca that it is today. While it may not have achieved Adler’s lofty goal of making Aspen the Athens of the West, Aspen does bring together culture, wealth and athleticism as Paepcke had hoped.
Stranahan’s vision.
Back to the Physics Center; with Adler’s strong influence at the Aspen Institute and the rise of physics and physicists in the US, the arrangement between the Institute and Physics did not last long. I was told of an early attempt to engage physicists and philosophers that failed because of Adler’s insistence of first agreeing on “the pyramid of knowledge”, which had physics at the bottom and philosophyon top. In 1968, the Aspen Center for Physics became an independent entity and was free to chart its own course, guided a board of volunteer physicists. Over the years, 200 or so leading theoretical physicists have shaped the Center’s programs and have run the Center,with the help of a full-time staff of only two (up from one 8 years ago).
Stranahan and the ACP founders had a vision for how a summer physics think tank should work. The formula was to bring the best theorists together in an informal setting for a significant amount of time (weeks or months) and free from their usual responsibilities (students, teaching, and phones). There, they would talk with on another and not at one; they would think big thoughts and come up with great ideas.
The decision to exclude graduate students would differentiate Aspen from typical summer institutes around the world(e.g., Les Houches in Chamonix, Cargese in Corsica, the US Brandeis Summer Institute), which were primarily summer schools. The isolated location would minimize outside distractions. For many years, each of the three buildings had a handful of public phones and primitive paging system. This had the effect on cutting down on phone calls as well as occasional entertainment. I remember overhearing a call Murray Gell-Mann was having where he quipped, “I don’t know the English for it, but the Japanese is …” Physicists were (and still are) housed two to an office, with two desks, two chairs, a blackboard and a window. Seminars and discussions were held on a patio, originally unprotected from the elements with a small blackboard and within earshot of the Music Tent so that great physics ideas are sometimes accompanied by great music.
Equally important was doing all this in a place where physicists could bring their families along. As anyone who has ever visited knows, Aspen is a paradise with its outdoor activities, excellent restaurants, and good summer weather. The flip side is that the Center has had an image problem – sometimes viewed as the country club of summer institutes. The facts don't support this view – every summer about 1/3 of the participants attend for the first time, and while prices have risen from the early 1960s,when Aspen was still very sleepy during the summer months and rentals were cheap, the Center continues to get affordable rentals, in part because of its good reputation in town.
After starting the ACP, Stranahanmoved to Aspen and went on to do other things, though always watching after the Physics Center. He has been a cattle rancher (specializing in Limousin beef), started a microbrewery (Flying Dog), and established, a country day school in Woody Creek, where for years he has been the unofficial mayor. He founded the Woody Creek Tavern in 1980, a watering hole for locals and tourists of all kinds, including the late gonzo journalist Hunter S. Thompson who was a regular. Stranahan’s long relationship with Thompson included being his landlord and his prankster partner.
Getting established
Crucial to the success of Aspen was attracting the leaders of theoretical physics in order tomake the Center a “must-visit” summer venue. Three towering figures of 20th century physics played a big role in making Aspen successful: Phil Anderson, Hans Bethe, and Murray Gell-Mann. Each began coming to Aspen two years before he received the Nobel Prize. The trio set the scientific agenda, served as magnets to attract other top theorists and gave the ACP legitimacy. Any high-energy theorist would kill to come spend three weeks with Murray Gell-Mann, hearing what he thought was important and sharing his latest work with him. With his broad interests across physics, Bethe would help to get astrophysics going (more later). Anderson would shape condensed physics at Aspen for three decades.
Finding financial support for something new and different is never easy. Early grants from the Sloan and Needmor foundations were critical and Bethe donated part of his 1967 Nobel Prize money. (Bethe Hall, built in 1978 was named in his honor.) The turning point came in 1972, when the leaders of the Center convinced the National Science Foundation (NSF) to begin funding the Center, and NSF has been the primary source of support every since (currently at the level of $440K/year). Reviews over the years have often referred to this as the most cost effective program at NSF. Also important was the willingness of the government funding agencies to allow researchers to carry out their summer research for which they received “summer salary” in Aspen and to use research funds to defray travel.
In the mid 1990s, when the ACP was well established, University of Chicago astrophysicist David Schramm led a $3 million fund raising campaign that financed the final and largest building, Smart Hall, which completed the campus. The campaign hadbroad support not only from physicists and generous individuals in Aspen, but also the Smart Family Foundation of Connecticut.
More is different
Through his powerful intellect, strong views and great influence across the entire field, Phil Anderson has been a dominant figure in condensed matter physics for almost 50 years. His influential paper entitled More is Different [Science177, 393 (1972)] set the tone for the field and for the ACP. In counterpoint to the reductionist approach of particle physics where the quest is for evermore simplicity, condensed matter physics begins with the basic rules and studies the often unexpected, emergent phenomenon that arise in large systems with complicated interactions, such as superconductivity or even biological systems, an area of activity at the Center which has grown out of condensed matter physics.
David Pines of the University of Illinois at Urbana-Champaign and Elihu Abrahams of Rutgers Universitycame to Aspen a few years before Anderson,and have played crucial roles in building up condensed matter physics in Aspen. They recognized the importance of focused, multi-week workshops on the most exciting problems to attract talent, especially the young hotshots, and they worked to get attract a balance of university researchers and industrial lab researchers (mostly Bell Labs) where much of the talent in condensed matter physics was employed. A particular emphasis of the “Aspen school” was the investigation of strongly correlated electrons in metals. Work done at the ACP laid the foundations for understanding some of the mysterious properties of high-temperature superconductors (and other unconventional superconductors) that are so different from the usual BCS superconductors whose dynamics involve electron – phonon interactions.
From neutron stars to cosmology
In addition to Hans Bethe’s presence, the discovery of pulsars in 1967 and their identification as neutron stars shortly thereafter was crucial to getting astrophysics going. Neutron stars were rich with exciting physics – superfluidity and superconductivity, nuclear physics and general relativity. Pines, Gordon Baym, another Urbana theorist, and other condensed matter physicists were eager to understand the exotic physics of these objects and they needed astrophysicists. Moreover, the ACP was the perfect place to bring everyone together. Work done at the Center linked pulsar glitches to superfluidity within the neutron stars. In 1972, the National Aeronautics and Space Administration (NASA)began funding a yearly 3-week astrophysics workshop and astrophysics had a foothold in Aspen.
The rise of astrophysics to full parity with particle and condensed matter physics would involve University of Chicago physicist David Schramm and cosmology. Around 1980, Schramm and others began to realize that ideas in particle physics associated with unified theories could have profound cosmological implications and might revolutionize the sleepy field of cosmology, which had been the exclusive province of astronomers since the time of Hubble. Aspen with its interactive and informal environment would provide an incubator for this young, interdisciplinary field. Workshops were held almost every summer on the hot topics– big-bang nucleosynthesis, dark matter, inflation, large-scale structure, the cosmic microwave background, and cosmic strings – bringing together astronomers and physicists. Much of today’s consensus cosmology, with its particle dark matter, inflationary origins and dark energy can trace its roots to the Aspen Center for Physics. (In his Nobel Prize acceptance speech this past December, Adam Riess discussed how the High-z Redshift Team, which discovered that the expansion of the Universe is speeding up and not slowing down, regularly used the ACP to meet and plan their activities.) Conversely, cosmology was the vehicle for Aspen to “go big” in astrophysics.
Homeruns.
The number of papers attributed to visits to the Center is staggering – more than 10,000. But that doesn’t measure the real impact, the ideas that originated at the Center and changed the course of physics. Whether or not string theory is the theory of everything, it has changed the course of physics and has deep roots in Aspen. String theory began as a theory to describe the strong interactions between neutrons, protons and related particles, sometimes called the dual resonance model. Supersymmetry, the symmetry between bosons and fermions and a hallmark of today’s string theory, traces its origins to University of Florida theorist Pierre Ramond’s first summer in Aspen (1970), where as he put it, “he stopped calculating and started thinking” about the dual resonance model. When he got back to Fermilab, where he was a postdoc, he wrote the paper that added supersymmetry to string theory. (This is a typical pattern – think in Aspen, write at home.)
String theory was declared dead at 1974 Aspen workshop, having been beat out by Quantum Chromo-Dynamics (QCD) as the correct description of the strong (color) interactions between the constituents of the hadrons (quarks). A bold John Schwarz of Caltech doubled down: String theory is not the theory of the strong interactions, rather it is the theory that unifies the forces of the subatomic world with gravity! For the next ten years the Center would serve as the sanctuary for Schwarz, his collaborator Michael Green and a handful of others to try to make good on this promise. In the summer of 1984 the breakthrough came (cancellation of anomalies), triggering the first so-called string theory revolution.
The Green-Schwarz discovery was announced in grand fashion, at the second “Physics Cabaret” at the historic Hotel Jerome. In a skit where Schwarz played the role of Murray Gell-Mann, he rushes onto the stage to announce that he has discovered the theory of everything and that the Universe is ten dimensional; eventually, he is carried off the stage by a little man in a white coat. (The first Physics Cabaret in Aspen held in 1975, was inspired by Mildred Goldberger, wife of Princeton particle theorist Marvin Goldberger, who organized such events on the East Coast, including one at an American Physical Society meeting in New York where Tom Lehrer was featured. The 1975 Cabaret featured a skit that could have been the pilot for the US sitcom, The Big Bang Theory; in it, the young Edward Witten was seen picking up beautiful women in an Aspen bar.)