The formal inauguration of the Center for Theoretical Physics at the University of Michigan brought together distinguished speakers from a range of disciplines to look back on the achievements of physics in the 20th century, as well as to anticipate new developments in the 21st.
In the beginning…
“Returning to my Ann Arbor attempts, I became immediately very eager to see how far the mentioned analogy reached, first trying to find out whether the Maxwell equations for the electromagnetic field, together with Einstein’s gravitational equations, would fit into a formalism of five-dimensional Riemann geometry.”
Oskar Klein, “From my life of physics” in the anthology From a Life of Physics (1989 World Scientific).
The inaugural conference of the Michigan Center for Theoretical Physics (MCTP), entitled 2001: a Spacetime Odyssey, was held in Ann Arbor on 21-25 May. In keeping with the MCTP’s mission to provide a venue for interdisciplinary studies in theoretical physics and related mathematical sciences, the conference brought astronomers, cosmologists, particle physicists and mathematicians together to share their different perspectives on space-time at the beginning of the 21st century.
Two theories revolutionized the 20th-century view of space and time: quantum mechanics and Einstein’s General Theory of Relativity. The union of these theories provides a context for elem-entary particle theories with extra space-time dimensions, such as the inflationary model of Big Bang cosmology; dark matter and dark energy in the universe; radiation from quantum black holes; and the fuzzy space-time geometry of superstrings and M theory. These developments, which are derived in part from the 19th-century mathematics of Riemannian geometry and Lie groups, have in their turn inspired new directions in the pure mathematics of topology and knot theory. All of these different strands of the space-time story were represented at the conference.
The dawn of space-time
Ann Arbor was a particularly appropriate place for such a celebration because it was here that Oskar Klein first came up with the idea of extra space-time dimensions and of using Riemmanian geometry to explain not only gravity but also electromagnetism.
The conference began with “My life as a boson”, a historical recollection by Peter Higgs (Edinburgh) on the discovery of the particle that bears his name. Higgs described the history leading up to his 1964 paper, the controversy over the Goldstone theorem, and some interesting reactions to his paper. Only after Physics Letters had rejected his original version did Higgs produce a revised text predicting the existence of the new particle, which was then accepted by Physical Review Letters. He ended his talk with the hopeful mention of “indications of H at about 115 GeV” at CERN’s LEP electron-positron collider.
Joseph Silk (Oxford), Robert Kirshner (Harvard-Smithsonian Center for Astrophysics), Alan Guth (MIT), Paul Steinhardt (Princeton), Andre Linde (Stanford), Wendy Freedman (Carnegie Observatories) and Michael Turner (Chicago) each offered different perspectives on the universe. While new data pinpoint cosmological parameters with more and more accuracy, and evidence for the current acceleration of the expansion of the universe and the mysterious “dark energy” now seems convincing, controversy over their origins continued to swirl with Steinhardt’s presentation of the novel “ekpyrotic” alternative to inflation. Inspired by the Horava-Witten picture of an 11-dimensional M-theory universe sandwiched between two 10-dimensional boundaries, this scenario ascribes the Hot Big Bang to a smashing together of two three-dimensional surfaces (three-branes) in a five dimensional universe: the Big Crash.
Linde championed the old inflation with a vigorous deflation of Steinhardt’s ideas. Freedman then reported a new result – the first measurement of extragalactic background light, which turned out to be about twice that of individual galaxies. The mass associated with starlight was thus measured to be about 1% of critical density. Guth emphasized the evidence for inflation and its robustness.
Shing-Tung Yau (Harvard), Isadore Singer (MIT), Arthur Jaffe (Harvard) and Bruno Zumino (Berkeley) gave us a glimpse into the realm of higher mathematics and its intriguing applications to problems in quantum field theory, superstrings and M-theory. For Singer, this was a sentimental journey, and he recalled his arrival as an undergraduate in physics at the University of Michigan in 1941. Checking into his dormitory, he was told to go upstairs and make his bed. Sure enough, he discovered a hammer, some nails and a pile of two-by-four planks where his bed was supposed to have been.
Quantum gravity was the common theme of talks by James Hartle (UC Santa Barbara), Jacob Beckenstein (Jerusalem) and Stanley Deser (Brandeis). Hartle discussed the reconciliation of Einstein’s general relativity with quantum mechanics, including the many-worlds interpretation, wormholes in space and the possibility of time travel. Beckenstein presented the case for discrete energy levels for quantum black holes as a way of understanding their thermodynamics, which was pioneered by him and Hawking in the 1970s; and Deser gave an overview of gravity’s century, from Einstein to M-theory.
Discoveries overlooked
Particle phenomenology was covered by Lev Okun (ITEP, Moscow), John Bahcall (Princeton IAS), Helen Quinn (SLAC), Mary K Gaillard (Berkeley), Paul Frampton (North Carolina, Chapel Hill) and Martinus Veltman (Michigan). Okun recalled his early days in Moscow, the discoveries made there, such as the calculation of asymptotic freedom by Khriplovich in 1969 and the reaction (or lack thereof) in the West. He also recalled Sakharov’s reaction to the possibility of vacuum bubble creation by colliders: “Such theoretical work should be forbidden.”
Bahcall presented an overview of our understanding of solar neutrinos and described how upcoming data, particularly from SNO would sharpen it (as indeed happened soon after the conference)
Quinn reviewed the theoretical status of CP violation and current attempts to test it experimentally, while Frampton presented a model of spontaneous CP violation. Gaillard put the case for a derivation of the Standard Model from the compact-ification of the 10-dimensional heterotic string on a six-dimensional Calabi-Yau manifold. Veltman was broadly critical of current research directions, casting doubt on black holes, the acceleration of the universe and superstring theory, although he was positive about the construction of the superconducting Tesla linear electron collider. <textbreak=Superstrings>Superstring theory and its successor, M-theory, were covered by John Schwarz (Caltech) and Alexander Polyakov (Princeton). Schwarz re-viewed the phenomenon of anomaly cancellation from the Standard Model to the superstring, while Polyakov discussed the Plato’s cave “holographic” universe, in which our four-dimensional space-time is a boundary of a five dimensional anti-de Sitter space.
One of the missions of the MCTP is to convey the excitement of physics to the general public. The 2001: A Spacetime Odyssey conference achieved this very successfully with the collaboration of the Physics Department and the School of Art and Design at the University of Michigan. Ten new works by professional artists, with inspiration from physicists, were created for exhibition at the conference.
Most speakers agreed that participating in such a meeting had broadened their horizons, and perhaps even influenced their work. In his after-dinner speech at the conference banquet, Sheldon Glashow (Boston) assessed the current state of particle and astrophysics, and whether society cared enough to sustain it. After a good meal and fine wine, the future looked rosy.
