Proc. Natl. Acad. Sci. USA Vol. 90, p. 4765, June 1993 Colloquium Paper

This paper serves as an introduction to the following papers, which were presented at a colloquium entitled "Physical Cosmology," organized by a committee chaired by David N. Schramm, held March 27 and 28, 1992, at the National Academy of Sciences, Irvine, CA.

Physical cosmology DAVID N. SCHRAMM Department of Astronomy and Astrophysics, The University of Chicago, Chicago, IL 60637

The Colloquium on Physical Cosmology was attended by 180 much notoriety. The recent report by COBE of a small cosmologists and science writers representing a wide range of primordial anisotropy has certainly brought wide recognition scientific disciplines. The purpose of the colloquium was to to the nature of the problems. The interrelationship of address the timely questions that have been raised in recent structure formation scenarios with the established parts of years on the interdisciplinary topic of physical cosmology by the cosmological framework, as well as the plethora of new bringing together experts of the various scientific subfields observations and experiments, has made it timely for a that deal with cosmology. high-level international scientific colloquium on the subject. Cosmology has entered a "golden age" in which there is a The papers presented in this issue give a wonderful mul- tifaceted view of the current state of modem physical cos- close interplay between theory and observation-experimen- mology. Although the actual COBE anisotropy announce- tation. Pioneering early contributions by Hubble are not ment was made after the meeting reported here, the following negated but are amplified by this current, unprecedented high papers were updated to include the new COBE data. In fact, level of experimental and observational information on cos- a report from the COBE team is also included. Thus, the mological problems. The probes of cosmology are multidis- material presented here is truly "state of the art." ciplinary, with particle accelerators and particle detectors This colloquium was the third such event sponsored by the now joining telescopes in various wavelength regimes as Academy under a new program aimed at fostering academic means to probe our universe. For example, experiments in gatherings of scientists in active, interdisciplinary research. elementary particle physics not only constrain the candidates The colloquium was organized by a committee consisting of for cosmological dark matter but also test the predictions of David N. Schramm (University of Chicago, Chairman), cosmological nucleosynthesis. Such experiments are being P. J. E. Peebles (Princeton University, Cochairman), Sandra carried out both at accelerators and in new underground Faber (University of California, Santa Cruz), Riccardo Gio- observatories. New generations of experiments will begin vanelli (Cornell University), Alan Guth (Massachusetts In- investigating the Higgs sector, which may be intimately stitute of Technology), and Bernard Sadoulet (University of related to fundamental cosmological processes such as "In- California, Berkeley) and was planned by a program com- flation." mittee comprised of George Efstathiou (University of Ox- Astronomical observations from new dedicated ground ford), John Ellis (European Center for Nuclear Research), based observatories, as well as new instruments in space, Margaret Geller (Harvard University), Bernard Pagel (NOR- measure the expansion of the universe and map out giant DITA, Copenhagen), Martin Rees (University of Cam- large-scale structures made of thousands of galaxies. Radio, bridge), Rashid Sunyaev (Space Research Institute, Mos- cow), Brent Tully (Institute for Astronomy, University of infrared, ultraviolet, x-ray, and y-ray observations supple- Hawaii), Nicola Vittorio (University of Rome), and David ment the traditional optical observations. The microwave Wilkinson (Princeton University). background is being explored from the currently orbiting Originally aimed at a group of 60-70 participants in addi- Cosmic Background Explorer (COBE) satellite as well as tion to the speakers and session chairmen, the concept balloons and, most recently, in a new center being built at the proved so attractive that the event drew twice the planned South Pole. number of participants, including members of the scientific Theories to explain the observations incorporate aspects of press. It was the largest group ever served by the Academy's plasma physics, nuclear physics, particle physics, atomic Beckman Center. The timeliness and availability ofnew data physics, and condensed matter physics, as well as astrophys- (as well as rumors of soon-to-be-announced data) made for ical and gravitational physics. The controversy on how to one of the most stimulating conferences in the field. In fact, form structures rapidly in a universe that shows extraordi- it was so appealing that Sir Martin Rees postponed his nary smoothness in its background radiation has achieved audience to be knighted by the Queen of England in order to be able to participate in this meeting. One science reporter The publication costs of this article were defrayed in part by page charge commented that the high level of the participants made this payment. This article must therefore be hereby marked "advertisement" conference a modem cosmological analogue to the famed in accordance with 18 U.S.C. §1734 solely to indicate this fact. Solvay Conference in the first part of the century.

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