By George B. Field
Center for Astrophysics, Harvard College Observatory
and Smithsonian Astrophysical Observatory
Cambridge, Massachusetts

The present book grew out of a Symposium of the American Association for the Advancement of Science, "Redshifts of Galaxies and Quasars," which took place on December 30, 1972, in Washington, D.C.

In the past few years some astronomers have become increasingly convinced that there is something basically wrong with the conventional picture of the Universe. They question whether the redshifts of all galaxies are really due to the expansion of the Universe, as has been accepted since the 1920's. They believe that at least some redshifts are discordant, in that they cannot be attributed to the expansion. If they are right, modern cosmology is called into question. Dr. Halton Arp, an astronomer at the Hale Observatories in Pasadena, has developed this point of view.

Other astronomers have vigorously defended the conventional interpretation of redshifts. However, there have not been many opportunities for a direct confrontation of the two viewpoints in an open meeting. As chairman of the Astronomy Section of the A.A.A.S. for 1972, I thought it would be interesting and worthwhile to arrange a debate on the redshift controversy, and I invited Dr. Arp and Dr. John Bahcall to participate. Dr. Arp is well known for his work on globular clusters, stellar photometry, and unusual galaxies. Dr. Bahcall, a theoretical astrophysicist at the Institute for Advanced Study in Princeton, has an extensive background in neutrino astronomy, stellar structure, and the physics of quasars. Recently both Dr. Arp and Dr. Bahcall have been working actively on extragalactic problems. Both Dr. Arp and Dr. Bahcall have in the past been awarded the Warner Prize for excellence in research by the American Astronomical Society.

While a number of possible theoretical explanations of anomalous redshifts have been proposed, the participants agreed that there is little profit in debating them as long as the interpretation of the observations is disputed. We therefore agreed to focus the debate on observational evidence. Each participant spoke for 45 minutes and had opportunity for rebuttal. The floor was then opened for what turned out to be a lively discussion.

The present volume contains the material presented at the debate, as well as reprints selected by the participants to illustrate their points. Our purpose in publishing this volume is, first of all, to stimulate further research in this area. If Dr. Arp's interpretation is correct, a revolution in astronomy, and perhaps in physics, is in the offing. If, on the other hand, Dr. Bahcall's analysis is correct, then scientific progress would be served by a disproof, which may be stimulated by discussion of this kind.

Our other goal is to illustrate for students of astronomy the ambiguity which sometimes besets astronomical research. While students sometimes get the impression that questions have simple yes-or-no answers, working astronomers know that one can often reply only "probably" or "perhaps" to current questions. The redshift controversy should be understandable to students with relatively little background and we hope this book will be useful to them. We believe that the addition of selected preprints will aid in understanding the background of the controversy. In addition, students as well as experienced professional astronomers will enjoy reading some of the basic papers in extragalactic astronomy.

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