Science in Christian Perspective

A NEW AGE FOR THE UNIVERSE?
(A report by William H. Metz in Science 178, 600 (1972).
Copyright 1972 by the American Association for the Advancement of Science.

From: JASA 25 (June 1973): 66-67.

"It is my enormous pleasure to ask Allan Sandage to take us on a trip through that enormous dimension of time and space in which he feels at home"

-Martin Selswarzsehild, introducing the Henry Norris Russell lecturer, 138th meeting of the American Astronomical Society, Michigan State University, 15-18 August 1972.

The universe may have started with a big hang, or it may have always been in a steady state. There are few measurements of the nature of the universe, and the most important has been found greatly in error. Allan Sandage presented evidence for the big bang, and announced that new data on the time lapse since the initial explosion give an age for the universe that is consistent with the ages of life, the earth, and the stars. The well-known astronomer from Mt. Wilson and Palomar Observatories further predicted that within the next 10 years it may be possible to tell whether the universe will keep expanding forever or eventually slow down and contract.

Following the tradition of eminent astronomers such as Russell himself, who laid the groundwork for the understanding of stellar evolution, Sandage spoke eloquently and authoritatively. His presentation touched almost every point in modern cosmology; indeed, it seemed to signal that the study of the evolution of the universe had progressed a step closer toward becoming a full-fledged empirical science. However, some of the arguments made at the end of the talk were clearly speculative, arguments thought by some of the younger astronomers in the hall to be reminiscent of a grand but perhaps less rigorous age of astronomy.

Since Edwin Hubble established, in 1921, that the universe is expanding, it has been known that more distant galaxies recede faster. The constant of proportionality in the relation between the velocity and the distance of a galaxy (the Hubble constant) indicates an age for the universe under certain assumptions about the expansion. With the best techniques of his day, Hubble determined a constant which indicated an age of only 1.8 billion years. But even in the late 1930's this was known to be less than the age of the earth's crust. Either the simple "big bang" model was incorrect, or the Hubble constant was wrong. This famous discrepancy was a prime motivation for the "steady state" model developed by Hermann Bondi, Thomas Gold, and Fred Hoyle, which describes a universe that has no beginning or end, but continuously remakes itself according to a fixed and immutable pattern.

The original measurement of the bubble constant was in error. In fact, the Hubble constant has changed so often that it is a notable example of mutable constant. According to Sandage, "It has gone down linearly with tune," and has now reached a value that makes the age of the universe consistent with the age of its constituents. The most important announcement at the Russell lecture was that the new age of the universe, estimated from the remeasured Hubble constant, is 17.7 billion years, an age remarkably close to the best estimated age of the galaxies (12 to 15 billion years).

The Hubble constant is difficult to measure because there are random velocities of galaxies in addition to the velocities of expansion. Galaxies receding at such great speeds that these perturbations are insignificant are so far away that their distances are extremely difficult to measure. According to Sandage, "You have to look so far in order to see cosmological velocities that individual stars cannot be seen. So you have to devise a technique to bridge the gap between the place where precision indicators [of distance] exist and where the universe is really expanding without any perturbing effects."

Measurements of distance must be done in many successive steps, beginning with the calibration of Cepheid stars in our galaxy (a peculiar class of variable stars whose brightness can be determined by the cycle of variation in their intensities), next measuring the angular sizes of certain hydrogen regions in galaxies near ours, then using distances of further hydrogen regions to calibrate the absolute luminosities of galaxies having a cosmological velocity. Distance can be determined from absolute luminosities by the inverse square law.

In 1932, Hubble established a value of 530 kilometers per second per megaparsec as his constant (a megaparsec is about 3.3 million light years), but the scales of optical magnitude were not accurate for faint objects because certain nonlinearities in photographic plates were not understood. Furthermore, the absolute scale of Cepheid brightness was in error, as discovered by W. Baade in 1952. Correcting these two errors reduced the Hubble constant to about 265. In 1956, it was stated to be 180, the!) after corrections of Hubble's data for others errors, San-]age estimated in 1958 that the best value was 75. The value Sandage announced at the Russell lecture, based on the first complete remeasurement, was 55 ± 7. Sandage commented quite candidly on the contrast between his estimated error and the enormity of mismeasurement over the years.

Now that's an incredibly small error, 15 percent of the value. Hobble said his value was good to 15 percent also. HMS [Huiaason, Mayall, Sandage] said their value was good to 15 percent, and the value of 75 is good to 15 percent. Almost everybody, when (looting distances... quotes 15 percent. So that's kind of unrealistic, hot Martin Schwarzschild said today that one should always underquote the errors so as to give himself some enthusiasm to continue on with the problem.

The problem of the next 10 years, as Sandage sees it, is to look out to greater distances to see whether the linear relationship between the distance and velocity changes. The largest red shift used by Hubble or Sandage was 0.46, but Sandage thinks it will be possible to find the distances of certain galaxies with red shifts of 0.8 [The red shifts of some quasi-stellar objects (950's) are almost as great as 3.] The point of measuring objects with larger red shifts is that they may be far enough away so that the time for light to travel to us is a significant fraction of the age of the universe. If the universe is slowing down because of the braking action of its own gravitational farces, then the speeds of very distant galaxies will be observed as larger than one would expect because they would be observed at the expansion rate of an earlier age; in other words, the Hubble relationship would not be exactly linear. Thus, better data at large red shifts will allow astronomers to determine a second constant, called the deceleration parameter. In Friedmann's equation that describes many cosmological models, a deceleration parameter of -1 indicates a steady state universe, a value of + 1/2 indicates a flat Euclidean universe, and a value greater than + 1/2 indicates a universe that is decelerating and will eventually contract The best value available from the present data (1 ± 1) is not definitive, but slightly favors a "big bang" history for the universe.

After stating so succinctly the outstanding problem that must he solved to ascertain what the future of the universe will be, Sandage ventured the suggestion that there is already enough evidence to determine the past. Though many scientists have questioned whether the very large red shifts of QSO's are really indicative of velocities near the speed of light, Sandage presented some arguments in favor of the traditional interpretation. He then estimated that the light from 950's with the largest red shifts was emitted before 89 percent of the history of the universe had elapsed. Furthermore, data that Sandage presented in his talk suggested that the 200-inch Mount Palomar telescope should be able to detect 950's with red shifts larger than 3, but searches for objects listed in the 4th and 5th Cambridge catalogs of radio sources have not revealed any. Looking further out in space is equivalent to looking further back in time, and Saudagc suggests that suddenly the objects run out.

If one could substantiate that a red shut limit of 3 is real, have we actually observed the edge 0t the universe or the horizon of the universe in time? If so, this would be a fairly decent proof that the universe has not always been the way it is now, that it has evolved. This plus the agreement of time scales [the age of galaxies and the age of the universe] would sorely be an indication of an evolution: the world did begin.

While astronomers reared in the oriental cultures express very little interest in cosmology, scientists educated within the western Judeo-Christian tradition continue to be fascinated with questions about the origin of the world. The Russell lecture ended with a powerful allusion to the religious overtones of that fascination.

The best text that could be indicated here would be that in the beginning there was darkness upon the deep. There was light, and out of that light came everything that we now observe.

Astronomers, of course, will continue making observations.