Measuring the Mass of the Universe
But how do we find the mass of the universe? Probably the most obvious method is to simply count up all the galaxies we can see and estimate their mass. The astronomer J. H. Oort did just that about fifteen years ago, and he found that the mass of all the matter in galaxies was only about one percent of the amount needed to "close" the universe. Since that time, many researchers have attempted to find "the missing mass."
Astronomer J. R. Gott and others have made refined measurements of the mass of galaxies. Their "dynamical" method implies that galaxies may have a great deal of mass that telescopes cannot see. Yet, even with this more exact method, the density of the universe is still nowhere near the critical value. In fact, the density they find is only about five percent of the critical value.
Other studies indicate that galaxies are associated with an amount of mass some ten times larger than the mass in the visible parts of the galaxies themselves. But this mass is still at least ten times too small to stop the expansion of the universe. Of course, there is always the possibility that additional mass exists between the clusters of galaxies, but so far no one has been able to detect an appreciable amount.
Another method for estimating the mass and density of the universe is based on the abundance of the element deuterium — a form of hydrogen with one proton and one neutron. Deuterium was presumably made in the early history of the universe, as were a number of other elements. But the abundance of deuterium today is thought to be directly related to the density of the early universe. In other words, if we knew the present abundance of deuterium, we could calculate the original density of the universe, which would in turn give us a good idea of what the present density is. Recently, astronomers have used satellites to measure the amount of deuterium in interstellar space, and they find that the density corresponding to the observed amount of deuterium is very low, indicating that the universe will expand forever.
Similar studies all seem to point to one conclusion. The expanding universe began at a definite moment in time about 18 billion years ago and will apparently never contract. The universe will thus end, not with a big crunch, but with a whimper.
Telescopic Time Machine
But if all these measurements indicate that the density of the universe is small, and that the universe will thus expand forever, then why is it that astronomers have often considered the universe to be oscillating and thus closed?
The answer is that for years Sandage and other astronomers used the "classical" method of determining the deceleration of the universe. This method was simply a plot of dimness (distance) of galaxies against red shift (velocity). If the universe acts like an explosion, we would expect a straight line for such a plot, the objects farthest away having the greatest velocity (red shift).
However, when we view distant galaxies, we are actually looking back in time. Like a time machine, telescopes reveal the galaxies as they were billions of years ago, traveling at very high velocities because they haven't yet been slowed down by the gravitational attraction of the rest of the universe. Therefore, the distant galaxies should show a deviation from the expected red shift, i.e., their red shifts should be too high for their distance, when compared with nearby galaxies.
By measuring these deviations, Sandage was able to calculate the amount of deceleration the universe has experienced. The universe appeared to be slowing down rapidly, and ultimately it was expected to reverse its motion and collapse (and possibly begin another expansion).
Unfortunately, Sandage's method makes a very tenuous assumption: It assumes that the brightness of galaxies does not change over their lifetimes. But if galaxies evolve and get old, then they were probably brighter in the past, when their stars were still young and bright. Therefore, the distant galaxies we see may actually be farther away than we thought. This implies that their red shifts may not be disproportionately higher than nearby galaxies and that the universe has not been slowing down appreciably. When Sandage's calculations take this effect into account, he obtains a value for the deceleration near zero. So again, the universe will apparently never contract, but will continue to expand. According to the latest available evidence, the stars and galaxies of the universe will disperse forever until all is darkness and emptiness.
The Immortal Universe Dead?
This result — that the universe had only one (bright and awesome) beginning and that it will have only one (dark and dismal) end — is profoundly disturbing to many scientists, astronomers, and laymen alike. For many, the latest conclusions of modern astronomical science simply cannot be — or should not be — true.
"This expansion is such a strange conclusion," says Sandage. "One's first assumption is that it cannot really be true, and yet it is the premier fact." For modern nonreligious thinkers, there was great comfort in a secular immortality of the universe, a grand system without beginning or end, which could be achieved through the steady state or oscillating universe theories. But the triumph of the big bang cosmology has not only pointed to a definite beginning for the universe, but to an inevitable end as well. The universe not only is not immortal, its life span appears to be rather clearly defined.
The new cosmology is also very unsettling because it brings us face to face with the fundamental riddle of ultimate origins. As long as the universe could be plausibly said to be eternal, the question of origins could be pushed into the remote past, or perhaps dismissed, by simply saying the universe always existed., But the big bang cosmology has placed definite limits on the age of the universe, and the question of origins can no longer be easily avoided.
Perhaps this is what bothered Einstein, who, when he considered the implication of the expanding universe, wrote: "This circumstance of an expanding universe is irritating. . . . To admit such possibilities seems senseless to me."
Stated the famed Harvard astronomer Harlow Shapely: "In the beginning was the word, it was piously recorded, and I might venture that modern astrophysics suggests that the word was hydrogen gas." But in his book View from a Distant Star, Shapely was quick to note: "Whence came these atoms of hydrogen . . . what preceded their appearance, if anything? That is perhaps a question for metaphysics. The origin of origins is beyond astronomy. It is perhaps beyond philosophy, in the realm of the to us Unknowable."
A Limit to Cause and Effect
The big bang cosmology is also frustrating because it points to what may be a fundamental limit on the scientific concept of cause and effect. Questions concerning the prior history of the universe cannot be answered because in the first moments of its present existence the virtually infinite temperatures and pressures of the primeval cosmic egg would presumably have destroyed every particle of evidence that could have provided a clue to the cause of the great explosion. Such questions as "What was the universe like before the big bang?" may forever lie behind the insurmountable barrier of the moment of creation. "It is not a matter of another year, another decade of work, another measurement, or another theory," contends Dr. Robert Jastrow, director of NASA's Goddard Institute for Space Studies. "At this moment it seems as though science will never be able to raise the curtain on the mystery of creation."
Still another reason for why astronomers are irritated over the evidence for an expanding universe is that it seems to violate the spirit of Copernicus. Nicolaus Copernicus (1473-1543) is usually credited with being the first to propose that the earth was not the center of the universe. At the time, his suggestion that the sun, not the earth, was actually the center of the universe sounded dangerously heretical. But in the ensuing centuries, the sun too was dethroned from its alleged special position, as was our Milky Way galaxy and even our local group of galaxies. As a result, by the mid-twentieth century the official dogma of astronomical science was that there is no place in the universe which is the center of the universe and that the universe will look basically the same no matter where an observer is located.
The concept that there is no unique place in the universe is often extended to include time as well (i.e., that the universe also looks the same no matter when an observer looks). But this is incompatible with the big bang cosmology which specifically states that the universe did indeed look much different in the past and will look much different in the future.
"How can we believe," asks Massachusetts Institute of Technology astrophysicist Phillip Morrison, "that just a few billion years ago the universe was totally different from what we see today? I find it hard to accept the big bang theory. I would like to reject it." Yet the evidence is that we do indeed live at a unique moment in the life of the universe.
Finally, the new big bang cosmology has proved unnerving because in establishing that the universe had a definite moment of creation, astronomers have been brought — somewhat unexpectedly and a bit reluctantly straight into the problem of the existence of a Creator God.
"Consider the enormity of the problem," says Jastrow. "Science has proven that the universe exploded into being at a certain moment. It asks, 'What cause produced this effect? Who or what put the matter and energy into the universe?' "
Observes Dr. Jesse L. Greenstein, astrophysicist at the California Institute of Technology: "It is a terrible mystery how matter comes out of nothing. Could it have been something outside science? We try to stay out of philosophy and theology, but sometimes we are forced to think in bigger terms, to go back to something outside science."
Perhaps the supreme irony of modern cosmology is that the facts of science, so often considered a threat to belief in God and religion, are in fact providing a remarkable confirmation of the Genesis account: "In the beginning God created the heaven and the earth."