The universe began with a big bang, according to modern science.
But the origin and ultimate fate of that primordial cosmic egg remains an embarrassing
riddle that has brought astronomers — unexpectedly and a bit reluctantly — straight
into the problem of the existence of a Creator God.
Albert Einstein once observed that "the most incomprehensible thing about the universe is that it is comprehensible." Not everyone would agree with that statement, for, although man has been fascinated by the grandeur and mystery of the universe for many millennia, its ultimate size, structure, and origin have remained an intriguing but unsolved riddle.
Historically, it seems that every culture has created a myth to explain the nature of the cosmos. The Greeks intertwined the creation of the world with the whims and family disputes of the gods. But our more sophisticated civilization may also have generated some myths of its own, impelled by our conviction that physical laws are universal and our hope that the universe, on a grand scale, is fundamentally simple and, as Einstein believed, comprehensible.
From ancient times until only half a century ago, the prevailing cosmological belief was that the universe must be unchanging. The universe, according to conventional wisdom, was essentially static — a system of planets, stars, and nebulae which, in the large, was somehow held in a fixed and orderly arrangement. Indeed, when Einstein first proposed his relativity model of the universe, he added a special factor known as the "cosmological constant," which allowed the universe to remain static despite the mutual gravitational attraction which would tend to make the universe collapse.
An Expanding Universe
Then, in the late 1920s, astronomer Edwin Hubble discovered that in every direction all the distant galaxies appeared to be moving away from the earth. This conclusion was based on the famous "red shift" in the spectrum of the light coming from the galaxies. Just as the sound coming from a train whistle or ambulance siren is lowered in pitch or frequency if the train or ambulance is traveling away from the hearer, so the light from distant galaxies is lowered in frequency (reddened) if the galaxy is traveling away from the earth.
When Hubble plotted the estimated distances to the various galaxies as a function of their apparent velocities (as implied by the "red shift"), he found an amazing correlation: The more distant a galaxy, the greater its velocity. The implication was clear: The universe was not static; the universe was expanding.
But if the universe was expanding, it must have been smaller in the past. By working backwards in time, it was easy to show that the universe must at one time have been highly compressed. From such reasoning came the concept that the universe started from a great explosion some billions of years ago. Astrophysicist George Gamow put it more poetically. "The universe," he said, "began with a big bang."
Steady State?
0f course, other models for the expanding universe were also possible. Astronomer Fred Hoyle, for example, accepted the expansion of the universe (the evidence seemed overwhelming), but he argued that new matter may be constantly introduced (by some as-yet-unknown process), so that new galaxies are constantly being formed. Thus creation was viewed as a "continuous process," and a specific unique "origin" of the entire universe was precluded.
Philosophically, Hoyle's steady state cosmology had a great appeal.
There was something very satisfying in the concept that the universe was eternal, having no beginning and no end. The theory also avoided the knotty problem of what the universe was like before the beginning, as well as the embarrassing conundrum of how the universe was able to achieve the highly compressed state needed for big bang cosmology — During the 1960s, however, the steady state theory was severely discredited as a great deal of new evidence came to light.
First, an extension of Hubble's observations of the expanding universe clearly implied that the expansion must have begun at a definite time in the past, about 10 to 20 billion years ago. Second, the older star clusters also seemed to be about 10 billion years old. And finally, radioactive elements appeared to have been in existence about 5 to 10 billion years. The close agreement of these three calculations derived by diverse methods appeared to be a striking corroboration of the big bang model of the universe: There was a beginning.
Another major blow to the steady state theory was the discovery, in 1965, of the so-called cosmic background radiation. This whisper of radiation appears to fill all of space in every direction, and its existence was in fact predicted by astronomers as a remnant of the original big bang. Its discovery was a powerful confirmation of the big bang model of the universe.
Other observations on the numbers and locations of radio sources and quasars further undermined the credibility of the steady state theory. The result was that by the 1970s virtually all astronomers had concluded that the steady state was wrong and that the big bang was essentially correct.
Open vs. Oscillating
There remained, however, a perplexing question. Would the universe expand forever, or would it eventually stop expanding and collapse, perhaps to be reborn in another big bang?
If the universe expands forever, this obviously implies that the creation of the universe was a unique, one-shot affair. The universe was created at a definite time in the past — some billions of years ago and is now in the process of expanding to infinity. We therefore live at a unique moment in the history of the cosmos.
On the other hand, if every expanding phase of the universe is eventually succeeded by a contracting phase, which is followed by an expanding phase, ad infinitum, then the concept of a unique creation event loses all meaning. Such an "oscillating universe" has much the same philosophical attraction as the steady state. Indeed, astronomers have found the oscillating universe theory so attractive and, for some reason, so comforting, that they often comment on the compelling "theological" arguments for such a universe.
Actually, the implications of a perpetually oscillating universe are profound, especially as they relate to the theory of evolution. In effect, an oscillating universe could totally demolish all arguments against evolution which are based on probability.
The logic is as follows: 1) If the universe contains a finite amount of matter, and 2) if the universe is endlessly oscillating (i.e., if the universe is infinitely old), then 3) since there is only a finite number of combinations for a finite number of atoms, it follows that 4) every conceivable combination must eventually be repeated an infinite number of times!
This is not a new concept. In fact, the philosopher Friedrich Nietzsche developed this principle in his "doctrine of eternal recurrence," a notion which he had encountered in the Pythagoreans. Nonetheless, the point is that no matter how improbable an event (other than zero probability), if we consider an infinite number of trials, the event becomes an absolute certainty. Applying this reasoning to the theory of evolution, it would mean that the evolution of life was inevitable.
Thus it is interesting that while secular astronomers may consider an oscillating universe a philosophical and even a theological necessity, religious fundamentalists must view the implications of an oscillating universe with a certain amount of skepticism if not consternation.
Critical Parameters
We are faced, therefore, with a most intriguing question. Is the universe in fact "open" — will it expand indefinitely? Or is the universe "closed" — will it eventually fall back on itself, perhaps to be reborn? To resolve the question, astronomers need to know the rate at which the universe is presently expanding and the rate at which the expansion is changing. If both these factors can be measured, then the past, present and future of the universe can be determined.
In the past few years, astronomer Allan Sandage and others have painstakingly developed various distance-estimating methods to a relatively high level of reliability. Plugging in the red-shift-determined velocities, astronomers find the universe is expanding at a rate of about 55 kilometers per second for every million parsecs of distance (a parsec is about 30 trillion kilometers or 19 trillion miles).
But remember that in the big bang model of the universe the expansion is expected to slow down with the passage of time as the initial velocities of the different parts of the universe are slowed down by their mutual gravitational attraction. The universe acts somewhat as does a ball thrown upward from the surface of the earth. The ball slows down, stops, and eventually falls back to earth. If it is thrown with greater initial velocity, it travels farther before falling back. But, if the initial velocity is greater than what is called the "escape velocity," then the ball will never fall back but will travel upward forever, decelerating continuously as it goes, but never coming back.
If the planet from which the ball is thrown is more massive than the earth, we would expect its gravitational attraction to be greater and thus the escape velocity would need to be greater. For the expanding universe, a similar reasoning applies: There is the possibility that the expansion will stop and eventually reverse itself, or that it will continue indefinitely.
Obviously, the deciding factor is whether there is enough mass in the universe so that gravitational attraction will eventually overcome the expansion. The amount of mass in the universe is clearly related to the average density of the universe, and it turns out that the "critical density" needed to eventually stop the universe's expansion is only about four hydrogen atoms per cubic meter. This number may seem incredibly small, and, indeed, it represents a far better vacuum than the most sophisticated scientific instruments can produce. But the universe is inconceivably large, so the total amount of matter represented by such a density is very great. Now, if the actual density of the universe is smaller than the critical value, then the universe will expand forever; conversely, if the actual density is higher than the critical value, the universe will eventually contract, and everything will be squeezed in what some astronomers call the "big crunch."