First Scientific Argument: The Expansion of the Universe
By William Lane Craig
CBN.com Excerpted with permission from On Guard: Defending Your Faith with Reason and Precision
One of the most astonishing developments of modern astronomy, which Ghazali would never have anticipated, is that we now have strong scientific evidence for the beginning of the universe. Yes, science provides some of the most dramatic evidence for the second premise of the kalam cosmological argument. The first scientific confirmation of the universe’s beginning comes from the expansion of the universe.
The “Big Bang”
All throughout history men have assumed that the universe as a whole was unchanging. Of course, things in the universe were moving about and changing, but the universe itself was just there, so to speak. This was also Albert Einstein’s assumption when he first began to apply his new theory of gravity, called the general theory of relativity, to the universe in 1917.
But Einstein found there was something terribly amiss. His equations described a universe that was either blowing up like a balloon or else collapsing in upon itself. Perplexed, Einstein “solved” the problem by fudging his equations, adding a new term to enable the universe to walk the tightrope between exploding and imploding.
During the 1920s the Russian mathematician Alexander Friedman and the Belgian astronomer Georges Lemaître decided to take Einstein’s equations at face value, and as a result they came up independently with models of an expanding universe. In 1929 the American astronomer Edwin Hubble, through tireless observations at Mount Wilson Observatory, made a startling discovery that verified Friedman and Lemaître’s theory. He found that the light from distant galaxies appeared to be redder than expected. This “redshift” in the light was most plausibly due to the stretching of the light waves as the galaxies move away from us. Wherever Hubble trained his telescope in the night sky, he observed this same redshift in the light from the galaxies. It appeared that we are at the center of a cosmic explosion, and all of the other galaxies are flying away from us at fantastic speeds!
Now according to the Friedman-Lemaître model, we’re not really at the center of the universe. Rather an observer in any galaxy will look out and see the other galaxies moving away from him. There is no center to the universe. This is because, according to the theory, it’s really space itself that is expanding. The galaxies are actually at rest in space, but they recede from one another as space itself expands. To get a picture of this difficult idea, imagine a balloon with buttons glued to its surface. The buttons are stuck to the surface of the balloon and so don’t move across the surface. But as you blow up the balloon, the buttons will grow farther and farther and farther apart because the balloon gets bigger and bigger. Notice that there’s no center of the balloon’s surface. (There is a center point inside the balloon, but we’re focusing just on the surface of the balloon.) But an observer on any button will feel as if he were at the center of the expansion because he’ll look out and see the other buttons all moving away from him.
Now the two-dimensional surface of the balloon serves as an illustration of our three-dimensional space, and the buttons represent the galaxies in space. The galaxies are actually at rest in space, but they recede from one another as space itself expands. Just as there is no center of the balloon’s surface, so there is no center of the universe.
The Friedman-Lemaître model eventually came to be known as the big bang theory. But that name can be misleading. Thinking of the expansion of the universe as a sort of explosion could mislead us into thinking that the galaxies are moving out into a preexisting, empty space from a central point. That would be a complete misunderstanding of the model. The big bang did not occur at some point in a preexisting, empty space.
(You might say, “But what about the central point in the interior of the balloon?” Ah, you’re forgetting that it’s the surface of the balloon that is the analogy to space! The balloon’s two-dimensional surface happens to exist in a three-dimensional world, into which it is expanding. But in the Friedman-Lemaître model, there is no higher, fourdimensional world into which our three-dimensional space is expanding. So there’s just nothing corresponding to the space outside or inside the balloon.)
So we mustn’t be misled into thinking of the big bang as the explosion of a superdense pellet of matter into empty space. The theory is much more radical than that.
The Beginning of Time
As you trace the expansion of the universe back in time, everything gets closer and closer together. If our balloon had no minimum size but could just keep shrinking and shrinking, eventually the distance between any two points on the balloon’s surface would shrink to zero. According to the Friedman-Lemaître model, that’s what happens to space as you go back in time. Eventually the distance between any two points in space becomes zero. You can’t get any closer than that! So at that point you’ve reached the boundary of space and time. Space and time can’t be extended any further back than that. It’s literally the beginning of space and time.
To get a picture of this we can portray our three-dimensional space as a two-dimensional surface that shrinks as you go back in time.
Eventually, the distance between any two points in space becomes zero. So space-time can be represented geometrically as a cone. What’s significant about this is that while a cone can extend indefinitely in one direction, it has a boundary point in the other direction. Because this direction represents time and the boundary point lies in the past, the model implies that past time is finite and had a beginning. Because space-time is the arena in which all matter and energy exist, the beginning of space-time is also the beginning of all matter and energy. It’s the beginning of the universe.
Notice that there’s simply nothing prior to the initial boundary of spacetime. Let’s not be misled by words, however. When I say, “There is nothing prior to the initial boundary,” I do not mean that there is some state of affairs prior to it, and that is a state of nothingness. That would be to treat nothing as though it were something! Rather I mean that at the boundary point, it is false that “There is something prior to this point.”
The standard big bang model thus predicts an absolute beginning of the universe. If this model is correct, then we have amazing scientific confirmation of the second premise of the kalam cosmological argument.
Is the Standard Model Correct?
So is the model correct, or, more importantly, is it correct in predicting a beginning of the universe? We’ve already seen that the redshift in the light from distant galaxies provides powerful evidence for the big bang. In addition, the best explanation for the abundance in the universe of certain light elements, such as helium, is that they were formed in the hot, dense big bang. Finally, the discovery in 1965 of a cosmic background of microwave radiation is best explained as a vestige of the big bang.
Nevertheless, the standard big bang model needs to be modified in various ways. The model is based, as we’ve seen, on Einstein’s general theory of relativity. But Einstein’s theory breaks down when space is shrunk down to subatomic proportions. We’ll need to introduce subatomic physics at that point, and no one is sure how this is to be done. Moreover, the expansion of the universe is probably not constant, as in the standard model. It’s probably accelerating and may have had a brief moment of super-rapid expansion in the past.
But none of these adjustments need affect the fundamental prediction of the absolute beginning of the universe. Indeed, physicists have proposed scores of alternative models over the decades since Friedman and Lemaître’s work, and those that do not have an absolute beginning have been repeatedly shown to be unworkable. Put more positively, the only viable nonstandard models are those that involve an absolute beginning to the universe. That beginning may or may not involve a beginning point. But theories (such as Stephen Hawking’s “no boundary” proposal) that do not have a pointlike beginning still have a finite past. The universe has not existed forever, according to such theories, but came into existence, even if it didn’t do so at a sharply defined point.
In a sense, the history of twentieth-century cosmology can be seen as a series of one failed attempt after another to avoid the absolute beginning predicted by the standard big bang model. Unfortunately, the impression arises in the minds of laymen that the field of cosmology is in constant turnover, with no lasting results. What the layman doesn’t understand is that this parade of failed theories only serves to confirm the prediction of the standard model that the universe began to exist. That prediction has now stood for over eighty years throughout a period of enormous advances in observational astronomy and creative theoretical work in astrophysics.
Indeed, something of a watershed appears to have been reached in 2003, when three leading scientists, Arvind Borde, Alan Guth, and Alexander Vilenkin, were able to prove that any universe that has, on average, been expanding throughout its history cannot be infinite in the past but must have a past space-time boundary.
What makes their proof so powerful is that it holds regardless of the physical description of the very early universe. Because we can’t yet provide a physical description of the very early universe, this brief moment has been fertile ground for speculations. One scientist has compared it to the regions on ancient maps labeled “Here there be dragons!”—it can be filled with all sorts of fantasies. But the Borde-Guth-Vilenkin theorem is independent of any physical description of that moment. Their theorem implies that even if our universe is just a tiny part of a so-called multiverse composed of many universes, the multiverse must have an absolute beginning. Vilenkin is blunt about the implications:
It is said that an argument is what convinces reasonable men and a proof is what it takes to convince even an unreasonable man. With the proof now in place, cosmologists can no longer hide behind the possibility of a past-eternal universe. There is no escape: they have to face the problem of a cosmic beginning.
We can fully expect that new theories will be proposed, attempting to avoid the universe’s beginning. Such proposals are to be welcomed, and we have no reason to think that they’ll be any more successful than their failed predecessors. Of course, scientific results are always provisional. Nevertheless, it’s pretty clear which way the evidence points. Today the proponent of the kalam cosmological argument stands comfortably within the scientific mainstream in holding that the universe began to exist.
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