Explaining the Low-Entropy Condition
Several hypotheses have been proposed to explain the low-entropy condition of the early universe. One idea, called the inflation hypothesis, is that some unknown force rapidly stretched out the structure of space itself shortly after the universe began. This stretching of space helped to smooth out the distribution of matter and energy, which resulted in a state of lower entropy. In some thermodynamic systems (like the room full of air), a smooth distribution corresponds to a state of higher entropy; but when the dominant force is attractive, smoother distributions have lower entropy. Gravity tends to clump things together, so a smooth distribution of matter is farther from equilibrium when gravity is the dominant force. Thus, the rapid expansion of the universe effectively converted high-entropy states into low-entropy ones.
However, some controversy has arisen concerning this putative explanation. The details of the controversy are complicated, but the basic problem is that the explanation relies on assumptions that cannot be justified without presupposing the very thing that we are trying to explain! Thus the inflation hypothesis, even if true, doesn’t provide a genuine explanation for the low-entropy condition of the early universe.For further discussion of this problem, see Huw Price, “Cosmology, time’s arrow and that old double standard,” in Time’s Arrows Today, ed. Steven F. Savitt (Cambridge: Cambridge UP, 1995), 66-94.
Another controversial hypothesis suggests that the universe goes through cycles of high and low entropy. The standard model used in contemporary cosmology holds that the universe began with an explosion called the “Big Bang.” Some cosmologists have suggested that the universe might similarly end with an implosion—a “Big Crunch”—and the whole thing will start over again. This cyclic universe hypothesis is fascinating, but evidence from cosmology suggests that the universe will continue to expand forever. (See chapter 8.) Moreover, even if the universe did collapse in a Big Crunch, the collapse wouldn’t lower its entropy. A Big Crunch would result in a very clumpy final state, quite unlike the smooth condition of the early universe. Despite these problems, some physicists and cosmologists remain optimistic that a cyclic model of the universe might explain how it begins (again and again) in a condition of low entropy. Penrose has recently suggested that the universe might go through cycles even if it never re-collapses. Perhaps high-entropy conditions in the distant future will trigger a new Big Bang, and perhaps the last Big Bang was likewise preceded by a condition of high entropy, he speculates.Roger Penrose, Cycles of Time: An Extraordinary New View of the Universe (New York: Knopf, 2011) It remains to be seen whether this sort of non-collapsing cyclic model will hold up to scrutiny, but don’t hold your breath.
Yet another hypothesis says that our universe is just one of many universes—perhaps infinitely many—that comprise a “multiverse.” If there are sufficiently many universes, the fact that ours began in a state of low entropy can be explained as follows. Although a low-entropy state is unlikely to occur in any particular universe, it is bound to happen in a few universes, since there are so many. And it’s no surprise that we should find ourselves in one of the rare universes that began in a low-entropy state, the explanation continues. Biological organisms can’t survive in an environment where everything is at or near equilibrium! The existence of life depends on low-entropy conditions. Therefore, organisms like ourselves can exist only in universes like this one, and that’s why we find ourselves in such a special universe.
This multiverse hypothesis is wildly speculative, at best, but it is surprisingly popular among cosmologists today. The most attractive feature of the hypothesis is that it can easily explain why our universe began in a state of low entropy, simply by appealing to the so-called anthropic principle—the trivially true claim that all observers find themselves in places where their own existence is possible.
Some versions of the multiverse hypothesis speculate that all of the universes, including ours, exist together within extra dimensions of space and time that we do not perceive. If that is correct, then other universes might produce effects that could be detected in our universe. However, no such effects have yet been detected, and there isn’t much reason to expect that any ever will be.
On the other hand, the multiverse hypothesis suffers from numerous scientific and philosophical problems. Some of these problems are rather technical, and I won’t try to explain all of them here. But one major problem is easy to understand: other universes cannot be observed. Even if other universes exist, there is no way to detect them. The reason is that our universe includes all physical things that exist throughout space and time, or at least, all physical things that exist throughout the dimensions of space and time that we inhabit. If there are other universes, they must be outside of our dimensions of space and time! So if you want to know where these universes are, the answer is nowhere—that is, nowhere in relation to us. Point in any direction you like, you won’t be pointing toward another universe. Similarly, if you want to know when these universes exist, the answer is never—not in the past, present, or future of the time that we experience.
All of the aforementioned cosmological hypotheses are speculative, and there is little evidence for any of them, apart from the fact that our universe began in what appears to be an extremely improbable state. But there is another explanation for the low-entropy condition of the early universe that is neither ad hoc nor speculative, and which is supported by considerable independent evidence. I am referring to an explanation given thousands of years before the birth of modern science. In the words of the prophet Isaiah:
For thus says the Lord, Who created the heavens, Who is God, Who formed the earth and made it, Who has established it, Who did not create it in vain, Who formed it to be inhabited: “I am the Lord, and there is no other.” (Isaiah 45:18, NKJV)
God created the universe to be inhabited. As noted above, the existence of life depends on low-entropy conditions. A universe near equilibrium would not be inhabitable, nor would it be very interesting. It would contain no galaxies, stars, planets, or life. Given that God planned to populate his creation with biological creatures, it should come as no surprise that he created the universe in a low-entropy state.
As a Christian, I believe this explanation is a very good—and true—explanation for the low-entropy condition of the early universe. Of course, it’s a different sort of explanation than the ones considered above, and for all I know, one of those other explanations could be true as well. Perhaps God “stretched out the heavens,” as the inflation model suggests. (I am reminded of scriptures like Isaiah 42:5 and Jeremiah 51:15.) Or perhaps the universe is cyclical, and God will create it anew. And perhaps God created other universes besides this one. Surely God could do all of those things, if he wanted. So the theistic explanation of the low-entropy condition doesn’t preclude other explanations.
However, if the theistic explanation is correct, then those other explanations aren’t necessary to account for the fact that the universe began in a low-entropy condition. All of those other explanations could turn out false, and yet a Christian need not be confounded by this discovery. Although the condition of the early universe was unlikely to have occurred merely by chance, it is not at all surprising that God would have chosen to create the universe in such a special state. For this reason, the low-entropy condition of the universe may be regarded as evidence of God’s handiwork. In fact, as we’ll see in chapter 8, this is just one of many ways in which the heavens declare the glory of God.