Sean Carroll
HH: OK so far. Entropy is a synonym for disorder.
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SC: Left to their own devices, things tend to evolve toward increasing disorder. If you shuffle a deck of cards it’s very unlikely that they will end up precisely in numerical order. That’s just because there are many more ways to be disordered than to be ordered. Similarly, our universe is evolving from a very smooth state at early times to a messier, lumpy state at late times, as clouds of gas contract and form stars and galaxies. Our entropy is low but growing.
SC: Yes, the entropy is increasing as matter continues to clump together. Sir Roger Penrose has suggested that the universe will ultimately end up as a collection of black holes. But eventually those black holes will evaporate, as Stephen Hawking has pointed out. So we believe that the ultimate end state is nearly empty space, with everything very spread out. The question, then, is why we observe any matter in the universe at all, much less an extremely dense big bang.
HH: But not quite cold enough for the universe to seize up in a static heat death. I still don’t see how you’re going to get a big bang or another universe out of this situation.
SC: Not quite. You don’t have to produce a whole universe all at once. We think it’s easier for random quantum fluctuations to produce the start of inflation than it is for them to produce anything else, including Rockefeller Chapel. A crucial and still debatable step is that we think it’s more likely to fluctuate into an inflating universe than anything else.
