One of the topics from last Friday’s debate between William Lane Craig and Sean Carroll was the extremely low entropy of the early universe. As I type this blog post, the video of the debate isn’t available, so I’m going from memory. But I thought I heard Carroll argue that the extremely low entropy of the early universe is evidence favoring naturalism over theism.
In The Blackwell Companion to Science and Christianity, Carroll seems to make a similar point:
An example of fine-tuning well beyond anthropic constraints is the initial state of the universe, often characterized in terms of its extremely low entropy (Penrose 1989). Roughly speaking, the large number of particles in the universe were arranged in an extraordinarily smooth configuration, which is highly unstable and unlikely given the enormous gravitational forces acting on such densely packed matter. While vacuum energy is tuned to 1 part in 10120, the entropy of the early universe is tuned to 1 part in 10 to the power of 10120, a preposterous number. The entropy didn’t need to be nearly that low in order for life to come into existence. One way of thinking about this is to note that we certainly don’t need a hundred billion other galaxies in the universe in order for life to arise here on earth; our single galaxy would have been fine, or for that matter a single solar system.
If anything, the much-more-than-anthropic tuning that characterizes the entropy of the universe is a bigger problem for the God hypothesis than for the multiverse. If the point of arranging the universe was to set the stage for the eventual evolution of intelligent life, why all the grandiose excess represented by the needlessly low entropy at early times and the universe’s hundred billion galaxies? We might wonder whether those other galaxies are spandrels — not necessary for life here on earth, but nevertheless a side effect of the general Big Bang picture, which is the most straightforward way to make the earth and its biosphere. This turns out not to be true; quantitatively, it’s easy to show that almost all possible histories of the universe that involve earth as we know it don’t have any other galaxies at all. It’s unclear why God would do so much fine-tuning of the state of the universe than seems to have been necessary.
(Sean Carroll, “Does the Universe Need God?” The Blackwell Companion to Science and Christianity, Kindle location 6467 – 6493).
This passage from Carroll’s essay suggests yet another example of how cosmological fine-tuning arguments for God’s existence commit the fallacy of understated evidence: given that our universe is fine-tuned for life, the fact that the early universe had such extremely low entropy favors naturalism over theism.