I’ve just finished reading Sean Carroll’s From Eternity to Here, in which he discusses several theories of time. Specifically, he surveys past and current thinking regarding the “arrow of time” and its relationship to entropy and the Second Law of Thermodynamics.
I’d recommend the book to anyone who is interested in the concept of time and has a fairly good understanding of physics.
What struck me most about the book was the question that can’t be answered: why was the entropy of the early universe as low as it was, when we wouldn’t expect it to be? As we know from the second law, entropy always increases within a closed system. So we’re left with the possibility that either (1) the beginning wasn’t the beginning or (2) the universe is not a closed system.
This immediately made me think about the higher dimensional membranes (P-branes) that have been suggested by String Theory/M-Theory scientists. The basic idea is that our universe exists on the three-dimensional surface of a higher dimension membrane, and that there are possibly an infinite number of these membranes floating around. This is one variation of the multiverse idea.
It’s possible that our universe was formed by the collision of two membranes. This collision caused the big bang, inflation, etc. The totality of creation is in fact eternal, universes like ours are just local patches of space time that result from collisions between branes; or, as Sean Carroll suggests, baby universes that “pinch off” like bubbles from other universes. This pinching off could result from black holes or wormholes as well, I believe. The collision process or bubbling process occurs over and over again.
These ideas solve some important problems: (1) why was the entropy of our universe low at the beginning and (2) why does our universe appear finely-tuned for the emergence of intelligent observer. The answer could be that we’re just in one of possibly an infinite number of universes, so it’s not surprising. See also The Cosmic Landscape by Leonard Susskind. What this means is that (1) time, and space, did exist before the conventional beginning and (2) the multiverse is eternal. This would be consistent with the second law and the Copernican Principle.
Unfortunately for the religious, this doesn’t leave much room for a creator… the “god of the gaps” is getting smaller all the time. People will always need religion, but invoking it to explain cosmology is going to get harder as we continue to deepen our understanding of the universe.