In their new version of the cyclic approach, Steinhardt and Ijjas argue that they can surmount this problem. They have established that during each cycle a given region of space stretches far more than it contracts, ensuring the entropy it contains is thoroughly diluted. Cycle upon cycle, the total entropy across the entirety of space increases, as per the second law of thermodynamics. But in any finite region, such as the one giving rise to our observable realm, the entropic buildup that stymied Tolman is no longer a concern. Expansion dilutes away all matter and radiation, while the
...more
