Interesting new book that talks about simulated universes running inside simulated universes and how the physical attributes of universes could evolve over time, through a mechanism similar to natural selection. Simulated universes with certain physical traits would tend to survive longer and produce more habitable environments for more advanced civilizations to produce a higher number of simulated universes themselves with an increased amount of those physical traits, and so on. So, over time, there would be a tendency for simulated civilizations to reside in universes with the physics more suitable for life.

http://www.amazon.com/Computer-Simulated-Universes-Mark-Solomon/dp/0989832511/ref=sr_1_1?ie=UTF8&qid=1376689785&sr=8-1&keywords=computer+simulated+universes