The Ultimate Ensemble is a speculative possible feature of theories of everything (TOEs), suggested by Max Tegmark. Related to the Anthropic principle and Multiverse theories, the Ultimate Ensemble suggests that not only should worlds corresponding to different sets of initial conditions or different physical constants be considered real, but also worlds ruled by altogether different equations. The only postulate in this theory is that all structures that exist mathematically exist also physically. In those mathematical structures complex enough to contain self-aware substructures (SASs), these SASs will subjectively perceive themselves as existing in a physically "real" world. Tegmark observes that this simple theory, which has no free parameters at all and may thus be preferred over all other TOE's by Occam's Razor, is not observationally ruled out.

http://en.wikipedia.org/wiki/Ultimate_ensemble