Greenwood Research Books and Software - On-line catalog of books and software in mathematical physics, astrophysics, field physics, and engineering physics, including free astrophysics software downloads.
Which Mathematical Structure is Isomorphic to our Universe? - Max Tegmark. Some physical consequences of ``the ultimate ensemble theory'', where not only worlds corresponding to say different sets of initial data or different physical constants are considered equally real, but also worlds ruled by altogether different equations. HTML, PS and PDF.