A Huffington Post by MIT physicist Max Tegmark — promoting his new book, in part — discusses the implications of recent physics that implies our universe is just one in a multiverse.
That our universe is approximately described by mathematics means that some but not all of its properties are mathematical, and is a venerable idea dating back to the ancient Greeks. That it is mathematical means that all of its properties are mathematical, i.e., that it has no properties at all except mathematical ones.
…it also implies that our reality is vastly larger than we thought, containing a diverse collection of universes obeying all mathematically possible laws of physics. An advanced computer program could in principle start generating an atlas of all such mathematically possible universes. The discovery of other solar systems has taught us that 8, the number of planets in ours, doesn’t tell us anything fundamental about reality, merely something about which particular solar system we inhabit — the number 8 is essentially part of our cosmic ZIP code. Similarly, this mathematical atlas tells us that if we one day discover the equations of quantum gravity and print them on a T-shirt, we should not hübristically view these equations as the “Theory of Everything,” but as information about our location in the mathematical atlas of the ultimate multiverse.