Currently, supercomputers using a impressive-sounding technique called lattice quantum chromodynamics, and starting from the fundamental physical laws, can simulate only a very small portion of the universe. The scale is a little larger than the nucleus of an atom, according UW physicist Martin Savage. Mega-computers of the far future could greatly expand the size of the Sim Universe.
If we are living in such a program, there could be telltale evidence for the underlying lattice used in modeling the space-time continuum, say the researchers. This signature could show up as a limitation in the energy of cosmic rays. They would travel diagonally across the model universe and not interact equally in all directions, as they otherwise would be expected to do according to present cosmology.
If such results were measured, physicists would have to rule out any and all other natural explanations for the anomaly before flirting with the idea of intelligent design. (To avoid confusion with the purely faith-based creationist ID, this would not prove the existence of a biblical God, because you'd have to ask the question "why does God need a lattice?")
If our universe is a simulation, then those entities controlling it could be running other simulations as well to create other universes parallel to our own. No doubt this would call for, ahem, massive parallel processing.
If all of this isn't mind-blowing enough, Bostrom imagined "stacked" levels of reality, "we would have to suspect that the post-humans running our simulation are themselves simulated beings; and their creators, in turn, may also be simulated beings. Here may be room for a large number of levels of reality, and the number could be increasing over time."
To compound this even further, Bostrom imagined a hierarchy of deities, "In some ways, the post-humans running a simulation are like gods. However, all the demigods except those at the fundamental level of reality are subject to sanctions by the more powerful gods living at lower levels."
If the parallel universes are all running on the same computer platform could we communicate with them? If so, I hope the Matrix's manic Agent Smith doesn't materialize one day.
To borrow from the title of Isaac Asimov's novel I Robot, the human condition might be described as I Subroutine.
Editor's note: Whoa.
Image credits: Warner Brothers, J.F. Colonna, Boston University