It’s possible that what we think of as reality is a simulation being run on some powerful computer. Perhaps the entire universe as we think it exists is a simulation. Or perhaps the simulation is much simpler, and merely covers the solar system and space around it in detail, with everything else being only sketched in. Is there any way that we can determine whether or not this is the case?
In Carl Sagan’s novel Cosmos he suggested that there is a message buried deep in the digits of key transcendental numbers like pi. He suggested that this proved that the universe was designed; I think it more likely to prove that the universe is simulated. Finding a message embedded in the universe would be a pretty strong sign.
Another strong sign would be finding parts of reality that aren’t well filled in. For example, perhaps there are places which are unable to support lots of molecules. Perhaps pushing more in would cause the space to run more slowly, or perhaps it simply wouldn’t accept them. Of course there don’t seem to be any such spaces on Earth; the place to look would be interstellar space.
I personally tend to favor the many-worlds interpretation of quantum mechanics. I don’t know if that would be harder or easier to simulate; refusing to collapse the wave function might permit everything to run out of a few equations. Alternatively, perhaps the wave function does collapse, and perhaps that collapse is itself a sign of limitations of the simulation. Note that troubling aspects of quantum mechanics, such as non-local quantum entanglement, are much less troubling if they are being simulated.
Taking the other tack, is there any way to prove that our reality is not being simulated? That seems quite difficult to me. One could perhaps make some sort of argument based on complexity, but in some sense that begs the question, since our knowledge of complexity is based on our knowledge of the universe.
If it is possible to simulate our sort of universe–which has not been proved–then it seems very likely that all of existence contains far more simulations than it does actual universes. Given that, what are the odds that our universe is a real one? Most likely we are simulated. Fortunately, it doesn’t make any real difference to us, until they pull the plug.