My posts about computer simulations could probably use a little explaining. Here's the paper that made me take the idea seriously. It's very readable and, I think, fascinating; and it's better than reading my thoughts on the subject.
We run simulations all the time and it's not difficult to imagine us trying to run simulations of the development of our universe. If we did, and we have a naturalistic view of nature, it's possible that life would evolve in the simulation that was conscious like us. Do we have a good reasons for concluding that this has not already happened and that we exist in one of these simulations? I don't think so, in fact, unless we can think of good reasons why we will never reach a technological state much more advanced than now, or why, if we did nobody would run the simulations, there are good reasons to believe that we actually are in a simulation.
Greg has expressed some surprise at how I seem to have discovered religion. While I think it's a good idea to revise my estimates on some issues, mostly this means a change from vanishingly unlikely, to very unlikely. I still regard miracles as especially unlikely because there is so little decent evidence for them. Besides, the propositions are hardly very religious as we normally understand the word (I also don't think Greg was being serious).