When elon musk says it's possible that we're living in a simulation, it's fun to think about the computer that can handle this level of detail and complexity from the very minute to the billions of galaxies
And then the simulation only has to be detailed enough to provide you with a reasonably-plausible answer. As soon as you stop looking, the algorithm can just strip out the detail.
This trick isn't even that hard, graphics processors do it all the time.