It's always a possibility. Even so though, the computer does not need to simulate an expanding universe, only the illusion of one. For all we know the stars outside of our solar system could all be stationary. A fixed backdrop that just has its light properties fiddled with to create the illusion of movement. Even travelling at the speed of light, getting away from our solar system is likely to be a one way trip, never mind the mathematical impossibilities that come with attempting to travel at the speed of light, so it's extremely unlikely anyone will be able to make the trip to actually find out and report to us - a sneaky skill that programmers have been using since forever, and has been brought up in this thread many times (It's just like playing battlefield or CoD or whatever. The backdrop looks real enough, but if you got close you would see how fake it is. Clever area design is how you prevent people from getting close enough to find out).