It could happen

Imagine a computer in another universe. This computer is so powerful and can hold/manipulate so much data, that it can simulate an entire universe the size of our own. Someone just needs to create the initial starting conditions and rules and set it in motion. It would be like an infinitely more complex version of Conway's game of life. If such complex simulations were possible, is the simulation of the universe any different from the actual universe? Is a simulation of life the same thing as life itself? I mean down to the smallest particles, of course. I think the difference is negligible. If living creates were replicated so exactly in a computer, it is essentially the same as the real thing.

A computational system capable of such a feat, while amazing, would have to be staggeringly more advanced to do anything realistic with the data it computes. It is relatively simple to apply basic laws and rules to a system, but to analyze and see what things are arising in the system is exponentially more difficult. If our universe is a simulation, which I think isn't impossible given a larger universe with more resources (storing more data than we have particles), it is unlikely that whoever created the simulation is even aware of our existence. Such a tiny speck in time and space, sentient life has probably gone unnoticed in this demonstration. We might even be just the beta version. Maybe light was supposed to go faster.