If the universe is a computer simulation, how would the data for that simulation be stored? You'd need to keep track of positional data for each particle, and as it takes multiple atoms on a storage device to store one byte of data, you'd need multiple universes worth of matter in the form of drive hardware, which would just jumble together and collapse into a black hole if you placed it within any kind of reasonable proximity of itself, and even then the travel times for data would be ridiculous.