If that's the case, why go to the trouble of simulating such a massive universe--trillions of galaxies, 100 billion stars per galaxy, countless planets and other objects, etc.?
While the speed of light may prevent us from going to most of the universe physically (given our current understanding of physics), that's still a vast amount of compute just to give us the high fidelity impression that all this exists. What's the point? The sky could have just been simulated as dark and empty, or the universe could have contained a single galaxy.
Sure, I'm just pointing out that if the premise is that this hypothetical civilization is compute-constrained in some way and so everything beyond our local area is a facade, they have seemingly wasted resources on making the facade unnecessarily large and detailed. Perhaps the amount is insignificant to them, but it's still pointless waste.
While the speed of light may prevent us from going to most of the universe physically (given our current understanding of physics), that's still a vast amount of compute just to give us the high fidelity impression that all this exists. What's the point? The sky could have just been simulated as dark and empty, or the universe could have contained a single galaxy.