You don’t need to simulate an entire universe. You just need to simulate the perception of an entire universe, for a single agent. You can also do it at whateve

You don’t need to simulate an entire universe. You just need to simulate the perception of an entire universe, for a single agent. You can also do it at whatever time dilation you need to. You don’t even need any past or future, rather a Boltzmann brain style perceptual instant. If we accept a slow, hallucinatory, solipsistic simulation, you could run it on current hardware, if you were clever about the implementation.