Even if you don't run the simulation at all, you can't hold the state of a single moment of the simulation in this universe, if you need more bits to do so than

Even if you don't run the simulation at all, you can't hold the state of a single moment of the simulation in this universe, if you need more bits to do so than are available. I don't understand how it might even be possible to get around that by "trading space for time". Can you expand on that, at all?