You're assuming a simulation where you either care about accuracy for all elements, and/or where the observer can tell if you "cheat". Minecraft is an example

You're assuming a simulation where you either care about accuracy for all elements, and/or where the observer can tell if you "cheat". Minecraft is an example of the latter: if you leave a chunk, mobs despawn and decay and growth stops. But a simulation need not work that way. E.g. instead of continuing to run a simulation, it can simulate macro-indocators, and continue to simulate micro-details with a strong bias towards reverting to a prediction from the macro-indicators, and each element that gets there can be discarded. To go back to the Minecraft example, you set a "decay rate" for mobs that reflects a believable rate of dispersal, or simulate changes to vegetation towards what your generating function will produce until they match. Then when the player re-enters at t+a_lot, you just run your generating function where time is one parameter, and apply whatever reduced delta is still relevant. Yes, you'd still need to simulate a lot, but you'd be able to prune most things. So the question is meaningless without defining your requirements.