[taneq]

Look at it this way - if at any point in the future, we ever run even one simulation of the world at our current time, then our odds are 50/50 of being in that simulation. That's only extrapolating from our current capabilities, and not assuming either nested simulations or 'non-historical' simulations. (If we're in a simulation, but not one based on the real universe's past, then we can't even begin to extrapolate from our world to 'universe zero'.)

As for practicality, simulations don't need to support a higher density of life (although they very likely will use approximations and variable level-of-detail to effectively simulate space using less resources than the space itself would use) because they have other advantages; you can pause them, take snapshots, revert to earlier states, branch, etc.

Think of it as like virtualisation for the universe. Even though virtualisation takes up some system resources, there are still huge advantages to running virtual hosts.

As for simulating whole universes being a waste of resources - if we're in a non-historical simulation, we don't even have any conception of what "a waste of resources" means in universe zero. Maybe our entire universe, simulated on a regular grid smaller than the Planck length, is as trivial to store and manipulate on a 5-dimensional universe-zero computer as a 1-dimensional cellular automaton is on a modern desktop computer for us.

[breuleux]

> if at any point in the future, we ever run even one simulation of the world at our current time, then our odds are 50/50 of being in that simulation

That's the contention, though. Someone in the future might simulate some unknown one-year slice of the past, and leave it at that. That would lower the probability significantly below 50%.

> (although they very likely will use approximations and variable level-of-detail to effectively simulate space using less resources than the space itself would use)

The devil is in the details, though. You can save a lot of time approximating an ocean using fluid dynamics, but you're axing all the low level chemical reactions that would make live evolve in it. There are no ways to use variable levels of detail that won't make the simulation diverge from the original. And I'm not even mentioning the synchronization issues and the overhead you'll need to resolve them.

> they have other advantages; you can pause them, take snapshots, revert to earlier states, branch, etc.

Only if you use hardware that's analogous to modern computers, but that hardware is not good at simulation to begin with. Unless you use specialized simulation hardware you're probably going to have to endure billion-fold slowdowns, and I'm being generous.

Assuming you have good hardware for simulation, you can't assume the ability to pause, snapshot or branch, you have to build it in. Each of these features will add overhead and make the simulation slower and larger. Nothing is free.

> As for simulating whole universes being a waste of resources - if we're in a non-historical simulation, we don't even have any conception of what "a waste of resources" means in universe zero.

That's possible, although the fact that it is possible is basically all we can say about the idea. There is no way to evaluate the probabilities involved.

[taneq]

Ah, but I said "even one simulation of the world at our current time" which side-steps that issue.

Agreed about the fact that too many shortcuts in the simulation might make it unable to develop or sustain life, but then we don't know when the simulation would have started or how much it might have diverged from universe zero by now. Presumably it would be intended to diverge anyway because they already know the outcome if it doesn't.

Of course, while we can guess about this stuff, ultimately at this point our guesses are unfalsifiable so as fun as it is to speculate, we're really just shooting the breeze. :)