I've realized I'm somewhat skeptical of the simulation argument.

The simulation argument proposed by Bostrom argued, roughly, that either almost exactly all Earth-like worlds don't reach a posthuman level, almost exactly all such civilizations don't go on to build many simulations, or that we're almost certainly in a simulation.

Now, if we knew that the only two sorts of creatures that experience what we experience are either in simulations or the actual, original, non-simulated Earth, then I can see why the argument would be reasonable. However, I don't know how we could know this.

For example, consider zoos: Perhaps advanced aliens create "zoos" featuring humans in an Earth-like world, for their own entertainment or other purposes. These wouldn't necessarily be simulations of any actual other planet, but might merely have been inspired by actual planets. Similarly, lions in the zoo are similar to lions in the wild, and their enclosure features plants and other environmental feature similar to what they would experience in the wild. But I wouldn't call lions in zoos simulations of wild lions, even if the developed parts where humans could view them was completely invisible to them and their enclosure was arbitrarily large.

Similarly, consider games: Perhaps aliens create games or something like them set in Earth-like worlds that aren't actually intended to be simulations of any particle world. Similarly, human fantasy RPGs often have a medieval theme, so maybe aliens would create games set in a modern-Earth-like world, without having in mind any actual planet to simulate.

Now, you could argue that in an infinite universe, these things are all actually simulations, because there must be some actual, non-simulated world that's just like the "zoo" or game. However, by that reasoning, you could argue that a rock you pick up is nothing but a "rock simulation" because you know there is at least one other rock in the universe with the exact same configuration and environment as the rock you're holding. That doesn't seem right to me.

Similarly, you could say, then, that I'm actually in a simulation right now. Because even if I'm in the original Earth, there is some other Chantiel in the universe in a situation identical to my current one, who is logically constrained to do the same thing I do, so thus I am a simulation of her. And my environment is thus a simulation of hers.