[Epistemic status: Any time I make an anthropic argument, you should probably interpret it as trolling]

Sean Carroll argues that the simulation argument is false.

The simulation argument posits two kinds of universes: “high-level” universes that can simulate other universes, and “ground-level” universes that can’t. By the terms of the simulation argument itself, most universes will be at ground level, since every high-level universe can simulate many ground-level ones. So (says the argument) we should expect to be at ground level. But the simulation argument itself hinges on our observation that it looks like our universe is capable of simulating other lower-level universes. So apparently we aren’t on ground-level. So the simulation argument is probably false.

(I might be summing it up badly. Read the actual post for more.)

Suppose Carroll’s reasoning is right. What would a ground-level universe look like?

It would have to be pretty weird. It would have to ban the creation of Turing machines – since with enough time and resources any Turing machine could be expanded into a full-scale simulation. But Turing machines are pretty simple, and brains supporting conscious observers are pretty complicated. To have conscious observers but not Turing machines – well, once again, this would have to be pretty weird.

Brains would have to run off a science different from the local science accessible to in-universe researchers. Probably they would be run remotely, in the simulating universe, and then the results beamed into the simulated universe with no regard for the computational rules of the simulation. Maybe an alien dissecting a fellow alien’s head would just find a perfectly featureless crystal with no internal structure, which is observed to inexplicably send nerve impulses to the rest of the entity’s body. Such aliens might invent psychology, but never neuroscience, and even if they speculated about it, it wouldn’t matter – attempts to “simulate” neurons would fail, their workings forever beyond locally accessible physics. Even if they completely mastered their local science, their brains would remain a mystery.

I used the phrase “conscious observers” above. There are versions of anthropics that work for p-zombies, but we’re not p-zombies and we don’t have to use them; we can do anthropics conditioning upon consciousness. Try that, and the simulation argument doesn’t exactly depend on a ground-level universe where further simulations are impossible. It depends on a ground-level universe where further simulations containing conscious observers are impossible.

This changes the scenario a bit. Now people in ground-level simulations can expect arbitrarily complex physics, physics that allow the creation of as many Turing machines as they want, but which can’t possibly explain consciousness. They should be able to master every aspect of the universe around them except consciousness, which try as they might will remain refractory to their simulations. Consciousness will make perfect sense in the physics of the universe above theirs, but the simulators will have excised all consciousness-related rules from the ground-level sim. Try as the simulated scientists might, it’ll remain a mystery.

If Carroll’s deconstruction of the simulation argument is right, then the more trouble we have explaining consciousness, the more that should push us to believe we’re in a ground-level simulation. There’s probably a higher-level version of physics in which consciousness makes sense. Our own consciousness is probably being run in a world that operates on that higher-level law. And we’re stuck in a low-resolution world whose physics doesn’t allow consciousness – because if we weren’t, we’d just keep recursing further until we were.