I don't think you would need to simulate the entire universe, just enough of it that the consciousness receiving sense data can't encounter any missing info or "glitches" in the metaphorical matrix. Still hard of course, but substantially less compute intensive than every molecule in the universe.
And if you’re in charge of the simulation, you get to decide how many “consciousnesses” there are, constraining them to be within your available compute. Maybe that’s ~8 billion — maybe it’s 1. Yeah, I’m feeling pretty Boltzmann-ish right now…
> but substantially less compute intensive than every molecule in the universe
Very true, but to me this view of the universe and one's existence within it as a sort of second-rate solipsist bodge isn't a satisfyingly profound answer to the question of life the universe and everything.
Although put like that it explains quite a lot.
[Edit] There is also a sense in which the sim-as-a-focussed-mini-universe view is even less falsifiable, because sim proponents address any doubt about the sim by moving the goal posts to accommodate what they claim is actually achievable by the putative creator/hacker on Planet Tharg or similar.
And you don't have to simulate it in real time, maybe 1 second here takes years or centuries to simulate outside the simulation. It's not like we'd have any way to tell.
These are all open questions in philosophy of mind. Nobody knows what causes consciousness/qualia so nobody knows if it's substrate dependent or not and therefore nobody knows if it can be simulated in a computer, or if it can nobody knows what type of computer is required for consciousness to be a property of the resulting simulation.
