Jonathan Birch recently published an interesting critique of Bostrom's simulation argument. Here's the abstract:
Nick Bostrom’s ‘Simulation Argument’ purports to show that, unless we are confident that advanced ‘posthuman’ civilizations are either extremely rare or extremely rarely interested in running simulations of their own ancestors, we should assign significant credence to the hypothesis that we are simulated. I argue that Bostrom does not succeed in grounding this constraint on credence. I first show that the Simulation Argument requires a curious form of selective scepticism, for it presupposes that we possess good evidence for claims about the physical limits of computation and yet lack good evidence for claims about our own physical constitution. I then show that two ways of modifying the argument so as to remove the need for this presupposition fail to preserve the original conclusion. Finally, I argue that, while there are unusual circumstances in which Bostrom’s selective scepticism might be reasonable, we do not currently find ourselves in such circumstances. There is no good reason to uphold the selective scepticism the Simulation Argument presupposes. There is thus no good reason to believe its conclusion.
The paper is behind a paywall, but I have uploaded it to my shared Dropbox folder, here.
EDIT: I emailed the author and am glad to see that he's decided to participate in the discussion below.
It would be trivial for an SI to run a grainy simulation that was only computed out in greater detail when high-level variables of interest depended on it. Most sophisticated human simulations already try to work like this, e.g. particle filters for robotics or the Metropolis transport algorithm for ray-tracing works like this. No superintelligence would even be required, but in this case it is quite probable on priors as well, and if you were inside a superintelligent version you would never, ever notice the difference.
It's clear that we're not living in a set of physical laws designed for cheapest computation of intelligent beings, i.e., we are inside an apparent physics (real or simulated) that was chosen on other grounds than making intelligent beings cheap to simulate (if physics is real, then this follows immediately). But we could still, quite easily, be cheap simulations within a fixed choice of physics. E.g., the simulators grew up in a quantum relativistic universe, and now they're much more cheaply simulating other beings within an apparently quantum relativistic universe, using sophisticated approximations that change the level of detail when high-level variables depend on it (so you see the right results in particle accelerators) and use cached statistical outcomes for proteins folding instead of recomputing the underlying quantum potential energy surface every time, or even for whole cells when the cells are mostly behaving as a statistical aggregate, etc. This isn't a conspiracy theory, it's a mildly-more-sophisticated version of what sophisticated simulation algorithms try to do right now - expend computational power where it's most informative.
Unless P=NP, I don't think it's obvious that such a simulation could be built to be perfectly (to the limits of human science) indistinguishable from the original system being simulated. There are a lot of results which are easy to verify but arbitrarily hard to compute, and we encounter plenty of them in nature and physics. I suppose the simulators could be futzing with our brains to make us think we were verifying incorrect results, but now we're alarmingly close to solipsism again.
I guess one way to to test this hypothesis would be to try to construct... (read more)