I think we need to be careful here about what constitutes a computation which might give rise to an experience. For instance suppose a chunk of brain pops into existence but with all momentum vectors flipped (for non-nuclear processes we can assume temporal symmetry) so the
brain is running in reverse.
Seems right to say that could just as easily give rise to the experience of being a thinking human brain. After all we think the arrow of time is determined by direction of decreasing entropy not by some weird fact that only computations which proced in one direction give rise to experiences.
Ok so far no biggie but why insist computations be embedded temporally? One can reformulate the laws of physics to constrain events to the left given the complete (future and past) set of events to the right so why can’t the computation be embedded from left to right (ie the arrow we of time points right) or in some completely other way we haven’t thought of.
More generally, once we accept the possibility that the laws of physics can give rise to computations that don’t run in what we would view as a casual fashion then it’s no longer clear that the only kind of things which count as computations are those the above analysis considered.
I tend to see this as an issue of decision theory, not probability theory. So if causality doesn’t work in a way we can understand, the situation is irrelevant (note that some backwards-running brains will still follow an understandable causality from within themselves, so some backwards-running brains are decision-theory relevant).
I think we need to be careful here about what constitutes a computation which might give rise to an experience. For instance suppose a chunk of brain pops into existence but with all momentum vectors flipped (for non-nuclear processes we can assume temporal symmetry) so the brain is running in reverse.
Seems right to say that could just as easily give rise to the experience of being a thinking human brain. After all we think the arrow of time is determined by direction of decreasing entropy not by some weird fact that only computations which proced in one direction give rise to experiences.
Ok so far no biggie but why insist computations be embedded temporally? One can reformulate the laws of physics to constrain events to the left given the complete (future and past) set of events to the right so why can’t the computation be embedded from left to right (ie the arrow we of time points right) or in some completely other way we haven’t thought of.
More generally, once we accept the possibility that the laws of physics can give rise to computations that don’t run in what we would view as a casual fashion then it’s no longer clear that the only kind of things which count as computations are those the above analysis considered.
I tend to see this as an issue of decision theory, not probability theory. So if causality doesn’t work in a way we can understand, the situation is irrelevant (note that some backwards-running brains will still follow an understandable causality from within themselves, so some backwards-running brains are decision-theory relevant).