The “Deutsch Argument” for the Many-Worlds Interpretation (“Where Was The Number Factored?”)
Does the possibility of scalable quantum computers prove (or rather, “re-prove”) the Many-Worlds Interpretation, as Deutsch believes? If not, does it at least lend support to MWI? Is MWI a good heuristic way to thinkabout what a quantum computer does?
On the contrary, does MWI encourage intuitions about how a quantum computer works that are flat-out wrong? (E.g., that it can “try all possible answers in parallel”?)
If scalable quantum computers are built, do you think that will change people’s outlook on the interpretation of quantum mechanics (and on MWI in particular)?
Can MWI be tested? What about, as Deutsch once suggested, by an experiment where an artificially-intelligent quantum computer was placed in a superposition over two different states of consciousness?
Does the fact that humans are open systems—that unlike quantum computers, we can’t practically be placed in coherent superposition states—mean that MWI and the Copenhagen interpretation are indistinguishable by human observers?
Would a scalable quantum computer test quantum mechanics itself in a new way? Is the possibility of scalable quantum computing (or more generally, of a violation of the Extended Church-Turing Thesis) so incredible that our default belief should be that quantum mechanics breaks down instead?
Could quantum computing be impossible in principle without quantum mechanics breaking down? If so, how?
Suppose it were proved that BPP=BQP. Would that influence the interpretation of QM? Would it undercut Deutsch’s case for MWI, by opening the door to “classical polynomial-time hidden-variable theories”?
The Evolutionary Principle and Closed Timelike Curves
Is Deutsch’s Evolutionary Principle—that “knowledge can only come into existence via causal processes”—valid? If so, how should we interpret that principle? What counts as knowledge, and what counts as a causal process?
Is Deutsch’s “Causal Consistency” requirement a good way to think about closed timelike curves, supposing they existed? Why or why not?
Does the apparent ability of closed-timelike-curve computers to solve NP-complete problems instantaneously mean that CTCs would violate the Evolutionary Principle? If so, how should we interpret this: that CTCs are physically impossible? That the Evolutionary Principle is a poor guide to physics? Or that, if CTCs exist, then some new physical principle has to come into effect to prevent them from solving NP-complete problems?