Resolution of the Frauchiger-Renner paradox

[PeterDonis]

Suppose that we model observers by using only classical physics. Would a possibility of reversal in the classical phase space be a fundamentally different way for evidence to be unreliable, compared to ordinary ways that people forget things or that evidence is not always reliable?

Since the effects of such a reversal, assuming classical physics (and therefore a fully deterministic time reversible model), would be to undo everything that happened during the period that got reversed, yes, I would say this is a fundamentally different way for evidence to be unreliable.

Note, however, that classical physics does not contain any operation that would actually do such a reversal. It contains pairs of solutions that are time reverses of each other, but does not contain any way of switching between them in mid-stream, so to speak. So there is no analogue in classical physics to the kinds of "reverse decoherence" unitary operations that the Frauchiger-Renner scenario uses.

 

[Demystifier]

Since the effects of such a reversal, assuming classical physics (and therefore a fully deterministic time reversible model), would be to undo everything that happened during the period that got reversed, yes, I would say this is a fundamentally different way for evidence to be unreliable.

Fine. And assuming classical physics, do you think that such reversal is possible in principle? (I'm not talking about reversal of the whole Universe, but about reversal of the friend and his classical laboratory.) And if it possible in principle, does it mean that we cannot do science? Or if you say that it is not possible in principle, can you explain why it is not possible?

 

[PeterDonis]

assuming classical physics, do you think that such reversal is possible in principle?

I thought I already answered that in post #36, second paragraph.