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spxtr comments on [LINK] The Wrong Objections to the Many-Worlds Interpretation of Quantum Mechanics - Less Wrong
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I have commented there, and I will quote my comment here. To clarify, I am not anti-MWI, I am pro- experimental evidence.
It seems to me that you strawman a bit the main objection. Indeed, as you say
However, this does not answer the objection that
if you phrase it the way the MWI opponents usually mean it:
or than any other interpretation favored by a particular MWI opponent, as long as that interpretation makes exact same predictions as the orthodox QM.
You are certainly right, MWI does not need an extra collapse postulate, it comes out in many possible ways from using the L^2 norm for probability in conjunction with, say, unitarity, or some other equivalent experimentally justified assumption.
Unfortunately your “rightness” is rather hollow, because you still have no definitive experiment that would convince your opponent. And so the argument becomes philosophical rather than physical, as it cannot be resolved by the scientific method.
Needless to say, a QM formulation which would lead to a testable prediction beyond those derivable from the orthodox approach, would be an exceedingly big deal. But one can hope.
He asserts that such an experiment exists. I would love it if he were to expand on this assertion.
I don't have the expertise to evaluate it, but Brian Greene suggests this experiment.
That experiment sounds very problematic to me. He says "After you measure the electron’s spin about the x-axis, have someone fully reverse the physical evolution.... Such reversal would be applied to everything: the electron, the equipment, and anything else that’s part of the experiment.".
There is no explanation of the mechanics of how he thinks such a time-reversal could be implemented. We simply don't have the fine control over the quantum state of the entire measurement apparatus. In fact, the very assumption that quantum theory is even the true/applicable state of affairs at this macro scale is the kind of thing that many Copenhagenists dispute.
Conversely, if it were possible to have such a fine control over the entire system including the very equipment used to perform the measurement, well then, you might as well simply make a quantum measurement of the larger quantum system which includes that apparatus! There would be different outcomes depending on whether collapse has or has not yet occured.
It seems like whether or not this experiment even makes sense relies somewhat on whether MWI is true. Ultimately I think the very description of this experiment makes hidden assumptions, which beg the same question it is trying to answer.
Yes, dynamical collapse appears to make new falsifiable predictions. MWI doesn't, unless you take Deutsch's reversible quantum consciousness seriously.
And even if you do, then the only viewpoint you will have really falsified is one which postulates that (a) the state vector collapse is caused by consciousness, and (b) concludes that therefore any consciousness has to do the trick, even one simulated on a quantum computer. I have met exactly zero physicists who'd treat (a) seriously, but even if you believe in (a), (b) still doesn't need to follow (someone could believe that only real human brain makes the magic happen).
(I assume you were referring to experiment 3. from Deutsch's "Three experimental implications of the Everett interpretation in Quantum Concepts in Space and Time.")