I Determinism and causality in QM - a case

[PeterDonis]

if I had the option to choose A and also the option to choose B, I think a quantum measurement must be involved

Why? You can exercise such an option by flipping a coin, which is a classical process and doesn't involve any quantum measurement.

that is (in the context of MWI) the only mechanism that makes more than one future possible.

Wrong. The MWI is deterministic; there is only one future--one wave function.

You continue to misunderstand what the MWI says even though you have been corrected multiple times now.

in my example choice A and B are both possible, however some choice will be made between them if we view it subjectively

We've already gone round and round about "subjective". I don't see any point in rehashing that further.

If you insist to view it objectively in the context of MWI

You are the one that brought up the MWI, in the OP of this thread.

you can say both choices are made, so really there is no choice made, so free will, if it exist, has to be compatibalist.

In the context of any deterministic theory, any concept of free will consistent with that theory must be compatibilist, yes.

 

[entropy1]

Before I can even answer this, since we are assuming the MWI is true, you need to give me definitions of "objective" and "subjective" that are well-defined if the MWI is true.

If you say that MWI is deterministic, and that it means that when you measure a quantum property that the quantum gets entangled with the macroscopic state of the measurement device, and you call that strictly objective, then I would note that we always find a single measurement outcome, what I would call subjective (because it is a finding). I won't speculate but please tell me what is wrong with my argument. You tell me the physisist that found three non-commutating outcomes of the same measurement simultaneously. If the result of measuring $(|a \rangle + |b \rangle + |c \rangle)|M_0 \rangle$ is $|a \rangle|M_a \rangle + |b \rangle|M_b \rangle + |c \rangle|M_c \rangle$ (*) then objectively we have three outcomes, but the physisist won't tell his colleague that he found three outcomes, right? It seems to me that three physisists found a single outcome. We call each of the terms of (*) an "outcome".

 

[PeterDonis]

I won't speculate but please tell me what is wrong with my argument.

I already have. Multiple times. I would just be repeating myself if I did it again. You are not even thinking about what the MWI actually says. The MWI explains, explicitly, how each "you" in each individual branch observes a single measurement outcome. It seems like you don't even understand what the MWI actually says, and no matter how many times I explain it, you don't get it.

objectively we have three outcomes, but the physisist won't tell his colleague that he found three outcomes

You are misusing the term "the physicist". After the measurement, there is no "the" physicist. The physical system that you are labeling as "physicist" is now entangled with the measured system and has no definite state by itself. In terms of MWI "branches", each individual branch has a "physicist" in it that observes a single outcome, but there are three of them, not one, so there is no "the" physicist--"the" implies a single one, not three.

I have already explained this multiple times, and you still are not getting it.

 

[entropy1]

I have already explained this multiple times, and you still are not getting it.

If you say so then I guess I have to re-evaluate my thoughts about this issue.

 

[PeterDonis]

I guess I have to re-evaluate my thoughts about this issue.

Yes.

That seems a good note on which to close the thread. After you have re-evaluated and taken some time to consider what is posted here and what is in the literature about the MWI, you can start a new thread if you have further questions.