Thanks for the comments!

On Wednesday, April 13, 2022 at 8:55:48 PM UTC+3 (Brent) 

Physics doesn't care about "rationally justified", only about empirically 
> justified.

I admit that I have carried the subject to philosophy of physics, but only 
because this kind of subject cannot be addressed with just experiments. On 
the other hand, do you admit that your comment needs qualifications? You 
cannot possibly mean that we just obtain the Born Rule from experiments, 
and that this is all we care about. Did Einstein make any sense, 
complaining about who plays dice during a measurement? What was the point 
of attempts to introduce hidden variables, even at the cost of 
non-locality? What is the point of MWI, then? I suppose that you are a 
careful thinker, and if you object to MWI it would be on some rational 

  Both your examples suffer from choosing the simplest case where symmetry 
> can be invoked.

So that you would not be distracted from the basic issue: do you agree with 
always averaging over future selves (Deutsch) or do you take it for granted 
that the theory provides probability (Zurek and others)? Or none of the 
above? Correct me if I am wrong, but I gather that your responce is "who 
cares", or "po-tah-toes, pot-eight-os".

Once you've assumed the Hilbert space structure of QM, then Gleason's 
> theorem essentially forces the Born rule (correct me if I'm wrong, but I 
> think the theorem has been extended to the two-dimensional case).

I shall respectfully correct you, but not on the question you ask, because 
I cannot remember now, and I admit that I do not care to look it up (but I 
explain why). Gleason's theorem also requires the assumption of 
randomisation (God plays dice) and the assumption of non-contextuality of 
measurements. The reason I do not care about it any more is that I do not 
favour these two assumptions (especially the first one).

I think the problem is that MWI (but not Everett) assume all outcomes are 
> equally realized.  So how does a probability become assigned to them, what 
> does it mean.

I agree, and I am glad you are critical on this point.  I am intrigued, 
though, by the caveat "but not Everett": can you explain, please?

We're told it's the probability of finding ourself in a particular 
> world...but that seems very much like "collapse of the wave-function".  It 
> introduces the same problems of exactly when and where does it happen; with 
> only the advantage that consciousness is not understood in detail so the 
> mystery can be push off.

I emphasise that I have no comment on the above, because I do not endorse 
probability strictly speaking but only on an "as-if" basis. (I agree with 
Deutsch on this narrow point -- Physics doesn't care, really?)

Decoherence has gone part way in solving the when/where/what basis 
> questions, but only part way.

I guess you refer to the theoretical possibility of the environment 
occasionally failing to "decohere" the state. Here is one of the 
approximations that are required in the translation from objective, 
deterministic QM (without collapse) to the application of QM in the world 
of experience (with apparent collapse). Surely this approximation must be 
scrutinised, I agree.

George K.

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