From: *Bruno Marchal* <[email protected] <mailto:[email protected]>>
On 14 Aug 2018, at 04:30, Bruce Kellett <[email protected]
<mailto:[email protected]>> wrote:
If they are space separated, I am not sure I can make sense of being
in the same branch.
You appear to be referring to the presence of quantum fluctuations
continually splitting the classical Alice and Bob into multiple
copies -- the point that Jason has made.
That points is correct, but I was alluding to the infinity of Bob and
Alice couples associated with the singlet state. That is needed to
tackle the case where Alice and Bob makes non orthogonal measurements.
I was trying to make sense of the suggestion of many Alices and Bobs
before any measurement. That can easily be implemented by having Alice
select her measurement angle according to the time of some radioactive
decay. Since an infinity of decay times is possible, we get a
superposition of an infinite number of copies of Alice. But this makes
not difference to the basic argument -- one just picks out a typical
Alice. You are wrong when you claim that an infinity of couples are
required to make sense of measurements made at arbitrary angles. The
singlet state is rotationally symmetric, and can be expressed in any
base. But this does not mean that there actually exists a copy of the
observer for each of the potential bases. That idea makes no sense at
all; it is not part of quantum mechanics in any possible formulation.
The singlet state does not single out one base, despite the notation.
It describes an infinite of Alice and Bob right at the start.
Sure, the singlet state does not single out one base. But that does not
mean that it describes an infinity of observers. Just because you can
measure at any angle does not mean that there is actually an infinity of
observers making all those possible measurements. That notion is just crazy.
Bruce
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