> On 12 Jul 2018, at 04:04, Bruce Kellett <bhkell...@optusnet.com.au> wrote:
> From: Bruno Marchal <marc...@ulb.ac.be <mailto:marc...@ulb.ac.be>>
>>> On 9 Jul 2018, at 14:07, Bruce Kellett <bhkell...@optusnet.com.au 
>>> <mailto:bhkell...@optusnet.com.au>> wrote:
>>> Sure, this is a property of the singlet state in standard QM, because 
>>> Alice's measurement collapses the state so that only the correlated part is 
>>> available to Bob. It is that part of the explanation that is lacking in 
>>> your account. You do not see any non-locality, basically because you are 
>>> assuming it with being aware of what you are doing. Don't despair -- many 
>>> other highly trained physicists do exactly the same thing. But this does 
>>> mean that you have not explained anything -- you have simply assumed the 
>>> result. The individual measurements of Alice and Bob do influence each 
>>> other, or else no correlation could ever arise.
>> If there was a collapse? OK. But without collapse, the correlation are just 
>> due to the fact that the singlet state put Alice and Bob in infinities of 
>> branches, and only when they make a measurement they                 know in 
>> which branches they are. Up-down + down-up is the same state as up’-down 
>> +down’-up’. That is what you are not taking into account, I think.
> There are no infinities of branches. There are only two branches for each 
> measurement, when Alice and Bob can only ever get 'up' or 'down', two 
> possibilities on each measurement.

I can make sense, after the measurement, but not before. 

> After N trials, there are 2^N possible histories for Alice and 2^N histories 
> for Bob.


> There are no infinities, and no branches are created for magnet orientations 
> in which no one made a measurement. In the words of Asher Peres: "Unperformed 
> experiments have no results." There are no counterfactuals, all that is ever 
> used is actual data obtained by actual experimenters. When they make a 
> measurement, they create the branching.

Which propagate from there, and Alice and Bob will meet only their 
corresponding person on each branches. That explains the correlations, without 
needing FTL.

> Because the result of the measurement is unknown to them beforehand (no 
> superdeterminism), they locate on either the up or down branch.


> There are no up' or down' branches.

? (That contradicts directly what you just said). A up-branch is just a branch 
where Alice saw or would see “up”.

> You are just making this up.


> Each copy of Alice has a unique history consisting of a sequence of up and 
> down results recorded in her lab book. Similarly for Bob.


> All of these results were obtained in the same branch of the ever-branching 
> Everettian tree.

That is ambiguous, but I can make sense of this. 

> Each measurement splits a branch, but branches never meet or recombine.

Because they both measure in the same direction (not sure how they do that 
btw), but for Bell’s inequality, some measurement are not “orthogonal”. Partial 
fusion is in play, which forbids ti associate each personal experience with any 
definite Alice (Bob) in the branching.

> So the Alice that meets a Bob over coffee after the N trials is the Alice 
> with one particular branching history.

Again, this begins to be too much ambiguous, if not non sensical for me.

> The Bob she meets is necessarily in the same world,

At the moment of the meeting, yes. But that is a far cry to say that it is the 
“physical Bob” she started with, in the case of "non orthogonal measurements”. 
But OK, for this scenario.

> and he has a similar particular branching  history corresponding to just one 
> world. There are 2^N such meetings, each with unique branching histories. The 
> wonder of the singlet state is that for all these Alice/Bob meetings, 
> comparison of the data recorded in their lab books always gives correlations 
> that agree with quantum theory and violate the Bell inequalities.

To get them, they need non orthogonal measurement, with different probabilities 
(cos^2(some angle)), and your identity relations does no more work. 

> This mystery of many branches that always give the correct results is the 
> mystery that is to be explained. Introducing infinities of branches, and 
> infinities of measurements that were never made and therefore have no results 
> does not offer any explanation.

The explanation is the local development of the “universal wave”. The point is 
that there is no FTL which have been shown in any branches, only the illusion 
of them if we abstract from the existence of the others branches, where 
measurements are done, but get different.

> In fact, it is just plain silly. We only ever have data from experiments that 
> were actually performed by real people. There is no fantasy data, and no 
> fantasy branches floating around that have to be eliminated by some magic or 
> the other.  The magic of the singlet state is that no results counter to 
> quantum mechanics can ever be generated. And this can only be explained 
> non-locally. All other attempts flounder on stupidities.

Non locally in the sense that the singlet state requires the global wave 
function or the multiverse, but not “non-locally” in the sense of physical FTL 
influencing at a distance. 


> Bruce
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