> On 9 Jul 2018, at 14:07, Bruce Kellett <bhkell...@optusnet.com.au> wrote:
> 
> From: Bruno Marchal <marc...@ulb.ac.be <mailto:marc...@ulb.ac.be>>
>> 
>> We both agree that there is FTL signalling. What I say is that there is no 
>> FTL influence at all, in EPR, when developed in the Everett theory. I don’t 
>> see it. When they are space-separated, given they don’t know in which branch 
>> they are, they can find result which would violate Bell’s inequality, but 
>> this means that they will never met. Each Alice and Bob will only met those 
>> correlated to them. All interactions are local. No mysterious magic forcing 
>> the result of Bob or Alice to influence the outcome of the others. We need 
>> to take into account the many numbers of Alice (Bob), because none knows in 
>> which branch they are. They know only that they are correlated, and that 
>> means only that when they come back they will observe those correlations, 
>> but as there has not been any collapse, that is explained entirely by local 
>> interactions, as they were in the right branch at the start, due to the 
>> preparation of the singlet state. 
> 
> I think you mean 'no' FTL signalling in the first sentence.

Right.



> 
> It is not really a matter of branches when looked at from the point at which 
> Alice and Bob meet. They bring to this meeting a world line -- a personal 
> history, a path through these branching events. They are each like someone 
> who has undergone multiple duplications, ending in either M or W each time. 
> Each diary will contain some sequence of WWMWMM.... and so on. There are 2^N 
> such sequences for N duplications, each of the 2^N copies at the end of this 
> has one sequence. It is exactly the same for a sequence of binary quantum 
> measurements in MWI. At the end, when an Alice and a Bob meet, they carry 
> with them their world lines -- their particular sequences of '1' and '0' 
> results.
> 
> By starting from the final meeting point, we can unravel the chain of events 
> without getting confused as to which branch anyone is in. After N trials, 
> there are 2^N such meetings. The recording in lab books and walking to the 
> meeting between the experimenters is all local. No question about this. And 
> in every such meeting, the comparison of lab books will reveal results that 
> always agree with the quantum correlations and violate the Bell inequalities. 
> There are no surplus branches that have to be discarded by some mechanism. 
> All branches at this stage are good.
> 
> Where you are going wrong is in saying that they were in the right branch at 
> the start -- due to the properties of the singlet state. This is misleading 
> you, because you are not explaining how the correlations arise at spacelike 
> separations when the polarizer angles are set at random.


If Alice find up, she knows that she is in the branch where Bob will or has 
found down. The correlation are like Belman socks, with the MWI. The violation 
of Bell’s inequality are due to the fact they none can know chip branches they 
are in. The singlet state does not allow to single out the direction where a 
result would be definite.






> 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. 




> This a logical consequence of a correlation between two independent events. 
> Independent means no correlation. Here we have spacelike separated events 
> that do show a correlation. Consequently, the assumption of locality is not 
> tenable, even though we appear to have only local interactions. Whatever you 
> say about branching or Everett is not going to alter the basic logic of this 
> situation.
> 
> I think that after all these exchanges it is unlikely that you are ever going 
> to be able to accept this fact. But I do assure you that it is a fact.

The fact that Bob and Alice can measure the “spin" in non “orthogonal” 
directions can provide them clue about which partition of the multiverse they 
are in, and were at the start, but only among infinitely many directions. You 
talk like if there is one Alice with a definite spin, but Alice’s consciousness 
is distributed on the state with her spin in all directions, and the same for 
Bob. As I said, You fail to take into account Alice and Bob intrinsic ignorance 
of the direction of the spin when preparing the shared singlet state. I think.

Bruno




> 
> Bruce
> 
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