> On 17 Apr 2018, at 13:52, Bruce Kellett <[email protected]> wrote:
>
> From: Bruno Marchal <[email protected] <mailto:[email protected]>>
>>> On 16 Apr 2018, at 05:33, Bruce Kellett <
>>> <mailto:[email protected]>[email protected]
>>> <mailto:[email protected]>> wrote:
>>>
>>> From: Bruno Marchal <[email protected] <mailto:[email protected]>>
>>>>> On 11 Apr 2018, at 14:19, Bruce Kellett <
>>>>> <mailto:[email protected]>[email protected]
>>>>> <mailto:[email protected]>> wrote:
>>>>>
>>>>> From: Bruno Marchal < <mailto:[email protected]>[email protected]
>>>>> <mailto:[email protected]>>
>>>>>
>>>>>> If you believe in influence at a distance, you are the one needing to
>>>>>> show the evidence of that extra-ordinary fact.
>>>>>
>>>>> The fact is demonstrated by the experiments that test Bell inequalities
>>>>> on the singlet state.
>>>>
>>>>
>>>> Not at all. This proves the existence of influence at a distance when we
>>>> suppose that a measurement gives an outcome, but in QM without collapse, a
>>>> measurement gives all outcomes, with varying relative probabilities.
>>>
>>> The measurement on one of the spin-half particles in the singlet state has
>>> only two possible outcomes. As is often said in discussions of non-locality
>>> in Everettian QM, 'measurements that are not made do not have outcomes!’
>>
>> Contextually yes. Because Alice and Bob, in most experience, have a common
>> protocol, in most thought experience, but we need to take into account at
>> the start all Alice and Bob to see that there will be non influence at
>> distance, but only sharable self-localisation issues.
>
> That is interesting. What you are saying, quite clearly, is that the starting
> point is for Alice and Bob to rule out the possibility of non-locality. That
> is not a very open-minded or scientific stance. Surely the point of the
> thought experiments is to investigate whether or not the data can be
> accounted for in a purely local way. To assume from the start that there must
> be a purely local explanation is unscientific because you have already closed
> your mind to the possibility of non-locality.
That is not what I have done. But you need locality to apply quantum mechanics
when Alice and Bob prepare their singlet, or compared the correlation, and then
the many-world explains phenomenologically what it looks like an action at a
distance hs taken place, without attributing such action at a distance in the
global physical picture.
>
>
>>>>>> You did not. You have even considered a singlet state like if it
>>>>>> involves 4 parallel universes, when it involves infinitely many. See
>>>>>> more in the archive.
>>>>>
>>>>> The singlet state involves only four possible combinations of
>>>>> experimental results
>>>>
>>>> We have discussed this, and I have never agree with this. The singlet
>>>> state (in classical non GR QM) describes at all times an infinity of
>>>> combinations of experimental result.
>>>
>>> This is false. Even in Everettian QM there are only two possible outcomes
>>> for each spin measurement: this leads to two distinct worlds for each
>>> particle of the pair. Hence only 4 possible parallel universes. Where do
>>> you get the idea that there are infinitely many parallel universes? This is
>>> not part of Everettian QM, or any other model of QM.
>>
>> From Deutsch and many others, but you can deduce it from Everett long text.
>> Just take the universal wave seriously.
>
> I am taking the wave function very seriously for this simple (but closed,
> isolated) system of the singlet state formed from two spin one-half
> particles. The wave function is very simple:
>
> |psi> = (|+>|-> + |->|+>),
>
> within normalization factors.
OK, but that is equivalent with |psi> = (|+'>|-'> + |-'>|+'>), in any other
base {|+’>, |-‘>}.
> The first ket refers to particle 1 and the second ket to particle 2. Note
> that this wave function is intrinsically non-local in that it has no
> dependence on the spatial separation of the particles -- space and time are
> not relevant for this structure. The temporal evolution of this state is
> simply the free particle propagation of the two particles to arbitrary
> separations (at least until one or the other interacts with something else).
>
> Note that the standard expansion requires a set of basis vectors. I have
> written these symbolically as a |+> or |-> basis, but there is freedom in the
> choice of spatial direction for these basis vectors.
Yes, and that means that it describes correlation in all “worlds”, and that if
Alice find a result, Bob will find the correspond result, in the usual way
(cos^2(angle between the two states).
> But note particularly that the spin measurement is made in the basis chosen
> by the experimenter (by orienting his/her magnet).
OK.
> The outcome of the measurement is + or -,
For Alice and Bob, OK.
> not one of the possible infinite set of possible basis vector orientations.
> The orientation is not measured, it is chose by the experimenter. So that is
> one potential source of an infinite set of worlds eliminated right away. The
> singlet is a superposition of two states, + and -: it is not a superposition
> of possible basis vectors.
? (That is far too ambiguous).
> If you think about it for a little, the formalism of QM does not allow the
> state to be written in any way that could suggest that.
>
> I don't know what Everett says in his long text, but if it is any different
> from the above, then it is not standard quantum mechanics. Deutsch is a
> different case. He has a very strange notion about what constitutes different
> worlds in QM. Standard QM and Everett's interpretation are very clear:
> different worlds arise by the process of decoherence which diagonalizes the
> density matrix. The net effect is that worlds are, by definition, non
> interacting (contra Deutsch's ideas).
?
>
>
>>> But even if you can manufacture an infinity of universes, you still have
>>> not shown how this removes the non-locality inherent in the quantum
>>> formalism.
>>
>> You have not shown non locality.
>
> I have demonstrated non-locality in the Everettian context many times. The
> simplest demonstration was in the timelike separation of Alice and Bob's
> measurements. It is in the archives if you don't recall the details. The
> argument then is that any local influence that would explain the timelike
> separated measurements must also work for spacelike separated measurements,
> and that is not possible.
At all time there is an infinity of “worlds”. When Alice chose her direction,
that remains true, and her measurement will tell us if she belongs to a world
with “spin” down or up, she will automatically know that whatever Bob she will
meet, will have the corresponding results, no action at a distance here.
>
>> In the Everett, the locality is preserved by the fact that you need
>> interaction/measurement at some point, and the superstition get “contagious”
>> only at the speed of light, something zurek explained well in his account of
>> decoherence.
>
> This is what you suggested above -- your view is that locality is maintained
> by refusing to accept the possibility of non-locality. Sorry, but that does
> not wash, scientifically or logically.
That reasoning is the same as creationist. Your theory of evolution assumes
that God has not made the world in six days, so, there is no doubt that you can
only see confirmation of it. Of course that is not valid here, nor above.
>
>> Locality is also trivial if you look at each time to the entire multiverse
>> phase space structure. I don’t see how you perceive any influences at a
>> distance.
>
> You perceive them by doing the Bell-type experiments. Remember that quantum
> mechanics is ultimately defined in Hilbert space,
Exactly, and the phase space has to be taken into account to get the
interference right, so that it is physical, but the evolution of the wave is
entirely mechanical, computable, without jump and collapses in the big picture.
Nonlocality and and indeterminacy are subjective rendering due to our lack of
possibility of seeing all terms in the wave.
> and questions of spatial/temporal separation do not arise there, so it is all
> local in Hilbert space.
I am not saying more than this.
> The problem is that converting from Hilbert space (and/or configuration
> space) to normal 3-dimensional space with a distinct time variable, gives
> rise to some conceptual difficulties. Unless you can come to terms with these
> conceptual difficulties, you will never understand quantum mechanics. One of
> these conceptual difficulties is that in normal space-time, quantum mechanics
> is intrinsically non-local.
Only in the first person plural views, which exists by the two linearities at
the base of quantum mechanics (evolution and tensor products).
Everett is just incomplete, because he uses mechanism, and does not realise
that this forces to explain the wave in a similar phenomenological way. That is
what I did.
Bruno
>
> Bruce
>
>
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