On Thursday, July 26, 2018 at 4:59:01 PM UTC, Bruno Marchal wrote:
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> On 26 Jul 2018, at 09:55, [email protected] <javascript:> wrote:
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> *I think this discussion is a waste of time. You can't even understand why
> a classical wave which extends to infinity along an infinite plane implies
> FTL,*
>
>
> You are right. I can’t understand that. It makes absolutely no sense to
> me. Wave, in physics, are the paragon of locality. It is a local
> perturbation which “contagiates" its local neighbours.
>
*How can the amplitude get to infinity in all directions along a plane,
unless, when created, there is instantaneous propagation? AG** |and you
bring in collapse at every opportunity, even though I am not discussing it
in this context. *
>
>
> Were talking between QM. We must decide if we put the collapse axiom or
> not as part of the theory. That’s the key point in all the discussion about
> the nature of the superposition.
>
*That's really another issue, obviously an important issue, but I was not
discussing it in the context of my critique of superposition. AG *
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> Bruno
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> *Let's end this discussion. AG*
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> *Finally, FWIW, the mystery of QM is its probability prediction, which is
>> *different* from what one would expect classically. This is because the wf
>> is complex, and because the probability is calculated by taking the
>> norm-squared, one gets a different prediction for the interference, which
>> manifests mathematically by the existence of cross terms. A*G
>>
>>
>> Indeed, and the cross term invites us to take Feynman many path, or Dirac
>> superposition as physical reality.
>>
>>
>>
>>
>>
>>> That has been verified directly and indirectly by molecular and atomic
>>> physics, and even black hole and cosmology. It is not a question of
>>> interpretation: it is a fact that a state like up+down will pass with
>>> probability one a “polariser” (analyser) measuring in the base {up+down,
>>> up-down}, and that is not the case for a mixture of up and down particles,
>>> each of which pass with a probability 1/2.
>>>
>>> Before discussing any interpretation, we need to agree on the theory we
>>> are using. I am discussing Everett theory, which is Copenhagen minus the
>>> collapse postulate. Without the collapse postulate, no superposition ever
>>> reducse into a singular state projection. That contradicts the quantum
>>> linearity.
>>>
>>> Being a pure state like “up” is always relative to an instrument
>>> measure. All state are superposition when develop in other bases, and those
>>> are real, we can test them. A state like up is really up’ + down’. That is
>>> exploited in quantum computing, where some algorithm can superposed many
>>> computations at once, and, despite we cannot observe each individual
>>> result, we can test global information on all results, like "are they all
>>> the same or different? or question of parity of results, etc.
>>>
>>> The so called “many-world” interpretation is just QM-without-collapse
>>> taken seriously. No need to add some metaphysical world(s) here or there. A
>>> world can be defined by just any completion of a state that we can measure,
>>> but it is an open problem if that exists (except with mechanism: we have
>>> good reason to disbelieve such worlds).
>>>
>>> The instrumentalist idea that the superposition are only tools to
>>> calculate probabilities was inspiring a long time ago, but it does not
>>> work. Nature confirms their physicalness, notably by testing the observable
>>> difference between mixed state and superposition. We can add hidden
>>> variable, or Bohm’s Guiding particles Potential, but this has been shown to
>>> lead to FTL (even instantaneous) influence(*) and other magic things or to
>>> many-worlds.
>>>
>>> In my opinion, you are just saying that the physical reality do not obey
>>> Everett quantum mechanics, i.e. that some collapse occurs somewhere,
>>> instantaneously.
>>>
>>
>> *I never discussed collapse, one way or another. I just claim that there
>> is apparently no justification for the Copenhagen(?) INTERPRETATION of
>> superposition in QM. *
>>
>>
>>
>> It is a new axiom in the theory, before leading to any interpretation. I
>> agree with you, the collapse is just a coquetry added to avoid being
>> oneself and the (local) physical reality multiplied. But there is no
>> experimental evidence for such a collapse, and it entails FTL,
>> indeterminacy. With the SWE without collapse, the probabilities come only
>> from the impossibility to know which branch of the universal wave we are
>> in, like with mechanism we cannot know which computations support us. QM
>> confirms Mechanism here.
>>
>>
>>
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>> *I have asked for the justification many times, but no takers. *
>>
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>> In this list, few people believe in a collapse.
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>> *I don't think they can justify it. Of course, generally, postulates are
>> not amenable to justification, but in the case of superposition, the
>> interpretation I object to has a unique property; it's never applied in a
>> calculation! *
>>
>>
>>
>> That makes no sense. I can’t explain neither the two slits, nor the
>> working of an interferometer, nor the hydrogen atom, nor anything, without
>> the superposition principle. The collapse is never used, but the
>> superposition is just a consequence of the fact that state are represented
>> by wave, or by “vector” in a Hilbert space (which mainly a linear
>> (vectorial) space with some scalar product).
>>
>>
>>
>> *It just creates contradictions.*
>>
>>
>> Where?
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>> * Nor do I discuss Everett insofar as it's the dumbest theory I have ever
>> heard or, or can imagine. *
>>
>>
>> Everett theory is just the SWE. It is the addition of the collapse which
>> is the “dumb” move, I would say.
>>
>> Bruno
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>> *AG*
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>>> In 1927 Einstein gave a simple thought experience, the one particle in a
>>> sphere, and explain that if the collapse is physical, it has to violate
>>> special relativity. Hs EPR paper is closer to an experimental treatment, as
>>> Bell has shown, and QM seems to be vindicate, so the choice is really
>>> between many-worlds, or the abandon of special relativity (or the bandit
>>> that QM says anything about the physical reality).
>>>
>>> Bruno
>>>
>>>
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