On Wed, Jan 15, 2014 at 7:13 AM, Bruno Marchal <marc...@ulb.ac.be> wrote:

>
> On 15 Jan 2014, at 11:10, LizR wrote:
>
> On 15 January 2014 22:55, Bruno Marchal <marc...@ulb.ac.be> wrote:
>
>>
>> On 14 Jan 2014, at 22:04, LizR wrote:
>>
>> Sorry, I realise that last sentence could be misconstrued by someone
>> who's being very nitpicky and looking for irrelevant loopholes to argue
>> about, so let's try again.
>>
>> Now how about discussing what I've actually claimed, that the time
>> symmetry of fundamental physics could account for the results obtained in
>> EPR experiments?
>>
>>
>> Logically, yes.
>>
>> But you need "hyper-determinism", that is you need to select very special
>> boundary conditions, which makes Cramer's transaction theory close to
>> Bohm's theory.
>>
>
> I'm not sure what you mean by special boundary conditions. The bcs in an
> Aspect type experiment are the device which creates the photons, and the
> settings of the measuring apparatuses.
>
>
> The setting of the analyser must be predetermined. And not in the
> mechanist sense, where the choice of the analyser is still made by you,
> even if deterministically so. With only one branch, you are not just using
> irreversibility, but you are using the boundary condition selecting a
> branch among all in the universal wave.
>

In Wheeler's 'It<Bit' empirical quantum model, that is because in
controlled experiments the detector observers on the detection plane all
ask the same question, thereby always selecting the same spacetime/branch
for photon statistics.

>
>
>
>
> These are special but only in that the photons are entangled ... note that
> this isn't Cramer's or Bohm's theory (the transaction theory requires far
> more complexity that this).
>
>>
>> Those are still many-world theories, + some "ugly" selection principle to
>> get one branch. It is very not "natural", as you have quasi
>> microsuperposition (appearance of many branches), but the macro-one are
>> eliminated by ad hoc boundary conditions, which will differ depending on
>> where you will decide to introduce the Heisenberg cut. Also, QM will
>> prevent us to know or measure those boundary conditions, which makes them
>> into (local, perhaps, in *some* sense) hidden variable theory.
>>
>
> I don't understand the above. The theory is simply QM with no collapse and
> with no preferred time direction (it assumes any system which violates
> Bell's inequality has to operate below the level where decoherence brings
> in the effects of the entropy gradient). It is both local and realistic,
> since time symmetry is "Bell's 4th assumption" - it allows EPR experiments
> to be local and realistic (I am relying on John Bell for this information,
> I wouldn't be able to work it out myself). So it definitely is a "hidden
> variable theory".
>
>
> Yes, and I am willing to accept it is local. but it is "hyper-determined".
> It means that if I chose the setting of the two analyser in the Aspect
> experience by looking at my horoscope, that horoscope was determined by the
> whole future of the phsyical universe. Logically possible, you are right,
> but "ugly", as it is a selection principle based on boundary conditions. It
> is "more local" than Bohm, and it does not need a new potential, but it is
> sill using abnormal special data for the "TOE". It is no more a nice and
> gentle equation like the SWE, but that same equation together with tuns of
> "mega-terra-gigabyte of data".
>

Same comment as above but now controlled experiments also use the "gentle
equation like the SWE', but still in the context of an MWI reality. Richard

>
>
>
> I think for it to work the system is kept from undergoing decoherence or
> any interaction that would lead to MWI branching. EPR experiments only
> appear to work for systems that are shielded from such effects, I think? So
> there isn't a problem with the MWI - the whole thing takes place in one
> branch, with no quantum interfence etc being relevant. (I believe that EPR
> experiments lose their ability to violate Bell's inequality once
> interactions occur that could cause MWI branching within the system under
> consideration???)
>
> A recent paper suggests that decoherence in the experiment particle
preparations are a stronger source of branching than decoherence in the
detector. In terms of Wheeler theory, that amounts to the initial observer,
the prep&emit particle observer, being more capable of producing branching
by asking a variety of questions (decohered questions) or even random
questions, than the final detector observer asking just random questions is
capable of producing branching..
http://phys.org/news/2014-01-quantum-to-classical-transition-fuzziness.html

>
> ?
>
>
>
>
>> Many worlds is far less ad-hoc, imo. There is no Heisenberg cut, and the
>> boundary conditions does not play any special role, and indeed they are all
>> realized in the universal wave (and in arithmetic).
>>
>
> Please explain about the Heisenberg cut. I've heard the term, but don't
> know how it relates to EPR experiments.
>
>
> The Heinsenberg cut is where the wave should collapse in the Copenhagen
> QM.
> Von Neumann understood well that it is largely arbitrary.
>
> In all "one world theory", you have to justify why the superposition works
> so well for the micro-worlds, and disappear for the macro-world.  Using
> reversiblity, cannot by itself solve that problem. What works is
> reversibility and the boundaries conditions. God needs to know all the
> detail of the big crunch to program convenably the big bang, so as making
> an Aspect result consistent with "one-world", locality and determinacy.
>
> Bruno,

The micro-world data is all based on controlled experiments in one branch.
The macro world largely involves both decohered initial and final
 observers.

Doesn't that explain why
"the superposition works so well for the micro-worlds, and disappear for
the macro-world"
Richard

>
>
>
>
> Have you read Huw Price's book "Time's arrow and Archimedes' Point" ?
>
>
> No. I know it,  as it is often discussed on forums.
>
> I am not convinced, as I tend to not believe in any primitive time and
> space, at least when I tend to believe in comp (of course I *know* nothing).
>
> QM is indeed reversible (in large part), but using this to select one
> branch by boundary condition, is still like a form of cosmic solipsism to
> me. We can't refute it, and unlike most QM collapse theories, we can't
> criticize it from locality and determinacy, but that does not yet make it
> convincing compare to MW, and infinitely more so in the comp frame, where
> we can't avoid the many "dreams".
>
>  Bruno
>
>
>
>
>
>
>
>
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> http://iridia.ulb.ac.be/~marchal/
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