On 16 Jan 2014, at 04:05, Jason Resch wrote:

Hyper determinism makes little sense as a serious theory to me. Why should particle properties conform to what a computer's random number generator outputs, and then the digits of Pi, and then the binary expansion of the square root of 2, all variously as the experimenters change the knobs as to what determines the spin axis of the lepton their analyzer measures. Are radioactive decays of particles really such things that are governed by the behavior of a selected random source, or alternately, are they really such things that govern what the digits of Pi or the square root of 2 are?

Yes, that's my point. Price make a logical point, though. But we have to abandon QM for QM + a lot of extra-information to select one reality.

In that case why not come back to Ptolemeaus. The idea that it is the sun which moves in the sky is consistent too, even with Newton physics, if you put enough extra-data in the theory.

With one reality, a quantum computer works only because of extra- magical boundary conditions.

Bruno



Jason


On Wed, Jan 15, 2014 at 6:13 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.




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".



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???)

?




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.





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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