Is Noldus's Approach a Radical Redefinition of Quantum Mechanics?

[marcus]

http://arxiv.org/abs/gr-qc/0508104
Towards a fully consistent relativistic quantum mechanics and a change of perspective on quantum gravity
17 pages, submitted to CQG

"This paper can be seen as an exercise in how to adapt quantum mechanics from a strict relativistic perspective while being respectful and critical towards the experimental achievements of the contemporary theory. The result is a fully observer independent relativistic quantum mechanics for N particle systems without tachyonic solutions. A remaining worry for the moment is Bell's theorem."
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the PF poster Careful disagrees with me about this paper. I see this paper as proposing radical change in QM in order to make it compatible with Gen Rel.

However I mentioned this paper in a couple of other threads and Careful replied that to him it does not seem very radical or unusual.

For my part, I observe that a big problem in physics is that QM is so far only "relativistic" in the sense of SPECIAL relativity. And that means that QM is not really relativistic at all! there seems to be some fundamental difficulty making QM compatible with real relativity, namely with Gen Rel. And this noldus paper discusses these troubles and proposes to change QM! Or so it seems to me.

the proposed change in QM would make it give the wrong answers to Bell experiment, but only by a very slight amount. So maybe Noldus QM could be right, or maybe wrong, and we simply have not noticed because of not doing the experiments with enough precision. I don't understand this and would appreciate some clarification, if anyone can offer some.

So I think the Noldus paper is a radical and risky venture---one should think twice before proposing to reform QM, especially if it seems to contradict Bell theorem.

CAREFUL on the other hand, seems to understand this paper much better than i do and he seems to say that it is NOT so radical at all, and earlier papers by other people have explored these ideas. I don't know these earlier papers, but this is what he says.

 

[marcus]

here is what careful says in the "List" thread:

... In the paper of Noldus, it is never claimed that there is a new approach to quantum gravity, actually many physicists have gone along the same path before him. The author simply wants to investigate what can happen to quantum mechanics when you consistently apply the principle of general covariance and the reality assumption that all processes describing the outcome of an experiment are real and happen in spacetime (although the latter is not explicitly stated, it is clear from the context). Therefore, if you do not dispose of the wave function, you need to attach a reality to it (the author sees measurement as part of that same physical process, so no U/R split). Assuming this, he basically comes to some form of the self field approach to quantum mechanics, which was derived by other means previously by A.O. Barut and J.P. Dowling and is known not to give the correct predictions (although the know differences are rather small, within a bound of 5%), as the author clearly states. Logically, in such a viewpoint, the author is forced to revise the theory of spin (see it really as a spinning particle) which, as he claims, is not excluded to be possible within the framework of of classical Einstein Maxwell theory (and he provides a nice reference which indeed suggests this). So, the question is now, what next? The author seems even to want to go further and see the wavefunction itself as an effective description of a classical chaotic locally causal process (i.e. the wave function is a thermodynamical ``averaged´´ description of a chaotic, locally causal, deterministic process. The locally causal aspect of this approach (which is somehow suggested by its spacetime character) IS the DARING aspect of this approach since it requires that no perfect Bell experiment is ever to be performed. However, IMO, a Bell test which kills off local realism, does not need to kill off such approach; one might consider adding nonlocality scales at that moment in time.
To wrap up: this paper is just (as said in the abstract) the report of an exercise made by the author. Most physicists who think about QM for some while write a paper about it (however, most of these papers are boring and simply discussing some personal ontological viewpoints). It remains to be seen what comes next (and that will be the real test).

On rereading, i see that Careful does grant that at least one aspect of the paper is daring or risky. So to that extent we agree.

the link to this post is
https://www.physicsforums.com/showpost.php?p=852796&postcount=5
and to the thread context is
https://www.physicsforums.com/showthread.php?p=852796#post852796

here are Noldus other papers:
http://arxiv.org/find/grp_physics/1/au:+noldus/0/1/0/all/0/1

besides his PhD thesis, he has 4. the first 3 have already been accepted and published by a peer review journal "Classical and Quantum Gravity" (CQG) and this fourth one that we are looking at now he has also submitted to CQG.

 

[Careful]

**
the PF poster Careful disagrees with me about this paper. I see this paper as proposing radical change in QM in order to make it compatible with Gen Rel. **

It introduces radical changes in STANDARD QM, but - although from another point of view - a mathematically similar modification has been proposed by several other authors like A.O. Barut and de Broglie (look in google for the self field approach). It is just that people do not learn about these in the standard QM courses. So, in that respect, the author produces no new formalism (albeit he comes at it through different motivations which is always useful).

**However I mentioned this paper in a couple of other threads and Careful replied that to him it does not seem very radical or unusual. **

If you are aware of these alternative approaches, then this paper is not very radical, that is true.


**For my part, I observe that a big problem in physics is that QM is so far only "relativistic" in the sense of SPECIAL relativity. And that means that QM is not really relativistic at all! there seems to be some fundamental difficulty making QM compatible with real relativity, namely with Gen Rel. And this noldus paper discusses these troubles and proposes to change QM! Or so it seems to me. **

Here I agree, the marriage between QM and SR is very uncomfortable and you better start out from GR principles.

**the proposed change in QM would make it give the wrong answers to Bell experiment, but only by a very slight amount. So maybe Noldus QM could be right, or maybe wrong, and we simply have not noticed because of not doing the experiments with enough precision. **

I guess the author relies on the fact that if you consider the bare data and do not make additional assumptions such as fair sampling, then there does not exist any Bell experiment to date which violates the weak Bell inequalities (which is actually true). I must add that Bell experiments are pursued vigorously and that one is already engaged in this business for over 25 years (without any conclusive experiment - that makes you wonder no). Actually, you might want to search the Arxiv for papers in 2005 proposing new Bell type tests which might decide the issue (you shall be surprised about the amount).

**S o I think the Noldus paper is a radical and risky venture---one should think twice before proposing to reform QM, especially if it seems to contradict Bell theorem. **

It is risky, true, but possible and it has many advantages if you think about it. About Bell tests, it might be that this story turns out the same way as the supersymmetry tests, this is anyone's guess.