Are superstrings the only option? What about GR approaches?

[Careful]

**
I repeat: as long as the new theory (with no matter what fundamental principles, based upon the superposition principle or not, return to classical or not, something completely new and unexpected or not) has not derived AT LEAST compatibility with the *practical and empirically confirmed* parts of currently existing theories (GR and "practical QM"), then all arguments about the correctness of its starting principles is all just faith, religion, intuition, gut feeling or whatever you like to call it. **

I don't know why we speak about this all again, since I fully agree with you (apart from some small issues). Any dynamics one comes up, has to agree with undisputed experiment, period. Whether the underlying dynamics is a locally stochastic theory of a determinstic one with information loss, to what degree the Bell inequalities have to be violated, how the causal transmission of information has to be implemented are all open issues (to which I am open). Apart from Barut self field and Santos/Marshall SED, there is not so much done around this yet (and even these approaches are not known by most physicists !). There are very compelling reasons for the ZEP EM field and certainly there is a deeper content to that. Concerning Barut Self field, it appears to me very instructive to know of a nonperturbative rigorous theory (in that sense it is far superior to QED) which reproduces known effects. So, these are the first things to take into account when you want to address the above question.


**Everybody is free to LOOK for other approaches, but this is, to a high degree, a totally personal matter. **

Not entirely (!), I said practical QM is incomplete; so the fact of looking is not personal. IN WHICH DIRECTION one looks is more open to that comment (and even not entirely).

**
Well, it has also not been a very rewarding policy in science to neglect empirical success :-) **

Cannot agree more...

** Look at GR: Einstein knew that he needed to find Newton's gravity as a limiting case. In the same way, *practical* quantum theory restores classical results in many examples (the "practical part" being the judicious choice of how and when to apply Born's rule). **

Well yes, hence QM is incomplete (GR does not have that problem), therefore what is the discussion about? I only said that whatever approach you try, you need to find an answer to that question (whether it be gravitationally induced or spontaneous collapse models or whatever). Moreover, there are clear, well known relations between SED/Barut self field and standard QFT.

So I say one has to *look* for this dynamics, how to do that is an entirely different matter to which I have no prejudices whatsoever.

Cheers,

Careful

 

[vanesch]

** Look at GR: Einstein knew that he needed to find Newton's gravity as a limiting case. In the same way, *practical* quantum theory restores classical results in many examples (the "practical part" being the judicious choice of how and when to apply Born's rule). **

Well yes, hence QM is incomplete (GR does not have that problem), therefore what is the discussion about?

I'm more careful than you here, I think. I'm not convinced that QM has to be considered incomplete as a "toy model". You (as many others) don't like MWI scenarios because 1) they sound so strange and 2) they DO need, IMO, indeed an extra postulate about such a volatile concept as "conscious observation". But when you are willing to accept that, I think that QM can be made as complete as any other theory. I will not deny that this is intuitively uncomfortable, but it is logically thinkable.

It's a different mindset to consider a theory a priori badly constructed (and hence, one should not pay much attention to its foundations) as you seem to think about QT, and to consider that a theory could be well constructed and hence its foundations might, or might not last, and nature (experiment) is the ultimate judge of that.
In the first (your) case, you will simply try to start "anew from scratch", while in the latter (my) case, you'd be more reluctant to let go *entirely* a scheme that worked well.

I think this is the main difference: you say, because QM is ill founded, its founding principles have no real value ; I'm not so sure about that.
If, in the end, it turns out that nothing remains of the principles of QM, then you are of course on a head start because others will still try to save some of its structure, in vain ; if however, some principles are supposed to remain for ever with us then you've cut yourself off the correct track.

 

[Careful]

** I'm more careful than you here, I think. I'm not convinced that QM has to be considered incomplete as a "toy model". **

You are not grasping my point yet. QM is fine as a toy theory for predicting statistics of *repeated*, ``indentical'' experiments, but is incomplete as a *spacetime* theory (even James Hartle does not address this).

**You (as many others) don't like MWI scenarios because 1) they sound so strange and 2) they DO need, IMO, indeed an extra postulate about such a volatile concept as "conscious observation". But when you are willing to accept that, I think that QM can be made as complete as any other theory. I will not deny that this is intuitively uncomfortable, but it is logically thinkable. **

Well, two things : (a) you might guess what my grandmother says when I explain MWI to her (b) I excluded MWI as it stands now when I asked for a *dynamics* of single particles. And again, even the most perfect MWI theory possible does not make sense in a spatio temporal framework (you might want to think about that ! - there are very serious logical objections against it).

**
..
I think this is the main difference: you say, because QM is ill founded, its founding principles have no real value ; I'm not so sure about that.
If, in the end, it turns out that nothing remains of the principles of QM, then you are of course on a head start because others will still try to save some of its structure, in vain ; if however, some principles are supposed to remain for ever with us then you've cut yourself off the correct track. **

Wrong guess again , I do not say QM is ill founded, I say it incomplete in a crucial sense for QG. However, if you think about the dynamics for a single particle long enough, then you will understand that in order to regain *a large part* of the quantum statistics, one needs very different foundations. So, of course I am not saying one has to trow the child away with the bathtob (something many people like to think ) ! People did not dispose of thermodynamics either after it was explained through the means of statistical physics.

I ask you to read *carefully* my messages over again (no offense of course :-)), there is some specific point I highlight which you are missing ; that is : practical QM does not make sense in a *spatio-temporal* sense (for the universe). In your comments you are mixing up other ``realist issues'' with QM; QM has many different realist problems, it is important to keep them distinct. (anyway, I have to go now, we can perhaps continue this discussion in 2 weeks)

Cheers,

Careful