Why is there no 'classical' interpretation of movements in quantum mechanics?

1. Feb 25, 2012

Xilor

There are tons of interpretations of quantum mechanics, but I'm unaware of any that are 'classical' as in being local, having realism and determinism.
There is Bells famous work proving that that can't be true for certain aspects of quantum mechanics, but why aren't there any classical interpretation which apply to the movements of particles and which call entanglement just a completely different phenomena?

Using a real wave and by using chaos it seems to me that all the movement issues such as the double-slit experiment but even the quantum erasure experiment or the delayed choice experiment can be described at least conceptually just fine, some of the details would be strange, but far less so than breaking realism is to me. What am I missing here?

2. Feb 25, 2012

IttyBittyBit

3. Feb 25, 2012

Xilor

Unfortunately that goes quite a bit over my head, but from reading through it I couldn't really find any experimental evidence besides Bell work that shows that quantum mechanics can't be solved classically, any arguments seemed to be based on that and not for example particle movements.

4. Feb 25, 2012

juanrga

There exists QM (which is taught at ordinary textbooks) and then tons of misinterpretations of QM (e.g., many-worlds).

It is not true that by using «a real wave and by using chaos» you can describe quantum motion. 5 is not 2+1.

5. Feb 25, 2012

Xilor

Misinterpretations? I always thought they were quite well supported.

Anyway, where does it go wrong using real waves? Which parts of it don't work out?

6. Feb 25, 2012

juanrga

Many-worlds and similar stuff are nonsense:

http://www.mth.kcl.ac.uk/~streater/lostcauses.html#XII [Broken]

http://www.mat.univie.ac.at/~neum/physfaq/topics/manyworlds

and so on.

There are not «real waves» in QM. The state of a pure state in quantum mechanics is described by a ket $\left| \Psi \right\rangle$, which can have associated a complex phase.

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7. Feb 25, 2012

StevieTNZ

The Copenhagen interpretation can be ruled out by probing a macroscopic superposition state (again in reference to my love for Ghirardi's thought experiment).

8. Feb 25, 2012

Xilor

So which interpretation is the right one according to you?

That unfortunately doesn't really aid in helping to understand why it is that real waves don't work out. Fine, they aren't used in quantum mechanics, but why not? At least conceptually it seems very possible to me to use a real wave like a guiding wave of a particle with a defined position. Why doesn't this work out?

Last edited by a moderator: May 5, 2017
9. Feb 25, 2012

Mr_Physicist

Any interpretation of quantum mechanics must be consistent with experiment. A model or interpretation that only works if you ignore or exclude certain phenomena is not a model or interpretation worth pursuing.

10. Feb 25, 2012

Xilor

Well Bells argument only works on entangled particles, that seems to be something clearly different than the movement of particles. If a theory like that could predict all particle movements but leaves entanglement for different theories, why not use it? I understand it wouldn't be a perfect solution, but I don't really see why it isn't even mentioned anywhere as a reasonably valid idea.

11. Feb 25, 2012

Maui

Why is there no 'classical' interpretation of movements in quantum mechanics?

Is there classical motion in quantum mechanics?

12. Feb 25, 2012

Xilor

There's no motion in straight lines. But classically held notions about realism determinism and locality seem to be be preservable, at least with my limited amount of knowledge. And I'm wondering either why it's impossible like that, or at least why no one really seems to think that models preserving all 3 of those are viable.

13. Feb 27, 2012

juanrga

I think already said that QM is explained in textbooks. The two-volume set by Cohen Tannoudji gives a rather good treatment.

«Real waves» are not used in QM by the same reason that kinetic energies as 1/5 mv2 are not used, because world is not made in that way. «At least conceptually» is not a valid scientific argument. Sure that kinetic energy (mv2) is 'conceptually' simpler, but just does not work.

It is completely incorrect to use «a real wave like a guiding wave of a particle with a defined position», because even if we were to admit that particle has one always (it does not as QM explains), if we were to ignore mixed states, and if were to confound a pure quantum state with a real wave, this whole mess does not describe particle correlations among other stuff.

Last edited: Feb 27, 2012
14. Feb 27, 2012

DrChinese

Why would someone prepare a model which is less useful that the one currently in use?

Also, not sure if you use the word "real" in the same context as juanrga does. He means real as opposed to complex. You may real as opposed to mathematical constructs. Or do you mean real as in realistic (which is yet again different) ?

15. Feb 27, 2012

Naty1

two basic ideas:

You can argue that there is no 'classical description' of QM in part because they are 'different' theories. The former covers generally large scale apparently, continuous, observations, the other discrete, quantized,discontinuous behavior at small scales.

Secondly, we have different mathematical models....we haven't been completely smart enough to unify all our mathematics yet.....so we have [classical] theory for gravity (GR) on one hand and quanum theory for the standard model of particle physics. [Nothing is able to tie those together yet, but 'quantum gravity' is one effort to do so.]

wiki introduction on quantum mechanics:

http://en.wikipedia.org/wiki/Quantum_mechanics
I know some will disagree with parts of this description, but a fundamental constraint of quantum mechanics does not meet classical notions, not classical mathematics:

[There is not real 'wave-particle duality' within the context of QM; it is what it is....but 'classically' we use such descriptions to convey the analogy.]

Heisenberg uncertainty: I would argue that IS a 'classical' description....it bridges a gap between the commutativity and non-commutativy of classical and quantum mathematics...
It may make little sense in 'classical' reasoning [that you can't measure two particular observables simultaneously to whatever degree of accuracy your instruments will allow] because we don't such restrictions on large scales....we can make such measurements of,say,planets.

Xilor: To some extent you are reasoning from incorrect assumptions and reaching dubious conclusions...we all do that, so take it as a criticism if you must, but after you need do more homework you won't start from such perspectives...example:
Since no one else has taken issue, let me:

http://en.wikipedia.org/wiki/Principle_of_locality

we don't describe entanglement classically because nobody knows how!

One simple way to start getting broader perspectives : read the Wikipedia articles on each of those three... realism, determinism,locality....pick out a few things you don't get and question them in the forums...this stuff is subtle and we all gain from reading others descriptions...that's one reason I'm here.

Last edited: Feb 27, 2012
16. Feb 27, 2012

Xilor

How would it be less useful? Is usefulness determined by how unified things are? I don't see a problem with placing all particle interactions and inner particle workings in different models. Perhaps finding out what is really happening is less important than finding out how to do predictions, but surely if there's only a small chance that that is what is really happening and the same predictions are made are the same, why isn't the thought at least worthy of exploration?
I would be convinced that it would be worthy if it wasn't already disproven somehow. What however would be disproving is what I'm mainly asking about, as I do not know.

I meant with the wave being real as in opposed to mathematical constructs. For example it seems to me that in Bohmian mechanics (correct me if I'm wrong), there is a guiding wave which is more like some sort of nonlocal calculating device taking all particles in the universe into account. Replace that calculating device with something local and realistic which is actually out there, flying around, propagating due to it's own shape, interacting with the particle it is guiding and other particles (observers which eliminate the wave, mirrors, and so on), and you pretty much have the real wave I mean.
Thanks for clearing that confusion up, I was already wondering why he would respond about kets and complex phases which didn't seem to have a lot to do with what I was trying to ask.

Well I didn't really mean it should be called classical mechanics, I meant an interpretation of quantum mechanics which is split into two parts. One about the movements and positions or particles and interactions which would be local, realistic and deterministic. And one about inner particle variables like spin which would also handle entanglement which would not be local, but realistic and possibly deterministic.

That's why I'm here, to find out where my thinking is going wrong.

Well I'm aware locality must be broken in entanglement, I'm wondering why this combinations of realism, determinism and locality seems to be excluded by everyone for particle movements as well as entanglement. I just don't understand why a rule found for quantum entanglement must be true for all of quantum mechanics, the terms both have the word 'quantum' in them but that doesn't really seem like a reason strong enough to force them together in that way. Maybe I'm still too much in a classical mindset, but locality and realism especially still give me the: "it must be like that!" vibe, and while locality is broken in entanglement it would be great if it could be preserved in particle movements in my mind. Locality breaches through entanglement might still make some 'sense' (physics isn't about sense of course, but it helps) but I just can't picture particles being nonlocally influenced by all particles in the universe.

The articles which I had red a few times before didn't really spawn any questions, these were luckily not the pages containing maths that probably require a few years of study.

Edit: In hindsight, I've always wondered how close true locality would be. Is that only particles less than a Planck length away? Or should particles even overlap?

Last edited: Feb 27, 2012
17. Feb 28, 2012

juanrga

Excellent point! Yes, I had taken to him to mean "real" in the sense of complex numbers. But he means something different, thanks by your correction!

18. Feb 28, 2012

juanrga

It is less useful on that (i) explains less than current models and (ii) cannot be used to do predictions.

Although you mean real in the sense of non-mathematical, the remarks given before about quantum states still apply. It is also evident that you do not understand what is math and what is real. Your claim that a wave is something REAL, when is a mathematical construct with a limited validity, says it all.

Another problem of your philosophical approach is that the movements and positions of particles and their interactions are non-local, realistic, and non-deterministic.

19. Feb 28, 2012

Xilor

I'm not claiming anything, I am asking why it has to be like that. Why doesn't a REAL wave work? Why is a purely mathematical model preferred over that?

Again, I'm aware that no current models have particle movements which are local, realistic and deterministic, so I am asking why this is the case. Which experimental evidence or arguments derived from those show that particle movements have to be non-local and non-deterministic?

20. Feb 28, 2012

Demystifier

One of the possibilities is that particle trajectories in spacetime are classical (or at least local), but that the usual local relativistic proper time is not the true physical time. Instead, a nonlocally modified proper time can account for all nonlocal correlations. For more details see
http://xxx.lanl.gov/abs/1102.1539