Interpretations of Quantum Mechanics (is there a general consensus?)

ardenmann0

If it doesn't represent a real field, how can it interfere with itself in the double slit experiment?

We can't detect gravitational waves right now, but it does not mean they do not exist.
It just mean our instruments are not sensitive enough to detect them directly right now.

Naty1

Vectronix:
There are many interpretations...check here in Wikipedia
for background and introduction

http://en.wikipedia.org/wiki/Quantum...ulus_formalism



It's probably the 'abstract vector space' formulation thats leads to major disagreements.

Here are a few quotes I saved from QUANTUM MECHANICS by Albert Messiah:

This first may be the most controversial:

So some new mathematical models became popular:

* This is a 'one liner' referring to the Heisenberg uncertainty principle.

So what we have, in my own words, are models. They provide some great insights, have been shown to offer many experimental predictions which have been verified to great precision, but which still leave remaining interpretational issues.

Ken G

My point is that with multiple particles, complete information in quantum mechanics refers not only to the particles themselves, but also to their correlations. The importance of correlations doesn't mean we are not dealing with things that "reside" in 3-space, it just means that correlations are more sophisticated animals. We would face an analogous issue if we were interested in purely classical correlations between density variations between two species in 3 space, like two types of gas. There our density correlation functions would be mathematically dependent on 3X2 space, not 3 space, because we'd be interested in questions like the probability of finding density increases in one gas given that we have nearby density increases in the other. Yet even so, no one would question that the density distributions themselves "reside" in 3 space. The mathematical animal needed to talk about correlations in 3 space is a higher dimensional object, but I don't see why that needs to compromise our sense of where these correlations "reside." It's like how in relativity, we think of events as residing in spacetime, but the fields in relativity are tensors, not vectors that take on values in spacetime. So they are more sophisticated mathematical objects, to maintain the correct invariances, yet we still think of relativistic fields as "residing" in spacetime.

Ken G

Yes I think that was well put, though I would personally question his adherence to realism at the cost of allowing retrocausality. The reason I think one should hold causation and drop realism is that causation is epistemic and realism is ontic, and I view physics as primarily epistemic, so we should always hold epistemic principles above ontic ones. That might be the most boiled-down way to restate Bohr's approach.

bohm2

If one isn't a wave function "realist" it doesn't matter, but if one assumes wave function "realism", doesn't that necessarily also lead to:

1. configuration space "realism" (e.g. if wave function is real, then the 3-D space of our ordinary experience must be an illusion). Or
2. at least a need to explain and find a way to recover 3-D space from configuration space and wave function ontology.

Some argue that there are problems with taking option 1. above (e.g. David Albert), however as noted by Maudlin and summarized here by Ney:
So, then what is the "N" of 3-N dimensional space about if not particles?

Ontological Reduction and the Wave Function Ontology
http://www.rochester.edu/college/fac...veFunction.pdf

bhobba

Come again - you don't need to recover anything - it makes probabilistic predictions about what happens in 3D space just like for example a probability vector predicts how a dice behaves in 3D space.

Thanks
Bill

bohm2

I'm only talking about one who is a wave function realist.

Pollock

The original question was Interpretation of QM;is there a general concensus? Why dosen't someone answer that question ?.
Does anyone still take the Copenhagen view as the best available?.What other interpretations are currently favoured?.

bhobba

No there isn't. And there are people who still adhere to Copenhagen as the best there is. What do you mean by currently favoured? These days with more to choose from its probably even more 'jumbled'. But a new one called Consistent Histories (some people say its Copenhagen done right) now has a lot of adherents and the Ensemble Interpretation of Einstein (also known as shut up and calculate - its my view) has come on strong.

Thanks
Bill

bhobba

Even then its the same thing - the quantum state resides in 3D space - but its exact nature is an open question.

Thanks
Bill

bohm2

The wave function cannot exist in 3-D space. Predictions of QM depend on the 3N-dimensional space that get lost in the 3-D representation (e.g. information about correlations among different parts of the system, that are experimentally observed are left out). For a philosophical discussion of this see the following thread:

The reality of configuration space
http://www.physicsforums.com/showthread.php?t=554543

Ken G

You're saying that if the wavefunction is regarded as real, then the space on which it takes on values must be the space in which it "lives." If the particles are instead regarded as real, then the wavefunction can just be thought of as a way to organize information about those particles, in which case the particles can still "reside" in 3 space while the wave function takes on values from some information space. I think that's true, I just don't really buy the idea that either the wave function or the particles are real. It's all just the spaces we use to picture the information-- the information of a wave function takes on values from configuration space, but that's nothing new, we have many ways of organizing information about particles that is accessed from configuration space. But even the particle concept, and the 3-space concept, are just more ways of organizing information. Why do we need to say which mode of information is real? All information is real, but it's still just information.

Hence I think a lot of this issue relies on what we think is "existing in" 3D space. The wavefunction of multiple particles is not a function on 3D space, we can agree there, but I don't see that it has any problem referring to other entities that "reside" in 3D space. We are interested in tracking correlations, so the correlations can't exist in 3D space, but what they are correlating can. I don't see why this issue is any different from using phase space to talk about N gas particles in a box, for example. The 6N dimensional phase space of those N particles is also not a 3 dimensional object, but it is clearly referring to particles that can be pictured as "residing" in 3 space, and moving through 3 space. It's just the mathematical treatment, like if we say F=ma we are looking at a second time derivative of a 3D position, but if we say F(x)=dp/dt and p=m*dx/dt, we are looking at two first time derivatives on a 6D space of x and p. No one thinks these two different formulations call into question the reality of whether particles "reside" in 3 space, if one is a realist in regard to particles, there is just a difference between the entities we are interested in versus what space we use to track our information about them. But I don't really see any point in being a realist in regard to either particles or wavefunctions-- physics manipulates information, get over it, is my attitude. (That isn't "shut up and calculate", it's "talk as much as you like, but what you are talking about is information.")

bohm2

Sure, but then realists are likely to ask "information about what" and "whose information"?

StevieTNZ

Here is a paper by Renato Renner and co, entitled: Completeness of quantum theory implies that wave functions are physical properties

http://arxiv.org/abs/1111.6597

bhobba

Cant follow that one. It can be considered a complex function f(x1,....,xn) - the xi are positions of n particles in ordinary 3d space - it doesn't have to emerge from anything. f gives the probability amplitudes of the particles having those positions. Such functions can be expanded in terms of a infinite but countable basis for theoretical convenience but that does not mean it literally resides in such abstract spaces. If you consider the f real then there is an issue exactly where it resides - it may reside just as a conjecture in some rolled up higher dimensional space that the xi are also in - but 3d space does not have to emerge from anything - its existence is built into the xi.

martinbn

I am with bohm2 on this one. And I am puzzled about what the meaning of 'real' is to people that say that the wave function is real! Usually it is said that it is real in the same way as the electromagnetic field is, but it is obviously not real in that way. To me real means that there is an object that is in 3D space that intereacts with other objects. Then clearly the wave function is not such a thing. So what does real mean to those poeple?

bhobba

Real means it has an external existence and not just a calculational device. In saying it is real like an electromagnetic field it is meant it has an external existence. There are all sorts of possibilities of how that can be - here is an interesting one:
http://arxiv.org/pdf/1104.2822v1.pdf

You mentioned Bohm2 - Bohms pilot wave would be something that also had real existence - the theory is a bit vague about exactly what it is.

Thanks
Bill