QM Interpretations: Most Popular & Why?

[curiousphoton]

The following are the interpretations of QM:

Bohmian · CCC · Consistent histories · Copenhagen · Ensemble · Hidden variable theory · Many-worlds · Pondicherry · Quantum logic · Relational · Transactional

Which is the most accepted by the theoretical physics community? Obviously all have some supporters but I'm interested in finding out which is the most popular and why?

Thanks.

 

[DrChinese]

There have actually been surveys done on this here. And I have seen some informal surverys as well. In many ways the most popular answer may be "Don't know, not sure if I should care". Not saying that is my opinion or that most specialists hold that view, but I would say it reflects the viewpoint of a lot of working physicists.

 

[Bob_for_short]

Ensemble, of course. It is not so opposite to the others though.

Why ensemble? Because one point does not give you all information about the quantum state. One point is a too poor experiment. You cannot even tell/prove where it comes from.

As in the macroscopic case, in the microscopic case you also deal with compound systems. And any compound system needs many exchanges to reveal its true face. More pixels, better image.

 

[RUTA]

I find the majority of physicists don't care about interpretations, subscribing to Mermin's "shut up and calculate." Physics Today 57, #5, 10-11 (2004).

 

[Bob_for_short]

I find the majority of physicists don't care about interpretations, subscribing to Mermin's "shut up and calculate." Physics Today 57, #5, 10-11 (2004).

They keep exactly to the ensemble interpretation: everybody calculates probabilities in our, single Universe according to the wave (quantum) mechanics.

 

[hamster143]

They keep exactly to the ensemble interpretation: everybody calculates probabilities in our, single Universe according to the wave (quantum mechanics).

That's like saying that all agnostics are Buddhists, because Buddhism allows the possibility of all other gods.

Among physicists who do express preference for an interpretation, many-worlds interpretation is very popular.

 

[Demystifier]

The following are the interpretations of QM:

Bohmian · CCC · Consistent histories · Copenhagen · Ensemble · Hidden variable theory · Many-worlds · Pondicherry · Quantum logic · Relational · Transactional

I never heard about CCC and Pondicherry. What are those? Some links?

 

[Bob_for_short]

Among physicists who do express preference for an interpretation, many-worlds interpretation is very popular.

How about the experimentalists? Are they content with one-point data in a double-slit experiment or do they care about measurement statistics in this world?

 

[vanesch]

How about the experimentalists?

I also prefer Many Worlds - and I am (or used to be) an instrumentalist/experimentalist. But I don't consider MW necessarily as "true", I only consider it as a very helpful mental picture to get some intuition for quantum-mechanical experiments. It avoids the difficult question of "what is a measurement" and "when does the wave function collapse" - and when you do so, all apparent paradoxes of EPR experiments and of retarded quantum erasers and so on disappear.

 

[Bob_for_short]

I also prefer Many Worlds - and I am (or used to be) an instrumentalist/experimentalist. But I don't consider MW necessarily as "true", I only consider it as a very helpful mental picture to get some intuition for quantum-mechanical experiments. It avoids the difficult question of "what is a measurement" and "when does the wave function collapse" - and when you do so, all apparent paradoxes of EPR experiments and of retarded quantum erasers and so on disappear.

Sorry to hear that.

 

[vanesch]

Sorry to hear that.

 

[curiousphoton]

Among physicists who do express preference for an interpretation, many-worlds interpretation is very popular.

So far many-worlds is my favorite. Is the fact that you have 12 interpretations of QM (and you may basically choose a favorite because one is not technically more correct than another) a major downfall to the theory?

I never heard about CCC and Pondicherry. What are those? Some links?

Wikipedia

 

[Count Iblis]

My opinion is that either MWI is true or QM itself is not exactly valid.

 

[f95toli]

How about the experimentalists? Are they content with one-point data in a double-slit experiment or do they care about measurement statistics in this world?

Remember that not everyone who is doing "QM experiments" are working in optics. The double slit is a nice "toy" but it is far from the only system where you can see "weird" quantum effects.
There are plenty of people (me included) who work on system where there is only a single "quantum object" and not an ensemble, this includes just about everyone working with single qubits (solid state systems, ion traps etc).

Personally I am in the "shut up and calculate" camp, and so is just about everyone else I work with.

 

[Bob_for_short]

...There are plenty of people (me included) who work on system where there is only a single "quantum object" and not an ensemble, this includes just about everyone working with single qubits (solid state systems, ion traps etc).
Personally I am in the "shut up and calculate" camp, and so is just about everyone else I work with.

The more you will work with your "single quantum object", the more data you will analyse, the better you will understand what an "ensemble" means. It is an ensemble of data about your single system, it goes without saying, and that's why it is sufficient to shut up and calculate.

 

[Demystifier]

My opinion is that either MWI is true or QM itself is not exactly valid.

My opinion is that MWI is correct but not complete.
(MWI by itself in its minimal form cannot explain the origin of the Born rule.)

 

[f95toli]

The more you will work with your "single quantum object", the more data you will analyse, the better you will understand what an "ensemble" means. It is an ensemble of data about your single system, it goes without saying, and that's why it is sufficient to shut up and calculate.

True, but that is hardly a unique property of quantum systems. Most experiments involves taking averages of some sort at one point or another even if it just means increasing the integration time of your multimeter; but that has more to do with achieving a better signal-to-noise ratio than of any fundamental property of the system you are measuring.
There are certainly examples where one can -at least in principle- see the "quantumness" of a systems using a single shot readout. An obvious example being to first manipulate a single using MW pulses and then reading out its state using a measurement pulse. Now, the final result of such a procedure is obviously single-valued (since the qubit will end up in one of two states) but what comes before that (the manipulation) is very much a series of "quantum operations".
Any interpretation (or -in my case- lack of interpretation) should surely take into account not only what we see after the measurement pulse but also what is happening when we are manipulating the qubit; because even though we are not measuring we are certainly doing SOMETHING to the qubit with our pulses.

 

[Demystifier]

Wikipedia

CCC = consciosness causes collapse

Pondicherry interpretation: as I understand it, seems to be a variant of the instrumentalist interpretation - QM is nothing but a tool for calculating probabilities.

Am I correct?

 

[Dmitry67]

So far many-worlds is my favorite. Is the fact that you have 12 interpretations of QM (and you may basically choose a favorite because one is not technically more correct than another) a major downfall to the theory?

There is a problem with Born rule. THere were claims that it hadbeen succesfully derived from 'pure' QM formalism, and another claims, that the derivation was circluar.

But MWI is deterministic, so it is not clear what the 'probability' means in that context. So yes, there is some mystery, but I don't see it as a weakness, instead, it is a hint that we are missing something interesting about the reality.

Then, the 'appearence' of the classical world is based on the Quantum Decoherence. QD has some difficulties:

The choice of basic of decoherence is arbitrary. So you should define the basic based on some definition of the 'macroscopic system'. When 'macroscopic system' and basis are defined, you can define the 'branch'. But systems have different states, and in some branches we even don't exist! So the choice of a basic is branch-dependent.

But these difficulties are rather technical: we don't know how the brain works, but it is not a fatal probalem for physics. So we can not correctly and completely define a 'state' and 'basis' or complicated system, but it is not fatal.

And it is much better that that 'collapse' nonsense from CI - CI is absurd, it just can't be true.

 

[Bob_for_short]

...But MWI is deterministic, so it is not clear what the 'probability' means in that context. So yes, there is some mystery, but I don't see it as a weakness, instead, it is a hint that we are missing something interesting about the reality.

The missing part is simple: we have to recognize that even in a microscopic world we need many points of measurement to get some information. Information is not reduced to one point. On the contrary, the more points, the more accurate information about a system. Just like a photograph. The trick is that we think of microscopic world as of elementary, reducable-to-one-point world. It is this idea that fails.

The classical world also "appears" as the inclusive picture (sum of many different QM events). Again, a photograph is a right example.

 

[Dmitry67]

It might make sense, but it not the MWI... on the other side, QD is not a part of MWI either... I mean, it is not absolutely required... so may be you're right...
But I've heard about the Informational Interpretation, looks like it is close to what you are explaining.

 

[DrChinese]

Is the fact that you have 12 interpretations of QM (and you may basically choose a favorite because one is not technically more correct than another) a major downfall to the theory?

Not at all. And that is why it is not such a big deal to many working in the field. To many, the subject of interpretations is more of a minor curiosity than anything else.

But it does mean that there is the "possibility" that additional refinements to theory may be possible. Since any refinement would almost certainly be an extension to current theory - which is now 80+ years old - it is exciting to consider. So there is a lot of research going into discovering theoretical differences between one interpretation or another. For example: Bohmian type interpretations require some assumptions which may make them explicitly testable. Just yesterday, I started a thread about a newly proposed test to distinguish their viability.

But even the discovery of one particular interpretation being correct would not invalidate existing physical theory.

 

[Demystifier]

But MWI is deterministic, so it is not clear what the 'probability' means in that context. So yes, there is some mystery, but I don't see it as a weakness, instead, it is a hint that we are missing something interesting about the reality.

I agree. What I disagree with you, is what that reality might be.

 

[vanesch]

The missing part is simple: we have to recognize that even in a microscopic world we need many points of measurement to get some information. Information is not reduced to one point. On the contrary, the more points, the more accurate information about a system. Just like a photograph. The trick is that we think of microscopic world as of elementary, reducable-to-one-point world. It is this idea that fails.

The classical world also "appears" as the inclusive picture (sum of many different QM events). Again, a photograph is a right example.

The problem with the "ensemble" view of quantum mechanics is that there's nothing to understand, so you cannot devellop a "feeling" for what "goes on" (even if it doesn't go on that way, at least you can imagine it). Of course the ensemble view is a "correct" view of quantum theory: you scribble weird symbols on paper, apply formal calculation rules and in the end you crunch out probability distributions.

That's nice for the guy for whom one has made a measurement instrument, and one tells him that the instrument measures "this". But it is a pain for the one that makes an instrument: how are you supposed to make it ? If you set up an experiment, you need some kind of intuition of "what goes on", and so you need a kind of mental picture. Why do we say that a beam splitter splits a beam ? It is easier to picture it that your photon wave packet comes in, gets split into two packets by the beam splitter, that these two packets do this and do that, then recombine, and click here or there. But if you do that, you are actually thinking in MWI terms: you've considered that after the beam splitter, your photon is *simultaneously* in one branch and in another. For a single photon, this might still be feasible as a "classical light pulse", but if you apply the same reasoning to EPR pairs and so on, you can really make a parallel between "things happening in parallel" and the actual calculation. If you now make one extra step, and say that upon measurement, the measurement apparatus ALSO gets into two simultaneous states, then you are completely in MWI.

When do you apply the Born rule ? When it comes to you ! You tell yourself that you are also simultaneously observing different results, but "you" are one of those you's, and your "you" ensemble distribution is then given by the Born rule. It sounds crazy, it is maybe crazy, but it gives you quite some intuition on "how to picture things". I've never met any other interpretation that gives you such a close link between the formal calculation and the "lab situation".

 

[Fredrik]

Pondicherry interpretation: as I understand it, seems to be a variant of the instrumentalist interpretation - QM is nothing but a tool for calculating probabilities.

Mohrhoff has certainly been pushing that view too (e.g. in an article called "Quantum theory needs no interpretation", if I remember the title correctly), but I think his "Pondicherry" interpretation is a lot more weird than that. I skimmed the Pondicherry article a few years ago and I don't remember much of it, but it contains some stuff about the nature of space and time. For example, he thinks that a photon that goes through a double slit doesn't consider the two slits as being at different locations in space.

If you search for Ulrich Mohrhoff at arxiv.org, you'll find a large number of articles that all seem to be saying roughly the same thing. I read some of the others too (a few years ago) and I thought they were interesting and inspirational, but not very useful.

 

[Fredrik]

The following are the interpretations of QM:

Bohmian · CCC · Consistent histories · Copenhagen · Ensemble · Hidden variable theory · Many-worlds · Pondicherry · Quantum logic · Relational · Transactional

An "interpretation of QM" is an attempt to interpret the mathematics of QM as statements about what's "actually happening" in physical processes that can't be described classically. Therefore, I don't consider the "ensemble interpretation" an interpretation. It's just the rejection of the idea that QM is telling us something about what's "actually happening".

I also don't consider "quantum logic" an interpretation. It's just an attempt to state the theory in a different way. Instead of having axioms that define a mathematical structure on the set of states of physical systems, we use axioms that define a mathematical structure on the set of experimentally verifiable statements.

I consider "consciousness causes collapse" complete crackpot nonsense.

A lot of people consider the Copenhagen interpretation to be the statement that measuring devices are classical and that wave function collapse is exact. I don't think anyone actually believes that. In particular I don't think Bohr and Heisenberg thought that. If we remove the craziness by instead saying that a measurement is a physical interaction that entangles the eigenstates of the system with macroscopically distinguishable states of a system (the measuring device) that's approximately classical, then the Copenhagen interpretation is indistinguishable from the ensemble interpretation, and also completely consistent with decoherence and quantum logic.

Decoherence is a phenomenon that can be studied in the framework of the ensemble interpretation, so I don't know why anyone would consider that an interpretation. The study of decoherence has improved our understanding of measurements. It has given us a definition of what a measurement is (see the preceding paragraph), but it doesn't tell us much about what's "actually happening".

I haven't had time to study Bohm yet, but I'm under the impression that it at least consists of a set of well-defined statements that can be used to predict the probabilities of possible results of experiments. That makes it a theory. Consistent histories might fall into that category too, but I don't fully understand it. All the others seem to be nothing more than loosely stated ideas about what sort of things are happening. None of them seems to be defined by a list of well-defined statements, or give us a consistent set of answers to the question "What's actually happening?" in every conceivable scenario. So I can't consider them to be anything more than failed attempts to interpret QM.

 

[Dmitry67]

BTW, the list in not complete: there is also "Objective Collapse" theory: it is not an interpretation (even Wiki puts it in a list of interpretations) because it is experimentally verifiable.

I remember Penrose liked the idea of "Gravitation caused collapse" but I think it is less and less popular.

Frederik, I hope MWI does not fall for you in the category of "nothing more than loosely stated ideas about what sort of things are happening"?

 

[hamster143]

It seems to me that ensemble is basically a lipstick-on-a-pig version of hidden variables, which were falsified more than 40 years ago. If there's only a single unique universe, and every system exists in no more than one state at a time, then our inability to see things as such (which gives rise to the appearance of wavefunction) is due to our ignorance of "hidden variables", describing the system on some deeper level. But local hidden variables were killed by Bell in 1964, and nonlocal hidden variables are too much of a stretch.

 

[Count Iblis]

It seems to me that ensemble is basically a lipstick-on-a-pig version of hidden variables, which were falsified more than 40 years ago. If there's only a single unique universe, and every system exists in no more than one state at a time, then our inability to see things as such (which gives rise to the appearance of wavefunction) is due to our ignorance of "hidden variables", describing the system on some deeper level. But local hidden variables were killed by Bell in 1964, and nonlocal hidden variables are too much of a stretch.

Not everyone agrees that local hidden variables are ruled out:

http://arxiv.org/abs/0908.3408

http://arxiv.org/abs/0707.4568

http://arxiv.org/abs/quant-ph/0701097

 

[Fredrik]

Frederik, I hope MWI does not fall for you in the category of "nothing more than loosely stated ideas about what sort of things are happening"?

It does, but I admit that it's possible that I have just failed to understand it.