The Debate on Quantum Interpretations: MWI, CI, and BM

[Descartz2000]

Would it be accurate to say MWI is holding strong in the preferred interpretation, CI is dying out (if not dead already), and BM is continuing to be accepted by more researchers (or better yet, it is being studied by more physicists now more than ever)?

 

[f95toli]

The number of physicists who are actually actively working on various interpretations is so tiny that I doubt it is possible to see any "trends". There are of course a few well known physicists that have come out in support for one interpretation or another (e.g Max Tegmark) but as far as I know none of them are working on that full time.

Also, remember that the vast majority of all working physicists are simply not interested in interpretations and many -like me- are outright supporters of the "shut up and calculate" approach. Interpretations it is perhaps something that is discussed during tea- or coffee breaks but that is all.

 

[Dmitry67]

Would it be accurate to say MWI is holding strong in the preferred interpretation, CI is dying out (if not dead already), and BM is continuing to be accepted by more researchers (or better yet, it is being studied by more physicists now more than ever)?

Based on my observation of this forum this is definitely true.

 

[Fredrik]

The reason why the CI is "dying out (if not dead already)" is that it never had a proper definition, and that this made it possible for people to make all sorts of wild claims about what it was saying. Eventually this led to an absurd definition becoming the most popular one. So it's not so strange that the current version of the CI is crap. It looks like it was defined by people who didn't understand the ideas behind the interpretation at all.

Those ideas are alive and well today (better than ever I think), in the "ensemble interpretation" (also known by other names). The CI is dead, but only because some idiot(s) redefined it to mean something stupid. I would say that the ensemble interpretation is what the CI was supposed to be.

I haven't done any research to verify that this is how it happened. I just can't imagine that Bohr and Heisenberg would have thought that the current version of the CI is reasonable.

 

[Dmitry67]

Yes, but Bohr showed that there was a smooth transition from micro- to macroscopic world. In fact, his first naive model (with electron orbits) was adjusted to fit both worlds.

So (as I think) in the first part of 20th century scientists were occupied with more serious problems, hoping that somehow the quantum weirdeness would disappear on the macroscopic scale. So I would not call CI 'stupid' - it was naive.

Then it appeared that contrary to other properties, the superposition does not tend to disappear on the macroscopic scales with systems of billions of particles (superconductive rings experiments). On the other hand, 'measurement devices' in Quantum Computers became so tiny that the problem became evident.

Finally, the discovery of Quantum Decoherence was the last nail in the coffin of CI, because there is no need to the mysterious 'collapse' at all.

Interestengly enough, popular books are usually based on CI, completely ignoring other interpretations, except many be MWI, but the way how they are explaining the MWI... they'd rather not say anything about it...

 

[Fredrik]

So (as I think) in the first part of 20th century scientists were occupied with more serious problems, hoping that somehow the quantum weirdeness would disappear on the macroscopic scale. So I would not call CI 'stupid' - it was naive.

There's nothing naive about what I believe was the original CI, i.e. what's now called the ensemble interpretation. Consider the following facts:

a) A theory of physics must associate a probability with each possible result of each member of some set of experiments. (That's the minimum requirement for falsifiability).

b) Since the world we live in appears classical to us, we have no choice but to define a "result of an experiment" as a state that can at least to a very good approximation be described in classical terms. (Note that the "state" I'm talking about here is the operationally defined real-world concept, and not its counterpart in the mathematical model).

c) If we want QM to predict probability 1 for the possibility that a second measurement of the same observable, immediately after the first, will have the same result, then we must use the "collapsed" state vector after the measurement.

Note that all of this applies both to the MWI and the ensemble interpretation too. Now a lot of people are saying that the CI is defined by the additional assumptions that measuring devices do not follow the Rules of Quantum Mechanics (even though their component parts do), and that collapse is a additional physical process (i.e. not described by a Hamiltonian) that projects a state vector onto an eigenstate. (I will call this the "stupid CI" below). But to me this sounds like nothing more than a huge misunderstanding of the ensemble interpretation. Like I said before, I can't imagine that Bohr and Heisenberg would have thought that these assumptions are reasonable.

Not only are they not reasonable. They are completely unnecessary because of my b) and c) above. Anyone who can't see this doesn't understand what a theory of physics is. That's why I believe that the original CI simply tried to explain my a,b,c above, and was misunderstood by others. That's why I can't say that "the CI was naive". The part that bugs me the most about that statement is actually the "was". As if the "stupid CI" actually has anything to do with what Bohr and Heisenberg where thinking back then. I think the CI has been redefined since its invention by people who didn't understand it, and the their version of it is stupid.

I admit that there's a possibility that Bohr and Heisenberg didn't fully understand my a,b,c back then as well as I do now, and that they therefore suggested the "stupid CI" as a way to think about QM that even though it's obviously flawed, would at least allow physicists to interpret the mathematics as predictions of probabilities of possible results of experiments. (Now that I think about it, that actually sounds quite plausible. My a,b,c is a better way to do that, but if they didn't understand that at the time...). In that case, the "stupid CI" isn't stupid, but it's also not an interpretation, since it doesn't make any suggestions about what "actually happens" that are meant to be taken seriously (like the MWI), or even speculates about "what the world is really like" (like Pondicherry).

Interestengly enough, popular books are usually based on CI, completely ignoring other interpretations, except many be MWI, but the way how they are explaining the MWI... they'd rather not say anything about it...

This I agree with. Presentations of the MWI are usually much worse than presentations of the CI.

 

[Descartz2000]

The reason why the CI is "dying out (if not dead already)" is that it never had a proper definition, and that this made it possible for people to make all sorts of wild claims about what it was saying. Eventually this led to an absurd definition becoming the most popular one. So it's not so strange that the current version of the CI is crap. It looks like it was defined by people who didn't understand the ideas behind the interpretation at all.

Those ideas are alive and well today (better than ever I think), in the "ensemble interpretation" (also known by other names). The CI is dead, but only because some idiot(s) redefined it to mean something stupid. I would say that the ensemble interpretation is what the CI was supposed to be.

I haven't done any research to verify that this is how it happened. I just can't imagine that Bohr and Heisenberg would have thought that the current version of the CI is reasonable.

Thanks for your posting. I am not as familiar with the ensemble interpretation as I am with some of the others. I will check it out. MWI seems too strange for me to accept even though it solves many of the issues that other interpretations can't. CI I have never thought was a strong theory the way that it is. I am most fond of BM, but I am aware there are issues here too. It seems, there are no solid interpretations of QM, at least if we want to accept the Universe as a rational place (unlike MWI). I am not a physicist, but I think it would be discouraging to work in this field with the current state of QM the way that it is. I know new discoveries will surface, and paradigm shifts will occur, but it seems like it has been an arduous task for new ground breaking discoveries in QM in recent years.

 

[DrChinese]

... and BM is continuing to be accepted by more researchers (or better yet, it is being studied by more physicists now more than ever)?

I would say there is more study on it today than 10 or 20 years ago, based on my review of recent articles in arxiv. Of course, we have some very active members here with very strong pro-Bohmians views too. And they make some very persuasive points. So that may bias my perspective as to levels of study and research.

I think that in the mainstream physics community, Bohmian Mechanics is making little progress. This is probably due to the fact that are a lot of no-go theorems in place, such as GHZ, which seem to rule out hidden variables entirely. Now, I am aware that the Bohmians don't accept these as being "anti-non-locality" but they are definitely anti-realistic. So that does not bode well for the future acceptance of Bohmian theory. Also, Bohmian theory would take a major leap forward if some new useful predictation arose from the theory itself. I realize that most Bohmians think that standard QM IS Bohmian theory (and so they have nothing to prove). But to non-Bohmians, this argument makes no sense. If a preferred reference frame were discovered, that would be big news! And again, I realize that all versions of BM don't include a preferred frame.

In sum: It does not appear that any hidden variable theory is supportable. There is additional research which says that no local theory may be supportable either! So maybe we live in a non-local and non-realistic universe.

 

[f95toli]

I am not a physicist, but I think it would be discouraging to work in this field with the current state of QM the way that it is.

Most physicist are quite happy with things the way they are. The reason is simply that QM is extremely good at predicting the outcome of experiments which is -to most of us- is what really matters. It seems to be more of an issue to people who are interested in QM, but do not actually work with it.
Interpretations is simply a non-issue for most physicists, as far as I remember there wasn't even a mention of the CI or any other interpretation in any of the books I used as a student and I don't think I've ever had a serious conversation about interpretations with a colleague. I am pretty sure that most physicists haven't even heard of a e.g. "pilot waves" (although they've obviously heard of Bohm, he made a number of important contributions to QM that had nothing to do with interpretations).

Maybe I should point out that I spend most of my time working on projects where the aim is increase the coherence time of solid-state qubits, meaning the mechanisms behind decoherence etc are obviously important issues. However, to me (and my colleagues) these are essentially technical challenges (we want to increase T1 and T2 of macroscopic objects in order to be able to better use various QM effects) that have little to do with philosophy.
That said, it IS interesting to see how far we can "push" QM; I am facinated by (and somewhat involved in) for example experiments where relatively large (tens of microns) mechanical oscillators are cooled into their ground state, or say experiments where photons are coupled to solid state qubits in order to e.g. create Fock states. I guess these are in some ways "tests" of QM.

 

[Dmitry67]

and that collapse is a additional physical process (i.e. not described by a Hamiltonian) that projects a state vector onto an eigenstate. (I will call this the "stupid CI" below)

There is another "flavor" of CI, where it is not a physical process, but where wavefunctions are "just a knowledge about the system". In fact, it solves some problems (like, superliminary speed of collapse), but for me there are many problems with that 'flavor' of CI:

1 If wavefunctions (Hamiltonian) are just a 'knowledge' about the reality, then what IS a reality?
2 Why primitive thing (particle) is described based on the complicated thing: knowledge, a property of conscious systems, and we even don't know what the consicousness is.

In any case, now it has just a historical interest. But I remember that Jambaugh was the only person who seriously defended CI on this forum.

 

[Fredrik]

Thanks for your posting. I am not as familiar with the ensemble interpretation as I am with some of the others. I will check it out. MWI seems too strange for me to accept even though it solves many of the issues that other interpretations can't. CI I have never thought was a strong theory the way that it is. I am most fond of BM, but I am aware there are issues here too. It seems, there are no solid interpretations of QM, at least if we want to accept the Universe as a rational place (unlike MWI). I am not a physicist, but I think it would be discouraging to work in this field with the current state of QM the way that it is. I know new discoveries will surface, and paradigm shifts will occur, but it seems like it has been an arduous task for new ground breaking discoveries in QM in recent years.

If we take the usual stuff about Hilbert spaces and the probability rule as the definition of QM, then we have a complete theory (in the sense described in my point a in my previous post). At that point, we can choose to make additional assumptions if we want to. The obvious possibilities are:

1. Make no additional assumptions at all. This is the "shut up and calculate" (SUC) interpretation.

2. Assume that QM can be used on every physical system (including the entire universe), that a state vector represents all the properties of a physical system, and that its time evolution as described by the Schrödinger equation is a description of what "actually happens". This is the MWI.

3. Assume that QM doesn't tell us anything about what "actually happens", i.e. that it's just a set of rules that tells us how to calculate proabilities of possibilities. This means that you can't use QM on a system that includes yourself, and that a state vector can't be thought of as a representation of all the properties of a physical system (as in the MWI). Instead it can be thought of as a representation of all the properties of an ensemble of identically prepared systems. Hence the name "ensemble interpretation".

In my opinion, SUC shouldn't be considered an interpretation. An interpretation should describe a way to interpret the mathematics as a description of what "actually happens", or at least speculate about "what the world is really like". I'm also reluctant to call the ensemble interpretation an interpretation, since its really saying that no interpretation is possible. These are the only reasons why I don't just state assertively that it isn't an intepretation:

A. There's no reason whatsoever to believe that it must be possible to interpret any good theory as a description of what actually happens. As I said before, the only condition that a set of statements must satisfy (in addition to logical consistency and that sort of stuff) to be statistically falsifiable and therefore qualify as a theory, is that it associates a probabilty with each possible result of each member of some set of experiments. If we state the opinion that QM can't tell us what actually happens, we're at least suggesting that the world is "undescribable".

B. It seems very reasonable to assume that something "actually happens", even though QM doesn't tell us what that is, and that whatever that is, it can be described by mathematics. However, this would mean that the variables of the model that actually describes reality aren't observables, i.e. that they don't correspond to equivalence classes of measuring devices in the real world. So the ensemble interpretation is at least suggesting that there's a more fundamental theory that describes reality in terms of unobservables. This is a speculation about what the world is really like.

"A" is the idea behind the ensemble interpretation, and B is what's suggested by it.

I don't think the MWI is irrational. It's just a very straightforward interpretation of the most accurate theory ever discovered.

 

[Fredrik]

There is another "flavor" of CI, where it is not a physical process, but where wavefunctions are "just a knowledge about the system". In fact, it solves some problems (like, superliminary speed of collapse), but for me there are many problems with that 'flavor' of CI:

1 If wavefunctions (Hamiltonian) are just a 'knowledge' about the reality, then what IS a reality?
2 Why primitive thing (particle) is described based on the complicated thing: knowledge, a property of conscious systems, and we even don't know what the consicousness is.

I agree with you here. I'll quote myself from another thread:

...the view that the wavefunction represents our knowledge of the system. I just find that one weird and kind of dumb. At the very least, it would require some technical definition of "knowledge" to make sense.

In any case, now it has just a historical interest. But I remember that Jambaugh was the only person who seriously defended CI on this forum.

There's been others, but I suspect that most people who appear to be defending it are really defending the ensemble interpretation and not the "stupid CI", which I still think is just a misunderstanding of the original ideas.

 

[limarodessa]

Dear sirs.

What do you think about ideas of Russian researcher M. B. Menskii?

Mister Menskii figures that MWI allows to solve conceptual inconsistencies of a quantum mechanics.

It is a question of the mechanism of a collapse of a wave function.

Professor Menskii states that the key role in it belongs to consciousness.

http://ufn.ru/en/articles/2000/6/c/
http://ufn.ru/en/articles/2001/4/l/
http://ufn.ru/en/articles/2005/4/c/

There is free articles on Russian:

http://ufn.ru/ru/articles/2000/6/c/
http://ufn.ru/ru/articles/2001/4/m/
http://ufn.ru/ru/articles/2005/4/c/


Thanks.

 

[Fredrik]

There are no conceptual inconsistencies that the MWI needs to solve, but the rest of what you said sounds like standard stuff. The mechanicsm for collapse is decoherence. There's nothing special about consciousness, but since it involves transitions between macroscopically distinguishable states (i.e. states that can be approximately described as classical) of someone's memory, it's natural to use those memory states to label the different worlds.

 

[limarodessa]

"...There are no conceptual inconsistencies that the MWI needs to solve, but the rest of what you said sounds like standard stuff. The mechanicsm for collapse is decoherence..."

Thanks. Just the mechanism of decoherence for "collapse" of a wave function tries to feature Mr. Menskii.

But it also allows to expand these representations. Mr. Menskii states that decoherence does not happen at all.

Certainly for this purpose it is necessary to view the closed system.

From this the interesting deduction follows:

Entanglement NEVER disappears. Entanglement states do not collapse, as decoherence does not exist.

"...There's nothing special about consciousness, but since it involves transitions between macroscopically distinguishable states (i.e. states that can be approximately described as classical) of someone's memory, it's natural to use those memory states to label the different worlds..."

I figure, that not all business is so simply.

Mr. Menskii states that from MWI it is possible to output the nature of a consciousness.

http://elibrary.ru/item.asp?id=9551777
http://www.maikonline.com/maik/showArticle.do?auid=VAF85TGTMJ

 

[Fredrik]

Thanks. Just the mechanism of decoherence for "collapse" of a wave function tries to feature Mr. Menskii.

But it also allows to dilate these representations.

If you're using software to translate from russian to english, it's not doing a very good job.

Mr. Menskii states that decoherence does not happen at all.

If he's just saying that decoherence is never complete, in the sense that the coefficients of the off-diagonal terms of the density matrix never reach zero even though they get very close, then that's totally standard too. Complete decoherence/exact collapse would be inconsistent with QM.

This explains classical character of the alternatives and unusual manifestations of consciousness arising “at the edge of consciousness” (i.e., in sleep or trance) when its access to “other alternative classical realities” (other Everetts worlds) becomes feasible.

Are these articles published in a peer-reviewed journal? I have to ask because this sounds like typical crackpot stuff. But then I didn't read the article, so I don't know what "unusual manifestations" he's talking about.

If these articles are unpublished, then it's against the forum rules to use them here.

 

[Fra]

There is another "flavor" of CI, where it is not a physical process, but where wavefunctions are "just a knowledge about the system". In fact, it solves some problems (like, superliminary speed of collapse), but for me there are many problems with that 'flavor' of CI:

Although I might add that I'm starting to get a littled bored of some non constructive interpretation discussions I'll add my vote that this "flavour of CI" that is most close to my interpretation.

The collapse and the schrödinger eq are not in contradiction. One describes the expected evolution in between measurements, and the former describes the revision of the information as a result of measurement. The collapse is simply and information update. So they are complementing each other. Clearly the expected evolution looses meaning when NEW information arrives.

Also, as decoherence appraoch sheds light on, the collapse is not something objective, it's relative. However the transformations that restores some new invariants from this has to do with complexity scalings and the birds view of this is not an answer since it doesn't relate to an inside observer. It's a realist construct that doesn't solve the real problem.

But in my view this has nothing to do with conscioussness. That's something that those who do not like this view keeps repeating over and over again, for unclear reasons. Observation or measurement, or representation of measurement results have nothing to do with human consioussncess IMO.

1 If wavefunctions (Hamiltonian) are just a 'knowledge' about the reality, then what IS a reality?

I would say that the image of reality, is as close to reality you can get. However this image is evolving. But no one can predict this evolution, we are only guessing. Those models that are making deterministic predictions, are still only guessing since the basis or axioms of this theory is still just a guess. (a good one, but nevertheless a guess, and image)

You might ask like I do. What exactly is an ensemble? The problem is not the mathematical abstraction, the question wether the ensenble abstraction is a physically realistic abstraction?

Clearly there are a number of idealisations. To repeat the same measurement over and over again? it's not hard to see the idealisations made here. Also in order to recover perfect distributions from a real experiment and infinite number of measurements must be done. How lone TIME would this take? Also what physical memory device would be able to represent all this information? This are serious issues IMO.

To those who take the intrinisic information to be dumb, I would like to ask how you can defined rejecting the above as non-significant problems?

But this is why I think we can not just make up indifferent interpretations, these discussions actually show us right onto things that are not satisfactory with the MODEL. It has nothign to do with the interpretation. But maybe some interpretation can make the development of QM easier.

THIS is my preference for the dumb intrinsic information/Knowledge view. But this view applied right to the standard QM does not make sense - but then my conclusion is not that the interpretatin is dumb, I think QM is an approxiation.

In particular does QM not describe the scaling of the information state or ensembles if you like to respect real constrains like bounded observers as opposed to imaginary birds views.

2 Why primitive thing (particle) is described based on the complicated thing: knowledge, a property of conscious systems, and we even don't know what the consicousness is.

An image of reality needs a representation. Any constraint on the representation context, constraints what reality can be "represented" and thus acted upon.

That human science depends on humans should be obviosu though and not need further explanation. Some monkey also learn to make tools. But this is a somewhat different discussion.

I think picutre I'mtrying to convey we do not need "human consciussness" all we need is a physical system whose actions are weighting the possible futures and thus in a sense beeing "aware" of the consequences of it's own actions. But this can be implemented as a evolving logical system, which is selected for self-preservation. We don't need to bring in fuzzy humans consiousness idea into this.

Our picture of particles, and their properties have emerged as a result of processing information. So in my view, particles are not fundnamental, it's a picture of reality that has emerged. What we should explain is why.

I see particles more like a frequently observer coherent system, that are populating our universe, the question is why the specific particles and not others with other properties. Is there some logical system where these particles are "preferred".

This is yet and unanswered question. String theory has some ambitions there, but I think we need something more thoughtful. AS I see it, this is deeply entangled with the foundations of QM as well.

But in that quest, I definitely defend the idea of wavefunction as the observers knowledge of the system. I insist that this is not dumb at all, it's IMO one of the golden grains of QM. At least that's how I see it. However, if you take it really serious, like I suggest, then current formalism is an approximation (interpretations aside).

I think most would have to agree that QM (interpretations aside) is NOT an intrinsic measurement theory. I think (unlike rovellis RQM) that this can not be cured just by an reinterpretation.

Do we need and instrinsic measurement theory? I say yes. The revolution the QM started, is not yet completed. WE just took one step. Unfortunatelky I think we need something even more weird.

/Fredrik

 

[limarodessa]

...If you're using software to translate from russian to english, it's not doing a very good job...

I thank you dear sir Fredrik.

I already wrote here at a forum that my English language - is bad. I from Ukraine. I ask to excuse me.

...Are these articles published in a peer-reviewed journal?... If these articles are unpublished, then it's against the forum rules to use them here...

The journals in which mister Menskii's papers have been published - there are magazines of "Higher Attestation Commission of Russia" :

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

But if it's against the forum rules, I never use them here in the future.

Also I should inform that I do not agree with many concepts of mister Menskii.

...I have to ask because this sounds like typical crackpot stuff...

But I should note that ideas about the quantum nature of consciousness were stated by Wigner E.P and Schrodinger E.

In particular Wigner E.P and Schrodinger E. (especially Wigner) have guessed that the consciousness can influence ( affect ) to a reality :

Wigner E.P., in Quantum Theory and Measurement (Eds J.A. Wheeler, W.H. Zurek) (Princeton: Princeton University Press, 1983) p. 168; Originally published in The Scientist Speculates (Ed. L.G. Good) (London: Heinemann, 1961) p. 284

Schrodinger E. What is Life? The Physical Aspect of the Living Cell (Cambridge: The University Press, 1944)


Besides, I would be very grateful to you, if you would write in more explicitly ( in more details ) about this aspect of the problem:

If he's just saying that decoherence is never complete, in the sense that the coefficients of the off-diagonal terms of the density matrix never reach zero even though they get very close, then that's totally standard too. Complete decoherence/exact collapse would be inconsistent with QM.

Thanks.

 

[Demystifier]

GHZ, which seem to rule out hidden variables entirely.

It does not. More precisely, it does not rule out nonlocal CONTEXTUAL hidden variables. Even Zeilinger and his coauthors admit that the Bohmian interpretation (which is nonlocal and contextual) is compatible with GHZ. Why do you think it isn't?

 

[Dmitry67]

Demystifier, I am sure I had already asked this question, sorry, but it was a long time ago, when I was probably too aggressive against BM and I don't remember your answer.

So in GR, is the hidden preferred frame global or local? For example, in the expanding Universe, are all local frames consistent with each other (which means that there is a hidden 'preferred place' in the Universe, but very far from that place preferred frame is superluminal), or it is a local concept, for example, it is possible that 'preferred hidden frame' can be the same as 'at rest relative to CMB', which is different in different places in the Universe?

 

[Demystifier]

Demystifier, I am sure I had already asked this question, sorry, but it was a long time ago, when I was probably too aggressive against BM and I don't remember your answer.

So in GR, is the hidden preferred frame global or local? For example, in the expanding Universe, are all local frames consistent with each other (which means that there is a hidden 'preferred place' in the Universe, but very far from that place preferred frame is superluminal), or it is a local concept, for example, it is possible that 'preferred hidden frame' can be the same as 'at rest relative to CMB', which is different in different places in the Universe?

Dmitry, I am glad to see that you are no longer so aggressive against BM. (I hope it's partially my merit too. )

As I said several times, there are more than one relativistic variants of BM. (By the way, there are also more then one variants of MWI, depending on how they attempt to explain or justify the Born rule.) In most of them the hidden preferred frame is global (which I don't like), but in some of them it is local. In fact, in the latter case the "preferred" frame is not a priori preferred, but emerges through a particular solution of equations that do not contain an a priori preferred frame at all. So yes, it is possible that 'preferred hidden frame' can be the same as 'at rest relative to CMB', which is different in different places in the Universe.