New Quantum Interpretation Poll

[bohm2]

Here, we present the results of a poll carried out among 33 participants of a conference on the foundations of quantum mechanics. The participants completed a questionnaire containing 16 multiple-choice questions probing opinions on quantum-foundational issues. Participants included physicists, philosophers, and mathematicians. We describe our findings, identify commonly held views, and determine strong, medium, and weak correlations between the answers. Our study provides a unique snapshot of current views in the field of quantum foundations, as well as an analysis of the relationships between these views...

The statements that found the support of a majority(i.e., answers checked by more than half of the participant)were, in order of the number of votes received:
1. Quantum information is a breath of fresh air for quantum foundations (76%).
2. Superpositions of macroscopically distinct states are in principle possible (67%).
3. Randomness is a fundamental concept in nature (64%).
4. Einstein's view of quantum theory is wrong (64%).
5. The message of the observed violations of Bell's inequalities is that local realism is untenable (64%).
6. Personal philosophical prejudice plays a large role in the choice of interpretation (58%).
7. The observer plays a fundamental role in the application of the formalism but plays no distinguished physical role (55%).
8. Physical objects have their properties well defined prior to and independent of measurement in some cases (52%).
9. The message of the observed violations of Bell's inequalities is that unperformed measurements have no results (52%).

A Snapshot of Foundational Attitudes Toward Quantum Mechanics
http://lanl.arxiv.org/pdf/1301.1069.pdf

 

[DrChinese]

Cool paper! There were 33 respondents, and these included some of the top names in the field.

A few additional comments from the paper:

-Interpretations themselves: 42% identified with Copenhagen, 18% with MWI, 0% with Bohmian, and the remainder split amongst various non-specific (such as "information based").

-They conclude: "Yet, nearly 90 years after the theory's development, there is still no consensus in the scientific community regarding the interpretation of the theory's foundational building blocks. Our poll is an urgent reminder of this peculiar situation."

 

[bohm2]

-Interpretations themselves: 42% identified with Copenhagen, 18% with MWI, 0% with Bohmian, and the remainder split amongst various non-specific (such as "information based").

I'm not sure but I feel left out, for some reason.

 

[DrChinese]

I'm not sure but I feel left out, for some reason.

Gosh, I have no idea why.

It is interesting that even though there were no Bohmians, 12% saw action-at-a-distance in Bell tests. And 36% had some notion of non-locality (although that could mean almost anything).

 

[George Jones]

Cool paper!

Yes!

There were 33 respondents, and these included some of the top names in the field.

I would like to know the ages of the respondents, and the age distributions for the responses to the questions.

 

[stevendaryl]

Cool paper! There were 33 respondents, and these included some of the top names in the field.

A few additional comments from the paper:

-Interpretations themselves: 42% identified with Copenhagen, 18% with MWI, 0% with Bohmian, and the remainder split amongst various non-specific (such as "information based").

-They conclude: "Yet, nearly 90 years after the theory's development, there is still no consensus in the scientific community regarding the interpretation of the theory's foundational building blocks. Our poll is an urgent reminder of this peculiar situation."

Is Copenhagen actually an interpretation? It seems to me an attempt, one that's mostly successful, to get on with using quantum mechanics without waiting for agreement about what it all means.

 

[Nugatory]

Is Copenhagen actually an interpretation? It seems to me an attempt, one that's mostly successful, to get on with using quantum mechanics without waiting for agreement about what it all means.

From a historical perspective, it seems fair to consider Copenhagen an interpretation (the first one?). That doesn't necessarily conflict with your equally fair description of it.

 

[bohm2]

From a historical perspective, it seems fair to consider Copenhagen an interpretation (the first one?).

I believe the pilot-wave interpretation predated the Copenhagen interpretation. It just wasn't as well received.

 

[kevinferreira]

Gosh, I have no idea why.

It is interesting that even though there were no Bohmians, 12% saw action-at-a-distance in Bell tests. And 36% had some notion of non-locality (although that could mean almost anything).

12% means 4 people according to the paper, maybe that could be the 3 mathematicians and 1 philosopher...!

 

[atyy]

The poll only included many-worlds worlds in which the respondents were not Bohmian. In other worlds, there were definitely Bohmians;)

 

[DrChinese]

I believe the pilot-wave interpretation predated the Copenhagen interpretation. It just wasn't as well received.

I would be cautious on this point, there may be a slight bit of revisionism going on with this particular idea (not on your part, from the recent historical paper I am fairly sure you are familiar with). There are some rabid dBB folk out there who are trying very hard to twist historical opinion around in some very odd ways. You can see it in Wiki and several other prominent spots, and their views are quite at variance with the mainstream. The basic idea is that Bohmian mechanics should be considered as the "standard" or first interpretation and that Bohr and others squeezed out that viewpoint in favor of Copenhagen. That is far fetched, seriously.

Much of the school of thought known as Copenhagen really came out of the same conference where de Broglie presented his early ideas on the matter. Obviously, people were trying to get their heads around the new ideas being presented. And as has been pointed out by many, Copenhagen can really mean a lot of different things anyway. I think of it as a minimalist interpretation where the formalism rules, not as an expression (for example) of Bohr's viewpoint.

 

[DrChinese]

The poll only included many-worlds worlds in which the respondents were not Bohmian. In other worlds, there were definitely Bohmians;)

They were all Bohmian in some branches.

 

[atyy]

Technically, people like Valentini, although definitely Bohmian, are not in favour of the Bohmian "interpretation", since the consideration of non-equilibrium presumably allows deviations from quantum mechanics, ie it is a different theory and not just an interpretation. Do the questions allow for this possibility?

 

[kith]

Technically, people like Valentini, although definitely Bohmian, are not in favour of the Bohmian "interpretation", since the consideration of non-equilibrium presumably allows deviations from quantum mechanics, ie it is a different theory and not just an interpretation. Do the questions allow for this possibility?

Yes. Nobody chose the answer "There is a hidden determinism" to the question "What is your opinion about the randomness of individual quantum events?"

It is quite interesting that not a single one of these foundations researches takes the possibility of (deterministic) hidden variables seriously.

 

[atyy]

Yes. Nobody chose the answer "There is a hidden determinism" to the question "What is your opinion about the randomness of individual quantum events?"

It is quite interesting that not a single one of these foundations researches takes the possibility of (deterministic) hidden variables seriously.

Interesting indeed. However, since no names were attached to the votes, we don't know who voted for what. So how do we know they took the poll seriously?

 

[kith]

We don't know for sure but I personally think the people answered honestly. Why should they spoil Schlosshauer's and Zeilinger's poll instead of just not taking part if they are not interested in contributing?

The fair sampling loophole seems more important to me. ;-)

 

[atyy]

We don't know for sure but I personally think the people answered honestly. Why should they spoil Schlosshauer's and Zeilinger's poll instead of just not taking part if they are not interested in it?

The fair sampling loophole seems more important to me. ;-)

 

[Demystifier]

The fair sampling loophole seems more important to me. ;-)

Agree!
For example, at page 8 they say:
"Similarly, the fact that de Broglie–Bohm interpretation did not receive any votes may simply be an artifact of the particular set of participants we polled."

For comparison, in another recent unfair sampling of leading quantum foundationalists:
M. Schlosshauer, Elegance and Enigma - The Quantum Interviews (2011)
3 of 17 (i.e., 18%) people prefer de Broglie–Bohm interpretation.

 

[vanhees71]

Well, this seems to be a somewhat strange poll. Because they have asked "experts" on "interpretation", which tend to have sometimes strange views on this issue (don't take me too literally, I'm also interested in these issues and find it important). That nobody votes for the "Minimal Statistical Interpretation" or "Ensemble Interpretation" (which I think is pretty much the same, although you can never be sure ;-)). Also to vote for "Copenhagen interpretation" is a very uncertain issue, because there are as many "Copenhagen interpretations" as there are people claiming to follow this interpretation. It's a pretty unsharp notion (thanks to Bohr and Heisenberg who were a bit too "philosophical" and not enough "mathematical" to my taste), what you call "Copenhagen interpretation". I think it's pretty problematic.

I'm clearly a follower of the "Minimal Statistical Interpretation", and with this there is no trouble and this also is the way, how quantum theory is applied to real-world applications since measurements are always done on an ensemble of many equally but statistically independently prepared "quantum systems". I don't know of any example for an experiment, where there is a contradiction to empirical evidence. Concerning "locality" one has to clearly distinguish "local interactions", which so far seem to be realized in nature, because there is no contradiction to the standard model of elementary particle physics, and this is a local relativistic QFT, and "non-local correlations" as described by "entanglement", which are well established by real experiments now, which clearly are in favor of the violation of the Bell inequality (and similar inequalities) and with the predictions of quantum theory (in its minimal interpretation).

I don't see any need for additional elements of interpretation, be it "many worlds" (adding unobservable parallel universes to the interpretation, a collapse of the quantum state (as proposed by the Copenhagen-type interpretations), or unobservable "trajectories" a la de Broglie/Bohm (which attempts to introduce a kind of "nonlocal realism", whatever the precise meaning of this notion might be), solipsism (only a recognition of a measurement result by a "conscious observer" determines the quantum state in terms of a Collapse, which is a pretty strong flavor of the Copenhagen type, usually known as the "Princeton Interpretation"). All the observable facts are identical in all those interpretations, and the "down-to-earth-no-esoterics" minimal statistical interpretation has no problems, although some people think that there is a problem, because this admits that one cannot make predictions about the behavior of a single system, which of course is true, but as I said above, when you have a probabilistic theory, you have to use an ensemble to prove its predictions. As long as there is no deterministic theory which is as successful as quantum theory, I think we have to live with this "incompleteness of quantum theory". Whether or not nature is intrinsically and irreducibly probabilistic and inderterministic is of course another question, which can only be decided when one has such a deterministic theory, which then should be non-local due to the issue with the Bell inequality, and so far nobody has been able to find such a theory which is as comprehensive and successful as quantum theory.

 

[VantagePoint72]

I don't see any need for additional elements of interpretation, be it "many worlds" (adding unobservable parallel universes to the interpretation, a collapse of the quantum state (as proposed by the Copenhagen-type interpretations), or unobservable "trajectories" a la de Broglie/Bohm (which attempts to introduce a kind of "nonlocal realism", whatever the precise meaning of this notion might be), solipsism (only a recognition of a measurement result by a "conscious observer" determines the quantum state in terms of a Collapse, which is a pretty strong flavor of the Copenhagen type, usually known as the "Princeton Interpretation"). All the observable facts are identical in all those interpretations

All the observable facts with respect to how quantum mechanics is currently formulated. In principle, a clever person might be able to find ways in which the various interpretations would distinguish themselves in predictions for proposed, testable extensions to the postulates of quantum mechanics. That is exactly what people who work on quantum foundations spend a great deal time trying to think of. Taking the position that there's no point distinguishing between different models that we haven't yet figured out how to experimentally distinguish is functionally useless.

 

[harrylin]

A Snapshot of Foundational Attitudes Toward Quantum Mechanics
http://lanl.arxiv.org/pdf/1301.1069.pdf

Very interesting, thanks!

 

[harrylin]

The poll only included many-worlds worlds in which the respondents were not Bohmian. In other worlds, there were definitely Bohmians;)

I had to read that twice before it "clicked"

 

[stevendaryl]

I don't see any need for additional elements of interpretation, be it "many worlds" (adding unobservable parallel universes to the interpretation, a collapse of the quantum state (as proposed by the Copenhagen-type interpretations), or unobservable "trajectories" a la de Broglie/Bohm (which attempts to introduce a kind of "nonlocal realism", whatever the precise meaning of this notion might be), solipsism (only a recognition of a measurement result by a "conscious observer" determines the quantum state in terms of a Collapse, which is a pretty strong flavor of the Copenhagen type, usually known as the "Princeton Interpretation").

I don't see that Many Worlds amounts to injection "additional elements" to quantum theory. If electrons and atoms and molecules can be in superpositions of states, then there is no reason, a priori, that people and solar systems and universes can't be in superpositions of states. To me it seems that it's not Many Worlds that requires something additional, but the other way around, you need something additional to allow for microscopic superpositions and disallow macroscopic superpositions.

 

[stevendaryl]

All the observable facts are identical in all those interpretations, and the "down-to-earth-no-esoterics" minimal statistical interpretation has no problems, although some people think that there is a problem, because this admits that one cannot make predictions about the behavior of a single system, which of course is true...

That seems wrong to me. The whole point of EPR is that in certain situations you CAN make predictions about the behavior of a single system. If you produce a twin-pair with total spin 0, and one experimenter measures spin-up for one of the particles along some axis, then you know with certainty that another experimenter is not going to measure spin-down for the other particle. If a hydrogen atom is excited and later emits a photon, quantum mechanics allows us to predict with near-certainty what the possibilities for the energy will be.

I think that it's absolutely not correct for people to say (I'm not sure if you're saying this, or not) that people have trouble with quantum mechanics because they can't accept intrinsic uncertainty in nature. That's not true at all. There is no conceptual difficulty with allowing for nondeterministic dynamics. You can imagine that particles are equipped with a kind of random-number generator, and what they do depends not only on their current position, momentum, etc, but also on the value of the internal random number. That might be annoying to people like Einstein who believe that "God does not play dice", but there is no conceptual difficulty with it. But the point of EPR is that quantum mechanics ISN'T like that. It doesn't work like an ordinary stochastic theory, precisely because of the ways in which makes some DEFINITE predictions. It's the nonlocal correlations that make QM strange, not the probabilistic aspects, and I don't see how an "ensemble interpretation" helps to understand those nonlocal correlations.

 

[kith]

That nobody votes for the "Minimal Statistical Interpretation" or "Ensemble Interpretation" [...]

Maybe supporters of the Ensemble Interpretation think that there are no foundational problems and don't attend such conferences. ;-)

I'm clearly a follower of the "Minimal Statistical Interpretation", and with this there is no trouble and this also is the way, how quantum theory is applied to real-world applications since measurements are always done on an ensemble of many equally but statistically independently prepared "quantum systems".

If you have a real ensemble in your experiment -i.e. a gas of atoms-, this is straightforward. But if you prepare one system at a time and repeat your experiment over and over again, it seems a bit odd to me to say that the only physical reality lies in the abstract ensemble.

However, this view is quite similar to the spirit of Copenhagen. Both agree that the physical properties of a single system described by a superposition are not well-defined. The only difference is that the copenhagenist would say that in an ensemble of systems in an eigenstate, the corresponding physical property is a property of every single system.

 

[kith]

That seems wrong to me. The whole point of EPR is that in certain situations you CAN make predictions about the behavior of a single system.

That depends on the interpretation. You have to repeat your measurement to confirm that Bob always gets the predicted value. So you always have to do experiments with (sometimes abstract) ensembles of systems. Now if all experiments are done with ensembles, why should the physical theories we deduce from them be about single systems and not only about the ensembles? Personally, I don't stick to this interpretation, but it certainly is a valid one.

[edit]:

It's the nonlocal correlations that make QM strange, not the probabilistic aspects, and I don't see how an "ensemble interpretation" helps to understand those nonlocal correlations.

Why need they be understandable? Locality is an assumption. Bell's theorem tells us that we can't have locality, realism and independent choices of measurement simultaneously. So if locality is important for you, you can pick a local interpretation. Of course, you probably get a different drawback by violating one of the other assumptions. ;-)

 

[stevendaryl]

That depends on the interpretation. You have to repeat your measurement to confirm that Bob always gets the predicted value. So you always have to do experiments with (sometimes abstract) ensembles of systems. Now if all experiments are done with ensembles, why should the physical theories we deduce from them be about single systems and not only about the ensembles? Personally, I don't stick to this interpretation, but it certainly is a valid one.

Well, I don't agree that all experiments are done with ensembles. I only have one car, one cell phone, one home computer (okay, actually I have two or three, but that's not really enough to count as an ensemble). I notice certain regularities in their behavior: if you do such and such, then such and such will happen. The point of science (it seems to me) is to understand those regularities. The "ensemble interpretation" seems to miss the point: The reason that my computer behaves such and such a way when I do such and such is because there is an imaginary ensemble of a huge number of identical computers, and the vast majority of them behave in that way?

But there is another question about the ensemble view, which is: what varies from one member of the ensemble to another?

Notice that there is a definite answer to this question in classical statistical mechanics (modulo coarse-graining, which brings up conceptual problems in classical probability theory, as well, which I don't want to get into right now). You imagine an ensemble of systems, all of which have the same values for macroscopic quantities (such as total energy, total number of particles, total momentum, total charge, etc.) but differ in their microscopic descriptions. So the ensemble interpretation there is a way of dealing with lack of knowledge: We know certain facts about the actual system under consideration. This knowledge gives rise to an imaginary ensemble of systems, all of whom agree with our actual system in the details that we've measured. So our actual system is assumed to be one of the systems in that ensemble, we just don't know which.

Using ensembles for quantum systems is a little stranger, it seems to me, because of the questions of what is the same for all systems in the ensemble, and what varies. If we assume a hidden variables interpretation, then we can assume that the systems in the ensemble differ in the values for those variables. Alternatively, we could just say that different systems in the ensemble differ in the results of measurements. In that case, the ensembles are more like "alternate histories", kind of like in the "many worlds interpretation".

So I don't see that ensembles do anything for us, in terms of interpretations of quantum mechanics. We need an interpretation even to make sense of the ensembles.

[edit]:
Why need they be understandable?

I think that the impetus for doing any science is understanding the world. We certainly can't demand that the world be understandable, but the assumption that it is understandable has great power in developing science. It's possible to develop science as just mysterious rules for manipulating data to get predictions, but I think that the real advances in science come from those who attempt to actually understand what's going on.

Locality is an assumption. Bell's theorem tells us that we can't have locality, realism and independent choices of measurement simultaneously. So if locality is important for you, you can pick a local interpretation. Of course, you probably get a different drawback by violating one of the other assumptions. ;-)

Personally, I don't care about locality, except for the fact that it makes physics simpler. One could imagine an interpretation in which a measurement instantaneously collapses the wavefunction everywhere in the universe. But that interpretation opens up a huge can of worms: In which rest frame is the collapse instantaneous? What makes an interaction a "measurement"? Giving up locality is not an answer, it's just choosing a different set of questions.

 

[DennisN]

Thanks, interesting read (both paper and thread)!

The poll only included many-worlds worlds in which the respondents were not Bohmian. In other worlds, there were definitely Bohmians;)

Hilarious!

 

[FPinget]

Since the poll did not specify when or which Einsteins' view was considered "In wording our question, we deliberately did not specify what exactly we took Einstein's view of
quantum mechanics to be. It is well known, in fact, that Einstein held a variety of views over his lifetime" it seems to me that this question - in principle - is somehow not quite precise or perhaps is not contextualized? Fernando Pinget

 

[vanhees71]

Using ensembles for quantum systems is a little stranger, it seems to me, because of the questions of what is the same for all systems in the ensemble, and what varies. If we assume a hidden variables interpretation, then we can assume that the systems in the ensemble differ in the values for those variables. Alternatively, we could just say that different systems in the ensemble differ in the results of measurements. In that case, the ensembles are more like "alternate histories", kind of like in the "many worlds interpretation".

Let me concentrate on this point, which touches the essence of the ensemble interpretation.

First of all any measurements, be they made on "classical" systems or on "quantum" systems are always on ensembles. Many times, you prepare the system in a certain way and then measure observables. Nowadays you can do experiments with single particles and so on, but you always work with ensembles.

What's the same in the ensemble is first of all the preparation procedure. In quantum mechanics it makes only sense to say that a single system is in a certain pure or mixed state when you have established by measurements that a certain preparation procedure leads to the statistical properties of an ensemble of such prepared systems as predicted by the quantum mechanics. Only in this way you can make the correspondence of the abstract mathematical object, describing the state, i.e., the statistical operator of the system (for a pure state that's a projection operator, so we can describe both pure and mixed states simply by a statistical operator) with the system.

After you have established that a certain preparation procedure indeed admits the association of the so prepared system with the statistical operator, you can predict the outcome of any measurement you can do on the system. Again you have to do many measurements on equally prepared systems to establish to a sufficient accuracy that the measured statistical properties coincide with the probabilistic prediction of quantum mechanics. So there is no need for more than the "minimal statistical interpretation".

To a certain extent this is not too far from the Copenhagen interpretation. The big additional element compared to the Statistical interpretation is the idea of the "state collapse". There is no need for such a state collapse at all. To the contrary the whole problems with causality brought up by EPR comes from the assumption of a collapse, where instantaneously the state changes after a measurement. If you simply admit that the quantum mechanical state refers to ensembles, describing/predicting their statistical behavior and onlyt this, but not the single system, there's no need for a state collapse. Of course you must establish the connection of the state to the single system in some way, and that's done in the above described way as a concrete preparation procedure applied to the single system.

 

[stevendaryl]

First of all any measurements, be they made on "classical" systems or on "quantum" systems are always on ensembles.

That seems obviously wrong to me. If I look at my watch, I'm looking at a single watch. If I look at a thermometer, I'm looking at a single thermometer. The ensemble view is a way to think about scientific measurements, and the meaning of probability, but it doesn't seem at all correct to say "any measurements...are always on ensembles."

What's the same in the ensemble is first of all the preparation procedure.

I don't agree with that, either. Yes, people like to be able to have repeatable experiments, because they increase the confidence in the quality of the data. But there are times in which the experiment just isn't repeatable. We witness the light of a supernova explosion from a distant star. A total eclipse of the sun allows us to study the corona. A strange combination of factors produces a once-in-a-century "superstorm". The fact that these observations were not carefully prepared in a way that makes them repeatable does not mean that they aren't governed by science. And as a matter of fact, in my mind, the whole point of science is not repeatable experiments, but making useful predictions about things that have not happened yet.

In quantum mechanics it makes only sense to say that a single system is in a certain pure or mixed state when you have established by measurements that a certain preparation procedure leads to the statistical properties of an ensemble of such prepared systems as predicted by the quantum mechanics.

Sorry, I just don't have much patience with this point of view. For one thing, what counts as a "preparation"? We set up equipment in a certain way, we look at dials and meters and we note the values we see there. All of that stuff is itself physical interactions. Physics describes human beings as much as it describes atoms and electrons.

Your point of view is mixing up the issue of what is good laboratory practice with what physics describes. Physics applies whether or not good laboratory technique is followed. A theory of physics that only applies to experiments conducted by physicists seems useless and uninteresting to me.

 

[DrChinese]

Since the poll did not specify when or which Einsteins' view was considered "In wording our question, we deliberately did not specify what exactly we took Einstein's view of
quantum mechanics to be. It is well known, in fact, that Einstein held a variety of views over his lifetime" it seems to me that this question - in principle - is somehow not quite precise or perhaps is not contextualized? Fernando Pinget

Welcome to PhysicsForums, Fernando!

True, not a precise question. And intentionally so, per the authors. The view that Einstein held until his death was that it was not conceivable to him that there could not exist a more complete specification of the quantum system, at least in principle. That was an opinion expressed in EPR (1935). Of course he was not aware of Bell's Theorem, that having arrived 10 years after his death.

If Einstein had lived to learn of it, I am quite certain he would acknowledge that if there is a more complete specification of the system possible, that in fact there must be influences which are not bounded by c. Which would in turn mean that relativity requires tuning. So either way, one of Einstein's fundamental beliefs must be considered incorrect.

All of those at the conference would be familiar with the above, and that is the context. Obviously you do not have to judge Einstein on a point in which future events (Bell, 1964) change perspectives, and I am sure many chose NO in light of that.

 

[kith]

Giving up locality is not an answer, it's just choosing a different set of questions.

Well, we have local interpretations of QM and realistic ones. In local interpretations, we have weirdness due to non-realism and in realistic ones we have weirdness due to non-locality. It seems to me that you want to get rid of both kinds of weirdness which isn't possible for any underlying theory because of Bell's theorem. Now for you, what would a fundamental theory have to explain in order to be considered "understood" (as you do with classical mechanics if I get you right)?

 

[stevendaryl]

Well, we have local interpretations of QM and realistic ones.

What local interpretation are you talking about? I don't know of one.

In local interpretations, we have weirdness due to non-realism and in realistic ones we have weirdness due to non-locality.

I'm not convinced that the bohm model is really a coherent interpretation. One of the things that doesn't make sense to me about the bohm model is that, even though particles have definition positions at all times, their dynamics is governed by a "quantum potential" that is pretty mysterious. There is an assumption (as someone has pointed out) made by the bohm interpretation, which is that the initial distribution of particle positions is made to agree with the square of the Schrodinger wave function, but I don't see how in a realistic model, that makes sense. If you only have a single electron, for instance, what sense does it make that it has a "distribution"?

I don't really think of the bohm model as a serious interpretation of quantum mechanics. I realize that that means that maybe there aren't any serious interpretations.

It seems to me that you want to get rid of both kinds of weirdness which isn't possible for any underlying theory because of Bell's theorem. Now for you, what would a fundamental theory have to explain in order to be considered "understood" (as you do with classical mechanics if I get you right)?

What I really have are telltale signs that an interpretation is bogus. One of them is that the interpretation singles out certain kinds of interactions (measurements, or observations) or certain kinds of systems (conscious minds). Nonlocality is distasteful to me, but I think I would accept a nonlocal theory if it were satisfactory in other ways.

 

[bohm2]

A theory of physics that only applies to experiments conducted by physicists seems useless and uninteresting to me.

That has always been my view. Which is why I don't much favour the instrumentalist approach. Physics kind of becomes the science of meter readings.

 

[DrChinese]

What local interpretation are you talking about? I don't know of one.

MWI is local. Retrocausal/Time Symmetric interpretations (such as Relational BlockWorld) are also local. However, such local ones are not realistic. They sacrifice some key causal element of nature to achieve their results.

 

[bohm2]

The view that Einstein held until his death was that it was not conceivable to him that there could not exist a more complete specification of the quantum system, at least in principle. That was an opinion expressed in EPR (1935).

I recall reading a paper discussing how Einstein was very unsatisfied even with the EPR paper as was written by Podolsky. I can't recall the details? An interesting quote from Pauli suggesting that Einstein was not as adamant about 'determinism' as he was about 'realism' is the following passage taken from a letter from Pauli to Born:

Einstein gave me your manuscript to read; he was not at all annoyed with you, but only said that you were a person who will not listen. This agrees with the impression I have formed myself insofar as I was unable to recognise Einstein whenever you talked about him in either your letter or your manuscript. It seemed to me as if you had erected some dummy Einstein for yourself, which you then knocked down with great pomp. In particular, Einstein does not consider the concept of “determinism” to be as fundamental as it is frequently held to be (as he told me emphatically many times), and he denied energetically that he had ever put up a postulate such as (your letter, para. 3): “the sequence of such conditions must also be objective and real, that is, automatic, machine-like, deterministic.” In the same way, he disputes that he uses as a criterion for the admissibility of a theory the question: “Is it rigorously deterministic?” Einstein’s point of departure is “realistic” rather than “deterministic”.

 

[DrChinese]

I recall reading a paper discussing how Einstein wasn't happy even with the EPR paper. I can't recall the details? An interesting quote from Pauli suggesting that Einstein was not as adamant about 'determinism' as he was about 'realism' is the following passage taken from a letter from Pauli to Born:

Einstein gave me your manuscript to read; he was not at all annoyed with you, but only said that you were a person who will not listen. This agrees with the impression I have formed myself insofar as I was unable to recognise Einstein whenever you talked about him in either your letter or your manuscript. It seemed to me as if you had erected some dummy Einstein for yourself, which you then knocked down with great pomp. In particular, Einstein does not consider the concept of “determinism” to be as fundamental as it is frequently held to be (as he told me emphatically many times), and he denied energetically that he had ever put up a postulate such as (your letter, para. 3): “the sequence of such conditions must also be objective and real, that is, automatic, machine-like, deterministic.” In the same way, he disputes that he uses as a criterion for the admissibility of a theory the question: “Is it rigorously deterministic?” Einstein’s point of departure is “realistic” rather than “deterministic”.

Good quote. And I think that captures the spirit of both Einstein's position on realism ("the moon is there even when no one is looking") as well as the point of the poll question: no matter how you approach it, Einstein had to be wrong on one point; but each person might see which point he was wrong on to be different for a variety of reasons. That could be either because of one particular statement in the EPR paper or because of their own particular interpretation. Or perhaps some other statement of Einstein's. I don't believe that Einstein's views on all 3 of the below can be correct:

i. No spooky action at a distance.
ii. Moon is there even when no one is looking.
iii. QM is not complete.

 

[StevieTNZ]

Where's Euan Squires interpretation?! Gosh. Had they asked me the question, that would be listed in the result

 

[Demystifier]

Well, we have local interpretations of QM and realistic ones. In local interpretations, we have weirdness due to non-realism and in realistic ones we have weirdness due to non-locality. It seems to me that you want to get rid of both kinds of weirdness which isn't possible for any underlying theory because of Bell's theorem.

What would you say about this interpretation
http://arxiv.org/abs/1112.2034 [to appear in Int. J. Quantum Inf.]
which interpolates between local and realistic interpretations, and in a sense is both local and realistic (or neither).

 

[bhobba]

but as I said above, when you have a probabilistic theory, you have to use an ensemble to prove its predictions.

I actually hold to the Ensemble interpretation but I am not so sure that's true. There are a number of foundations to probability theory, not just ensembles, such as Kolmogorov's axioms, that can also be used. Its just a lot more abstract whereas visualizing an ensemble is much more concrete.

Thanks
Bill

 

[vanhees71]

DrChinese, you fogot the obvious 4th possibility: Einstein is right on all points!

(I) Relativistic local quantum field theory by construction doesn't admit spooky (inter)actions at a distance due to the microcausality property of these theories. As any quantum theory it admits long-range correlations, but these have nothing to do with interactions. The EPR problems with causality only arise when you believe in an instantaneous collapse of the quantum state, but that's an unnecessary addendum to the metaphysics by the followers of (some flavors of) the Copenhagen or Princeton interpretation. With the minimal statistical interpretation there are no such problems, and that's all you need to apply QT to the real world.

(II) Of course, the moon is there when nobody is looking, because at least the cosmic background radiation is always looking. Alone this "photon gas" is sufficient to decohere the moon and make it behave as a classical object to an overwhelming accuracy. I'm pretty sure that you'll never be able to detect some quantum behavior on big systems like the moon.

(III) Nobody knows whether QT is complete or not as long as it is not refuted by some reproducible observation. So far, all observations are compatible with the predictions of QT.

Now it may well be that QT is complete. Then the behavior of objects in the real world is only predictable in the sense of probabilities and nature is inherently indeterministic. Then it is really impossible to prepare a particle such that both position and momentum are determined, and you can only associate a (pure or mixed) quantum state, determined by some preparation procedure (in the most simple case you have a macroscopic system and let it alone for a sufficiently long time so that it reaches thermal equilibrium with the corresponding Stat. Op. \hat{R}=\exp(-\beta \hat{H})/Z with Z=\mathrm{Tr} \exp(-\beta{\hat{H}})). The only thing you can say about the system is the probability to find values of an observable when you measure it, and this prediction you can only verify by repeating the experiment often enough and then get the probabilities as limits of the relative rates at which the various outcomes of the measured quantity occur. An observable is determined, if the system is prepared in the pure state represented by an eigenstate of the operator that corresponds to this observable. Also this has only a probabilistic meaning, i.e., it says that you expect with probability 1 that the observable should take the corresponding eigenvalue whenever you measure it on a such prepared system (ideal exact measurements assumed for the sake of the theoretical argument). Also this prediction you can only check experimentally by measuring a large enough ensemble to make sure that you really get the one and only one outcome, i.e., with 100% probability.

Thus quantum theory is complete, if nature really is inherently indeterministic as predicted by quantum theory. If not, it's incomplete, and one would have to find a better theory which includes quantum theory as some limiting approximately valid description. If there is such a more comprehensive theory that is deterministic, according to the violation of Bell's inequality (while QT gives the correct probabilistic predictions also in these most "quantic" cases!) it must be a nonlocal (if it's relativistic that means necessarily nonlocal in both space and time) theory. So far nobody could come up with a non-local theory which is consistent with all observations.

On the other hand, history teaches us that usually physical theories are incomplete, and thus I guess that also QT is incomplete, but whether we find something "more complete" or not is not clear at all yet!

 

[bhobba]

Of course, the moon is there when nobody is looking, because at least the cosmic background radiation is always looking. Alone this "photon gas" is sufficient to decohere the moon and make it behave as a classical object to an overwhelming accuracy. I'm pretty sure that you'll never be able to detect some quantum behavior on big systems like the moon.

I believe the moon is there if no one is looking and that decoherence solves the measurement problem. But to be sure decoherence only makes it look like a 'classical' object for all practical purposes in that no experiment can determine otherwise. For it to be considered classical you need some interpretive framework like decoherent histories.

Thanks
Bill

 

[harrylin]

DrChinese, you fogot the obvious 4th possibility: Einstein is right on all points!

(I) Relativistic local quantum field theory by construction doesn't admit spooky (inter)actions at a distance due to the microcausality property of these theories. As any quantum theory it admits long-range correlations, but these have nothing to do with interactions. The EPR problems with causality only arise when you believe in an instantaneous collapse of the quantum state, but that's an unnecessary addendum to the metaphysics by the followers of (some flavors of) the Copenhagen or Princeton interpretation. With the minimal statistical interpretation there are no such problems, and that's all you need to apply QT to the real world. [..]

vanhees, I think that this isn't the first time that I ask this, but could you provide a reference for the above?
According to DrChinese (and he has defended this view rather successfully for years on his website and on this forum), Einstein was wrong about QM on at least one point so that what you say is impossible. I would like to understand your side of the argument. Indeed, it is unclear to me what you hold of Bell's theorem. I did find your post https://www.physicsforums.com/showthread.php?p=4020550 but there you say that Bell proposed hidden observables, which may have been a slip of the pen, and it is probably unrelated to the real point of how this could work according to you.

thanks,
Harald

 

[DrChinese]

DrChinese, you fogot the obvious 4th possibility: Einstein is right on all points!

...

(II) Of course, the moon is there when nobody is looking, because at least the cosmic background radiation is always looking. Alone this "photon gas" is sufficient to decohere the moon and make it behave as a classical object to an overwhelming accuracy. I'm pretty sure that you'll never be able to detect some quantum behavior on big systems like the moon.

...

On the other hand, history teaches us that usually physical theories are incomplete, and thus I guess that also QT is incomplete, but whether we find something "more complete" or not is not clear at all yet!

Although I don't agree with the 4th possibility, at least a third of the respondents in the survey did!

Regarding II: This statement is definitely a metaphor for EPR realism, and should not be interpreted so literally. Einstein said: "I think that a particle must have a separate reality independent of the measurements. That is: an electron has spin, location and so forth even when it is not being measured. I like to think that the moon is there even if I am not looking at it."

The existence of quantum objects - when not observed - is not being denied by those who advocate non-realism. Instead, as a "non-realist", I would say that when a particle is in an eigenstate of position, it is not in any eigenstate of momentum. I would further say that the position eigenvalue was determined as part of a future measurement context.

As to the "history teaches us" argument: this really isn't an argument at all. And certainly the experimental evidence is dramatically pointing the other way.

 

[vanhees71]

You are right, as I stressed several times, there is not the slightest evidence against quantum theory yet, and as long as there is none, there's no reason to think that quantum theory is incomplete.

The issue with an electron is of course more subtle. In general it's clear that, according to quantum theory, we cannot even be sure that the electron is present, if we don't have prepared one somehow and/or we have measured one of its properties.

Of course, there are no position and no momentum eigenstates, because these observables have a continuous spectrum. That's the content of the Heisenberg-Robertson uncertainty relation. For any (pure or mixed) state one can prepare a particle in, the standard deviations of these quantities obey
\sigma(x) \sigma(p) \geq \hbar/2.
If I decide to prepare the particle with a small uncertainty in position in some direction, I necessarily have to live with a large uncertainty of momentum and vice versa.

According to QT, it doesn't make sense to say that the position or momentum of a particle is determined. We can only know probabilities about these quantities, and these probabilities can only be measured by preparing many particles in the same way and measuring the position or momentum of the particle. So you can make an experiment, measuring the position of the particles in the ensemble to get the probability distribution for position (and compare it with the predictions of QT) and then another experiment on an ensemble of equally prepared particles to measure its momentum distribution. The standard deviations of these distributions fulfill the Heisenberg-Robertson uncertainty relation.

It's not possible to measure both position and momentum of the very same particle at once. One can show that measuring a particle's position with high accuracy necessarily disturbes the particle's momentum to a large extent vice versa. You can only decide to make a "weak measurement", i.e., measure the position only with a certain lower accuracy (i.e., larger systematic error) \epsilon(x) trading this lower accuracy for a somewhat lower disturbance \eta(p) of the momentum and vice versa.

It is very important to distinguish these noise-disturbance relation from the above mentioned standard deviations. There have been made fascinating experiments about this question recently, making it to the (semi-)public press. The most simple example is about measuring spin components of neutrons:

Experimental demonstration of a universally valid error–disturbance uncertainty relation
in spin measurements
Jacqueline Erhart1 , Stephan Sponar1 , Georg Sulyok1, Gerald Badurek1, Masanao Ozawa2
and Yuji Hasegawa1 *
NATURE PHYSICS | VOL 8 | MARCH 2012
DOI: 10.1038/NPHYS2194

Unfortunately the paper explains the theory behind this experiment, which should make it to any modern textbook if you ask me, in a very complicated way. Perhaps I'll open a thread on this later, because I just got into this fascinating subject. I think it can be discussed on the level of a quantum-mechanics 1 lecture. Unfortunately precisely this issue is mixed up in many (even modern) textbooks, and this is due to Heisenberg's original publication on the uncertainty relation. Ironically, Bohr has pointed out this mistake in interpretation right away. Unfortunately the wrong interpretation, however, made it into the textbooks :-(.

 

[Duplex]

Nice paper.

"Finally, looking back, we regret not to have included the" shut up and calculate "interpretation ... in our poll."

Yes, a popular interpretation...

However, a response rate of 94% is high, but 33 respondents are not really enough statistically to draw any firm conclusions.

Another bias could be that the title of the conference "Quantum Physics and the Nature of Reality" (with financial support from the Templeton Foundation) can attract slightly more sheep than goats - more philosophical researchers so to speak?

Just for fun, I checked the graph of the Copenhagen Interpretation in Google Ngram Viewer up to 2008. The Copenhagen Interpretation seems to culminate (in books) around 1995.

 

[vanhees71]

Nice paper.
Another bias could be that the title of the conference "Quantum Physics and the Nature of Reality" (with financial support from the Templeton Foundation) can attract slightly more sheep than goats - more philosophical researchers so to speak?
1995.

That was precisely my suspicion. This cited paper from my last posting is an example for the way people in this community can make simple things pretty complicated. That's a pitty, because this is an experiment which is understandable on the level of an undergraduate introductory quantum-theory course level. The formalism is so simple in this case (all that's required is the two-dimensional Hilbert space for spin 1/2 measurements) that one can do all this as a miniproject for the students, and you learn a lot from it. I'll open another thread on this in a moment.

What's the real challenge is to understand the difference between the standard deviations, fulfilling the Heisenberg-Robertson-Schrödinger uncertainty relation and the noise-disturbance uncertainty relation by Ozawa, which here is nicely demonstrated (also experimentally to a high accuracy!) to violate the naive assertion that you can simply use the Robertson uncertainty relation or, to put it in the view of interpretation problem, to interpret the Robertson uncertainty relation as a relation for the product of the measurement accuracy ("systematic error") of one observable A and the perturbation ("disturbance") of another observable B that is not compatible with the first one. This was the interpretation by Heisenberg in his first paper. Bohr corrected him immediately after that. If I remember right, that's very comprehensively treated in on of the volumes of

Mehra, Rechenberg, The Historical Development of Quantum Mechanics.

 

[DrChinese]

Another bias could be that the title of the conference "Quantum Physics and the Nature of Reality" (with financial support from the Templeton Foundation) can attract slightly more sheep than goats - more philosophical researchers so to speak?

Just for fun, I checked the graph of the Copenhagen Interpretation in Google Ngram Viewer up to 2008. The Copenhagen Interpretation seems to culminate (in books) around 1995.

Pretty impressive group of names there, not the sheep by any means. I think you are off the mark on that. But this is certainly not a representative sample either, though I doubt if many people would really care whether their preferred interpretation was more popular or not.

Copenhagen is a lot of things to a lot of people, as I think has been pointed out already. There has been a proliferation of "new" interpretations (or at least names of interpretations) recently. And yet, nothing has really captured much of anyone's imagination either.

"Shut up and calculate" seems to win even when it is not mentioned, as this is what everyone does at the end of the day.

 

[Duplex]

Pretty impressive group of names there, not the sheep by any means. I think you are off the mark on that.

Agree. I made ​​myself a little unclear. What Zeilinger and several others on the list have contributed to physics have my respect and admiration.

"Shut up and calculate" seems to win even when it is not mentioned, as this is what everyone does at the end of the day.

Agree. At least a simple math in the evening I think…

“Counting sheep is a mental exercise used in some cultures as a means of lulling oneself to sleep.”
http://en.wikipedia.org/wiki/Counting_sheep