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.