-Comment on recent preprint by Pusey, Barrett and Rudolph.

A quantum system is said to have a state, also known as a wavefunction. The minimal interpretation of the state is that it encodes our knowledge about measurement outcomes. But many of us want to be able to think about some out-there reality. In particular, I would personally want to be able to visualize what happens in-between quantum measurements before I can say I feel I 'understand' quantum theory. I want what Schroedinger called 'Anschaulichkeit', which by my limited understanding of German combines the notions of visualizable and comprehensible into one word.  





Different proposals for how to think of the wavefunction (called PSI) were labelled in a paper by Harrigan and Spekkens as either PSI-epistemic or PSI-ontic. The former means one thinks of the wavefunction as representing our knowledge about something (e.g. measurement outcomes, or a hidden variable that determines probabilities of measurement outcomes), and the latter that it is a real out-there object. The PSI-ontic approach, as exemplified by Bohmian mechanics (see, for instance, “The Emperor's New Swindle” for more on Bohmian mechanics) where the wavefunction plays the role of guiding classical particles around, does offer Anschaulichkeit. PSI-epistemic approaches seem to leave open the possibility of some tantalizing underlying reality which we have limited knowledge about, but which could if identified provide Anschaulichkeit.  


In a recent pre-print three researchers claim to disprove the possibility of PSI-epistemic interpretations, or, if one reads their claims more carefully, that an underlying hidden variable type of reality is impossible. The pre-print of Pusey, Barrett (and FQXi member, whose research on time and quantum mechanics is profiled here) and Rudolph was given extraordinary attention in an article in Nature, last month, and has since been the subject of many blog posts (including posts by FQXi members Matt Leifer and Scott Aaronson that are worth reading). The Nature article was so positive that it risks inducing a back-lash, and I think it should be noted that the authors (two of whom I see weekly) declined to be interviewed as the policy of some journals is to disallow papers that have been discussed in the media before publication. Thus any ire, whether of the jealous or righteous type, should not be directed at the authors. Perhaps with the exception that the title of their paper, 'the quantum state cannot be interpreted statistically,' could have been more specific. 



Let me try to summarise their argument. They suppose a particular kind of PSI-epistemic model is possible and then show a contradiction with quantum statistics. The kind of model they consider is essentially a hidden-variable one. The idea is that at the time of preparation of a quantum system one also sets the value of some hidden variable q. This is *not* assumed to be local as far as I can tell. Here q is assumed to determine the probabilities of different outcomes. But, also for the sake of argument, q is assumed not to uniquely determine the quantum state, i.e. the same value of q can be associated with the preparation of several different quantum states. 



To show a contradiction with quantum statistics, they consider a setting where the same value of q is associated with four possible states (state 1, state 2, state 3 and state 4), i.e. there is some non-zero probability that that particular value of q, call it q_x, is prepared for each of the four states under consideration. A measurement is then considered. It has four outcomes. They design the measurement such that if state 1 is prepared outcome 1 never happens, if state 2 is prepared outcome 2 never happens and so on. This now gives a contradiction with the idea that q_x can be realised for all four states as well as determine the measurement probabilities. This is because for q=q_x we would have to have the probability of outcome 1,2,3 and 4 all being zero, yet one of them must always happen!



So the argument, modulo potential subtleties like hidden assumptions, puts another nail in the coffin for hidden variable theories, adding to the contributions by Bell and others. As it is quite clean and does not appear to assume the hidden variable is local, one can imagine it turning up in text-books at some point. 



I view it as consolidating existing paradigms rather than forcing a significant rethinking. To get the reaction from someone who is strongly associated with PSI-epistemic interpretations, I also emailed Chris Fuchs. He is a key defender of the idea of the quantum state representing our knowledge of something, and in talks he frequently writes the wavefunction on a piece of paper and puts it on his head to emphasize this point! Chris Fuchs says that although he likes the result it was quite clear from previous results that the hidden variable approach would not work, and "...there has been a particularly thriving community of researchers the last few years trying to argue that nonetheless---i.e., even without hidden variables---quantum states should be given a statistical or epistemic interpretation, and that one achieves the greatest clarity of what quantum theory is about by doing so. For those non-hidden-variable epistemicists, the theorem makes no difference (i.e., it knocked down a straw man)."   



In any case many interested in foundations will agree that the paper reinvigorates a fundamental debate and deserves attention. A very interesting paper by Colbeck and Renner has just appeared (arXiv:1111.6597v1) apparently deriving a very similar result from even more minimal assumptions, and I know that at least one more related paper will appear on the arXiv soon. My personal inclination remains to not think of the wave-function as a real object. It appears to me that Bohmian mechanics (as well as many-worlds) go wrong by taking the theoretical description as their starting point as opposed to the experimental phenomena. I guess this is the reason these interpretations tend to be associated with theorists while experimentalists, who never see wavefunctions apart from in calculations, often opt for the Copenhagen approach. (I also don’t see how one can reconcile the wavefunction and its collapse being real with the relativity of simultaneity but that is another discussion). But whilst I criticize aspects of these ideas I am also very sympathetic to anyone trying to come up with a good way of thinking about quantum effects. The new no-go theorem of Pusey et. al. can help to guide such efforts.

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Dear Oscar,

Great summary! I do not wish to undermine the significance of PBR's work. However, at a risk of trumping my own one-man bandwagon, let me point out that this result dose not even knockdown a straw man. It does so only if you completely ignore my explicit results of the past five years. I have been able to reproduce---explicitly in some simple cases like EPR, GHZ, etc., and formally in more general cases---every conceivable quantum mechanical correlation in a manifestly local and realistic manner. I will give a more complete account of my results in my upcoming (FQXi sponsored) book on Bell's theorem, but for now you can find some of my papers on the subject here.

Best,

Joy

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Dear Joy,

Thanks for that.

Interesting point. I don't really know your approach (it is a shame I was not around for your talk in our group) but it sounds very interesting.

Best,

Oscar

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Hello Oscar,

It is an intersting article.

I consider the wavefunction like purely rational in its proportions. When Schrodinger has invented his equation, he wanted to unify the waves and the mass so the fermions and the bosons. He wanted to show a road deterministic to calculate the different correlations. The duality waves/particules can be extrapolated in a pure road respecting the proportions. That said I do not see the necessity to insert bizare hidden variables. Copenaghen is always a good partner of the rationality. My theory of spherization in 3D says that the sense of rotation iomplies the comportments of wave or mass.So two main senses of rotation seem essential at 180 degrees in logic. If the quatum statistics do not permit to see clear about the serie utilized for the calculation of these proportions. So it is because there are several errors.The equations of Schrodinger permits to calculte the proportions of these waves. The rotations spinals and orbitals are also proportional if and only if the 3D is respected.

That's why the hidden variables are rational if they exist. The duality wave/particule can be extrapolated if the serie is finite for the systems of uniqueness. The measurments shall be proportional considering a logic correlation with the quantum statistics.

The rotations and a sense differenciating bosons and fermions answer logically. Now if the rotations are proportional with the waves, so the linearity must be differenciated also. Because the frequences are rational also for the fermions, so the bosons and the fermions oscillate but 3 comportments must be inserted instead of 2 implying the duality wave particule. The rotations seem the answer with the entangled ball spheres of course. If and only if the system of uniqueness and its finite number is understood of course and utilized with the biggest rationalism.

The proportions and the causes and effects are rational respecting the proportions.

A quantization is rational after all !

It is always the nice war of Copenaghen and EPR.But the rationalism wins always.Beautiful article Oscar.

Regards

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Dear Oscar,

You state that your "personal inclination remains not to think of the wave-function as a real object". Then you argue that Bohmian mechanics incorrectly takes the theoretical description as their starting point as opposed to the experimental phenomena. But this objection also applies to Pusey, Barrett, and Rudolph. What amazes me is that the relevant experiments were reported in Science and in Nature in June of 2011 and yet are seemingly unknown by those who care about these things.

These experiments are summarized in Physics-based Disproof...". The experiments were based on Aharonov's 'weak measurement theory' and the results support the deBroglie model, which, as JS Bell points out, assumes the field to be "just as 'real' and 'objective' as say the fields of classical Maxwell theory." What seems to me to remain is to connect this field with the probability interpretation normally accorded the wave function. I believe that I have succeeded in doing so, and hope to present this soon.

Regards,

Edwin Eugene Klingman

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Humans are so arrogant, assuming that their brain -- which evolved to comprehend a classical world only -- must in 80-odd years also achieve "Anschaulichkeit" of the quantum world through the same neural channels and utilizing the same cognitive modeling.

I am reminded of a quote by John Marburger, in his review of the play "Copenhagen": "We cannot help but think of the [detector] clicks as caused by little localized pieces of stuff that we might as well call particles. This is where the particle language comes from. It does not come from the underlying stuff, but from our psychological predisposition to associate localized phenomena with particles."

We still have quite a ways to go.

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Oscar,

I think the phrase "a quantum system has a state" should be replaced with "a quantum system moves from state to state". The moving is more fundamental than the state.

To Quote Einstein: the energy of a light ray spreading out from a point is not continuously distributed over an increasing space, but consists of a finite number of energy quanta which are localized at points in space, which move without dividing, and which can only be produced and absorbed as complete units.

This is "visualizable and comprehensible".

The wave-function (Schrodinger equation) is goofy because it is assuming that a quantum measurement is capturing a particle that can be static, and it cannot do this without introducing probability.

Particles are real objects out there but they move in a way that is discontinuous. Check Out:

http://www.digitalwavetheory.com/DWT/10_The_Skinny.html

No Multidimensional Spheres Needed :)

Don Limuti

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Thanks for this, Oscar. Nicely done.

Though personally, I think the paper suffers from petitio principii -- assuming that particles know in what state they have been prepared only guarantees observation of what one expected to see, simply by the quantum entanglement principle. In other words, taking the wave function as physically real assumes measured results a priori.

I think the authors have reached the right conclusion (a probabilistic reality cannot be physical) for the wrong reasons. I agree with EPR's description of what is physically real ("If, without in any way disturbing a system...") and therefore with Joy Christian's continuous function framework.

Tom

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F=ma and the equivalency and balancing of gravity and inertia both fundamentally require force/energy that is potential, actual, and thoughtful/theoretical (in union). This space would be equally (and both) invisible and visible, thereby including observer and observed and also force/energy that is gravitationally, inertially, and electromagnetically equivalent/balanced. This included/involves instantaneity (fundamentally), including balanced and equivalent attraction and repulsion. This space combines, includes, and balances larger and smaller space as the same space.

The key is to show integrated and interactive space -- to a limited extent, of course -- as it/this involves observer, observed, space, experience, the body, vision, and thought. I DEMONSTRATED ALL OF THIS AS DREAM EXPERIENCE, AND I HAVE FUNDAMENTALLY (AND GENERALLY) UNIFIED PHYSICS.

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FQXi.org -- still lying about this matter? I'm going to make your denial and evasion of all of this very public.

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Not just Feynman denied Anschaulichkeit of quantum physics. My last essay arrived at two questions: Is using ict and ih an absolute necessity or is at least on of them possibly based on mistakes? W

hile I already found conclusive arguments that proved SR wrong, in particular presented by Paul Maret, my suspicion concerning QM seem to be outside the focus of NPA.

This year young people in Germany voted at third place for a new word "Guttenbergen" (to Guttenberg or Guttenberging) in the sense of plagiarizing, because of someone who lost his Dr. title and his minister job after his dissertation turned out to contain plagiarized but perhaps unimportant stuff. Maybe, once they will create the word "Einsteinen" for plagiarizing something horribly wrong as happened with dramatically serious consequences in 1905.

As an engineer, I consider

- careful foundation of theory on sound models and appropriate mathematics,

- as diverse as possible experimental check of consistent interpretations,

- and Anschaulichkeit in the sense of compatibility with common sense

preconditions for trustworthy.

When I tried to understand QM, I read the papers by Schroedinger and found out that he used complex calculus in order to decrease the degree of DEQs from four to three. OK, but an overlooked trifle was that while they all at that time were used to apply FT on functions of time they changed the point of view to the Hamilton's one.

Here at FQXi I got aware that the experiment by Stern/Gerlach seems to have played a key role. Admittedly, I do still not comprehend it.

You might consider me having become too old and even a crank after decades at university. Maybe, I am completely wrong and Einstein was right. However, isn't there still a lot of unfulfilled hope for SUSY, for correct application of SR on GPS, for quantum computers that work as promised, for unification ...

Eckard Blumschein

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I think that the deep meaning of the wave function is clear when we study the vacuum fluctuation, with the creation of a pair particle-antiparticle.

When there is a pair fluctuation, then a electric dipole is created, and this electric dipole exist after the pair destruction (there is a increasing ring with the light velocity), this is not a problem because the dipole is observable because the pair existed for a finite time.

The crucial point is that the relativistic wave function of the pair can exist in only two possible description:

1.when the pair is created the wave function exist instantaneous in all the Universe, but the Universe is finite, then this is not possible

2. when the pair is created the wave function front have a finite velocity (I think the light velocity), but there is a problem when the pair disappear: the increasing wave function ring cannot exist for ever, because this ring generate electromagnetic field and this ring have a continuous charge: it is not consistent.

It is possible that the wave function is a real distribution of a particle in the space (I think a curvature, but this is not important), like a bubble, or a drop, that make movement in the space with interaction with potentials: I see the wave function like a bubble that interact with the splits border, crossing simultaneously the splits, and interacting with the wall atoms producing the interference fringes; it is only necessary the instantaneous absorption (connected with the entanglement) of the whole particle (projection) in the atom, and the wave function is (for me) a real object in the space that the observation destroy.

These are only words, and I am thinking some simple experiment to verify this opinion.

Saluti

Domenico

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Didn't think I would come to this decision. But it has to be something like PSI epistemic, Knowledge. (Haven't read the papers yet.) because all of iterations of the Object univerese over which the wavefunction is spread can not simultaneously exist and be reality. They, (the sequence of iterations), unlike the data forming space-time obsereved reality, are not within the same uni-temporal reality. They are preceeding the switch to consideration of the observed reality ,which has been thought of as wavefunction collapse and do not exist when that "collapse" occurs. That doesn't mean that there is no association with reality but the wavefunction does not co-exist unobserved with the observed space-time.

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Eckard wrote: "I still imagine it was or will be possible to experimentally check whether light behaves like a wave with limited speed re space or like a bullet without this restriction."

In a gravitational field the speed of light varies precisely as the speed of a bullet does (confirmed by the Pound-Rebka experiment). If there is an ether and the gravitational field somehow makes the speed of the light waves in the ether vary, it would still be highly improbable for this variation to mimic precisely the variation of the speed of the bullet.

Pentcho Valev pvalev@yahoo.com

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Truly unifying physics. First we fix and determine force/energy in physics. See the language? Force/energy is fundamental.

Second, intelligibility, rationality, logic, and reasonableness must rule.

Next, gravity and inertia need to be at half strength force/energy.

Instantaneity must be fundamental to any true and real unification of physics, as that also includes time. Attraction and repulsion must be equivalent and balanced.

Space must be shown as equally (and both) visible and invisible in keeping with fundamentally enjoining and balancing visible and invisible space. This is the only way to unify and balance gravity, electromagnetism, and inertia. It also fundamentally demonstrates/includes instantaneity.

The purpose of vision is to advise of the consequences of touch in and with time. This must also be included.

The ideal/theoretical requirements of truly unifying physics have never been stated before. Tactile and visual experience are fundamental to truly unifying physics. Bodily experience is fundamental/foundational to thought and physics.

Dream experience is consistent with, and it includes, everything in this post.

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Instantaneity fundamentally and truly unifies and balances force/energy in physics.

INSTANTANEITY unifies and balances electromagnetism, inertia, and gravity ALL AT ONCE. Dreams prove this.

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Any truly fundamental unification or explanation of physics includes vision -- it is necessarily consistent with how vision is possible. It includes the visual experience or manifestation of the body/eye -- it includes bodily experience. Observer and observed.

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Enjoining and balancing invisible and visible space electromagnetically, inertially, and gravitationally WITH INSTANTANEITY would fundamentally and generally unify physics.

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Gravity enjoins and balances visible and invisible space; and gravity, invisible and visible, is key to distance in/of space. The unification of physics begins with gravity.

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Victor Stenger in his book, The fallacy of Fine-Tuning, quotes Dirac's "dismissive footnote" on the name "wave function" which only appears once in DIrac's text:

"In the early days of quantum mechanics all the examples of these functions were in the form of waves. The name is not a descriptive one from the point of view of the modern general theory" [Stenger, p.83]

On nuclear synthetics, would coalescence theories be PSI-ontic and Thermodynamic ones PSI-epistemic?

The wave one and the non-wave one different faces fo PSI? Bras and kets are descriptive enough and those proposed terminologies loose the generality at pulse despreading levels.

I don't really like the idea of categorizing transformations into two main groupings ontological and epistological--they do not have that "point of view invariance" the Stenger talks about in his book. If you want to nail down some stuff, his book will help you do it.

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