Is the Wave Function Real? Evidence from the Frankenstein Photon Experiment

[DrChinese]

It is sometimes said that wave functions are not real, and simply represent the observer's knowledge of the system. I would like to comment against this point by presenting an experimental setup which would tend to indicate that the wave function is quite real. As far as I know, this setup per se has never been executed (although I am hoping someone might recognize it as something which has been).

To follow the setup, you should be familiar with the following experiment:

Bell inequalities and quantum mechanics, J. H. Eberly (2001)

See Figure 1, the Bell analyzer loop, in which a beam is split into H and V components. Those are then recombined so that the H/V information is erased, leaving a beam with the same properties as it was originally.

So if you took a pair of entangled particles, Alice and Bob, and ran each through a Bell analyzer loop, the recombined Alice and Bob are still entangled. This is what the above paper is saying.

---------------------

Here is my twist:

Frankenstein photons:
=====================

Split Alice into Alice-H and Alice-V. Split Bob into Bob-H and Bob-V. Now recombine Alice-H with Bob-V (which is identical to Alice-V). Recombine Bob-H with Alice-V (likewise identical to Bob-V). You will now have 2 Frankenstein photons that are polarization entangled!

Now, if the above is accurate (I don't see how it could be expected to be otherwise), then you would have to admit that you are mixing the wave functions of different photons to obtain an effect that clearly does not occur with either portion of the component wave functions alone.

So I conclude that the wave function is quite real. Your thoughts?

 

[LostConjugate]

Thanks for bringing up this subject Dr, this is my favorite subject.

Now, if the above is accurate (I don't see how it could be expected to be otherwise), then you would have to admit that you are mixing the wave functions of different photons to obtain an effect that clearly does not occur with either portion of the component wave functions alone.

Is this different from other experiments where the wave function is the only explanation?

I think what is meant by the wave function not being "real" is that it is not a direct observable.

 

[DevilsAvocado]

Great post/question DrC, I’ll be back ASAP!

 

[RUTA]

Is this different from other experiments where the wave function is the only explanation?

I think what is meant by the wave function not being "real" is that it is not a direct observable.

Competing interpretations of QM can be divided into wave function realism and non-realism. Bohmian mechanics, for example, assumes the wave function acts as a guide for the quantum particles moving about the experimental equipment. Thus, for BM the wave function is very real. In Relational Blockworld, the wave function is only a description of the experimental equipment, there are no quantum particles moving therein. Thus, for RBW the wave function has no ontic status at all.

 

[billschnieder]

Superpositions of mutually exclusive objects are not considered real in ordinary logic. Why should the case be different for QM? In other words, if "Dead cat" and "live cat" are mutually exclusive, the superposition "Both dead and alive" can not be real, even in QM.

Let x correspond to one wall of your room and y the perpendicular wall, x and y therefore correspond to real material ontological "objects". Now consider the transformation x' = x + y, y'=x -y. Would you then say that x'and y' are material ontological objects? Of course not, they run through the room without any wall. Similarly, for a Hilbert space, there is no implicit association between transformed basis vectors and ontological entities. Correspondence to reality has to be independently established in each case.

Therefore the wave function is not necessarily real.

 

[RUTA]

Here is my twist:

Frankenstein photons:
=====================

Split Alice into Alice-H and Alice-V. Split Bob into Bob-H and Bob-V. Now recombine Alice-H with Bob-V (which is identical to Alice-V). Recombine Bob-H with Alice-V (likewise identical to Bob-V). You will now have 2 Frankenstein photons that are polarization entangled!

Now, if the above is accurate (I don't see how it could be expected to be otherwise), then you would have to admit that you are mixing the wave functions of different photons to obtain an effect that clearly does not occur with either portion of the component wave functions alone.

So I conclude that the wave function is quite real. Your thoughts?

As an experimentalist you orient pieces of equipment so that geometrically you can trace a path from source to detector(s) defined by beam splitters, crystals, mirrors, polarizers, etc. To obtain a wave function for the outcome(s) at the detector(s) of your particular experimental arrangement, you simply start (computationally) with the relationship between source and detector(s) without any intermediary equipment, then modify it step by step according to the arrangement of each piece of equipment defining the path from source to the detector(s).

Typically, wave function realists assume the wave function moves sequentially from the source through each piece of equipment and impinges on the detector(s) to produce the outcome(s), per the computational sequence of the wave function's constuction. "Weirdness" can result if one alters the arrangement of equipment so as to produce new outcomes at odds conceptually with those of the previous arrangement. [Note: QM is not violated, just the consistency of corresponding ontological stories in both cases.]

Of course, the wave function non-realist avoids these conundrums altogether. They understand the wave function is a description of the spatiotemporal entirety of the experiment -- all the equipment, its spatial arrangment and orientation, from initiation to termination. So, if you change the arrangement, you change the outcomes per the new wave function. There is no complicating factor of having to tell consistent stories about quantum entities moving through the experimental equipment in its differing configurations. It doesn't matter WHAT you arrange experimentally, you don't need to invoke anything other than facts concerning the experimental equipment to construct the corresponding wave function, so there's absolutely no way to empirically discern the existence or non-existence of said wave function.

 

[LostConjugate]

RUTA, that was a great read.

Say we programmed a very intelligent artificial intelligence and leave it to itself. Now this AI is sitting inside a computer and starts to contemplate why it's bits flip. It can discern a pattern through experimentation and even devise functions with Fourier transforms that give the AI information about what happens when it's bits flip.

Though no matter the experiment, the AI will never understand the mechanism that allows it's bits to flip.

 

[IcedEcliptic]

If the wave function is not real, and pilot waves are not real, then how does the double-slit experiment show interference?

 

[glengarry]

From Speakable and unspeakable in quantum mechanics, by J.S. Bell, p. 171. This is from an essay of the same name.

The 'Problem' then is this: how exactly is the world to be divided into speakable apparatus...that we can talk about...and unspeakable quantum system that we can not talk about? How many electrons, or atoms, or molecules, make an 'apparatus'? The mathematics of the ordinary theory requires such a division, but says nothing about how it is to me made. In practice the question is resolved by pragmatic recipes which have stood the test of time, applied with discretion and good taste born of experience. But should not fundamental theory permit exact mathematical formulation?

Now in my opinion the founding fathers were in fact wrong on this point. The quantum phenomena do not exclude a uniform description of micro and macro worlds...system and apparatus. It is not essential to introduce a vague division of the world of this kind. This was indicated already by de Broglie in 1926, when he answered the conundrum

'wave or particle?'

by

'wave and particle.'

But by the time this was fully clarified by Bohm in 1952, few theoretical physicists wanted to hear about it. The orthodox line seemed fully justified by practical success. Even now the de Broglie-Bohm picture is generally ignored, and not taught to students. I think this is a great loss. For that picture exercises the mind in a very salutary way.

I would say that, in terms of the types of mathematics that are taught to budding physical theorists, the one that is the most powerful and yet receives the least amount of attention, is the idea of wave theory itself. The theoretical physicists of today, therefore, are highly skilled in terms of discrete, matrix-like mathematical systems, but when it comes to issues such as deriving the specific harmonic solutions to the wavefunction itself, most theoretical physicists tend to find themselves at a loss, and there is consequently a profound lack of spatio-temporal intuition at play in the contemporary literature.

 

[RUTA]

I would say that, in terms of the types of mathematics that are taught to budding physical theorists, the one that is the most powerful and yet receives the least amount of attention, is the idea of wave theory itself. The theoretical physicists of today, therefore, are highly skilled in terms of discrete, matrix-like mathematical systems, but when it comes to issues such as deriving the specific harmonic solutions to the wavefunction itself, most theoretical physicists tend to find themselves at a loss, and there is consequently a profound lack of spatio-temporal intuition at play in the contemporary literature.

My colleagues in physical chemistry deal extensively with wave functions to generate pretty pictures of orbitals. The solid state physicists also rely heavily on a conceptual view using the wave function, speaking of current densities flowing through various lattices. I think where one can use this picture effectively, the ontological mysteries are minimal (for many of my colleagues in these areas, I would say the conundrums of QM are non-existent). However, those who specifically study QM conundrums tend to find the matrix formalism better suited for analysing such phenomena. I can't imagine trying to model the quantum liar paradox via Schrodinger's equation. What a mess :-)

 

[RUTA]

If the wave function is not real, and pilot waves are not real, then how does the double-slit experiment show interference?

For an explanation whereby there are no quantum entities moving from the source, through the slits and subsequently impinging on the detector to cause a click in the twin-slit experiment, see the material in Section 2 concerning Figure 4 of “Reconciling Spacetime and the Quantum: Relational Blockworld and the Quantum Liar Paradox,” W.M. Stuckey, Michael Silberstein & Michael Cifone, Foundations of Physics 38, No. 4, 348 – 383 (2008), quant-ph/0510090. In this interpretation of QM, the only entities with ontological status are the pieces of the experimental equipment. Thus, the choice is not limited to "wave or particle" or "wave and particle," as Bell argued. There is another option, "neither wave nor particle," i.e., no "quantum/screened off entities" at all.

 

[yoda jedi]

Competing interpretations of QM can be divided into wave function realism and non-realism. Bohmian mechanics, for example, assumes the wave function acts as a guide for the quantum particles moving about the experimental equipment. Thus, for BM the wave function is very real. In Relational Blockworld, the wave function is only a description of the experimental equipment, there are no quantum particles moving therein. Thus, for RBW the wave function has no ontic status at all.

ψ-epistemic.

 

[LostConjugate]

ψ-epistemic.

Elaborate

 

[IcedEcliptic]

Elaborate

Yes, please do so extensively.

 

[GeorgCantor]

How about a new quantum conundrum - the Real-Unreal duality? If a 'particle' can be both a wave and particle, why couldn't it be both real and unreal, depending on the mode of inquiry? How else would you reconcile conservation of mass/energy with tunneling or quantum jumps and real wavefunctions? Both sides to the debate(real vs unreal) seem to have good arguments for their case.

 

[RUTA]

Elaborate

"epistemic -- of, relating to, or involving knowledge"

As opposed to

"ontic -- of, relating to, or having real being"

So, "psi epistemic" means the wave function is knowledge about ... , it doesn't necessarily "exist" or have "being." In BM, psi definitely exists and acts on the quantum particles, so psi is ontic. Of course, it could be both, but in RBW it's purely epistemic.

 

[glengarry]

My colleagues in physical chemistry deal extensively with wave functions to generate pretty pictures of orbitals. The solid state physicists also rely heavily on a conceptual view using the wave function, speaking of current densities flowing through various lattices. I think where one can use this picture effectively, the ontological mysteries are minimal (for many of my colleagues in these areas, I would say the conundrums of QM are non-existent). However, those who specifically study QM conundrums tend to find the matrix formalism better suited for analysing such phenomena. I can't imagine trying to model the quantum liar paradox via Schrodinger's equation. What a mess :-)

So, my thinking is that your chemist and solid-state friends are much more directly involved with "physics proper," whereas the QM guys seem to be much more in tune with issues of a more "game theoretical" nature. (I'm thinking that QM'ers would probably be much tougher bluff against in hold 'em poker.) I guess, along with Bell, I just have a problem with people's desire to construct direct correlations between the Gendanken experiments of QM and the reality, as it exists, "out there." Bell absolutely despised the notion of "quantum logic," in the sense of being a kind of radical upheaval of the system of thought that has been around since ancient times.

 

[LostConjugate]

"epistemic -- of, relating to, or involving knowledge"

As opposed to

"ontic -- of, relating to, or having real being"

So, "psi epistemic" means the wave function is knowledge about ... , it doesn't necessarily "exist" or have "being." In BM, psi definitely exists and acts on the quantum particles, so psi is ontic. Of course, it could be both, but in RBW it's purely epistemic.

Thanks RUTA. I guess that is no different than what we already talked about above.

It is intuitive that at it's very nature, the make up of things involve a chaotic mix of harmonic oscillations. This is clear in that nature itself is not very blocky, or hard edged as you learn in wave mechanics that hard edges involve a great number of high frequency functions in Fourier analysis and high frequencies undergo rapid damping and interference.

If the very fundamentals of things are made up of such oscillations though how could a detector made of the same fundamentals detect such a thing.

 

[IcedEcliptic]

Thanks RUTA. I guess that is no different than what we already talked about above.

It is intuitive that at it's very nature, the make up of things involve a chaotic mix of harmonic oscillations. This is clear in that nature itself is not very blocky, or hard edged as you learn in wave mechanics that hard edges involve a great number of high frequency functions in Fourier analysis and high frequencies undergo rapid damping and interference.

If the very fundamentals of things are made up of such oscillations though how could a detector made of the same fundamentals detect such a thing.

This sounds like String Theory, would that be a fair assessment?

 

[LostConjugate]

This sounds like String Theory, would that be a fair assessment?

Could be, I know very little about String Theory, only ever read a layman's book about it once or twice.

 

[GeorgCantor]

Thanks RUTA. I guess that is no different than what we already talked about above.

It is intuitive that at it's very nature, the make up of things involve a chaotic mix of harmonic oscillations. This is clear in that nature itself is not very blocky, or hard edged as you learn in wave mechanics that hard edges involve a great number of high frequency functions in Fourier analysis and high frequencies undergo rapid damping and interference.

If the very fundamentals of things are made up of such oscillations though how could a detector made of the same fundamentals detect such a thing.

Pauli exclusion principle?

 

[LostConjugate]

Huh? I always thought of the Pauli exclusion as distinguishing fermions.

 

[DrChinese]

Superpositions of mutually exclusive objects are not considered real in ordinary logic. Why should the case be different for QM? In other words, if "Dead cat" and "live cat" are mutually exclusive, the superposition "Both dead and alive" can not be real, even in QM.

This is what I am saying, that the superposition is quite real. You wouldn't have entangled Frankenstein particles otherwise.

 

[IcedEcliptic]

This is what I am saying, that the superposition is quite real. You wouldn't have entangled Frankenstein particles otherwise.

What is a Frankenstein particle?

 

[DrChinese]

To make sure everyone has a good idea of the setup...

 

[DrChinese]

What is a Frankenstein particle?

A name I made up to describe a particle consisting of half of Alice plus half of Bob. You wouldn't really expect to be able to create one of these. But I say you can. You can split Alice into 2 halves (an H> and a V> component) and recombine them to recreate the original Alice. Ditto for Bob. So I say you can swap identical components as well. The big caveat being that you must NOT be able to tell which is which.

 

[IcedEcliptic]

A name I made up to describe a particle consisting of half of Alice plus half of Bob. You wouldn't really expect to be able to create one of these. But I say you can. You can split Alice into 2 halves (an H> and a V> component) and recombine them to recreate the original Alice. Ditto for Bob. So I say you can swap identical components as well. The big caveat being that you must NOT be able to tell which is which.

I get it, a patchwork creation. That's very clever, and I get the concept. Thank you Dr. Chinese.

 

[SpectraCat]

So, my thinking is that your chemist and solid-state friends are much more directly involved with "physics proper," whereas the QM guys seem to be much more in tune with issues of a more "game theoretical" nature. (I'm thinking that QM'ers would probably be much tougher bluff against in hold 'em poker.) I guess, along with Bell, I just have a problem with people's desire to construct direct correlations between the Gendanken experiments of QM and the reality, as it exists, "out there." Bell absolutely despised the notion of "quantum logic," in the sense of being a kind of radical upheaval of the system of thought that has been around since ancient times.

You keep impugning the "QM guys", but what you have not ever acknowledged is that the theory of QM is now incredibly mature, and has passed the important tests of 1) agreement with experiment and 2) made predictions that were subsequently verified by experiment. No other theory dealing with physics on the atomic scale can make that claim (I am lumping dBB in with SQM here). Furthermore, it is becoming increasingly clear that even the weirdest aspects of QM theory have experimental basis ... while no-one has done *the* definitive loophole-free Bell test, Aspect and Zeilinger and the like have been hammering on that problem from so many angles that it is almost inconceivable that Bell's theorem will be proven wrong experimentally.

So, from your posts here and in other threads, you seem to think that QM is a bunch of mathematical hooey ... fine. It certainly has it's distasteful aspects, I think most posters here will agree. On the other hand, any theory that is put up against QM will have to show similarly excellent agreement with experiment, and have some other benefits as well.

Finally, I can't understand your position (again gleaned mostly from your posts in other threads) that QM has nothing to do with physics. It is a theory about physics, which accurately reproduces/predicts the results of physical experiments. Over its history, QM has led physicists to develop a much deeper understanding of the world around us, and develop related theories such as QED and QCD to deal with directly with quantization of the fundamental forces of nature. All of these theories have had amazing success at accurately describing physical phenomena. So what in the heck do you mean when you say QM has nothing to do with physics?

With regard to the OP's question, I would say that wavefunctions are indeed ontic entities. I take this from the interference experiments such as the double slit for massive particles. I cannot conceive how such a pattern could be generated unless the entities propagating through the slits have properties analogous to the wavelength and phase of a classical wave. The QM wavefunction both accurately describes and predicts the behavior of massive particles in such experiments, so I think it has earned the right to be called "real", at least until a better candidate for describing the "reality" of the observed phenomena comes along.

 

[yoda jedi]

Elaborate

the quantum state is not just incomplete, but epistemic, i.e. a representation of an
observer’s knowledge of reality rather than reality itself.

...​

 

[IcedEcliptic]

...​

This is from another thread, yes? How could I have known what your view is? I would be interested to see why you believe that QM is incomplete and a limitation of our knowledge, rather than a reflection of nature. Spectracat refutes that very nicely I think.

 

[yoda jedi]

This is from another thread, yes? How could I have known what your view is? I would be interested to see why you believe that QM is incomplete and a limitation of our knowledge, rather than a reflection of nature. Spectracat refutes that very nicely I think.

refuted ? very far to be settled...

 

[RUTA]

A name I made up to describe a particle consisting of half of Alice plus half of Bob. You wouldn't really expect to be able to create one of these. But I say you can. You can split Alice into 2 halves (an H> and a V> component) and recombine them to recreate the original Alice. Ditto for Bob. So I say you can swap identical components as well. The big caveat being that you must NOT be able to tell which is which.

Looking at your set up, I don't see how the outcomes for Chris and Dale will differ at all from those of Alice and Bob, given the location of Chris and Dale's measurement devices. If they move the devices so as to intercept the crossing routes and thereby measure pure |V> or |H> components, then of course you'd get something different. But, that would be a different set up and therefore be represented by a different wave function.

I fail to see why this set up in any way entails wave function realism. I read the caption to the picture, but the conclusion doesn't follow necessarily from the premises. You write,

"These statistics should not be possible unless the Wave Function is itself real. That is because Chris and Dale were created by combining Wave Function components."

I think you're tacitly assuming the reality of the wave function when you talk about "splitting it" and "recombining it." But, I can compute the same wave function for Chris and Dale by simply following the algorithm using the particular placement and orientation of the specific types of equipment in the set up without any reference to a wave function "doing" this or that through the devices.

 

[DrChinese]

Looking at your set up, I don't see how the outcomes for Chris and Dale will differ at all from those of Alice and Bob, given the location of Chris and Dale's measurement devices...

I fail to see why this set up in any way entails wave function realism. I read the caption to the picture, but the conclusion doesn't follow necessarily from the premises. You write,

"These statistics should not be possible unless the Wave Function is itself real. That is because Chris and Dale were created by combining Wave Function components."

I think you're tacitly assuming the reality of the wave function when you talk about "splitting it" and "recombining it." But, I can compute the same wave function for Chris and Dale by simply following the algorithm using the particular placement and orientation of the specific types of equipment in the set up without any reference to a wave function "doing" this or that through the devices.

Maybe you are right, and this is sort of what I am asking. I am saying that if you split a wave function into 2 components, those components can be mixed and matched with components from other particles. In the "right" circumstances, you could create an entangled photon from these components.

Now, my argument is: it is not JUST that we are creating the 100% probability of there being a photon at Chris and another at Dale - no question about that. You would expect that by basic logic. The question is: can you have a superposition formed from DIFFERENT particles? You seem to agree that this is feasible, but not surprising. And yet, I don't recall ever seeing a reference saying as much (that it is feasible). (You do see comments from time to time, on the other hand, that particles do not interfere with each other, but I do not think this is rigorously true.)

Assuming it is feasible: how can you combine wave functions - i.e. potentials - to form a single particle - which acts as if it is in a superposition of wave states - unless the underlying wave functions are real, physical entities? I.e. more real than simple "knowledge" of the system.

 

[RUTA]

Maybe you are right, and this is sort of what I am asking. I am saying that if you split a wave function into 2 components, those components can be mixed and matched with components from other particles. In the "right" circumstances, you could create an entangled photon from these components.

Now, my argument is: it is not JUST that we are creating the 100% probability of there being a photon at Chris and another at Dale - no question about that. You would expect that by basic logic. The question is: can you have a superposition formed from DIFFERENT particles? You seem to agree that this is feasible, but not surprising. And yet, I don't recall ever seeing a reference saying as much (that it is feasible). (You do see comments from time to time, on the other hand, that particles do not interfere with each other, but I do not think this is rigorously true.)

Assuming it is feasible: how can you combine wave functions - i.e. potentials - to form a single particle - which acts as if it is in a superposition of wave states - unless the underlying wave functions are real, physical entities? I.e. more real than simple "knowledge" of the system.

What do you mean by "split the wave function" and "match components from other particles?" If you wanted to "mix a photon with an electron" what would that mean? You have two different sources and two different detectors. So, you're already thinking in a realist fashion about "entities" (wave functions and particles) moving through the experimental equipment. Imagine yourself constructing the experiment. Do you EVER watch "screened off" entities moving through the apparatus? By definition, no. All you can observe are the pieces of equipment and the experimental outcomes. And, you can construct the wave function for the experiment using only information about what you observe. What are the pieces of equipment? Where are they located relative to one another in space? How are they oriented relative to each other? What is the relative temporal sequence of observed events, e.g., when do you turn on source, rotate a mirror, observe a detection event? You construct the wave function using answers to questions like these, so replace your wording about "splitting the wave function" and "matching components" with wording about the experimental set up and you can say goodbye to your "real" quantum entities :-)

 

[DrChinese]

What do you mean by "split the wave function" and "match components from other particles?" If you wanted to "mix a photon with an electron" what would that mean? You have two different sources and two different detectors. So, you're already thinking in a realist fashion about "entities" (wave functions and particles) moving through the experimental equipment. Imagine yourself constructing the experiment. Do you EVER watch "screened off" entities moving through the apparatus? By definition, no. All you can observe are the pieces of equipment and the experimental outcomes. And, you can construct the wave function for the experiment using only information about what you observe. What are the pieces of equipment? Where are they located relative to one another in space? How are they oriented relative to each other? What is the relative temporal sequence of observed events, e.g., when do you turn on source, rotate a mirror, observe a detection event? You construct the wave function using answers to questions like these, so replace your wording about "splitting the wave function" and "matching components" with wording about the experimental set up and you can say goodbye to your "real" quantum entities :-)

I agree with your perspective about context of experiment. What I am questioning is the issue about components, even in a relational format. I would say that all components of the wave functions contribute to the outcome, even when classical logic would say that only the "selected" component did. In other words, classical logic says that Chris and Dale are only ever composed of Alice OR Bob. But I say they are composed of pieces of both Alice AND Bob. Otherwise, they wouldn't be entangled when the component probabilitie amplitudes are from different particles.

I would think you, of all people, would agree with that assessment. But I am not sure it is a unique or surprising result. As I mention, I haven't seen references on it.