Is Wave-Particle Duality Really Real? An Analysis of the Double Slit Experiment

[Frame Dragger]

There are no interference effects of that kind between light waves that are polarized 90 degrees to each other. Classical EM predicts that the pattern on the screen will simply be the sum of the patterns from the individual slits. The same as QM predicts.

Cite?

 

[DrChinese]

There are no interference effects of that kind between light waves that are polarized 90 degrees to each other. Classical EM predicts that the pattern on the screen will simply be the sum of the patterns from the individual slits. The same as QM predicts.

As Frame Dragger asks, I too would be interested in a citation - or at the very least a description of a dataset that has the properties I detail above. I don't think there will be any on this kind of experiment other than a quantum explanation. I can imagine that a classicist might think the predictions would be the same, but I just don't see how. I see a lot of hand-waving that realistic theories yield similar predictions to QM, but these often don't hold up when analyzed in detail.

 

[conway]

As Frame Dragger asks, I too would be interested in a citation - or at the very least a description of a dataset that has the properties I detail above. I don't think there will be any on this kind of experiment other than a quantum explanation. I can imagine that a classicist might think the predictions would be the same, but I just don't see how. I see a lot of hand-waving that realistic theories yield similar predictions to QM, but these often don't hold up when analyzed in detail.

I have to confess that I didn't read your scenario carefully enough to be sure that I understood it. I simply replied to some specific things you said in the body of your posts that seemed to go against what I think I know about classical e-m theory. Perhaps I'm not understanding your point at all. Are you really saying that there are experiments you can do with an ordinary laser, a pair of slits, some polarizers and a photographic plate, where you end up with an interference pattern different than what would be expected from garden-variety e-m theory?

If that's your claim then I disagree with it and am willing to try and explain my objections. If that's not your point then I've simply misunderstood what you were saying.

 

[Frame Dragger]

I have to confess that I didn't read your scenario carefully enough to be sure that I understood it. I simply replied to some specific things you said in the body of your posts that seemed to go against what I think I know about classical e-m theory. Perhaps I'm not understanding your point at all. Are you really saying that there are experiments you can do with an ordinary laser, a pair of slits, some polarizers and a photographic plate, where you end up with an interference pattern different than what would be expected from garden-variety e-m theory?

If that's your claim then I disagree with it and am willing to try and explain my objections. If that's not your point then I've simply misunderstood what you were saying.

I give you 10 out of 10 for honesty when you could have evaded. There is a terrible TERRIBLE wikipedia article about this very scenario... but it had a great picture. In it, the contrast between the expected linear trajectory of the photon as predicted in a classical model vs SQM was shown. If I remember correctly even at 90 degrees there is still interference. I don't know if it's visibile however, and that is pissing me off! Now I should go and try and cite MY sources... oy!

 

[Mentz114]

This may be of interest. See page 41 for an experimental setup similar to the two-slits, with tourmaline polarisers.

 

[DrChinese]

Are you really saying that there are experiments you can do with an ordinary laser, a pair of slits, some polarizers and a photographic plate, where you end up with an interference pattern different than what would be expected from garden-variety e-m theory?

What I am saying is that once you know the outcome of an experiment, it may seem to match a classical expectation - but that the same classical expectation may not be supportable from theory alone. I am certainly advocating the idea that whenever the polarizers are in the Crossed mode, there is NO interference. That would be the expected result as far as I know from anyone's prediction. I mean, who wants to predict something different than experiments show?

So the question is: would a classical (realistic) wave explanation *actually* predict this? And I am saying: NO, there is no realistic dataset which supports that result. As with all quantum experiments, the context of the observation is important. Classical (realistic) theories are context-free. So there MUST be a difference somewhere. Clearly, the Crossed polarizers are a specific context and are fully independent of the source - just as in standard Bell tests. So I am asking: what theoretical basis is there for asserting that the quantum result can be obtained from a realistic perspective? Because I don't believe there is one.

And just to be clear: I recognize that this question is in some ways moot. After all, the (classical) wave picture of light is refuted by papers such as "Observing the quantum behavior of light in an undergraduate laboratory". And further, I know that most folks just assume that there is close correspondence between the classical picture and the quantum picture in many cases. When there is a difference, the quantum picture rules. But I think that this is a case in which the classical picture does not apply at all.

 

[DrChinese]

This may be of interest. See page 41 for an experimental setup similar to the two-slits, with tourmaline polarisers.

That is a cool paper. Where/how did you find it?

 

[Frame Dragger]

Wow.. that's a copy of a (partial apparently) dissertation from the MIT library that's been added to their digital archives. That IS a great paper... and you've got the very issue we're talking about... aaaaannnndddd the matrices are pretty clear. Of course, that doesn't help Dr. Chinese in terms of eliminating the Classical point of view as a valid description of these events. Then again, I'm not sure anything out there does one way or the other. There you go doc, if you didn't already have the doctorate you would have material for another dissertation. Fond memories, right? ;) Yeah...

Oh... http://libraries.mit.edu/archives/index.html I think that might be a good starting point for lots of goodies.


EDIT: I should add... purely as a historical document I really enjoyed reading that paper. Thank you VERY much Mentz114, for sharing it!

 

[conway]

I'm sorry I have to repeat myself but I still haven't understood what you are trying to claim. Do you mean to suggest there a difference between what I've called "garden-variety e-m theory" and what you are calling "classical (realistic) wave theory"? I don't like to push people for a "yes-or-no" answer but in this case I honestly don't see any way around it. Specifically:

Are you really saying that there are experiments you can do with an ordinary laser, a pair of slits, some polarizers and a photographic plate, where you end up with an interference pattern different than what would be expected from garden-variety e-m theory?

 

[conway]

Okay, I think I now know what you mean by "classical (realist)" vs "garden-variety". There is a line of argument whereby people say "obviously you cannot explain such-and-such with the classical wave theory, but if you modify the theory by assuming that for example conservation of energy may be temporarily violated..." etc. So I'm thinking what you mean to say is "Of course the standard wave theory doesn't explain the interference experiment, but beyond that, even if you modify the standard theory by the addition of some bizarre ad-hoc assumptions, you still cannot explain the facts.

I think that's what you're getting at. In other words, you are taking my statement and making it even stronger by expanding it to cover the scope of all possible wave theories.

If that's what you mean, I'd just as soon simplify the discussion by stipulating that I'm not interested in invoking exotic modifications of the wave theory. When I said "garden-variety", that's what I meant.

 

[DrChinese]

I'm sorry I have to repeat myself but I still haven't understood what you are trying to claim. Do you mean to suggest there a difference between what I've called "garden-variety e-m theory" and what you are calling "classical (realistic) wave theory"? I don't like to push people for a "yes-or-no" answer but in this case I honestly don't see any way around it. Specifically:

Are you really saying that there are experiments you can do with an ordinary laser, a pair of slits, some polarizers and a photographic plate, where you end up with an interference pattern different than what would be expected from garden-variety e-m theory?

No, the experiments come out as you would expect.

The authors of EPR were local realists (there were a lot around then), and didn't realize that the assumption of realism added severe constraints to classical theory. Bell later showed everyone what some of those assumptions were.

So just saying that "everyone knows" that the classical result is the same as the quantum prediction won't work. Since entanglement gives us a tool, we can probe all kinds of cool things today. But even the old double slit has things to tell us that are still relevant.

 

[DrChinese]

Okay, I think I now know what you mean by "classical (realist)" vs "garden-variety". There is a line of argument whereby people say "obviously you cannot explain such-and-such with the classical wave theory, but if you modify the theory by assuming that for example conservation of energy may be temporarily violated..." etc. So I'm thinking what you mean to say is "Of course the standard wave theory doesn't explain the interference experiment, but beyond that, even if you modify the standard theory by the addition of some bizarre ad-hoc assumptions, you still cannot explain the facts.

I think that's what you're getting at. In other words, you are taking my statement and making it even stronger by expanding it to cover the scope of all possible wave theories.

If that's what you mean, I'd just as soon simplify the discussion by stipulating that I'm not interested in invoking exotic modifications of the wave theory. When I said "garden-variety", that's what I meant.

I follow your point, and it fits with what I am claiming. Naturally, anyone today is going to be on board with the quantum treatment and so there is not much serious debate. The "garden variety" perspective works for most situations. And if everyone thinks it is identical in all respects to a classical (local realistic) perspective, then that is OK for most any discussion. But if you try to get "rigorous" about the point (not that it is necessary), the argument cannot hold up.

The double slit is a wonderful experiment to show the wave-particle duality of both light and matter. The polarizers are a nice twist to show that the which path information can be learned without even disturbing the light as it travel to the screen. ZapperZ often posts a reference to a paper by Marcella that ties the double slit directly to the Heisenberg Uncertainty Principle. So there is plenty to be learned from this one experiment.

 

[DrChinese]

Consider a change to the setup I mention in post#18:
-------------------------------------------------------------
To make this clear, consider the following two setups A and B, which are identical except for the settings of the polarizers in front of each slit. In each case, the source beam is polarized to 0 degress and the L (left) slit has a +45 degree polarizer. The R slit has a ++45 degree polarizer in the A setup but has a -45 degree polarizer in the B setup. Sorry for the crude drawing...

A. Inteference IS seen
...======
... Source
...== | ==
... |
... V
== /L/ = /R/ ==

.===Screen===B. NO Interference seen
...======
... Source
...== | ==
... |
... V
== /L/ = \R\ ==

===Screen===

--------------------------------------------------------
New version:

...======
... Source
...== | ==
...| = |
...| = |
.../ = \ <---- Polarizers are here now
...| = |
...| = |
...| = |
...| = |
...| = |
...| = |
...v = v
=== L = R ===

===Screen===i) the distance from the source to the slits is increased substantially;
ii) there is a barrier (marked as "=" above) between the source and the slits that separates the 2 side, but only up to the point where the slits are... after that, the light passing through the 2 slits can interact/interfere as usual;
iii) the polarizers are moved to a spot in between the source and the slits, close enough to the source that the polarizers can be considered spacelike separated;

Now, assuming that the barrier in between the 2 sides does not upset the experiment (just a guess really), we can see that the experiment resembles a Bell test with spacelike separated Alice and Bob (the Left and Right polarizers being the analog to Alice and Bob). And we know what that means: a Bell inequality. If it were possible to make a sensitive test with a double slit, then I would expect the result to shown explicitly that the old-style classical prediction cannot hold. We know the angle settings because they are the same as a traditional Bell test exactly.

 

[conway]

I'm sorry for your wasted effort but I no longer have any idea what we're talking about. I'm going to have to drop out of the discussion.

 

[DrChinese]

I'm sorry for your wasted effort but I no longer have any idea what we're talking about. I'm going to have to drop out of the discussion.

I guess "No, the experiments come out as you would expect" might be ambiguous.

 

[conway]

Yes, I generally had trouble understanding what you meant with that kind of statement.

 

[Phrak]

Just to add to my prior post: I think the situation could probably be formulated into an inequality using logic from Bell's Theorem.

You do realize that Bell's inequality refutes quantum mechanics, right?

 

[jtbell]

Bell's inequality refutes quantum mechanics

How so?

 

[Fredrik]

"Contradicts" would probably be a better word than "refutes".

 

[Phrak]

Yeah. 'Refutes' is not the right word.

How so?

Should Bell's inequality be true, some predictions of quantum mechanicanics are incorrect.

Violations of Bell's inequality could support quantum mechanics.

To be sure, quantum mechanics predicts statistical results that would violate Bell's inequality. Quantum mechanics predicts that Bell's inequality should be violated, and with particular statistical results.

And, to be sure, it's a common error to invert the meaning of the inequality. Bell could just as easily have inverted the inequality to it's inverse, and we'd be free of confusion--though I think he initially believed it would be found experimentally supported and 'action at a distance' found false.

 

[mintparasol]

There is NO chance that a particular photon polarized at 0 degrees could pass through both a +45 polarizer and a -45 degree polarizer in the quantum mechanical view. The operative formula is the COS^2(L-R) rule, where L-R=90 degrees so that the result is 0 and there is no interference.

On the other hand, in the classical perspective, there IS a chance that any particular photon polarized at 0 degrees could pass through both a +45 polarizer and a -45 degree polarizer. Do you see why? The rule is different because the probability is resolved independently for each slit, unlike in the quantum view in which it is the relative angle of the L and R slits is important. So now you get COS^(L-0)*COS^(R-0) and there should be some interference because the result is .25 which is >0.

Well at least you are thinking about it...

I would be interested in a demonstration of a classical wave effect which eliminates all interference when partial polarizers (or classical equivalent) are present in a setup similar to the double slit. You use the example of audio, and I think a careful consideration of your analogy will demonstrate that the interference will NOT be eliminated after all - as it would need to be to match light in a double slit.

Of course there is a lot more to the story on the quantum side anyway. If light were waves (only) then a lot of things would be different (in contradiction to experiment - see for example: http://people.whitman.edu/~beckmk/QM/grangier/Thorn_ajp.pdf" ). If light polarization operated as you imagine, things would be different with entangled particle pairs (in contradiction to experiment).

You may not be aware of all of the experiments out there (who is?), but you might want to at least ask before talking about the emperor's clothes. The double slit is just one piece of the puzzle.

Ok, I've printed off that paper for further reading, thanks!

I'm just wondering if we could arrange some mechanism to put our bass wave +45 degrees out of phase at the left slit and -45 degrees out of phase at the right slit, would the math work in the same way for soundwaves? Would there be any interference detectable rear of the slitted screen?

 

[conway]

But sound isn't polarized. Its a longitudinal wave while light is a transverse wave. In any case, there is no interference with light if the waves from the two slits are polarized at 90 degrees to each other. This is predicted by classical physics exactly the same as QM and does not represent any kind of mystery.

 

[DrChinese]

You do realize that Bell's inequality refutes quantum mechanics, right?

I am sure we agree that a violation of a Bell inequality refutes classical realism, and is consistent with QM. I simply think of the inequality as a boundary condition on (local) realism.

 

[Frame Dragger]

I am sure we agree that a violation of a Bell inequality refutes classical realism, and is consistent with QM. I simply think of the inequality as a boundary condition on (local) realism.

I have to say that's a good way of putting it. I've been doing a good deal of reading on deBB, and a refresher on The TI, and more and more it seems that dBB and a few other theories are simply the ones that have not been swept aside by modern experimental evidence. dBB basically hinges on the QM being in violation of Bell's Inequalities, and not classical realism. The argument of (mechanical) bias in experiments such as a "2 channel" test, keeps dBB alive unlike most other theories which required LHV's.

However, the switch from locality to non-locality in dBB seems logically contrived for the sole purpose of maintaining a particular interpretation of reality as something other than emergent phenomena from a quantum soup of superpositioned probabilities. That doesn't make it wrong, and from everything I'm reading dBB can't be refuted right now and if nothing else it does a very good job of highlighting the huge gap in explaining how the microscopic and macroscopic worlds combine to form what we experience as reality in SQM. I think that the TI is probably on the right track, but it's hard to say that those theories, or MWI are more contrived than dBB.

Given all of that, I still fall on the side of SQM for the sake of the results it provides and predictions it makes. Bell expected "Spukhafte Fernwirking" to be experimentally disproved, and instead it is now experimentally observed on a regular basis.

In my view, one of the ways this debate can be settled would be the emergence of even a VERY rudimentary computer capable of using qubits to complete an algorithm. Failure would mean little, but success in line with expectations of SQM would be pretty damned confirmatory. The problem with modern approaches is that they still use Classical mechanics that exploit quantum behaviour... which can be explained by theories such as dBB. Go figure.

The bottom line is that Bell kind of draws the line between the Classicist and SQM view of reality. It's a boundary in the common usage and not just the scientific term of art.

 

[DrChinese]

I have to say that's a good way of putting it. I've been doing a good deal of reading on deBB, and a refresher on The TI, and more and more it seems that dBB and a few other theories are simply the ones that have not been swept aside by modern experimental evidence. dBB basically hinges on the QM being in violation of Bell's Inequalities, and not classical realism. The argument of (mechanical) bias in experiments such as a "2 channel" test, keeps dBB alive unlike most other theories which required LHV's.

However, the switch from locality to non-locality in dBB seems logically contrived for the sole purpose of maintaining a particular interpretation of reality as something other than emergent phenomena from a quantum soup of superpositioned probabilities. That doesn't make it wrong, and from everything I'm reading dBB can't be refuted right now and if nothing else it does a very good job of highlighting the huge gap in explaining how the microscopic and macroscopic worlds combine to form what we experience as reality in SQM. I think that the TI is probably on the right track, but it's hard to say that those theories, or MWI are more contrived than dBB.

...

The bottom line is that Bell kind of draws the line between the Classicist and SQM view of reality. It's a boundary in the common usage and not just the scientific term of art.

I agree with what you are saying. dBB gets by because the context is non-local. Another interesting set of interpretations is the Time Symmetric group (including Relational BlockWorld RBW), in which a future context is allowed to influence the present. These have the "benefit" of being local, contextual (non-realistic) and time symmetric. Of course you swap one assumption for another, so whether the result is net better is a matter of preference.

 

[Frame Dragger]

I agree with what you are saying. dBB gets by because the context is non-local. Another interesting set of interpretations is the Time Symmetric group (including Relational BlockWorld RBW), in which a future context is allowed to influence the present. These have the "benefit" of being local, contextual (non-realistic) and time symmetric. Of course you swap one assumption for another, so whether the result is net better is a matter of preference.

This is true, and possibly experimentally verifiiable. If phonons can be detected emerging from a sonic event horizon it would be a step towards showing that a process like Hawking Radiation might exist... and that hinges on virtual particle annihilation (or lack thereof)... which is also a kind of single particle along a worldline view, but not in one temporal "direction". I suppose we'll have to wait and see.

 

[eaglelake]

In the book he makes an example of the double slit experiment we all did in high school and says that if we fire one photon at the slitted screen, we'll get an interference pattern on the rear screen.

If you fire one photon through the slits you will get one dot on the second screen. A single photon is always detected as a single particle (a dot), never as a wave. In fact, the single dot doesn’t reveal any wave properties. It is only when you detect many photons does the distribution of scattered photons begin to look like an interference pattern. There are sites on the web that show how the interference pattern is built up one photon at a time.

I am bothered that an author would make such a statement, but apparently it is all too common. No experiment has ever shown a particle behaving like a wave. The point is this – a quantum particle is not a wave.

 

[Frame Dragger]

If you fire one photon through the slits you will get one dot on the second screen. A single photon is always detected as a single particle (a dot), never as a wave. In fact, the single dot doesn’t reveal any wave properties. It is only when you detect many photons does the distribution of scattered photons begin to look like an interference pattern. There are sites on the web that show how the interference pattern is built up one photon at a time.

I am bothered that an author would make such a statement, but apparently it is all too common. No experiment has ever shown a particle behaving like a wave. The point is this – a quantum particle is not a wave.

Annnnd... you're wrong. In fact, even when passing C60 or Rubidium atoms (one at a time) there is interference consistant with passage through both apertres of the experiment. There are sites on the web that show how 8th dimension lizards run the country... that doesn't make them accurate. Interference patterns of the type you describe are not consistant with a purely particle-theory of light. Light's wave-like properties are as well established as its particle-like properties.

As for experiment with photons... you'rre wrong again? I don't know what else to say... you can in fact set up simple controls for these experiements which eliminate interence by more than specifically polarized photons passng throuhg the apertures.

EDIT: Addition: "A quantum particle is not a wave." True. Photons are quanta which have wave and particle -like properties. They are neither waves, NOR particles and feel free to call them "quanta" not "quantum particles". That latter is... meaningless and semi-redundant.

 

[eaglelake]

Annnnd... you're wrong. In fact, even when passing C60 or Rubidium atoms (one at a time) there is interference consistant with passage through both apertres of the experiment. There are sites on the web that show how 8th dimension lizards run the country... that doesn't make them accurate. Interference patterns of the type you describe are not consistant with a purely particle-theory of light. Light's wave-like properties are as well established as its particle-like properties.

As for experiment with photons... you'rre wrong again? I don't know what else to say... you can in fact set up simple controls for these experiements which eliminate interence by more than specifically polarized photons passng throuhg the apertures.

EDIT: Addition: "A quantum particle is not a wave." True. Photons are quanta which have wave and particle -like properties. They are neither waves, NOR particles and feel free to call them "quanta" not "quantum particles". That latter is... meaningless and semi-redundant.

No need to be a wiseguy! If you do not understand something, just ask for a clarification.

I responded to the statement, “if we fire one photon at the slitted screen, we'll get an interference pattern on the rear screen.”, which is not true. A single photon is always detected as a single dot on the detection screen. A single photon is never smeared over the screen in an interference pattern, as a wave would be. If you want to see wave effects then you must repeat the same experiment many times.

The original statement by mintparasol referred to a single photon, while you are talking about, “passing C60 or Rubidium atoms (one at a time)”, which is about MANY atoms. “One at a time” means more than one! You seem to imply that the interference pattern is built up “one (atom) at a time”. I agree! That is exactly what I said. So, where is the disagreement?

The basic question is, “ When does a photon, or any quantum particle, look like a particle and when does it look like a wave”? We either observe one or the other, but never both at the same time. (Bohr’s complimentarity principle)

The answer is – if you detect a single particle it looks like a particle. It looks like a wave only after you have detected many of them. [1] (and, then, only in special circumstances.)

Best wishes.

[1] A. Tonomura, et al, Amer. J. Phys., 57, 117-120 (1989)

 

[Frame Dragger]

No need to be a wiseguy! If you do not understand something, just ask for a clarification.

I responded to the statement, “if we fire one photon at the slitted screen, we'll get an interference pattern on the rear screen.”, which is not true. A single photon is always detected as a single dot on the detection screen. A single photon is never smeared over the screen in an interference pattern, as a wave would be. If you want to see wave effects then you must repeat the same experiment many times.

The original statement by mintparasol referred to a single photon, while you are talking about, “passing C60 or Rubidium atoms (one at a time)”, which is about MANY atoms. “One at a time” means more than one! You seem to imply that the interference pattern is built up “one (atom) at a time”. I agree! That is exactly what I said. So, where is the disagreement?

The basic question is, “ When does a photon, or any quantum particle, look like a particle and when does it look like a wave”? We either observe one or the other, but never both at the same time. (Bohr’s complimentarity principle)

The answer is – if you detect a single particle it looks like a particle. It looks like a wave only after you have detected many of them. [1] (and, then, only in special circumstances.)

Best wishes.

[1] A. Tonomura, et al, Amer. J. Phys., 57, 117-120 (1989)

No... you missed my point entirely. The experiment involving Rubidium showed a single atom having a unique wavefront just as a single photon does. The fact that it takes multiple passes (as you say, a buildup) to make the pattern visible is a limitation of our detection methods. If one could image a photon more exactly there would be a wavefront causing an interference pattern, visible or not. The dual nature of the quanta seems pretty clear. That's a limitation of the experimental apparaturs, but it's clear from the distribution... built over time as you say... that each individual photon, atom, etc, while observed at any given time to be particle or wave -like... has both properties at all times.

 

[Mentz114]

FrameDragger:

The fact that it takes multiple passes (as you say, a buildup) to make the pattern visible is a limitation of our detection methods.

I don't see how. A particle detector is designed to detect particles and that's what it does. What apparatus would you use to detect a 'Rubidium wave' ?

 

[Frame Dragger]

FrameDragger:


I don't see how. A particle detector is designed to detect particles and that's what it does. What apparatus would you use to detect a 'Rubidium wave' ?

The same way you do with buckyballs (C60) a la http://www.users.csbsju.edu/~frioux/two-slit/c60-slit.htm

 

[Mentz114]

The same way you do with buckyballs (C60) a la http://www.users.csbsju.edu/~frioux/two-slit/c60-slit.htm

That doesn't answer the question. The note you linked to shows the wave function that models the experiment. The wave function gives us probabilities of detecting the particle at certain locations. If you send one particle through, you detect one at the screen. If you send a 100 particles through one by one, they will make a pattern like the square of the wave function at the screen. The particle goes through one slit or the other but we cannot find out (even in principle) which slit, and still get the interference pattern building up.

I enjoyed that little note.

For more on single-photon interference look up Hong-Ou-Mandel.

 

[Dmitry67]

I wanted to remind that the balance between particle and wave behavior is interpretation-dependent.

For example, in BM there are real particles, just guided by the wave.
In MWI, there are only waves (and dots we see on the screen are the result of quantum decoherence)

 

[Frame Dragger]

That doesn't answer the question. The note you linked to shows the wave function that models the experiment. The wave function gives us probabilities of detecting the particle at certain locations. If you send one particle through, you detect one at the screen. If you send a 100 particles through one by one, they will make a pattern like the square of the wave function at the screen. The particle goes through one slit or the other but we cannot find out (even in principle) which slit, and still get the interference pattern building up.

I enjoyed that little note.

For more on single-photon interference look up Hong-Ou-Mandel.

Understood, clearly this was a misinterpretation on my part. However that does not eliminate the fact that in the absence of observation even a single photon must have properties which that experiment allows to build into an a clear interference pattern.

The distribution of many (as you say) photons allows for the interference pattern to be observed, but presumably both properties ARE always present. Even when light appear to travel as a wave, it is subjected to the effects of gravity, and when it appear to register as a single particle on a screen, it clearly has wave-like properties. The pattern at the end of the experiment can be predicted based on the arrangement of the test, and the material being tested, if not the position of each individual "strike" on the screen.

The belief the the pattern is simply a function of many particles acting without wave-like behaviour flies in the face of experimental evidence, but is compatible with non SQM or dBB theories. Even dBB postulates a pilot wave to explain experimental evidence.

Dimitry67: Well, it's interpretation dependant in the case of MWI and some others, but that is a conjecture and not really a mechanical theory. Right or wrong, it's purely ad hoc. dBB... well.. that's a separate theory that emerged before SQM, and not just a separate interpreation of QM behaviour. I still think it's wrong and somewhart contrived, but to relegate it to an interpreation of the theory it rejects is probably unfair.