Are classical optics and quantum mechanics double slit experiments fundamentally the same?

[aletheia]

And that means you haven't read any textbook on quantum mechanics nor quantum field theory

No! Your comment means that you (and others, since it’s not the first time…) believe that you can disprove an argument without knowing the argument — which, from a medical perspective, is delusional (Im not saying that you are delusional and I don’t mean to offend, I make this reservation because of the pejorative nature of the word).
You have absolutely no idea about what I mean ontologically when I propose it.
It’s not even far from everything that has been discussed here — a discrete event after a field excitation-propagation.
If my word-choosing is not precisely the academic works physicists use officially, that doesn’t mean that you don’t need to see the argument before you assume I don’t have enough understanding of the matter.
Cheers.

 

[flippiefanus]

Except, this sounds to me like you're infering one event, photon emition, from the photon detection. That's not how thermal sources work, at least by the mathematics. Photon numbers are neither certain nor conserved in the interaction between the source/field or the field/detector.


When or how was this ever in contention?

For what it is worth, there does exist ways to prepare single photon states using heralding, in which case the emission of the photon can be correlated with its detection. However, as you state, such a case would not be considered a thermal source.

 

[flippiefanus]

What physical state of the electromagnetic system is modified by the source, reaches and interacts with the two slits, such that changing either slit changes the later probability distribution of localized energy-momentum exchanges at the detector?

Most experimental sources would produce states that would be affected by slits in a way that can be determined by the detector system. So, yes you are correct: there is a causal link between that which is radiated by the source and what is being detected. I think the issue is whether one can make any statement about the quantised nature of that which exists between these two points. Sometimes one can infer that the quantised nature must prevail in the radiation even while it is not measured. For example, it would be difficult to explain entanglement without such a quantised nature. Another example is a single-photon source, as I mentioned in a previous post. But with thermal sources it is not so easy. On the other hand, the lack of coherence may prevent such thermal radiation from producing an interference pattern. I guess the issue of coherence is beyond the scope of this discussion.

 

[Paul Colby]

Fine — if you’re still attached to semantics, don't call it a photon before detection.

What is “it” in terms of currently accepted theory?

 

[jeffn1]

What is “it” in terms of currently accepted theory?

From what I know, I would view it as "energy" in the photon field that has not sufficiently excited the field (locally?) to generate the photon. (Keeping head down because probably not using proper terminology)(I'm a "layperson").

 

[aletheia]

Most experimental sources would produce states that would be affected by slits in a way that can be determined by the detector system. So, yes you are correct: there is a causal link between that which is radiated by the source and what is being detected. I think the issue is whether one can make any statement about the quantised nature of that which exists between these two points. Sometimes one can infer that the quantised nature must prevail in the radiation even while it is not measured. For example, it would be difficult to explain entanglement without such a quantised nature. Another example is a single-photon source, as I mentioned in a previous post. But with thermal sources it is not so easy. On the other hand, the lack of coherence may prevent such thermal radiation from producing an interference pattern. I guess the issue of coherence is beyond the scope of this discussion.

Exactly!
Whatever the formalism calls “that which is radiated”, it originates from a physical change in a material source, develops as an extended/wave-like electromagnetic structure through the apparatus, and eventually terminates in another interaction with material matter at the detector.
So the sequence is not merely:
source state → mathematical probability → detector mark.
There is a physical causal chain:
material source → excitation/field restructuring → wave-like propagation through the slits → localized energy-momentum exchange with material matter.
The beginning and the end are materially anchored.
The intermediate stage is spatially distributed.
The final localized outcome is directly observed.
My question is: what physically happens in the material source that initiates this ordered sequence of events that results in one mark on the screen?

 

[aletheia]

What is “it” in terms of currently accepted theory?

Im not the one obsessed with semantics.
Im speaking about an obvious causal relation between emission and absorption of “it”.
Could you please explain what you are having difficulty understanding about “it”?

 

[BvU]

Exactly!
Whatever the formalism calls “that which is radiated”, it originates from a physical change in a material source, develops as an extended/wave-like electromagnetic structure through the apparatus, and eventually terminates in another interaction with material matter at the detector.
So the sequence is not merely:
source state → mathematical probability → detector mark.
There is a physical causal chain:
material source → excitation/field restructuring → wave-like propagation through the slits → localized energy-momentum exchange with material matter.
The beginning and the end are materially anchored.
The intermediate stage is spatially distributed.
The final localized outcome is directly observed.
My question is: what physically happens in the material source that initiates this ordered sequence of events that results in one mark on the screen?

Have you seen the video "How big is a photon" mentioned in a similar thread here ? ...

 

[Paul Colby]

Im speaking about an obvious causal relation between emission and absorption of “it”.
Could you please explain what you are having difficulty understanding about “it”?

Interference patterns happen for multiple “it”s, right? From post #5 “it” was water waves, sound waves or EM waves. “It” could also be particle beams of various flavors. Each of these physical systems are quite different yet exhibit similar wave phenomena.

In post #1, two expressions, one from classical EM and one from quantum EM were given. Both describe the same interference patterns, as they must. The second theory, QED, is a more complete theory. From this you asked a question I don’t follow. Part of my semantics issue is aimed at rooting out what you’re still missing or misconstruing.

[edit] You should take the time to view “How big is a photon”. The experiment shown really underscores misconceptions (flawed mental pictures) I think are quite common, even amongst physicists. The experiment worked exactly as I would have guessed. But then, I’ve had a lifetime of misconceptions I’ve been working through.

 

[PeterDonis]

My reasoning comes from observation.

There is no observation that tells you that light traveling in free space is made of photons. So I don't know what you're referring to here.

While physicists worry about the measurement, Im more interested in the physical reality of the experiment, i.e., in the double slits, what is made and what is happening from the source to the screen.

And, as I said, whatever is happening from the source to the screen, the math does not support the claim that it is photons propagating.

 

[PeterDonis]

Classical optics equation describes what QM equation predicts.

Except when it doesn't, as I pointed out in my post #22, which you did not quote.

 

[PeterDonis]

You have absolutely no idea about what I mean ontologically when I propose it.

So far, it doesn't appear that anyone in this thread but you understands whatever issue you think you're asking about. If you can't frame a question that anyone else here can understand, we might as well close this thread. Is that where we are?

 

[PeterDonis]

From what I know, I would view it as "energy" in the photon field that has not sufficiently excited the field (locally?) to generate the photon.

What does this even mean? It looks like personal speculation, which is off limits here. Please don't clutter the thread.

 

[anuttarasammyak]

Classical optics equation describes what QM equation predicts.

Light has been broadly considered as wave in CM. Newton considered it particles but wave nature of phenomena, interference, diffraction, Maxwell prediction of EM wave, classical optics, have had prevailed. In the begging of 20th century Einstein revived particle theory by photoelectric effect and got Nobel prize later.

Young’s double slit experiment for electrons is performed. Interference was observed like classical optics. Electron is particle at injection and at screen, but is wave between.
FYI experiment video https://www.hitachi.com/rd/research/materials/quantum/doubleslit/index.html (Historycally Davidson Germer first performed experiment by crystal difraction. )

So integration of wave view and particle view was the big question in 1920s which generates QM which should correspond to CM including Newton’s equation of motion for electrons and classical optics for light.

 

[PeterDonis]

QM which should correspond to CM

Except where it doesn't, as I said in post #22. And in addition to that, there's this:

Newton’s equation of motion for electrons

This is simply false for QM, so I don't know why you're claiming QM corresponds to CM here. The only regime relevant to this thread in which CM is a good approximation is the double slit experiment for light of high enough intensity that individual photon impacts are not detectable. CM does not predict that electrons exhibit wave properties at all, so it is not a good approximation for a double slit experiment for electrons at any intensity.

 

[PeterDonis]

Interference was observed like classical optics.

But classical optics does not apply to electrons. It only applies to light.

 

[anuttarasammyak]

FYI experiment video https://www.hitachi.com/rd/research/materials/quantum/doubleslit/index.html

FYI experiment video of single photon Young double slit experiment by Hamamatsu Photonics in 1982. https://photonterrace.net/en/photon/duality/

[EDIT]

TL;DR: Do the quantum and the classical wave interference pattern represent the same physical reality?

Has this question been explicitly discussed in the quantum-foundations literature?

Classical optics:
I(x) ∝ |E₁(x) + E₂(x)|²

Single-quantum case:
P(x) ∝ |ψ₁(x) + ψ₂(x)|²

What appears statistically in QM is the same interference structure from wave optics?

New theory has to inherit all success of old theory and add systematic corrections for what old theory fails. In this sense QA could be "Does interference structure of classical optics come from QM?" "Yes, it should be to be a good new theory."

A failure of classical optics is observed for very low intensity light. CO keeps the same pattern with extreme weakness but in the experiments clear dots appear on the screen.

 

[aletheia]

So far, it doesn't appear that anyone in this thread but you understands whatever issue you think you're asking about. If you can't frame a question that anyone else here can understand, we might as well close this thread. Is that where we are?

I don’t think so.
That response wasn’t even about the content of this nice thread — that was a response from the (well) deleted comment from another user who posted a paper not mainstream physics.
That aside, we’re pretty much understanding (slowly but surely) each others.
I think that the discussion has been enlightening (at least for me).
I’d like to thank everyone that has engaged in this discussion so far.
I won’t extend my comments today since I have acknowledged that it was delivered to me some materials that I haven’t got the time yet to study it — but I’ll certainly be back here in a couple of days or so.
Cheers.

 

[bhobba]

If you really think my problem is “basic math”, then it’s on you — for not understanding it and for this passive-aggressive argument.

It isn't. Its resolution in QM is actually deep.

Here is a deeper explanation:
https://arxiv.org/abs/quant-ph/0703126

Even that is not the full story, but to go further would be above undergrad IMHO

Thanks
Bill

 

[bhobba]

For massless fields with spin 1 or more, we can't construct position operator, so one can't think about photons traveling along any path between source and screen.

For what photons are, not the POP scIence version, see the following I frequently post:
https://digitalcommons.usu.edu/cgi/viewcontent.cgi?article=3211&context=physics_facpub

Its math is at the upper-undergrad level, so it may be a bit advanced.

Thanks
Bill

 

[PeterDonis]

I think that the discussion has been enlightening (at least for me).

Fair enough.

 

[flippiefanus]

My question is: what physically happens in the material source that initiates this ordered sequence of events that results in one mark on the screen?

The original work of Max Planck already gave us some understanding of what happens in the material source: every interaction (responsible for producing the radiation) is quantised, which means that it involves quantised excitations of the fields taking part in the interaction. For the outgoing field, this quantised excitation propagates like a wave, as described by the free space propagator (once the excitation has left the source material). The free space propagation process produces the extended field that illuminates the slits, which then modulates the extended field and this dictates how the propagation beyond the slits proceeds. As a result, the excitation after the slits produces interference, which is then detected as a single quantum at a single (but finite) point on the output plane, according to a probability distribution as defined by the interference.

Apart from the work of Planck, much of this understanding has been contributed by various physicists over the intervening years. I do not propose that this understanding answers all possible questions. However, our understanding of the physical process can only be obtained in a reliable way from what is being observed and logically inferred. The latter implies that we can go beyond that which we directly observe, provided that it is related to what we observe by logical deduction. Beyond that, we can debate and philosophise, but we cannot know for sure. So, when we ask questions that cannot be related to observations and their associated logical deductions, the scientifically correct answer is: we don't know.

 

[aletheia]

Have you seen the video "How big is a photon" mentioned in a similar thread here ? ...

I have know saw it indeed — it’s quite good. Thanks.

For example, it would be difficult to explain entanglement without such a quantised nature. Another example is a single-photon source, as I mentioned in a previous post. But with thermal sources it is not so easy. On the other hand, the lack of coherence may prevent such thermal radiation from producing an interference pattern. I guess the issue of coherence is beyond the scope of this discussion.

actually, for the sake of my understanding at least, neither quantum entanglement nor quantum coherence shouldn’t be out of scope for Quantum Theory Foundations.

as a physician working at ER, I apply exclusively evidence based medicine; I come from the most academic medicine school in my country, which is one of the best of Latin America;

that’s important here for two reasons:
first — I’m not arguing against the validity of experimental or theoretical physics;
second — I’m very used to approaching systems as a whole, therefore integrating different validated knowledges from very different specialties;

so, I’m taking a deep dive in the photon from both QM & Cosmology, since I’m assuming that the same fundamental laws that governs the photon behavior must be the same, whether in the double slits QM experiments or from the 8 billion light-years away photons from the quasar used in Bell's 2018 cosmic experiment (Handsteiner et al., PRL 121, 080401 (Physical Review Letters, 2018; Zeilinger — 2022 Nobel);

my next questions:
if the photon is an excitation of EM fields (QED), if it approaches every possible inertial reference at “c” (SR), if it does not have a valid own inertial reference (SR), if it does not experience time or distance (SR), if it does not have a size limit per se (“how big is a photon” video), if emission-absorption is made in null proper spacetime interval (ds² = 0, SR), why, in quantum entanglement non-locality theory, it is said that the random adjustment of the measurement settings (polarizer angles) is something from the past?

if time is relative (SR), isn’t the 8 billion years only relative to the quasar-Earth massive inertial referential and not to the inexistant photon’s own referential?

does not the claim that these results effectively shut the ‘freedom-of-choice loophole’ — dismissing every local-realistic option — presumes a concept of absolute time (SR) that the very principles of relativity contradict?

 

[PeterDonis]

actually, for the sake of my understanding at least, neither quantum entanglement nor quantum coherence shouldn’t be out of scope for Quantum Theory Foundations.

as a physician working at ER, I apply exclusively evidence based medicine; I come from the most academic medicine school in my country, which is one of the best of Latin America;

that’s important here for two reasons:
first — I’m not arguing against the validity of experimental or theoretical physics;
second — I’m very used to approaching systems as a whole, therefore integrating different validated knowledges from very different specialties;

Please stop posting these kinds of statements. We all know what subforum we're in. What you do as a physician is irrelevant here. Generalities about your approach are just noise.

I’m taking a deep dive in the photon from both QM & Cosmology, since I’m assuming that the same fundamental laws that governs the photon behavior must be the same, whether in the double slits QM experiments or from the 8 billion light-years away photons from the quasar used in Bell's 2018 cosmic experiment

First, we don't know that any of the laws we currently know about the behavior of light are "fundamental". They might all be approximations to something else that we'll discover in the future.

Second, "the same fundamental laws" can still manifest themselves in a lot of different ways that require different methods of analysis. So the statement your're making here is really just more generalities, i.e., noise. Please stop doing that and focus on the actual specific questions you want to ask.

if the photon is an excitation of EM fields (QED)

Ok so far. But if you're going to pick QED as your theoretical model, then you need to stick to it. Which you don't:

if it approaches every possible inertial reference at “c” (SR)

In QED photons don't have well-defined spacetime worldlines at all, and there is a nonzero amplitude for events of photon emission and absorption to not be null separated (which is often described as a nonzero amplitude for photons to "move" at a "speed" other than c, but that's really misleading because, as just noted, in QED photons don't have well-defined worldlines at all).

if it does not have a valid own inertial reference (SR)

True, but irrelevant, first because it doesn't matter as far as analyzing experiments (whether in QED or SR), and second because SR is not QED.

if it does not experience time or distance (SR)

Wrong even in SR. Irrelevant if you're using QED.

if it does not have a size limit per se (“how big is a photon” video)

That video, while interesting, is not really a good basis for the kind of discussion you appear to want to have. Also it's not clear how it's relevant here anyway.

if emission-absorption is made in null proper spacetime interval (ds² = 0, SR)

See above comments about "c".

why, in quantum entanglement non-locality theory, it is said that the random adjustment of the measurement settings (polarizer angles) is something from the past?

Where is this said? Please give a specific quote from a specific valid reference (textbook or peer-reviewed paper). We can't discuss vague descriptions like this.

if time is relative (SR)

True if interpreted appropriately, but irrelevant if we're using QED.

isn’t the 8 billion years only relative to the quasar-Earth massive inertial referential

Times on cosmological scales like this are usually meant as standard FRW coordinate time since that's the usual reference frame used in cosmology. That is, 8 billion years according to a comoving observer. Which is not the same as an observer on Earth, or necessarily on the quasar either.

and not to the inexistant photon’s own referential?

You already said there is no such thing so I have no idea why you're asking this.

does not the claim that these results effectively shut the ‘freedom-of-choice loophole’ — dismissing every local-realistic option

What results? Please give a specific valid reference (textbook or peer-reviewed paper).

presumes a concept of absolute time (SR) that the very principles of relativity contradict?

Can't discuss this without some specific reference as a basis for discussion. And you still need to make up your mind whether we're discussing SR or QED.

 

[flippiefanus]

my next questions:
if the photon is an excitation of EM fields (QED), if it approaches every possible inertial reference at “c” (SR), if it does not have a valid own inertial reference (SR), if it does not experience time or distance (SR), if it does not have a size limit per se (“how big is a photon” video), if emission-absorption is made in null proper spacetime interval (ds² = 0, SR), why, in quantum entanglement non-locality theory, it is said that the random adjustment of the measurement settings (polarizer angles) is something from the past?

if time is relative (SR), isn’t the 8 billion years only relative to the quasar-Earth massive inertial referential and not to the inexistant photon’s own referential?

does not the claim that these results effectively shut the ‘freedom-of-choice loophole’ — dismissing every local-realistic option — presumes a concept of absolute time (SR) that the very principles of relativity contradict?

Not sure if I understand your question. The fact that photons gives a null for the Minkowski metric does not mean everything must follow suit. Human beings and experimental equipment have mass and therefore do not produce a zero in the Minkowski metric. Therefore, the past is clearly defined. There is also a time-like direction for a given reference frame, which allows things to evolve. The statement that "time is relative" does not mean it is arbitrary. There are well-defined exact ways in which the evolution of time transforms among different reference frames. One can take these transformations into account when analysing results obtained from physical experiments to draw conclusions that are valid within the context of SR.

 

[Paul Colby]

I have know saw it indeed — it’s quite good. Thanks.

Given your original question concerning photons and the double slit experiment, how have your views changed? The experiment showed that the interference pattern persists even with a significant path length change in one of the two paths.

 

[aletheia]

What results? Please give a specific valid reference (textbook or peer-reviewed paper).

Therefore, the past is clearly defined. There is also a time-like direction for a given reference frame, which allows things to evolve. The statement that "time is relative" does not mean it is arbitrary. There are well-defined exact ways in which the evolution of time transforms among different reference frames. One can take these transformations into account when analysing results obtained from physical experiments to draw conclusions that are valid within the context of SR.

I may simply be misunderstanding one point in Rauch et al. (2018);
they wrote: “Using the wavelength of cosmic photons to implement the measurement settings requires the assumption that the wavelength of each photon was set at emission” [1].
in the same experimental description, however, the incoming quasar light is separated into red and blue channels, and the detector signal is then used to trigger the corresponding measurement basis at the EOM [1];
so what exactly does “the wavelength of each photon was set at emission” mean here?
is it only a causal/statistical-independence statement — i.e., that the physical variable used to generate the setting originated with the quasar emission and was not selectively corrupted or previewed during propagation?
or does it mean that the particular red/blue result for each individual detected cosmic photon was already a definite physical fact at emission?
if it means only the former, then what exactly is being pushed 7.78 billion years into the causal past: the causal origin of the variable used to generate the setting, or the actual binary setting realized at the laboratory?
Reference
[1] D. Rauch et al., “Cosmic Bell Test Using Random Measurement Settings from High-Redshift Quasars,” Physical Review Letters 121, 080403 (2018). DOI: 10.1103/PhysRevLett.121.080403; arXiv:1808.05966.

 

[aletheia]

Given your original question concerning photons and the double slit experiment, how have your views changed? The experiment showed that the interference pattern persists even with a significant path length change in one of the two paths.

I do very much appreciate your time, attention and patience (and all the users that have engaged in the thread).
I have surely increased significantly both my understanding of fundamentals of QM and the mindset of physicists.
If I’m here “annoying” physicists is quite exactly the forum’s goal, since I’m exactly at the point where textbooks or AI won’t provide me the clarifications that I need.
Thank you very much (to all of you).

 

[PeterDonis]

“Using the wavelength of cosmic photons to implement the measurement settings requires the assumption that the wavelength of each photon was set at emission”

More precisely, that the 4-momentum wave vector of the light was set at emission. In terms of wavelength, that determines the wavelength (and frequency and energy and momentum) relative to the emitter.

But those are not necessarily the same as the corresponding observables relative to the receiver. The 4-momentum wave vector gets propagated along the worldline of the light, but the observables relative to the receiver are determined by taking appropriate inner products of the light's 4-momentum vector with 4-vectors describing the receiver's 4-velocity and spatial axes.

what exactly does “the wavelength of each photon was set at emission” mean here?

See above.

D. Rauch et al., “Cosmic Bell Test Using Random Measurement Settings from High-Redshift Quasars,” Physical Review Letters 121, 080403 (2018). DOI: 10.1103/PhysRevLett.121.080403; arXiv:1808.05966.

I assume you mean this paper?

https://arxiv.org/abs/1808.05966

Please give links to references.

what exactly is being pushed 7.78 billion years into the causal past

That phraseology (which unfortunately the paper uses) is misleading. Nothing is getting "pushed" backwards in time.

What they mean is that the spacetime event of emission of the light is the last point in spacetime where any kind of influence over the light could have been made that would have an effect on the measurement settings in the experiment. Note that this depends on another assumption made in the paper, that nothing influences the propagation of the light between emission at the quasar and detection in the experimenters' lab.

 

[aletheia]

More precisely, that the 4-momentum wave vector of the light was set at emission. In terms of wavelength, that determines the wavelength (and frequency and energy and momentum) relative to the emitter.

But those are not necessarily the same as the corresponding observables relative to the receiver. The 4-momentum wave vector gets propagated along the worldline of the light, but the observables relative to the receiver are determined by taking appropriate inner products of the light's 4-momentum vector with 4-vectors describing the receiver's 4-velocity and spatial axes.

Understood.

See above.


I assume you mean this paper?

https://arxiv.org/abs/1808.05966

Yes

Please give links to references.

I’m getting used to the forum.
Now I understand that I may provide links to mainstream well established articles — I’ll remember next time.

That phraseology (which unfortunately the paper uses) is misleading. Nothing is getting "pushed" backwards in time.

Now I think I finally fully understood where my interpretations weren’t precise.
Thanks for the attention and for the patience.