4
$\begingroup$

In the double-slit experiment, we shine a light wave through two closely-spaced parallel slits at a screen, and observe an interference pattern on the screen. We then reduce the intensity of the light source until we can observe single energy quanta, like Geiger counter clicks, which we call photons, and we observe the same interference pattern in the distribution of where the quanta arrive. We infer that light behaves in some ways like a wave, because it creates an interference pattern, and in some ways like a particle, because we can count the individual photons. It seems like a single photon can interfere with itself. Weird!


Question: How do we know the light travels in quanta? Could it not be the case that the light has a continuous wave nature, and only the interaction between the light wave and the source, and the light wave and the detector, is quantized? Separately from each other, of course, because of causality.

If this hypothesis was true, we should see that quanta would be deposited on the detector at the same average rate they were removed from the source, but there would be no correlation between the precise timing of each. In the usual experimental setup, there is no way to know this because the energy quanta taken from the source are not counted. Has this been experimentally tested?

$\endgroup$
10
  • 4
    $\begingroup$ Introductory chapters to QM books typically discuss the group of phenomena that couldn't be explained classically, but that we can explain using the discrete nature of light: black body radiation, photoelectric effect, atom emission and absorption, etc. $\endgroup$
    – Roger V.
    Commented Mar 1, 2023 at 12:44
  • 1
    $\begingroup$ @RogerVadim Could not all of these effects also be explained by quantized interactions with a classical electromagnetic field? $\endgroup$ Commented Mar 1, 2023 at 12:45
  • 5
    $\begingroup$ No. But you cannot expect people here to reproduce the context of textbooks... I suggest asking more specific questions. $\endgroup$
    – Roger V.
    Commented Mar 1, 2023 at 12:47
  • $\begingroup$ there are many experiments that measure the speed of light .... there is correlation when the source is on and the detector detects ..... that would counter your theory. $\endgroup$ Commented Mar 1, 2023 at 14:53
  • $\begingroup$ @PhysicsDave I have never heard of the speed of light being measured by the transit time of individual photons. Got a link? $\endgroup$ Commented Mar 1, 2023 at 14:55

4 Answers 4

2
$\begingroup$

You are right that the the experiment is compatible with a classical description of light (an EM wave). There is a theory, Stochastic Electrodynamics, capable of reproducing many results of quantum mechanics, like black body radiation, specific heat of solids and, to some extent, the stability of atoms.

The way this is done is to assume that the so-called quantum fluctuations are actually a real EM field that permeates all space and can be experimentally measured as Casimir force.

You can take a look at this paper:

Stochastic Interpretation of Quantum Mechanics Assuming That Vacuum Fields Are Real

Emilio Santos, Foundations 2022, 2(2), 409-442.

https://www.mdpi.com/2673-9321/2/2/28

At paragraph 5, The Particle Behaviour of Light we read:

"Firstly, I point out that the absorption of light in the form of localized spots in a photographic plate or clicks in a photodetector are not valid arguments for the particle behaviour of radiation. In fact, the former is caused by the granular (atomic or molecular) nature of photografic plates. The latter derive from the fact that photocounters are manufactured so that they click when the radiation arriving during a detection time surpasses some threshold, which is compatible with light being continuous (waves)."

Hopefully, this answers your question.

$\endgroup$
7
  • 1
    $\begingroup$ I see now that this is actually an old answer. But it leaves out a very important element. Stochastic Electrodynamics (and its sister Stochastic Optics) is not generally accepted science. It is a controversial local realist interpretation of all nonlocal entanglement phenomena. As such, SED completely denies the existence of quantum nonlocality. Nonlocality has been experimentally demonstrated in hundreds of forms, including the entanglement of particles that have never existed in a common light cone. And the GHZ theorem alone is a direct refutation of all local realist theories. $\endgroup$
    – DrChinese
    Commented Nov 12, 2023 at 19:45
  • $\begingroup$ @DrChinese, Stochastic Electrodynamics (SED) is a perfectly fine scientific theory, it was and still is developed by at least three research groups at universities in Mexico, US and Netherlands and it is based on a plethora of peer-reviewed papers published in prestigious journals over many decades. Even more, SED is not actualy a new theory, it is just classical electromagnetism (which is mainstream science) applied to the actual conditions in our universe, where the zero-pont field (experimentally confirmed in Casimir experiments) exists. $\endgroup$
    – Andrei
    Commented Nov 14, 2023 at 6:46
  • $\begingroup$ @DrChinese, No, there is not a single experiment which proves any true non-locality. If it were, relativity would have been falsified and universally rejected which is clearly not the case. GHZ theorem assumes statistical independence, just as Bell's. In SED (and electromagnetism in general) this assumption is false due to the correlations between charges (electrons, nuclei) and their EM fields. $\endgroup$
    – Andrei
    Commented Nov 14, 2023 at 6:52
  • $\begingroup$ I can't help it that Local Realists (such as those espousing your SED) are deniers of the plain and simple results of Nobel prize winning experiments. Experiments by Zeilinger and many many others prove evidence of nonlocality. Entanglement between photons that have never existed in a common light cone is a great example. arxiv.org/abs/1209.4191 Also the GHZ theorem/experiment demonstrates remote (FTL) change of state of photons, and does not depend on quantum probabilities. drchinese.com/David/Bell-MultiPhotonGHZ.pdf $\endgroup$
    – DrChinese
    Commented Nov 15, 2023 at 15:26
  • $\begingroup$ @DrChinese, there is a non-signaling theorem proving that entanglement cannot be used to transmit any information faster than light. So, those experiments cannot prove non-locality. It's a matter of interpretation. You can postulate a non-local mechanism, as in Bohm's theory, or you can employ a "bertlmann’s socks" local explanation (superdeterminism). Both explanations are compatible with GZH. I don't see your point with those photons "that have never existed in a common light cone". They did not interact directly, they interacted with other things and those things interacted directly. $\endgroup$
    – Andrei
    Commented Nov 16, 2023 at 7:45
2
$\begingroup$

If this hypothesis was true, we should see that quanta would be deposited on the detector at the same average rate they were removed from the source, but there would be no correlation between the precise timing of each. In the usual experimental setup, there is no way to know this because the energy quanta taken from the source are not counted. Has this been experimentally tested?

A strong and relatively readable experimental demonstration of the quantum nature of light is provided in the following reference. Look in particular at Figure 3. This shows that the source emits 2 photons in coincidence, and both are counted. This specifically answers your objection about counting energy quanta from both the source and the destination.

Further, there are many factors at play in considering classical versus quantum light. This is a complex subject, and there are many important papers and books that discuss this in considerable depth. Look at the references provided (such as work by Mandel, Glauber, Hanbury Brown, Aspect and others) to getter a better idea of this.

As demonstrated in the paper's theory portion, quantum light (photons) produce exactly one click each - something that cannot be true for classical light (for a variety of reasons). Their experiment excludes the classical model by 377 standard deviations.

Observing the quantum behavior of light in an undergraduate laboratory http://people.whitman.edu/~beckmk/QM/grangier/Thorn_ajp.pdf

Abstract: While the classical, wavelike behavior of light (interference and diffraction) has been easily observed in undergraduate laboratories for many years, explicit observation of the quantum nature of light (i.e., photons) is much more difficult. For example, while well-known phenomena such as the photoelectric effect and Compton scattering strongly suggest the existence of photons, they are not definitive proof of their existence. Here we present an experiment, suitable for an undergraduate laboratory, that unequivocally demonstrates the quantum nature of light. Spontaneously downconverted light is incident on a beamsplitter and the outputs are monitored with single-photon counting detectors. We observe a near absence of coincidence counts between the two detectors—a result inconsistent with a classical wave model of light, but consistent with a quantum description in which individual photons are incident on the beamsplitter. More explicitly, we measured the degree of second-order coherence between the outputs to be g(2)(0)=0.0177+/-0.0026, which violates the classical inequality g(2)(0)>=1 by 377 standard deviations.

$\endgroup$
-1
$\begingroup$

If this hypothesis was true, we should see that quanta would be deposited on the detector at the same average rate they were removed from the source, but there would be no correlation between the precise timing of each. In the usual experimental setup, there is no way to know this because the energy quanta taken from the source are not counted. Has this been experimentally tested?

A common application of this is a Compton Telescope, where the photon resulting from the interaction in the first detector shows up at the second detector just when you'd expect.

Your mistake is to expect nature to match the mathematical objects you wish to use to model it. This is a common misunderstanding due to the way we teach physics as mathematics on a whiteboard. Students must accept this to get a passing grade, but nature is under no obligation to conform.

The way physics contacts reality is through experiments. The math models the patterns the experiments reveal, often very effectively, but it is never "real".

"Stop telling God what to do." -Neils Bohr

$\endgroup$
22
  • 1
    $\begingroup$ 'Your mistake is' @StackExchangeSupportsIsrael is asking a question. That cannot be a mistake. $\endgroup$
    – my2cts
    Commented Jul 16 at 13:15
  • $\begingroup$ Could you extend your answer ? How does a Compton telescope support (or not support) the existence of photons? $\endgroup$
    – my2cts
    Commented Jul 16 at 13:17
  • $\begingroup$ @my2cts I can't, because "to exist" is a philosophical mess. I can only urge you to do experiments. $\endgroup$
    – John Doty
    Commented Jul 16 at 13:28
  • $\begingroup$ Is your position that the question whether photons (or perhaps anything) exist is meaningless? $\endgroup$
    – my2cts
    Commented Jul 16 at 13:34
  • $\begingroup$ My position is that we probe phenomena with experiments and observations. We construct models that capture the results. Every model has its limits. For some, like the photon model, those limits are very broad. Does that mean that photons "exist"? It doesn't matter to me: I count photons without worrying about such issues. $\endgroup$
    – John Doty
    Commented Jul 16 at 13:53
-3
$\begingroup$

Yes, I totally agree with your proposition.

Conventional physics is fundamentally inadequate at accommodating choice.

In my view the universe is inherently analogue or continuously variable, and quantum phenomena arise from the dual actions of projection to the boolean domain and amplification.

In maths, a projection is a function which loses information. If the universe is indeed analogue, and if we are to make boolean statements about the universe, at some point there needs to be a projection from the analogue domain to the boolean. Here, where the information is lost, is where the quantum weirdness arises. It is in fact, precisely what we would expect to see.

The weirdness arises from the misleading belief that the boolean statement is the fundamental truth. When in reality, the primary analogue experince is the fundmental truth.

A model which is more robust than convention quantum theory is to think of boolean statements as "votes" (in the boolean domain) in relation to the underlying analogue reality. The universe, through the action of choice, has elected to case a "vote" as to what is going on.

It is an understated fact that paradoxes resovle in pairs, and by the action described above, namely the passing of information (imperfectly) from the analogue domain to the boolean, through the free choice of the conscious universe, the paradoxes of quantum weirdness and free choice resolve each other.

$\endgroup$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.