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As We know that light shoaws dual nature or I would rather say that Sometime we can explain some phenomenon using wave analogy and other with particle nature(photon analogy). Phenomena like the photoelectric effect, Compton effect, etc can be understood using photon analogy and phenomena like interference, diffraction, polarization, etc can be understood using wave analogy.

A similar thing we do with particles, we say that we can associate de Broglie wave to each particle and so on. I learned quantum mechanics at the undergraduate level. What I see here is that quantum mechanics provide convenience to explain wave nature on particles. So here we see that particle nature emerges in the classical limit. So that you can solve both Kepler's planetary motion and particle in a box with the same theory without getting into duality.

Question: As we quantum mechanics fixed the dual nature of particle (like an electron), Is there a theory that fixed the dual nature of light? What does it assume light as?

At this level, I never deal with light in quantum mechanics so Maybe there is a flaw in my thinking. I saw this question which may be like what I'm asking but this doesn't clear my doubt. Answer first and second is pretty much contrary to me.

Young Kindaichi
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  • maybe this answer of mine might help https://physics.stackexchange.com/questions/90646/what-is-the-relation-between-electromagnetic-wave-and-photon/90649#90649 – anna v Sep 27 '20 at 10:30
  • The first answer by John helps a lot to me, your one on the contrary seems to support particle nature of light or you trying to say we can take both pictures of light. But the fact to these picture is that is the interference pattern become at instant or take a long time. – Young Kindaichi Sep 27 '20 at 10:43
  • @YoungKindaichi can you clarify what you are asking. At the moment your question seems to be a duplicate of What is the relation between electromagnetic wave and photon? or possibly Is the wave-particle duality a real duality?. – John Rennie Sep 27 '20 at 10:46
  • Possibly also of interest is Do photons truly exist in a physical sense or are they just a useful concept like $i = \sqrt{-1}$? – John Rennie Sep 27 '20 at 10:48
  • Let me rephrase it in one sentence. What current knowledge of science concludes about light and electron(example of particle) ,here concludes means with which nature we can understood every phenomenon? – Young Kindaichi Sep 27 '20 at 11:21
  • this is for electrons https://physics.stackexchange.com/questions/238855/is-it-wrong-to-say-that-an-electron-can-be-a-wave/238866#238866 – anna v Sep 27 '20 at 11:28
  • Why this down vote? – Young Kindaichi Sep 27 '20 at 14:07
  • https://physics.stackexchange.com/a/90657/247238 Here in this question @JohnRennie – Young Kindaichi Sep 29 '20 at 04:34
  • says that Light is not a wave nor a particle but instead it is an excitation in a quantum field. I don't understand this thing. what do you mean by excitation in the quantum field? Is the quantum field a physical concept or a mathematical tool? Please me with this @annav and JohnRennie, because you see according to anna, light consists of photon particles and all phenomena can be explained through this, although in some cases waves give much better approximation. It seems contradictory facts. – Young Kindaichi Sep 29 '20 at 04:39
  • There are two trends in the way physicists see nature: a) the pragmatic one, where data and observations dominate and mathematical models are tools for fitting data and predicting new situations b) the platonic one, where the forms, i.e. in this case the mathematics, create reality inevitably.// in b) the quantum fields are assumed to exist, on which creation and annihilation operators create what we measure as particles and their interaction. I belong to the a) group, mainly because I was first taught quantum field theory for nuclear physics problems, and certainly nuclear physics is not – anna v Sep 29 '20 at 04:54
  • the underlying reality. I consider QFT a great mathematical tool and look for experimental verification of its predictions. – anna v Sep 29 '20 at 04:56

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Let me rephrase it in one sentence. What current knowledge of science concludes about light and electron(example of particle)

Let us be clear. Nature means observation , measurements and experiments.

This double slit experiment with light, where the intensity of the laser is brought to single photon at a time shows the dual nature for photons/light. Light is emergent from a multitude of photons.

phot

In the far left plane the photons one by one leave a footprint on the (x,y) of the frame. It looks random, but the accumulation shows the light interference through double slits for that wavelength. The accumulation is a probability distribution in finding the photon at a given (x,y)

The same is true for electrons,

electr

The wave nature appears slowly as the electrons accumulate, the probability of finding the electrons at a given (x,y).

These two experiments show that what is waving experimentally is the probability distribution, and it is the basis of quantum mechanics where the solutions $Ψ$ of the quantum mechanical wave equations give $Ψ^*Ψ$ , the probability of interaction.

This is what observation of nature gives us up to now.

,here concludes means with which nature we can understood every phenomenon? –

This has led to very sophisticated mathematical models, based on the quantum mechanics postulates, presently quantum field theories, which can fit existing data and be amazingly predictive of new experiments.

This has led to two streams of thought:

Physicists who are theoretically inclined to be a type of platonists, i.e. that mathematics molds reality, given the mathematics , reality has to follow. These physicists believe that the fields of QED and QFT in the elementary particle standard model are the underlying reality, and nature has to follow it.

Experimentally inclined physicists believe that observations and data exist, and our up to date models describe them, but there could be a deeper level of nature not yet explored with our experiments that would show a different behavior given the right energies. That is why new experiments are being designed with higher energies and/or newer detectors. That is, not every phenomenon can be understood with current theoretical models.

I believe the last case is true.

anna v
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  • As you have shown the interference of laser light with the help of photon analogy. – Young Kindaichi Sep 27 '20 at 14:03
  • Is it take time to show an interference patterns? – Young Kindaichi Sep 27 '20 at 14:04
  • Your answer seems to suggest that light should be treated as photon. Is in all phenomena we can do this? – Young Kindaichi Sep 27 '20 at 14:07
  • In general when there are interactions, the particle nature takes over, and it is the accumulation of many same boundary condition measurements that will show a wave behavior in the probability distributions. Photons are different than electrons for example, because light emerges from the confluence of zillion of photons, whereas if you have a zillion electrons you just have a zillion electrons (an electron beam). This is because the quantized Maxwell equations describes photons, and the simple ones describe mathematically light. – anna v Sep 27 '20 at 14:18
  • http://cds.cern.ch/record/944002?ln=en .There is nothing like that with the other particles in the particle table. – anna v Sep 27 '20 at 14:19
  • The photons could come with anyt time difference , and the pattern would be the same. It is the spill over electric fields of the topology of the slits that sets up the boundary conditions for the scattering "photon+double slit" (same for electron), – anna v Sep 27 '20 at 14:27
  • What about other wave phenomena like polarization etc. Can these also be understood with the help of photons? If yes why we need waves? – Young Kindaichi Sep 27 '20 at 15:16
  • Yes, all light phenomena can be modeled at indiividual photon levels. We need the probability waves in order to predict interactions, the wavefunction carries this. But light , classical QED is very useful for complicated probems particularly. We know it is correct , it emerges from the quantum, and it is much simpler for macroscopic cases. – anna v Sep 27 '20 at 15:34
  • Thank you so much for this explanation, it's meant lot to me. But you see as I thought these topics, a new question just wake up, How I can ask you about that particular question? – Young Kindaichi Sep 27 '20 at 18:25
  • For example, the immediate question that arises in my mind is that, What about the explanation given in Purcell's book about electromagnetic waves , that is these waves are disturbance of electric field lines in the medium when particle get accelerated. – Young Kindaichi Sep 27 '20 at 18:29
  • You can ask a new question. For the Purcell one, the Michelson Morley experiment showed definitively that light does not need a medium, so it cannot be correct the way you state it. see https://en.wikipedia.org/wiki/Michelson%E2%80%93Morley_experiment . give the page in this copy for what you state https://www.academia.edu/40348585/Electricity_and_Magnetism_by_Edward_Purcell_3rd_Edition – anna v Sep 28 '20 at 04:34
  • As in the string case, we have seen that in approximation a large number of particle motion can be replaced by continuous motion of the string for a low number of modes.. Can we do the same with lightwave? In particle case, it's length scale of interaction which tells us when to use classical mechanics and when to use quantum mechanics, what about in the case of photon? what pattern tells us which is a better way to describe the experiment? – Young Kindaichi Sep 28 '20 at 04:47
  • The classical electromagnetc solutions give correct results, and the classical string solutions may apply to light wave behavior given the boundary conditions. Photons are by definition quantum mechanical particles and do not obey classical EM equations – anna v Sep 28 '20 at 05:03
  • There are two questions I added , One for the criterion of when to use classical electromagnetic wave? Like we have criterion for particles. – Young Kindaichi Sep 28 '20 at 05:29
  • I see in physics..stackexchange now new questions by you. Where did you post them? – anna v Sep 28 '20 at 07:54
  • Really nice answer. Do you think this is correct: https://physics.stackexchange.com/questions/582445/collision-of-two-beams-of-light/582575#582575 – Árpád Szendrei Sep 29 '20 at 15:30