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We know from the double-slit experiment conducted "one photon at-a-time" that a light-wave, upon encountering two closely-spaced apertures, is able to split into two halves and travel through both. For we know that this is how each light-wave is able to destructively interfere with itself.

But why can I find nothing published about this property of light-waves? Am I not looking in the right places, or has this topic never been elucidated? Is a statement of Huygens' principle all we have?

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    $\begingroup$ You may want to read Feynman's little book "QED: The strange theory of light and matter". It describes, in simple terms, how one can intuitively understand the physics of light at the quantum mechanical level. $\endgroup$
    – CuriousOne
    Apr 23, 2016 at 18:50

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Saying "the light wave splits" is not an accurate description of what we understand about the theory of light. That's why you haven't seen it discussed.

The shape of the electromagnetic field (mode) fills all of space, subject to boundaries (to include containers, obsticles, etc. That is, the mode has a shape determined by the boundaries.). Some of the field occupies one slit, some the other. But the mode is set up when the slits are created. The mode exists whether or not it's been excited by quanta: it has a zero-point energy. The mode as a whole can be excited and populated with quanta. The field interacts with the detector: a quantum of excitation is removed from the field, and a quantum of excitation is created in the detector. This occurs at specific locations in the detector, that is, a particular pixel "lights up".

At no time does a wave split.

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  • $\begingroup$ I'm fascinated by your answer. You end by saying that at no time does a wave split, but, according to your description of the double-slit, at no time does a wave even exist. I mean, literally. The concept of a wave never arises once in your description. But then what about the field of optics, which attributes interference patterns to phase-differences, i.e. an undeniable property of waves? And yet we see the same interference pattern, that is, based on phase-difference, build up one photon at-a-time. Or am I misunderstanding you and you didn't just toss light-waves out the window? $\endgroup$ Apr 24, 2016 at 2:00
  • $\begingroup$ The shape of the mode is determined by the wave equation. So interference, and all the other wave phenomena are accounted for. The mode can have zero quanta of energy, or one or $10^{18}$. The interactions occur one at a time, and if there are very few of them to start with, you can see the interactions occur one at a time ... and the interference pattern develops. $\endgroup$
    – garyp
    Apr 24, 2016 at 2:21
  • $\begingroup$ It seems like what you're saying is that light-waves aren't real. Electromagnetic radiation's "mode" is merely shaped according to wave-like behavior. But this mode is devoid of energy, and hence isn't the light itself, and in fact exists in the set-up before you even flick the light switch on. Roughly speaking, is this what you're saying? $\endgroup$ Apr 24, 2016 at 5:39
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    $\begingroup$ We use different pictures and different languages and different metaphors when we describe the different theories and descriptions. All of the descriptions are interpretations of the mathematical theory. And all of the pictures, descriptions and metaphors have limitations. I don't think too many people would be comfortable saying that light waves aren't real. But the quantum theory of radiation has the energy tied up in quanta of excitations of a mode. Even in the ground state there is energy (light) but it cannot be extracted. Is an oscillator in the ground state oscillating? $\endgroup$
    – garyp
    Apr 25, 2016 at 12:29

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