The double-slit experiment with one single photon at a time is the sledge hammer which is designed to kill classical physics and so open to a new form of physics named quantum mechanics as the essence of modern physics.
The experiment consists of sending a sequence of photons one at a time through a double slit in a thin wall and recording the emergence of a macroscopic interference (fringe) pattern on a screen behind assuming a new dot for each new photon.
The pattern is the same as the interference patterns generated by a classical macroscopic wave hitting the wall and generating two macroscopic waves from the slits which interact constructively and destructively and so form a macroscopic fringe pattern on the screen.
We thus have a quantum version of the experiment with one photon at a time and a classical version, both building the same macroscopic fringe pattern on the screen.
The catch of the quantum explanation of the quantum version is that the single photon after somehow passing through the double slit with a left and right slit, somehow appears after the slit in a superposition of "left pass" and "right pass" as two mutually exclusive possibilities carrying an interference pattern of possibilities, which is made real dot by dot on the screen (by "collapse of the wave function").
The sledge hammer argument is now that the quantum version cannot be given a classical explanation because a classical particle/phtoton has to make the choice of "left pass" or "righ pass" which will remain after passing and so does not form any interference pattern, just two one-slit patterns.
The strategy is thus to promote quantum physics by an experiment arranged to show deficiency of classical physics.
Let us take a closer look at the quantum version asking what the physical meaning of "one photon at a time" may be. What is the evidence that only one photon at a time reaches the double slit? How to produce exactly one photon?
It seems that the evidence of "one photon at a time" is that there is "one dot at a time appearing on the screen". The argument is thus that one dot is generated by exactly one photon. Is this really so sure?
What if many photons are in fact involved with the capacity to pass both slits and form a classical real but very weak interference pattern before hitting the screen with a random excitation of one dot. The calibration of the intensity of the source would then be adjusted to produce one dot at a time, which de facto involves many photons capable of generating an intereference pattern with random realistion.
It thus may be possible to explain a "one dot at a time" double slit experiment in terms of classical wave physics. The sledge hammer argument would then vaporise.
PS After a discussion with chatGPT we agree that the one-photon experiment is extreme, but we seem to disagree about the value of extreme experiments to guide development of non-extreme physics. Why not stick to non-extreme experiments for non-extreme physics? What can be learn about normality by pushing into non-normality? What to learn about normal life from extreme violence? chatGPT seems to believe in the value of extremism in physics more than I. And you?
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