# Feynman’s electron double slit experiment?

I have seen several questions on the site about this, but most of them get bogged down into new complex interpretations of quantum mechanics. For reference, I am a high school student just starting to learn quantum mechanics and thus sticking strictly to the copenhagen Interpretation.

If I understand the experiment correctly, the probability waves ( wavefunctions) of electrons emerging from each slit superpose to produce a resultant wave function whose modulus squared gives the probability distribution. The electron then appears on the screen due to he immediate collapse Of the wave-function upon interacting with the screen and an interference pattern of electrons is obtained if the experiment is run several times.

From what I’ve read and seen in several videos, if a detector is placed in-front of the slit, Such as Light scattering off the electrons, the interference pattern suddenly disappears and a distribution similar to that of macroscopic particles is obtained.

1. By what mechanism does detection collapse the wave function and turn the electron into a definite particle? Feynman, in his lectures, says that this has to do with the fact that photons carry momentum and photons scattering off electrons will inevitably affect the electrons in some way and destroy the interference pattern. However, this explanation sounds too specific to electrons and the method of detection (scattering light); I thought the collapse of the wave function upon detection was something universal.

2. How does this relate to heisenberg’s uncertainty principle?

Feynman says

Heisenberg proposed, as a general principle, his uncertainty principle, which we can state in terms of our experiment as follows: “It is impossible to design an apparatus to determine which hole the electron passes through, that will not at the same time disturb the electrons enough to destroy the interference pattern.”

This sounds more like the observational effect, which I’be read is different than the uncertainty principle, something more fundamental to QM

So we use a wave function to descried the probability of a particle's position (i.e. a photon on an electron for example), there is always a particle and there is always a wave function for the particle.

In the electron DSE you can consider the wave function to be variable/changing, it is going to change as the EM field in the experiment changes, even as the electron or photon is in flight. Also even before the electron has been emitted it is undergoing the effects of the EM field. As the electron is excited it begins to disturb the field and the field responds .... even at the detector. These EM forces are transmitted virtually, called virtual photons. A further constraint is that photons and electrons have a wavelength, and they have highest probability of travelling a path when its length is an integer multiple of the wavelength (Feynman).

So yes there is a collapse at the detector but with a light shining the EM field has been changed, the electron is free to choose a random path not constrained by the slits.

Your question 1 is an excellent one. The answer is that there is no such thing as a wave function collapse process. The Schrödinger and other wave equations of QM do not allow for it. Wave function collapse is the consequence of certain interpretations of quantum mechanics. Any interpretation that requires collapse must therefore be rejected.

• @Overwootch I would not say that particle detection is simple. Oct 22, 2020 at 18:25
• @my2cts I think some elaboration on your claim "there is no such thing as a wave function collapse process" would be appropriate. The Copenhagen Interpretation and wave function collapse are not the only perspectives, to be sure, but I was under the impression they had not been ruled out. Perhaps you can explain why you say wave function collapse doesn't exist. Oct 22, 2020 at 22:57
• I do not know enough quantum mechanics to answer your questions, but I know enough to know that dismissing the idea of wave function collapse is not something trivial and would require a compelling theoretical and/or experimental argument. Mainstream physics clearly currently considers the idea relevant and useful. "(Wave function) collapse is one of two processes by which quantum systems evolve in time; the other is the continuous evolution via the Schrödinger equation." archive.org/details/mathematicalfoun0613vonn Oct 23, 2020 at 13:27
• @electronpusher Thank you for the interesting quote . It claims that there is more dynamics then accounted for by the Schrödinger equation. However, at this point in time, the SE, QED, QFT, is all we have. The quote is pseudoscience. Oct 23, 2020 at 17:41
• I hope you realize that quote is from John Von Neumann (though that doesn't guarantee its veracity). If you're willing to consider that quote pseudoscience and maintain that wave function collapse cannot be a real process, then you are effectively considering the Copenhagen Interpretation pseudoscience (the "standard"/most prevailing interpretation of quantum mechanics). Do you also regard the other interpretations such as Many Worlds and Pilot Wave Theory as pseudoscience? I understand being pragmatic ("shut up an calculate") and avoiding putting stock in interpreting the mechanics, but Oct 23, 2020 at 19:17