Why is an electron's changing behaviour upon observation fascinating?

[EvilSapphire]

Due to limit on length, I couldn't properly describe what I wanted to ask on the title. I'm trying to understand the century old fascination physicists have on the double slit experiment. From what I understand, the fascination stems from the act of electrons changing the interference pattern upon observation (acting like particles instead of waves). I can't quite understand however how the expectation would be any different, since an observation would entail some kind of photon interacting with the electron, and since they are of comparable dimensions, it follows very logically such an interaction would change the electron's behaviour in some way. How does this subvert any kind of expectation of the outcome of the experiment? I've decided to learn more about this fascinating subject that is quantum physics which is supposed to explore the structure of reality, however I find myself confused on this most fundamental building block before I go any further. Would love to hear what I'm failing to realize here.

 

[PeroK]

What level do you intend to study QM?

You could try this: to start with:

 

[DrChinese]

I'm trying to understand the century old fascination physicists have on the double slit experiment. From what I understand, the fascination stems from the act of electrons changing the interference pattern upon observation (acting like particles instead of waves). I can't quite understand however how the expectation would be any different, since an observation would entail some kind of photon interacting with the electron, and since they are of comparable dimensions, it follows very logically such an interaction would change the electron's behaviour in some way. How does this subvert any kind of expectation of the outcome of the experiment?

It's true that a cursory examination might lead you to that conclusion. However, there need not be any interaction with another particle to cause the interference pattern to disappear. Further, that would not be the predicted result of such interactions anyway. A better experiment to understand this phenomena is below, with photons instead of electrons.

The general rule is: if you could obtain which slit information - regardless of whether you actually obtain it - there will be no interference.

a. Send a stream of photons through a double slit. There WILL be interference.
b. Place 2 polarizers over the slits, 1 over each slit. Orient them parallel to each other. There WILL be interference as before. However, the intensity will be 1/2 of previous.
c. Now orient one of the polarizers so it is 90 degrees offset from the other - they will now be orthogonal (crossed). There will be NO interference, just the 2 traditional bars when you have an observation. There reason is that the photons have been "marked" to show which slit they went through - even though we do nothing to learn that information.

The only variable that distinguishes b. from c. is the relative angle between the polarizers. If a photon goes through only 1 slit, how is that angle relevant? By your reasoning, the results of b. and c. should be identical (presumably showing interference).

https://sciencedemonstrations.fas.h...-demonstrations/files/single_photon_paper.pdf

 

[andresB]

Just to complement what Drchinese said

Interaction-free_measurement