Feynmann's electron double slit experiment

[Lostinthought]

Hi, I was trying to learn a bit of quantum mechanics from Feynman lectures. In the 3rd volume of the Feynman lectures, he talks of the double slit experiment with electrons. He says that if we keep a light source near the first slit, so that every time an electron passes it scatters light and let's us know that it has passed, if the wave length of the light is small enough we will not get the interference pattern. My question is, what if we remove the light source and keep another kind of a detector, something that detects the electrons field, will we still get an interference pattern?
More over is the destruction of the pattern related to the collision with photons or is it due to the very act of observation that let's the observer know which hole the electron went through?

 

[Simon Bridge]

if we remove the light source and keep another kind of a detector, something that detects the electrons field, will we still get an interference pattern?

The electric field is mediated by photons (light) so it would still be a light source ... any other way of detecting the electron which is good enough to tell us which slit it went through will destroy the diffraction pattern.

is the destruction of the pattern related to the collision with photons or is it due to the very act of observation that let's the observer know which hole the electron went through?

Anything capable of telling us the position of the electron will also give the electron a random kick - the more accurately we can tell the position, the bigger the kick - so the answer to your question is: the interaction ... we know which slit the electron came through because of the interaction, the ineraction causes both out knowledge and the changing of the pattern

Feynmans lectures on wave-particle duality are on youtube - he explains them much better in person than in the bound undergrad lectures.