Double hole experiment
Sandcastle
experiment. I am looking for first hand information, not something in a text
book.
In his Messenger Series of lectures presented in 1964, Richard Feynman
describes a double hole experiment which I will outline in this posting. If
you want to see the lecture, Microsoft provides it on the internet at
http://research.microsoft.com/apps/tools/tuva/index.html
Click on Featured Video Series then click on Lecture 6
Briefly, the experiment goes as follows:
1. We have a random source of electrons which send electrons through a
single small round hole in a plate.
2. Some distance away we have another plate with two small round holes in
it.
3. The distance between the two holes in the second plate is much less than
the distance between the plates.
4. We have a detection screen much further beyond the two hole plate than
the distance between the two holes.
5. If we count the number of electrons reaching the detection screen at
various locations, we see an interference pattern
6. However, if we cover up one or the other hole we see a single diffraction
pattern
7. We place a light just after the two holes and detectors to see which hole
the electron flies through
8. We detect that the electrons go through one hole or the other. Never
through both at once.
9. When the light is on, the screen shows the sum of the two diffraction
patterns rather than the interference pattern
10. When the light is dim enough that some electrons get by without being
detected, the screen shows a combination of diffraction and interference
patterns proportional to percentage of electrons being detected.
Questions I would like answered:
1. How far apart are the two holes?
2. How fast are the electrons moving?
3. What is the detection range?
4. If the two detectors are removed but the light remains, and the holes are
not in our view, do we see the same effect on the screen?
Discussion:
You could just surmise that the light disrupts the coherency of the electron
to eliminate some or all of the interference. Question 4 might support that
it is independent of the detection. But even if that is so, the fact that
electrons are only detected going through one hole or the other is in line
with the concept that the probability function collapses and the electron is
where it is detected. In that case the first three questions would give
some indication of the speed of that probability function collapse.
Other details that would be of interest:
5. How much of a vacuum is the experiment done in?
6. What is the number of electrons per second rate?
7. How was the detection screen configured?
8. Was this really done with holes or slits?