There’s more. The experimenters can set up detectors to look at the two holes, and monitor which one each electron goes through. When they do this, they never see the electron going through both holes at once. They see it go through one hole or the other. And when they do this, there is no interference pattern. The spots on the screen form two blobs, one behind each hole, just as you would expect if they were made by particles. The electrons also seem to know if they are being watched or not - and the same is true for photons and all other quantum entities.
Fascinating. Observations altering results. I wonder: does it change if you add the observation in mid experiment? Why don't observers interfere with each other? It seems that an observation, any observation, collapses the wave form in a specific way.
