All of us who had high school physics saw the basic light wave experiment. If we have a light source up above pointing down, and an opaque plate with two pinholes in itself, directly beneath the light source, on the table directly beneath the plate we see the basic wave interference pattern -- the exact same pattern generated on the surface of a pond when two pebbles are thrown in and the two sers of waves intersect.
What we didn't know, when we did that experiment, was this...
If instead of a steady light source we have a photon gun releasing photons one at a time, so that as some of them race downwards toward the two-hole plate their trajectory accidently takes them through one of the two holes, even though their is no "wave" coming through the other hole of the plate, they form the wave interference pattern on the table below (where the pattern is recorded on film).
Whereas, if the holes are covered-up one at a time, first one, then the other, the film shows no interference.
Do you understand what is going on? It is as though the falling photons look down and think, "Oh! Look! TWO holes! That means that I am supposed to form the wave interference pattern below! Okay!"
There is an answer: It's never really a wave interference pattern. It's a SPACE interference pattern. Get it?