“...well, it changes into a particle if we happen to be looking at it, then it stops when we look away”, and that is not behavior that would be compatible with these things actually being particles.”
Did you teach HS physics in 1963? You are quoting the same source as a well respected teacher I knew.
No, I wasn’t even born in 1963... maybe it was a past life :)
I wasn’t really quoting anyone, just that stuff in quotes summarizes the “standard” interpretation of the old double slit experiment. There have been refinements on that experiment in the last few years that call that interpretation into serious question though.