After reading up on particle-wave duality and the double-slit experiment, I came upon this in the article.
The most baffling part of this experiment comes when only one photon at a time is fired at the barrier with both slits open. The pattern of interference remains the same, as can be seen if many photons are emitted one at a time and recorded on the same sheet of photographic film. The clear implication is that something with a wavelike nature passes simultaneously through both slits and interferes with itself — even though there is only one photon present. (The experiment works with electrons, atoms, and even some molecules too.)
Would someone care to try and explain this? Or do we just not know enough as of yet to understand why this happens?