In 1802, Young performed a double-slit experiment with light in order to resolve whether light was composed of particles (confirming Newton’s view of light) or consisted of waves. His experiment showed that the light emerging from the slits produces a fringe pattern on the screen that is characteristic of interference, discrediting Newton’s corpuscular theory of light. It took about one hundred years until Einstein, with his explanation of the photoelectric effect in terms of photons, somewhat revived Newton's particle theory.
If the interference pattern is built up by recording individual clicks of the detectors and the time between successive clicks is much longer than the typical time of flight for the objects to travel from the source to the detector, it is a challenge to explain how the detection of individual objects that do not interact with each other can give rise to the observed interference patterns. According to Feynman, this is "impossible, absolutely impossible, to explain in any classical way and has in it the heart of quantum mechanics" .
This Demonstration employs a classical, locally causal model to simulate the double-slit experiment but does not rely on a solution of a wave equation to generate events . This Demonstration therefore shows that interference can be described with a particle-only model .
The red line represents the interference pattern as obtained from wave theory. The black dots represent the simulated, normalized intensities at the detectors. The graph is updated either event-by-event or, to speed up the simulation, every five events per detector on average.
 R. P. Feynman, R. B. Leighton, and M. Sands, The Feynman Lectures on Physics
, Vol. 3, Reading, MA: Addison-Wesley, 1965.