Consider a particle with some frequency of oscillation, where the phase of the oscillation is shown by the position of the hand on the clock. We show two potential paths for this particle to move to the detector at the END.

By sending the particle along different paths (marked "path A" and "path B" here) and measuring the phase offset when they get to the end, we can determine the likelihood of finding at particle at the END.

By taking the vector sum (shown in black) of the red and blue clockhands, we get a measure of the probability that we will find the particle at the END location. If the clockhands are close together (little interference), there is a high probability that we will find the particle at this location. If the clockhands are directly opposite one another, there is zero probability that we will find the particle here.

Probability of finding particle is low!

Probability of finding particle is high!

Try out the preset buttons above to show two scenarios (high and low probability of finding the particle).