Photon bunching

In physics, photon bunching refers to the statistical tendency for photons to arrive simultaneously at a detector. This disturbs our understanding of classical particles, which tells us that non-interacting particles should know nothing about each other, and so should arrive independently of one another. This apparent contradiction is explained by recognizing this not as a particle effect, but rather as a wave effect. Photon bunching is predicted by quantum mechanics, and manifests experimentally in the Hanbury-Brown and Twiss effect, which itself can be understood classically as a pure wave effect. Notice that there is nothing special about photons here - bunching is actually a property of all bosons. In fact, the tendency for bosons to clump together is central in the theory of Bose-Einstein condensates. Also, because of the Pauli exclusion principle, fermions experience the opposite effect and tend to arrive separately.

See also

* Hanbury-Brown and Twiss effect
* Degree of coherence
* Leonard Mandel