The photon is the ubiquitous particle of light which carries nearly all information we get from the outside world. It usually disappears while being detected. The retina, for instance, absorbs light, changing it into an electrical current which triggers the optical nerve. A similar phenomenon occurs on the photo-sensitive surface of usual light detectors, so that information carried by the photons is generally destroyed in the very process which records it. We certainly can see a macroscopic object as many times as we wish, but the photons which bring its image to our eye are at each time new ones.
To die while delivering its message is however not the ineluctable photon’s fate.
Serge Haroche: Life and death of a photon a new way to look (PDF)
