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Name: Bobby
Status: N/A
Age: 60s
Location: N/A
Country: N/A
Date: Sunday, September 15, 2002


Question:
How close must two observers be so both can see a single photon?


Replies:
A single photon can be observed by only one observer. It is "observed" when it interacts with something. When it interacts, it either is changed or gone completely. For example, in the photoelectric effect a photon strikes an electron, giving it energy and momentum which can cause the electron to escape and be detected elsewhere. The photon's energy and momentum is then changed (reduced) by the energy and momentum given to the electron.

A photon can also be absorbed by a molecule increasing the energy of the molecule by the photon's energy. This changes the state of the molecule, which explains where sunburns come from. Molecules in florescent materials are "excited" (moved to higher energy levels) when the photons in the light are absorbed. The florescent material then gives off light as the molecules slowly decay to lower energy levels, emitting photons.

Best, Dick Plano



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