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Is a photon a mathematical variable used to describe what we cannot see or measure in terms of mass? Or is it something you could actually capture and put on display saying, "Look, this is a photon."
I have found the definitions of photons I've come across to be rather confusing.
- Nate (age 32)
There are ways to generate single photons, which can then run around doing things like making visible tracks in the matter with which they interact. So in that sense, a photon is the sort of thing you could just point to. (In practice, they don't "capture" easily for very long.) They can have rather sharply defined values of energy and momentum.
On the other hand, if you have an ordinary beam of light, it is a little misleading to think of it as just a collection of many distinct photons, unlike say a beam of ping-pong balls. The photons don't have distinct identities. The beam itself doesn't have a specific number of them in it, but rather a range of possible numbers with different probabilities for getting different numbers if you do some sort of experiment to count them. This distinction becomes particularly important for beams like the electromagnetic wave from a radio station. It turns out that any beam with a precise number of photons in it has exactly zero expected value for the electric and magnetic fields, quite unlike the sorts of beams sent out by stations.
Look, I know this all sounds mysterious. For most of us, as you get deeper into it the mystery doesn't go away. This is just the world as we know it.
(published on 04/22/11)
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