Difference between revisions of "Photon"

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A '''photon'''
* is a [[fundamental particle]] belonging to a group of particles called the ''[[bosons]]'', which, according to the [[quantum field theory]], have [[integer spins]].
* Photons mediate the [[electro-magnetic force]], which includes both [[magnetism]] and [[electricity]].
When we "see", our eyes are receiving streams of photons reflected from the objects around us. 
In [[classical physics]] there was a disagreement about the fundamental nature of [[light]] - whether it was a [[particle]] or a [[wave]], as it seemed to exhibit the properties of both.  The accepted explanation now is that it is a particle, and that its wave-like properties arise from its lack of [[mass]] (so that it can distribute [[force]]s over long distances) and from the following [[interference]] phenomenon typical to all [[quantum particles]].
In [[quantum mechanics]], one can no longer say for sure what the outcome of an experiment will be.{{fact}} The only meaningful question is what the [[probability]] is that the experiment will produce a particular result. These probabilities are [[absolute squares]] of [[complex numbers]] called ''[[amplitudes]]'' associated to the possible outcomes of an experiment.
Now in [[classical physics]], if the outcome of an experiment could happen in 2 ways, with probabilities A and B, we would expect that the probability of this outcome would be A+B. However, in quantum mechanics, instead of adding the probabilities (that is, adding the squares of the amplitudes), we add the amplitudes first, and then square this to obtain the probability. These means that the amplitudes associated to the two possible outcomes can constructively or destructively interfere with each other, which gives rise to the wave-like behavior observed in quantum mechanics.
==See also==

Revision as of 16:41, 8 January 2010