# 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 | + | 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 forces 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. 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. |

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+ | 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 correct 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. | ||

[[category:physics]] | [[category:physics]] |

## Revision as of 17:15, 8 July 2008

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 forces 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. 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 correct 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.