We have been taught that anything occupying space/volume has mass. Light has both a particle nature-photon and wave nature. Since It has an momentum of h/λ, energy of hc/λ. Since a photon carries energy and experiments have put an upper limit to its mass of 1e-18 eV/c^2, does it possess dimensions, a shape ?
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anything occupying space/volume has mass This is a good explanation for kids, but in physics it doesn't make much sense. All particles are suppose to be pointlike, hence no shape. – jinawee Jan 14 '14 at 11:26
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possible duplicate of Does photon have size measurement because of its particle nature – jinawee Jan 14 '14 at 11:29
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How does Supposing Help,esp in case of photons? Mind providing a theoretical/ experimental proof. – HemShailabh Jan 15 '14 at 05:50
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The 'size' of a fundamental particle is ill-defined.
You could say that fundamental particles have no size because they are 'point-like' particles, but as I just explained here Do particles ever touch each other during a collision? a particle of light can freely split into a particle/anti-particle pair so long as the particle/anti-particle recombines to produce the photon (conserving energy/momentum). In this sense the photon is required to occupy a non-point-like amount of space. The volume swept out by these self-interactions is uniform, so regardless of the size, the 'shape' is spherical.
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Accepted that they have spherical shape though can you provide a link to theoretical/experimental proof. – HemShailabh Jan 15 '14 at 05:40
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All SM model interactions preserve the Poincaré group symmetries which includes rotational invariance. See http://en.wikipedia.org/wiki/Poincar%C3%A9_group , http://en.wikipedia.org/wiki/Symmetry_(physics) and http://en.wikipedia.org/wiki/Electroweak_interaction for more details. – kd88 Jan 15 '14 at 10:46