How do we know gluons travel at the speed of light? can this be derived or is it just an assumption based on the similarity to photons?
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4Does this answer your question? How do we know that gluons travel at the speed of light? – joseph h May 21 '22 at 00:04
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not entirely. As I understand it, Maxwells equations can be used to derive the speed of light, but this involves particles which react or involve electrictro-weak interactions. Gluons react strongly, and therefore treating them as a EM reacting (ie. limited by c) particle seems to be an assumption. – Don Yost May 22 '22 at 21:39
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The speed of light does not only apply to photons. It applies to all massless particles. Since gluons are indeed massless, it is necessary that they move with speed $c$. – joseph h May 23 '22 at 03:18
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Gluons are massless in the Standard Model, and all massless particles travel at $c$. This is pretty much by definition, but a hand-wavy way to explain it is that a massless particle will be accelerated "infinitely" if given any energy at all, i.e. it will reach the maximum possible velocity $c$ instantly. Don't read too much into that hand-wavy explanation though -- the real answer is that it's the way spacetime is structured.
Eric Smith
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Neutrinos are also massless in the Standard Model. But then, according to the "massless particles travel at " principle, the observed neutrino oscillations should be impossible. So, the question of what evidence exists for the massless gluon is reasonable. – John Doty May 21 '22 at 00:31