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Among the four fundamental forces, it is now pretty well-known that the electromagnetic and gravitational ones travel at the speed of light.

How about the other two (strong and weak nuclear forces)? Does it even make sense to talk about their speed?

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  • $\begingroup$ Do you understand weak and strong forces are short range? $\endgroup$ Nov 7, 2020 at 11:52
  • $\begingroup$ @CosmasZachos Yes, I do. I'm just thinking that short range doesn't mean they don't have speeds. $\endgroup$
    – Kal
    Nov 7, 2020 at 14:03
  • $\begingroup$ You mean speed of "microscopic-range classical signal, or "speed of virtual mediator"? The latter is a QM entity and is hardly meaningful. $\endgroup$ Nov 7, 2020 at 14:05

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Massless ones travel at speed of light, massive ones slower, weak force carriers have mass, strong force carriers don't.

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In theory the weak and strong forces both have infinite range, but the potential is a Yukawa potential which falls off exponentially with distance, instead of the $1/r$ potential of gravity and electromagnetism. The question of how they behave at long distance is purely academic because in practice they're unobservably weak beyond a few femtometers for the strong force or attometers for the weak force.

What propagates at the speed of light in the case of electromagnetism and gravity is "updates" to the field configuration, not the field as such. A perturbation of the charge creates a wave that propagates outward at $c$ from the perturbation; before that wave passes the field is in its old configuration and after it passes it's in its new configuration. The update of a Yukawa field would be a more gradual process because the waves can propagate at arbitrary sublight speeds. However, the leading edge of the update would still propagate at $c$.

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  • $\begingroup$ So if you have a configuration of hadrons interacting via strong and weak forces in a dynamical way, are there "updates" to the field configuration? Of course this would happen only on tiny scales, but the question is still relevant I think $\endgroup$ Nov 7, 2020 at 17:29

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