Where is Speed Speaks?

Why does light speed must be the maximum speed for all physical phenomenas?

• Hello guys, Einstein's Special Theory of Relativity speaks only of electromagnetic interactions, and since c is the speed of the photons, so for this theory it is natural that the hightest speed of interaction is precisely the speed of light, and we can only deal with all the problems that arise from this limited speed. The same, of course, can be said for the other three fundamental interactions: the gravitational, the weak, and the strong interaction. It happens, however, in my opinion for one arbitrary generalization of the laws of relativity, that the common thinking states that all fundamental interactions: the electrical, the gravitational, the weak, and the strong, have the same propagation velocity of the light: my impression is that this statement is only a convenient application of Ockham's razor, it sounds very metaphysical and not physical. From Physics we can not say anything about the speed of propagation for any of the three remaining fundamental interactions, because we know from theory and experiment only the speed of propagation of the electrical  interaction. I would like to know if anyone has ever thought or done some experiment to make a direct measurement of the speed of the interaction for any of the three remaining interactions

• Answer:

  The speed of light should not be regarded and just as an arbitrary number that measures how fast photons travel but rather the speed of all massless particles. In QFT, we learn that forces like gravity and electromagnetism are mediated by a massless spin-2 particle and a massless spin-1 particle i.e. the graviton and the photon, respectively. In the weak interactions, the mediators are massive, which has to be the case as they are effective at scales of 1/mW1/mW 1/m_W where mWmWm_W is the mass of the gauge boson. The gauge bosons responsible for the weak interaction acquire their masses through the Higgs mechanism, which produces the full spectrum of a massless spin-1 particle and the massive gauge bosons and the higgs, so the entire theory is self consistent.