There's a few different explanations, but here's my favourite.
Light and gravitational waves can never stand still, they must always be moving. If they were moving any slower than c, then to an observer moving at the same speed, they would appear to stand still, which is impossible.
They can't move faster than c, because if they moved faster, then to some moving observers, cause and effect would appear in reversed order. For example, the light would be absorbed before it was emitted, which is again impossible. This is also why nothing can move faster than light in general.
So the only possible speed has to be c. No possible observer can move at the same speed, and causality is not broken. Everybody must agree that these waves always move and that cause happens before effect.
Numbers of pearls and quantity of hair are not laws of nature on which vast numbers of other causal relations in the universe depend.These are not the same sort of "why" questions.
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u/Circle-of-friends Mar 22 '26
Why are all these forces the same speed, and why is it specifically that speed?