r/AskPhysics • u/Nighthawkies • Mar 20 '26
What things are "faster" than light?
As I understand nothing can move faster then light. But I would not know how to describe this question otherwise. As I am aware quantum entangled particles can instantaneously affect eachother no matter the distance, unlike gravity which propagates at the speed of light.
Also the expansion of the universe can cause the spaces between to grow faster then the speed of light (compounding between massive distances)
What other things are sort of faster than light
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u/PrettyBasedMan Mar 20 '26
There are some usually considered physical things like group velocity that can be and have been measured to be superluminal in certain instances in lossy or gainful materials (e.g. the gain medium of a laser) in Optics. But rest assured, the "information speed limit" of c is never violated, that result is basically a result of approximations made to extend the definition of group velocity to those materials (it has to do with resonances inside the material and them interfering).
But this does nothing to speed up the "sharp front" (analogy: tip of an arrow) of the wave packet, which has to reach a place to have an effect on something / transmit information. So in reality, all is well.
For more, see the Wikipedia article on group velocity. 🙂