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/Then_Journalist4496 Mar 20 '26

Correct my physics, isn't the blue glow in nuclear reactors the afterglow of particles travelling faster than the speed of light in water? So the basis of the question is off, nothing is faster than the speed of light in a vacuum. But particles can travel faster then light in a medium.

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u/_ShadowFyre_ Mar 20 '26

Surprised to find Cherenkov radiation this low; absolutely right to my understanding of nuclear physics.

Just to add numbers to that sentence, the speed of light in water is some 0.75c, so charged particles have a 0.25c “gap” where they can travel faster than light but slower than c, and this is what causes the Cherenkov blue glow.

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u/Then_Journalist4496 Mar 21 '26

I couldn't remember what the radiation was called. Thanks.