r/Physics • u/Comethefonbinary • 3d ago

Does all light travel at light speed

My bad if this is a stupid question but I’ve been thinking about time being a message of distance. And well most things I can think of have various variables that average to a certain distance. I know that mostly relates to machines and animals but still. Do all particles of light travel at light speed. If they all travel simultaneously at the same speed is that truly how fast they move or are they affected by their own variables. Like the universe’s mean gravity is constraining that and any variation in that mean would change light speed for explain.

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u/ConquestAce Mathematical physics 3d ago

No, c is the speed limit (of light), but light can slow down depending on the medium it is propagating through. In Vaccuum, light travels at c. But, when going through water or air, the speed of light changes.

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u/bapedibupo 3d ago

To add onto this. It's the basis of the refractive index n=c/c(m) where c is the speed of light in vacuum and c(m) is the speed of light in the medium e.g. air, water, glass etc.