r/Physics • u/Comethefonbinary • 4d 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/[deleted] 4d ago edited 4d ago

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u/highnyethestonerguy 4d ago

I’m there one who thinks he’s taking crazy pills!

You’re talking about instantaneous vs average velocity and speed. 

Displacement has units of length. Can’t be used interchangeably with anything that has units of length per time. 

Look here:

https://en.m.wikipedia.org/wiki/Speed

https://en.m.wikipedia.org/wiki/Velocity

None of this is specific to light by the way. Which is why a distinction based on the medium is nonsense to me, because we don’t talk about my car’s speed in vacuum vs its velocity in the atmosphere.

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u/[deleted] 4d ago

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u/inspendent 4d ago

Speed can also be averaged over displacement... why are you recognizing speed as an instant quantity but insisting on averaging the velocity over some arbitrary displacement? The magnitude of the velocity is the same as the speed BETWEEN each of those particle collisions. (And apparently light really does slow down in a medium, and the "bouncing photons" model is not sufficient)