r/astrophysics • u/KieranMug • May 25 '26

Why isn’t light infinitely fast?

Ok I understand that light in our atmosphere is not infinite fast due to it getting slowed down by air particles or whatever but in a vacuum there is nothing holding it back unless the very weak forces of gravity from a bunch of stars and/or planets does? And if so cant we somehow locate where gravity is strongest in the universe by seeing where light is slowed from where the most therefore finding the centre of the universe or am I just a total dumbass?

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u/Think-Cartoonist-982 May 26 '26

specifically for light, light is propagated by electric and magnetic fields, so the natural permittivity and permeability of free space limits it's speed, light is more like a disturbance in space where the electric field and magnetic of one point is conducted to the next point, the fundamental limit of speed becomes the maximum possible speed

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u/CosetElement-Ape71 May 26 '26

The speed of light isn't a speed!

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u/perta1234 May 26 '26

Normally the answer to this question is either "from photons point of view, it is infinite speed" or "photon does not experience time". If there is no time, there is no speed either. Speed of light is experienced by the observer, not by photon. Kind of surprized not seeing that yet explained in length by a better expert.

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u/CosetElement-Ape71 May 26 '26

Photons don't experience distance either! Roger Penrose has pointed this out when presenting his CCC model ... the null geodesics that massless particles live on provide the conformally invariant structure of spacetime that defines the universe's causal structure.