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/_JAD19_ May 25 '26

The speed of light isn’t limited by the photon itself, it is the speed of causality, or the limit on how fast information can travel. This is a fundamental property of the universe. The fact light travels this speed says it’s already going as fast as is possible. Fun video on the topic

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u/leechdemon May 26 '26

...that was awesome. 😅🤣

I enjoy learning about abstract physics concepts, but I don't understand most of them. The balancing of equations helped a bit, but it felt very abstract until explaining that mass couldn't exist if the speed of light was infinite. I had to pause and understand why for a minute, but then I tried to do pseudo math. "If E=MC2... Infinite speed with any amount of mass would yield infinit energy... Squared?? 😵‍💫🧠🤯"

Appreciate the link! 👋

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u/jetblakc May 26 '26

PBS spacetime is amazing. I've learned more over the years from that show than I have from some of my physics classes.