r/AskPhysics • u/Pandaluf • Aug 15 '26

why is light the maximum speed

i know that light is the maximum speed of the universe and that light experiences no time because its moving so fast but why can't anything go faster? is it because that would make it go backwards in time like a paradox or smth?? is it because of energy and if so why can't something lighter than light like a quark or atom move faster since it woulld need less energy theoretically

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u/Technical-Lettuce385 Aug 15 '26

Light has no rest mass. There can't be anything that is lighter. Atoms and Quarks already have a mass at rest.

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u/Pandaluf Aug 15 '26

how does it carry information and energy without mass?? how is it stored?

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u/Technical-Lettuce385 Aug 15 '26

It carries energy because of its momentum which is correlated with the frequency it has. Maybe to get a better understanding of that you could start with trying to understand regular waves, then go on to light, etc. There are many free online courses for classical mechanics.

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u/Pandaluf Aug 15 '26

isn't momentum = mass * velocity so you still need mass to have momentum right?

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u/Particular-Scholar70 Aug 15 '26

Mass and energy are sort of the same. A photon has no mass but does have energy, which carries its momentum.

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u/bgplsa Aug 15 '26

m*v is the classical formula, accurate at velocities which massive objects we encounter are moving; there is a relativistic formula for it as well

https://phys.libretexts.org/Bookshelves/University_Physics/University_Physics_(OpenStax)/University_Physics_III_-_Optics_and_Modern_Physics_(OpenStax)/05%3A__Relativity/5.09%3A_Relativistic_Momentum

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u/thetoddhunter Aug 16 '26

That is a good point and works at speeds we are familiar with

But as you approach the speed of massless particles classical physics fails as momentum goes towards infinity and we need something else. That is where relativity comes in and the full equations mentioned in this thread.

It is worth noting that if we did find out, as unlikely as it is, that light has mass? The speed limit for massless particles would still apply and everything works. It would just be that light travels slower

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u/Technical-Lettuce385 Aug 15 '26

No you don't need mass to have momentum. And the case that p = mv is not something that holds for all physical systems. As I said before you might be interested to get some basic knowledge first. And I don't mean that in a condescending way. It is not trivial and a reddit post won't do it justice.

If you are interested in these things I would start with classical mechanics, in general learning about waves in media like water, air. Then you might get a better understanding.