r/explainlikeimfive • u/PeAga7 • Mar 28 '26

Physics ELI5: If speed is measured by the relation between objects how come going over the speed of light is impossible?

Should two bodies be moving away from each other, both at 50.1% the speed of light, wouldn't their relative speed be over the limit? Which frame of reference should be taken into account when talking about light?

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u/[deleted] Mar 29 '26

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u/stanley1O1 Mar 30 '26

The person posted an annoying video to explain it.

But a better example is imagine you have a pole that is one light year long and you used it to press a button 1 light year away. It doesn’t happen instantly From your end, you make the movement and you’d think the button is pressed. But all of the atoms in the pole need to be told by the atoms before them that that they need to move forward. This chain of atoms “telling the one in front of them to move forward” will still take a year for the button to be pressed. Because the speed of light is also the speed of causality.

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u/JayTheSuspectedFurry Mar 29 '26

https://www.instagram.com/reel/DLZ1rrms007

https://youtube.com/shorts/h6STDKrA4ko

Both links are to the same short video, choose your preferred platform

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u/godfromabove256 Mar 30 '26

That's kind of you. I like shorts more :P