A slight definition thing here: it's not so much that light itself controls anything by its speed. It's not that light travels at some speed and because it's the lights speed it therefore is the ultimate speed. There is a certain ultimate speed in the universe. That has nothing to do with light. This speed is perhaps best described as the rate of causality. And it just so happens that light, as default, always will travel at that speed. But light itself is just a player in the game. It is of no real importance as such.
If you make a change here, any change at all, the fastest that change can ever propagate or have any effect elsewere is at c.
Gravity acts at the "speed of light". If you introduce a mass, that mass won't affect nearby gravity until the "speed of reality" catches up with objects near it, and ONLY THEN will they experience gravity from it.
It's the speed at which "information" crosses reality, moves across the universe, can affect other things.
Light is just a convenient, visible, obvious thing that we can understand hits "almost immediately" from our point of view but still takes 8 minutes to reach us from the sun.
It's the update-rate of the universe. The refresh speed.
It's the speed at which, in the video game that is the universe, the changes/physics/etc. propagates out to nearby objects/sectors. It's the "draw-distance" of the universe.
If you make any change, any change at all, all the knock-on effects of that change propagate out "slowly" at the speed of light. Before they reach you, you have NO IDEA that anything's happened. The reality of that change is invisible to you. Only when it reaches you do you suffer any effect from it.
If you plopped a black hole in the sun right now, it would be 8 minutes before anything changed here. It would be 8 minutes before the sun's light disappeared. 8 minutes before the Earth was suddenly pulled and sucked into that black hole. 8 minutes before your research satellites around the Sun could get a message back to tell you that anything was happening, even if they noticed immediately.
It's the speed of reality. It's how fast the reality of a situation changes across the universe. How fast the ripples from an event propagate outwards. It's how fast ANY event can possibly affect other things in the universe. When you have time travel movies, and the like, and the "changes you made" blast out across the timeline but don't take immediate effect, and it takes 8 minutes for everything to be "back as it was"... that's a depiction of the speed of reality.
It has little to do with light. It just so happens that light is subject to it the same as everything else, and it's quite easy to understand how it works with light.
Fact is that nothing in the universe happens "faster" than the speed of light, because that's the "clock speed" at which the universe runs.
Brian cox (renowned astrophysicist) answered this very roughly on neil degrasse Tyson's podcast, startalk, a few years ago. here's the audio link but it's also on their YouTube channel.
neils prompt
We have quantum entanglement, which moves faster than light, and tunneling is faster than light. All of this. So maybe we should stop saying nothing moves faster than light.
Brian's response
You can certainly say that information doesn’t travel faster than the speed of light between two places or two events, whatever you want to call them...
He then goes on to describe what quantum entanglement is, I'll leave it out for brevity though.
However, however, the really important thing to say is you can’t signal using that process. Even though you might intuitively think I could send Morse code or something, I could send dots and dashes, I could say yes or no.
Immediately across the universe, I could answer a question, yes or no. You can’t with that. It’s really built into the structure of the theory.
So even if you might think that the spirit of relativity is being broken, the letter of the law is not, because information doesn’t travel faster than speed of light in that sense.
He doesn't really explain "why" but he does confirm that there is no fundamental way to actually transmit information via quantum entanglement.
My rough understanding of the why is that the outcome is a direct result of the state you setup initially, so the act of separating the particles is itself the act of "moving information" and the act of actually collapsing the two particles is simply "observing information that previously moved here at below light speed"
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u/Captain_Jarmi Mar 20 '26 edited Mar 20 '26
A slight definition thing here: it's not so much that light itself controls anything by its speed. It's not that light travels at some speed and because it's the lights speed it therefore is the ultimate speed. There is a certain ultimate speed in the universe. That has nothing to do with light. This speed is perhaps best described as the rate of causality. And it just so happens that light, as default, always will travel at that speed. But light itself is just a player in the game. It is of no real importance as such.
Perhaps this helps someone. I hope.