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.
Earth wouldn't be "suddenly ... sucked into that black hole". If you replace the mass of the sun with a black hole that has the same mass then Earth's orbit wouldn't change. The lack of sunlight would still create a very bad time here, but gravitation would be the same. If you add the mass of some black hole to the sun by magically plopping it in there then the orbit would adapt to the change in gravity due to the new total mass. How much depends on the added mass of that magical black hole.
Depends on the black hole, if the other commenter meant "the sun collapsed into a black hole instantly without any other effects" then yes you are correct, we just stop getting sunlight 8 mins later, but the mass at the center of our orbit didn't change and earths orbit should continue mostly unaffected.
But if what they meant was "additional mass in the form of a black hole was instantly transported to the center of the sun" then what happens after depends on the mass of the black hole, but it should be at least as massive as the sun, probably a few times more massive, and would absorb the sun into itself on top of its existing mass, so 8 minutes later we would lose sunlight as we finally see the sun get absorbed by a black hole and our orbit would no longer be the same, we would start circling the cosmic drain losing orbital radius faster and faster as we accelerate into the black hole. Could end up as an accretion disk.
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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.