4 ms·
Note that gravity is very much bound by the speed of light! If you made the Sun vanish, the Earth would only stop orbitting around it a few minutes later. http
by tux3 5y ago
Note that gravity is very much bound by the speed of light! If you made the Sun vanish, the Earth would only stop orbitting around it a few minutes later.
https://en.m.wikipedia.org/wiki/Speed_of_gravity https://en.m.wikipedia.org/wiki/Speed_of_gravity
- k__ 5y agoYes, I didn't mean to imply that the link between a shadow and gravity is the speed of light. I wanted to say they are both emergent phenomenons... or something in that direction.
- amelius 5y agoYes, this breaks Newton's third law that every force should have an equal and opposite reaction force, and thus the sum of all forces are zero at all times.
- WJW 5y agoNewtons laws are not accurate at the quantum and relativistic scales anymore though.
- PeterWhittaker 5y agoYes, this. Of all the things I learned in SR, the example of two particles of the same charge approaching one another near c and the force vectors not lining up with the line between them was the most mind blowing. Instantaneously, conservation laws were violated, they held only over a “long enough” consideration of the interaction. Newtonian mechanics is a useful approximation at certain scales. At other scales, they are problematic.
- codesnik 5y agoalthough nothing really vanishes anywhere, no? I wonder, if sun or anything else would fully annihilate, would resulting gamma radiation still produce a gravitational pull just because of the energy contained in it?
- ben_w 5y agoCorrect, but this is a different hypothetical.
- Iolaum 5y agoIt doesn't. Conservation of momentum, which is an equivalent of Newton's third law, exists in General Relativity. The results of how a system would evolve under GR and the special case like the one above just happen to look strange on a superficial look. If one makes the effort to calculate all the constituents of momentum in such a system, from GR equations, they d verify their sum is conserved.
- Y_Y 5y agoI'd like to add that you can't make the Sun vanish. Aside from the moral and legal objections, physics won't let you do anything that would just "turn off the gravity". You'll have to be content with moving it away bit by bit in some continuous flow of mass-energy, again limited by the speed of light.
- blueprint 5y agoLook... we filed notice. It was on display in the bottom of a locked filing cabinet stuck in a disused lavatory with a sign on the door saying "Beware of the Leopard".
- blueprint 5y agoWhat if that's just the speed of the ability of the change in gravity to have an effect, rather than the gravity change's actual speed of propagation