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I don't know much about physics, but I always wondered if gravity is like a shadow. Appearently shadows can move faster than light, breaking with the rest of p
by k__ 6y ago
I don't know much about physics, but I always wondered if gravity is like a shadow.
Appearently shadows can move faster than light, breaking with the rest of physic knowledge, but when you look into the details, they adhere the laws of physics no problem.
Maybe, gravity is like that, not really a physical force, but the shadow of physical forces.
- oefnak 6y agoA shadow is not a thing that moves. What you see as a shadow is just the lack of light.
- alexnewman 6y agoThat is his point.
- k__ 6y agoYes, that's what I meant. Maybe, gravity is like that in some more complex (or abstract?) way.
- hellbannedguy 6y agoI get what you are saying completely. I have thought the same, but never mentioned it.
- lupire 6y agoStatic Gravity (instantaneously, when nothing is moving) is the curvy shape of the Universe, created by massive objects. In that sense gravity not really there, it's just a description of the shape. But when the universe changes shape (due to particles moving or being created or destroyed), those changes happen in gravitational waves that travel no faster than the speed of light.
- tux3 6y agoNote 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__ 6y 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 6y 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 6y agoNewtons laws are not accurate at the quantum and relativistic scales anymore though.
- PeterWhittaker 6y 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 6y 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 6y agoCorrect, but this is a different hypothetical.
- Iolaum 6y 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.
- withjive 6y agoSorry, "apparently" shadows do not move faster than light. Since they are... well... defined by light... I am curious though, as to where you got such a strong notion that shadows can move faster than light...
- k__ 6y agohttps://physics.stackexchange.com/questions/259732/speed-of-dark-experiment-does-it-really-travel-faster-than-light https://physics.stackexchange.com/questions/259732/speed-of-...
- withjive 6y agoYes that is a great of example of reading something on the internet and believing it completely? You just linked me to a Stackoverflow post about a theory, which turns out to just be completely wrong, while managing to include a few valid facts. Was a fun exercise, but please don't get your science this way.
- drooby 6y agoHey dude, sorry our tiny brains are struggling with the science. Do you mind sharing a link to the actual science?
- formerly_proven 6y agoOf course a shadow can move faster than light. Because a shadow is not actually an object moving at all.
- knome 6y agoThe moon is a little more than 0.1 light seconds in diameter. Any wag that took more than a tenth of a second to traverse the moon's surface would be moving slower than the speed of light across it. There's no way the ponderous wag displayed in the video was moving so quick. At best, it was moving half the speed of light across it. What would really be interesting of the things mentioned in the video linked from the stackoverflow question, would be how a perceiver would see the closing scissors occur. If you were 12 light years from the handle end of the scissors, and only 2 light years from the tips, if the closing motion took a year to occur, you would see the point move backwards from the tip to the handles, since the light would take longer to reach you to see the handles close than the tips.
- formerly_proven 6y ago"Projections" can move faster than light in general (e.g. the position of an electron beam can change faster than light).
- detritus 6y agoI just happened to watch this, which says pretty much the same https://youtu.be/Bq9xR5PUs6s?t=388 https://youtu.be/Bq9xR5PUs6s?t=388 "Is Infinity Real?" Sabine Hossenfelder, about 6:25 in. Perhaps this is what OP was referring to?
- alfiedotwtf 6y agoI’ve always wondered if gravity could be seen as like a flux, and measured by bounds vs time. So if any physicist here could shoot this down, I’d be most happy: Let’s say I ran between opposite ends of a basketball court. Back and forth, back and forth... what would happen if I started increasing my speed, slowly all the way to the speed of light? So my thinking is as you become significantly faster, you become heavier, but to yourself, you don’t see any change - so it’s not me who’s getting heavier as I start to run faster and faster to the speed of light, but the enclosed box of me between opposite ends of the court - i.e gravity is the flux of a moving object bound between a distance measured over some time period? i.e some sort of integral of moving matters between a distance, with respect to time. Sorry for my incorrect science... I was just curious how relevant my thinking is
- behindsight 6y ago> but to yourself, you don’t see any change This hints to me that you might be thinking of the concept of invariant vs relativistic mass[0] > i.e some sort of integral of moving matters between a distance, with respect to time. It might be easier if you intuit it as total energy (encapsulates the relativisic aspects) - but that description you wrote seems to be another way to rephrase the curvature of space-time analogy; you could say that what you are describing is retreading how "steep" the bend is, yes? 0: https://en.wikipedia.org/wiki/Mass_in_special_relativity https://en.wikipedia.org/wiki/Mass_in_special_relativity
- alfiedotwtf 6y agoYes? To be honest, I don’t know... despite 2 years of university physics, we sadly never got to the fun physics - relativity and particle physics
- IX-103 6y agoI don't think you can think of it as becoming heavier in the traditional sense, as the higher speed does not increase the force of gravity. There are several (roughly equivalent) ways to describe what happens as you approach the speed of light. One is that instead of gaining mass, you gain extra inertia, making changing the velocity require more force. This makes it appears to outside observers like your acceleration slows down. I don't particularly like this explanation as it doesn't explain why your rate of energy usage appears to go down (as that is more a function of your clock). I prefer the other explanations: Another is that your clock slows down relative to the outside world so you have less time to apply your force so you need more force to apply the same externally visible acceleration. Another is that the outside world looks shrunk in the direction of travel, so again you have less distance to a apply your force to drive the externally visible acceleration. This is effectively the same as previous since distance=time*speed.