Gottem. :)
Gottem. :)
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157 评论
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I wonder if we would feel the sudden disappearance of the centripetal force of the sun's gravity.
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After 8 minutes
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http://scienceprimer.com/lunar-and-solar-tides
Yes, the tidal effect of the sun would disappear, and that would probably make the oceans all fucky suddenly (after an 8 minutes lag).
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Does gravity travel at the speed of light?
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Of course. It can't travel faster
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Yes. General relativity.
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The speed of light is more than just the speed of light. Nothing can travel faster than the speed of light. Not particles, not gravitational waves (waves and particles are actually kinda equivalent anyway), not any kind of "information".
Consequently, if two events occur in a way that a particle would have to travel faster than the speed of light to travel between them, then it's impossible for one of those events to be caused by the other. They must be unrelated. So the soonest we will see any effect of the sun blipping out of existence, whatever the medium (light/gravity/??), is after 8 minutes.
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What about quantum entanglement? Is that also limited to the speed of light?
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Interestingly it's not, but the thing is that you can't actually use quantum entanglement to send information from one particle to the other, so it does not violate the principles of special relativity.
So usually this is explained with two scientists, Alice and Bob, on far away planets. They're each in the possession of a particle that is entangled with the other, and in a superposition of state 1 and state 2. When Alice measures the state of her particle, it collapses into one of the states, say state 1. When Bob measures the state of his particle immediately after, before any particle travelling at light speed could get there, it will also be in state 1 (assuming they were entangled in such a way that the state will be the same).
Due to special relativity, for some observers it could actually have been Bob who measured the state of his particle first, before Alice did. In the end, it doesn't really matter. They both got the same information: "state 1", but since they can't control what state the particle will collapse to, no information can be exchanged between Alice and Bob.
In quantum encryption, it is that bit of shared information that Alice and Bob can use as a key to encrypt and decrypt messages, but those messages are still sent the old fashioned way, using light waves traveling at light speed.
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The gravity does not travel, the gravity is.
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Changes in the gravitational field definitely travel, and do so at the speed of light.
Look up LIGO
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If it didn't travel, it wouldn't take 8 minutes to stop right?
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If the mass vanishes, then the gravity would also vanish, at the same time.
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False. If the mass vanished via magic, the effect would ripple out at the speed of light. Source, gravity waves which move at the speed of light.
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But vanishing is magic, it goes against the laws of physics, so you could apply any fictional logic
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After 8 minutes, almost certainly
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Gravity isn't a force, strictly speaking. Objects move along geodesics in spacetime (that's basically a straight line along a curved surface), and gravity bends spacetime, and therefore also these geodesics, around massive objects. So you don't actually get accelerated by gravity, that's why you don't feel anything during free fall. What we perceive as the force of gravity pushing us down, is the solid ground accelerating us upwards, when following the geodesic would have us fall instead.
So when the sun disappears, the geodesic that used to spiral around the sun suddenly straightens out, and the neutral movement, the new free fall, has the earth continuing in a straight line. You wouldn't be able to feel that. What the other person said about tidal forces is true tho, it would likely cause worldwide tsunamis
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157 评论