[ARCHIVED THREAD] - A question about gravity (Page 1 of 2)
Posted: 5/17/2013 2:19:29 AM EDT
| Does gravity have a "speed?" Since it behaves like an electromagnetic force in all other aspects, is it limited to the speed of light? |
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Interesting question. I suppose one way of making it less abstract is to imagine mass that undergoes fission. When that mass is converted into energy, how soon do other masses "feel" it? Since that is essentially transmitting information, it can't exceed c. Looked it up. http://en.wikipedia.org/wiki/Speed_of_gravity supports my hypothesis.
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Does gravity have a "speed?" Since it behaves like an electromagnetic force in all other aspects, is it limited to the speed of light? gravity on earth causes a fixed rate of acceleration 32 feet per second per second. It is a force, not a "speed". It has magnitude and direction. The magnitude of force between two objects is directly proportional to the product of the mass of both objects and decreases by the square of the distance between the two objects. |
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Quoted: Does gravity have a "speed?" Since it behaves like an electromagnetic force in all other aspects, is it limited to the speed of light? I'm flattered that you would choose arfcom for your searching needs, but : http://en.m.wikipedia.org/wiki/Speed_of_gravity
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Amateurly astrophysically speaking
Well, first of all, there is the acceleration of gravity which if I recall rightly for Earth is 32 feet a second a second. Then one can look at the various orbital and escape velocities such as 17K mph for orbital around Earth, 24K mph to escape Earth, and 37K mph to escape the solar system. There abouts, as I recall from figures I have not checked in years and am not going to bother to now. Finally, let's consider a black hole. Why can't it be seen? Because its gravity is so powerful that even light doesn't have sufficient escape velocity. So in answer to your question, gravity in a way has a speed.......and it is not limited to the speed of light. ________________________________________________________________________________________________ ("Time to face destiny!"--villain "Time to face gravity!"--007 turning him into shredded tweet, (w,stte), "Die Another Day") |
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Does gravity have a "speed?" Since it behaves like an electromagnetic force in all other aspects, is it limited to the speed of light? gravity on earth causes a fixed rate of acceleration 32 feet per second per second. This is the accelerationof gravity at the source, i.e. Earth. The acceleration of gravity of, say, Jupiter (with its greatly increased mass) would be much greater. I'm talking about the speed of gravity between objects. Put it this way: Imagine a solar system with, say, 8 planets (or nine, if you live in an alternate universe that doesn't include N de G Tyson). Their masses of each of the planets, plus the sun and all the other detrius (comets and asteroids) have a constant effect on each other, constantly changing because they orbit the sun. Suddenly a large mass of, say, the size of Jupiter, appears at one side of the solar system. How long would it take for the planets, etc. on the other side of that system to react to the gravitational effects of that system? |
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The recent pulsar spin-rate measurement suggests, indirectly, that the gravity propagates to to within 1% of c. Pretty sure that result was in the news last week where you saw the two stars with waves radiating out from them.
Definitely held not to be instantaneous or superluminal. There is a long wiki on the subject. ETA: that 1% figure represents the best experimental measurement of the speed of gravitation, i think. Generally held to be c, with the caveat that we have yet to directly measure gravity waves. (Hellooooo LIGO) |
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Matter bends space and space tells matter how to move.
Gravity is an actual warp in space-time therefore it's effects are instantaneous. When it's said that the gravity at the center of a black hole is so intense that not even light can escape, what is meant is that space time is bent in such a matter that the light travels out and returns to the point from which it originated. Gravity is one of the weakest forces but is one of the most pervasive. The gravity of the earth, which weighs trillions of tons, creates a force on a piece of iron so weak that a magnet weighing a fraction of an ounce can overcome it. The only force more pervasive that gravity is that which continues to cause the expansion of space time itself. Both of those forces are so pervasive that everything in the universe is affected by the presence of everything else, how much so depends on their relative distance. I think. |
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Does gravity have a "speed?" Since it behaves like an electromagnetic force in all other aspects, is it limited to the speed of light? gravity on earth causes a fixed rate of acceleration 32 feet per second per second. This is the accelerationof gravity at the source, i.e. Earth. The acceleration of gravity of, say, Jupiter (with its greatly increased mass) would be much greater. I'm talking about the speed of gravity between objects. Put it this way: Imagine a solar system with, say, 8 planets (or nine, if you live in an alternate universe that doesn't include N de G Tyson). Their masses of each of the planets, plus the sun and all the other detrius (comets and asteroids) have a constant effect on each other, constantly changing because they orbit the sun. Suddenly a large mass of, say, the size of Jupiter, appears at one side of the solar system. How long would it take for the planets, etc. on the other side of that system to react to the gravitational effects of that system? My understanding, which is admittedly limited on this subject, is that the effect would be immediate. This object would be effected by the Sun, which has the most pull on everything for obvious reasons, but as soon as anything orbiting the Sun came into proximity of this new "Jupiter", it and the the new planet would interact gravitationally. No idea how and what would end up happening, except that the Earth would most definitely spiral out of its orbit and crash into the Sun, since that's my proposed idea for Doomsday. |
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Does gravity have a "speed?" Since it behaves like an electromagnetic force in all other aspects, is it limited to the speed of light? gravity on earth causes a fixed rate of acceleration 32 feet per second per second. It is a force, not a "speed". It has magnitude and direction. The magnitude of force between two objects is directly proportional to the product of the mass of both objects and decreases by the square of the distance between the two objects. 
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The recent pulsar spin-rate measurement suggests, indirectly, that the gravity propagates to to within 1% of c. Pretty sure that result was in the news last week where you saw the two stars with waves radiating out from them. Definitely held not to be instantaneous or superluminal. There is a long wiki on the subject. ETA: that 1% figure represents the best experimental measurement of the speed of gravitation, i think. Generally held to be c, with the caveat that we have yet to directly measure gravity waves. (Hellooooo LIGO) I hadn't thought of the effect of a variable gravity source. LowBeta's post answers the question, I think. A "static source" such as a star or a planet is a model that suggests that gravity is uniform throughout the universe; however, given a very strong, variable gravitational force such as that presented by a rotating pulsar, we can see that the behavior of gravity is subject to the limits of spacetime. |
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Yes, gravity does travel at the speed of light. I highly recommend The Fabric of the Cosmos: Space, Time, and the Texture of Reality by Brian Greene. I finished it a couple weeks ago and am considering reading it again. this, gravity = speed of light for example, if the sun were to suddenly disappear we would notice the disappearance of light and gravitational forces simultaneously |
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Does gravity have a "speed?" Since it behaves like an electromagnetic force in all other aspects, is it limited to the speed of light? gravity on earth causes a fixed rate of acceleration 32 feet per second per second. It is a force, not a "speed". It has magnitude and direction. The magnitude of force between two objects is directly proportional to the product of the mass of both objects and decreases by the square of the distance between the two objects. I think he is asking how fast gravity moves. For example if you instantaneously created a chunk of mass, how quickly would other objects 'feel' the gravitational effect of the mass? Would it be instant, or would it be at the speed of light? |
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Does gravity have a "speed?" Since it behaves like an electromagnetic force in all other aspects, is it limited to the speed of light? gravity on earth causes a fixed rate of acceleration 32 feet per second per second. It is a force, not a "speed". It has magnitude and direction. The magnitude of force between two objects is directly proportional to the product of the mass of both objects and decreases by the square of the distance between the two objects. I think he is asking how fast gravity moves. For example if you instantaneously created a chunk of mass, how quickly would other objects 'feel' the gravitational effect of the mass? Would it be instant, or would it be at the speed of light? Instantly. But see my above post. No one knows "what" it is. |
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Does gravity have a "speed?" Since it behaves like an electromagnetic force in all other aspects, is it limited to the speed of light? gravity on earth causes a fixed rate of acceleration 32 feet per second per second. It is a force, not a "speed". It has magnitude and direction. The magnitude of force between two objects is directly proportional to the product of the mass of both objects and decreases by the square of the distance between the two objects. I think he is asking how fast gravity moves. For example if you instantaneously created a chunk of mass, how quickly would other objects 'feel' the gravitational effect of the mass? Would it be instant, or would it be at the speed of light? Newton says instantly Einstein says speed of light |
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Amateurly astrophysically speaking Well, first of all, there is the acceleration of gravity which if I recall rightly for Earth is 32 feet a second a second. Then one can look at the various orbital and escape velocities such as 17K mph for orbital around Earth, 24K mph to escape Earth, and 37K mph to escape the solar system. There abouts, as I recall from figures I have not checked in years and am not going to bother to now. Finally, let's consider a black hole. Why can't it be seen? Because its gravity is so powerful that even light doesn't have sufficient escape velocity. So in answer to your question, gravity in a way has a speed.......and it is not limited to the speed of light. Gravity's force on you or your falling speed is dependant on the amount of mass. If you could stand on the sun, and dropped a hundred pound weight (Provided you could even pick it up), it would slam into the ground unbelievably fast because it weighs 2702 pounds! If you think of gravity as the environment rather than something that ahppens it makes things a bit more clear. Take a bedsheet and put varying size balls on it. The amount of dip each ball created on the bedsheet is directly proportional to mass. Furthermore, the further you get away from each, the less steep the gravity well is, thus the escape velocity is lower. As far as DISTURBANCES in gravitic fields goes, such as two orbiting black holes, stars, planets, etc: I would assume that the disturbances would be felt at the speed of light in vacuum without gravity. (Speed of light being different depending on observer) |
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Does gravity have a "speed?" Since it behaves like an electromagnetic force in all other aspects, is it limited to the speed of light? It is faster than light. Otherwise, light could escape a black hole. Not true. Just spacetime is so warped that there is not an exit path for the light. |
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Interesting theory I heard on gravity on why it is so much weaker than the other electromagnetic forces. It is actually spread across multiple parallel universes in the string theory view of the universe, and only a fraction of it's force is present in our universe. |
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The existence of black holes indicates that gravity can absolutely overcome the speed of light. As far as I know this just means that at the event horizon of a black hole, the escape velocity is equal to c but not necessarily greater past that point. I think that is correct. |
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Does gravity have a "speed?" Since it behaves like an electromagnetic force in all other aspects, is it limited to the speed of light? gravity on earth causes a fixed rate of acceleration 32 feet per second per second. It is a force, not a "speed". It has magnitude and direction. The magnitude of force between two objects is directly proportional to the product of the mass of both objects and decreases by the square of the distance between the two objects. You missed the question. If a massive object spontaneously appears a million miles away, how long will it take for its gravity to have a physical effect on you right here? |
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Does gravity have a "speed?" Since it behaves like an electromagnetic force in all other aspects, is it limited to the speed of light? gravity on earth causes a fixed rate of acceleration 32 feet per second per second. It is a force, not a "speed". It has magnitude and direction. The magnitude of force between two objects is directly proportional to the product of the mass of both objects and decreases by the square of the distance between the two objects. You missed the question. If a massive object spontaneously appears a million miles away, how long will it take for its gravity to have a physical effect on you right here? I think it is the speed of light. Not sure though, I am going on memory. |
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I believe recent measurements put it around the speed of light. Never been detected before though this is the most promising experiment to date: http://www.ligo.caltech.edu/ |
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Taking from 2W0X1 above, how would we simultaneously be able to "feel" the loss of gravity of the sun and "see" the loss of the light? It takes 8.3 minutes for light from the sun to reach earth. If it goes out (not turning into a red dwarf, white giant, or supernova) then we won't know for 8 minutes or so... until the last of the light traveling from the sun to the earth has stopped.
Right? |
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Taking from 2X0 above, how would we simultaneously be able to "feel" the loss of gravity of the sun and "see" the loss of the light? It takes 8.3 minutes for light from the sun to reach earth. If it goes out (not turning into a red dwarf, white giant, or supernova) then we won't know for 8 minutes or so... until the last of the light traveling from the sun to the earth has stopped. Right? This all just theory IIIRC. We really don't know. |
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Does gravity have a "speed?" Since it behaves like an electromagnetic force in all other aspects, is it limited to the speed of light? gravity on earth causes a fixed rate of acceleration 32 feet per second per second. It is a force, not a "speed". It has magnitude and direction. The magnitude of force between two objects is directly proportional to the product of the mass of both objects and decreases by the square of the distance between the two objects. I think what he was asking can be translated as this "if the sun were to vanish right now, would we fly off into space instantly, or would we start flying off into space when/shortly after it gets dark?" |
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Does gravity have a "speed?" Since it behaves like an electromagnetic force in all other aspects, is it limited to the speed of light? gravity on earth causes a fixed rate of acceleration 32 feet per second per second. It is a force, not a "speed". It has magnitude and direction. The magnitude of force between two objects is directly proportional to the product of the mass of both objects and decreases by the square of the distance between the two objects. I think he is asking how fast gravity moves. For example if you instantaneously created a chunk of mass, how quickly would other objects 'feel' the gravitational effect of the mass? Would it be instant, or would it be at the speed of light? Newton says instantly Einstein says speed of light Yep. If a massive object suddenly appeared in space right next to me, there would be a certain period of time (very short) in which none of Newton's laws of gravitation would not apply because the gravity hasn't "traveled" to my location yet. The massive object would exist, I would exist, there would be X distance between us, but none of Newton's laws of gravity would work yet. Mathematically that's not possible, in Newton's world. Interesting. |