minimoman Posted September 24, 2011 Posted September 24, 2011 I realized today that, if the sun went out immedeatly, we would still see light for 8 minutes, but the earth would go out of orbit immedeatly. This means that the force of gravity works faster than the speed of light, and therefore could possibly be used to go faster than light in a spaceship, if the force of gravity could be harnessed. Any thoughts?
Janus Posted September 24, 2011 Posted September 24, 2011 I realized today that, if the sun went out immedeatly, we would still see light for 8 minutes, but the earth would go out of orbit immedeatly. This means that the force of gravity works faster than the speed of light, and therefore could possibly be used to go faster than light in a spaceship, if the force of gravity could be harnessed. Any thoughts? You are mistaken. For one, if the sun just went out, it would not have a change on the Earth gravitationally. For the the other, even if the Sun "went away", the Earth would still feel the effects of its gravity for ~8 min after it vanished. Gravity waves (which are what carry the information of changes in gravity) travel at the speed of light. 2
SamSneed Posted September 26, 2011 Posted September 26, 2011 I realized today that, if the sun went out immedeatly, we would still see light for 8 minutes, but the earth would go out of orbit immedeatly. This means that the force of gravity works faster than the speed of light, and therefore could possibly be used to go faster than light in a spaceship, if the force of gravity could be harnessed. Any thoughts? No... We would see the Sun disappear before we felt the effects. Light travels faster than gravitational events. I'm not sure what happens if a Sun goes supernova though. Our Sun "shouldn't" create a black hole if it goes supernova. But some Suns will create a supernova. Therefore, I'm not sure if a supernova will slow (or reverse) light once it goes.
SpeedFreek Posted September 26, 2011 Posted September 26, 2011 No... We would see the Sun disappear before we felt the effects. Light travels faster than gravitational events. I'm not sure what happens if a Sun goes supernova though. Our Sun "shouldn't" create a black hole if it goes supernova. But some Suns will create a supernova. Therefore, I'm not sure if a supernova will slow (or reverse) light once it goes. The post above yours, by Janus, was correct. We would feel the effects when we saw the the Sun disappear. Both light and gravity are predicted to propagate at c.
insane_alien Posted September 26, 2011 Posted September 26, 2011 gravity has been measured as moving at c (fair enough the error on the experiment was vast but it definitely discounts anything faster than 2c with the most probable value being c)
Moontanman Posted September 27, 2011 Posted September 27, 2011 (edited) Why does the Earth orbit a point that is exactly where the sun was 8 minutes ago? or is it will be in 8 minutes? I know it's not where we see the sun now... well ask and ye shall receive http://en.wikipedia.org/wiki/Speed_of_gravity In a field equation consistent with special relativity (i.e., a Lorentz invariant equation), the attraction between static charges is always toward the instantaneous position of the charge (in this case, the "gravitational charge" of the Sun), not the time-retarded position of the Sun. When an object is moving at a steady speed, the effect on the orbit is order v2/c2, and the effect preserves energy and angular momentum, so that orbits do not decay. The attraction toward an object moving with a steady velocity is towards its instantaneous position with no delay, for both gravity and electric charge. Edited September 27, 2011 by Moontanman
SamSneed Posted September 27, 2011 Posted September 27, 2011 (edited) You are correct. It does propagate at c. Edited September 27, 2011 by SamSneed
Schrödinger's hat Posted September 27, 2011 Posted September 27, 2011 So who is wrong...Einstein or Newton? They disagree on your assessment. Newton claims if the sun disappeared we would immediately be thrown out of orbit. Einstein suggest that is not the case. Newton.
SpeedFreek Posted September 27, 2011 Posted September 27, 2011 Also, I discussed this issue in another thread: http://www.sciencefo...post__p__628114
minimoman Posted September 28, 2011 Author Posted September 28, 2011 Im a little confused here though, i always though gravity was a field not a particle or a wave? I would think that if one second you are in a field and another second you are not in a field then you would instantly stop feeling the effects of the field
Schrödinger's hat Posted September 28, 2011 Posted September 28, 2011 Im a little confused here though, i always though gravity was a field not a particle or a wave? I would think that if one second you are in a field and another second you are not in a field then you would instantly stop feeling the effects of the field The field only updates at the speed of light.
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