In General Relativity, what would happen to the Earth the Sun disappeared?


by MegaDeth
Tags: disappeared, earth, happen, relativity
MegaDeth
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Jun11-11, 10:13 AM
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I'm not sure if this is in the right forum.

If the Sun disappeared, would the Earth's velocity change? Since the space-time fabric would 'spring' back into it's normal position, the effect of gravity on the Earth would dissipate? Thus, resulting in the Earth being thrown out of it's orbit?
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phinds
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Jun11-11, 11:00 AM
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Quote Quote by MegaDeth View Post
I'm not sure if this is in the right forum.

If the Sun disappeared, would the Earth's velocity change? Since the space-time fabric would 'spring' back into it's normal position, the effect of gravity on the Earth would dissipate? Thus, resulting in the Earth being thrown out of it's orbit?
What orbit? If the sun disappeared, then 8 minutes later the earth would HAVE no orbit because it would have nothing to orbit AROUND. It would just keep going in whatever direction it was headed in 8 minutes after the sun disappeared.
MegaDeth
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Jun11-11, 11:05 AM
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Quote Quote by phinds View Post
What orbit? If the sun disappeared, then 8 minutes later the earth would HAVE no orbit because it would have nothing to orbit AROUND. It would just keep going in whatever direction it was headed in 8 minutes after the sun disappeared.
Yes, I know that, but what I'm asking is, would it's velocity change since there's no gravity acting upon it from the Sun which has disappeared?

bcrowell
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Jun11-11, 11:14 AM
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In General Relativity, what would happen to the Earth the Sun disappeared?


You're going to end up in a logically self-contradictory position if you try to answer this question within GR. GR has local conservation of mass-energy, and therefore it doesn't allow the sun to disappear. GR becomes logically inconsistent if you assume violation of conservation of mass-energy.

If the sun was suddenly ripped out of the solar system and taken far away, GR says that the disturbance in the gravitational field would travel at c, so the earth would continue in its original orbit for another 8 minutes.
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Jun11-11, 11:25 AM
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Quote Quote by bcrowell View Post
You're going to end up in a logically self-contradictory position if you try to answer this question within GR. GR has local conservation of mass-energy, and therefore it doesn't allow the sun to disappear. GR becomes logically inconsistent if you assume violation of conservation of mass-energy.

If the sun was suddenly ripped out of the solar system and taken far away, GR says that the disturbance in the gravitational field would travel at c, so the earth would continue in its original orbit for another 8 minutes.
Thanks, that has helped me a lot. By gravitational field, I assume you're referring to the curvature of space-time?
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Jun11-11, 11:36 AM
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Quote Quote by MegaDeth View Post
Thanks, that has helped me a lot. By gravitational field, I assume you're referring to the curvature of space-time?
Right.


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