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

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Discussion Overview

The discussion revolves around the hypothetical scenario of the Sun disappearing and its implications for the Earth's motion within the framework of General Relativity (GR). Participants explore the effects on Earth's velocity and orbit, considering both the immediate and delayed consequences of such an event.

Discussion Character

  • Exploratory
  • Debate/contested
  • Technical explanation

Main Points Raised

  • Some participants propose that if the Sun disappeared, the Earth would continue in its current trajectory for about 8 minutes due to the finite speed of gravitational influence, which travels at the speed of light.
  • Others argue that the Earth would have no orbit after the Sun's disappearance, as it would lack a central body to orbit around, thus moving in a straight line in the direction it was headed at that moment.
  • One participant raises a concern about the logical consistency of the scenario within GR, stating that GR does not allow for the Sun to simply disappear due to the conservation of mass-energy.
  • A later reply clarifies that if the Sun were to be removed from the solar system, the gravitational field disturbance would also propagate at the speed of light, maintaining the Earth's orbit for a brief period.
  • There is a question about whether the term "gravitational field" refers to the curvature of space-time, which is affirmed by another participant.

Areas of Agreement / Disagreement

Participants express differing views on the implications of the Sun's disappearance, with some focusing on the immediate effects on Earth's motion and others emphasizing the theoretical constraints of GR. The discussion remains unresolved regarding the implications of such a scenario within the framework of GR.

Contextual Notes

Participants acknowledge the limitations of the hypothetical scenario, particularly regarding the conservation of mass-energy in GR and the assumptions involved in discussing the disappearance of the Sun.

MegaDeth
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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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MegaDeth said:
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.
 
phinds said:
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?
 
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.
 
bcrowell said:
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?
 
MegaDeth said:
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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