Does gravity attract instantaneously?

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Discussion Overview

The discussion centers around the question of whether gravitational attraction is felt instantaneously or if it propagates at a finite speed, specifically in the context of general relativity and hypothetical scenarios involving sudden changes in mass.

Discussion Character

  • Debate/contested

Main Points Raised

  • One participant questions whether the gravitational pull from a newly formed star 10 light minutes away would be felt instantaneously or after a delay.
  • Another participant asserts that it would take 10 minutes to feel the pull, stating that changes in gravity propagate at the speed of light, referencing gravitational waves as evidence.
  • A different participant discusses the implications of conservation of energy and momentum in general relativity, suggesting that sudden changes in mass violate the theory and lead to undefined outcomes.
  • This participant also provides a hypothetical scenario involving the sun exploding and splitting, indicating that the resulting change in the gravitational field would also propagate at the speed of light, leading to an eight-minute delay in experiencing the change.
  • Another participant raises questions about the relationship between hypothetical concepts like the Alcubierre drive and gravitational waves, expressing uncertainty about the nature of gravitational waves and their propagation limits.
  • A later reply reiterates the point that changes in gravity propagate at the speed of light, emphasizing that otherwise, mass could transmit information faster than the speed of light.

Areas of Agreement / Disagreement

Participants generally agree that changes in gravitational influence propagate at the speed of light, but there are competing views regarding the implications of sudden mass changes and the nature of gravitational waves.

Contextual Notes

Some discussions involve hypothetical scenarios that may not align with established physical theories, and there are unresolved questions regarding the definitions and implications of concepts like gravitational waves and sudden mass changes.

jadrian
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for example, if a star theoretically came into existence 10 light minutes away, would we feel its pull instantaneously? or would it take 10 minutes for us to feel its pull?
 
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It would take 10 minutes for us to feel the pull. Changes in gravity propagate at the speed of light. The easiest way to see this is by linearizing Einstein's equations of general relativity, so that the metric is a flat metric plus a small perturbation. Then it's easy to show that such perturbations travel at the speed of light and are called gravitational waves.
 
Conservation of energy and momentum is an essential ingredient in general relativity. Any question that postulates a mass that suddenly appears or disappears violates the theory, and there is no answer to what will happen as a result.

Sudden changes can occur that conserve energy and momentum, for example the sun could hypothetically (!) explode and split in two, one half going north, the other south. In such a case the change in the gravitational field will propagate at the speed of light, and we will feel the difference with an eight minute delay.
 
Is not acubierre drive, though hypothetical, related with gravitational waves. So are gravitational waves not supposed to not have any limit.
Are gravitational waves different from constant fluctuation of structure of space-time continium.
I a novice and have no knowledge even of E.F.E. Let alone solving it. But just ideas.
Forgive me if i am wrong.
 
phyzguy said:
It would take 10 minutes for us to feel the pull. Changes in gravity propagate at the speed of light. The easiest way to see this is by linearizing Einstein's equations of general relativity, so that the metric is a flat metric plus a small perturbation. Then it's easy to show that such perturbations travel at the speed of light and are called gravitational waves.

that was my intuition because otherwize mass could propagate info faster than c
 

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