Instantaneous Curvature in Mass Warp Spacetime?

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Discussion Overview

The discussion centers around the effects of mass loss from an object on the curvature of spacetime and how these changes propagate, particularly in relation to the speed of gravity and light. Participants explore the implications of these changes for an observer located one light year away from the object, considering both theoretical and conceptual aspects of gravity and radiation.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • Some participants propose that changes in gravity propagate at the speed of light (c), similar to light itself.
  • Others argue that for a distant observer, there is no change in the center of mass of a radiating object until the radiation reaches them, suggesting a delay in perceiving changes in curvature.
  • A participant suggests that once the emitted radiation reaches the observer, they would begin to feel the change in curvature, as they would then be within the region affected by the mass loss.
  • There is a discussion about the complexity of the question, particularly regarding how gravity does not exhibit aberration like light does, which may affect perceptions of gravitational changes.
  • Some participants express uncertainty about the specific mathematical formulations that demonstrate how gravity changes propagate at c, indicating a need for further exploration of existing forum discussions on the topic.
  • A participant corrects their earlier statement regarding the center of mass, clarifying that it does not change until the radiation begins to pass the observer.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the nuances of how changes in curvature are perceived by distant observers, with multiple competing views remaining regarding the propagation of gravitational changes and the implications of mass loss.

Contextual Notes

Limitations include the dependence on definitions of curvature and mass, as well as unresolved mathematical steps regarding the propagation of gravitational changes and their effects on observers.

TimeRip496
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Assuming a mass warp spacetime such that the curvature of spacetime extend one light year away from that object. If I am standing at 1 light year away from the object and the object start losing mass by emitting light, will you feel the change in the curvature first before the radiation reach you after 1 year or feel the change in curvature instantly the emitted radiation reach you?

My apologies for such qns as I am not smart at all.
 
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Changes in gravity propagate at c, just as does light, BUT your question is more complex than that because to a body far away from an object there IS no change in the center of mass of the object, as far as the distant body is concerned, as photons or mass leave an object.

SO ... I assume your question is really just "do changes in gravity propagate at c?" and they answer to that is yes.
 
To the question "do you start to feel the change at the same time the first emitted radiation hits you", I would think the answer is "Yes" :

Until then the star+emitted light lies in a spherical region outside of which you are, so as phinds said nothing changes. After that you are inside the expanding sphere and the gravity you feel (i.e. the curvature) changes.

This effect might be quite tiny - after all losing mass through radiation is what stars do for a living : ) but if we're talking say a supernova explosion, then I expect it might be noticeable, provided the gravity from the star is itself noticeable 1ly away.
 
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phinds said:
Changes in gravity propagate at c, just as does light, BUT your question is more complex than that because to a body far away from an object there IS no change in the center of mass of the object, as far as the distant body is concerned, as photons or mass leave an object.

SO ... I assume your question is really just "do changes in gravity propagate at c?" and they answer to that is yes.

When you say "more complex" and refer to the center of mass... are you hedging a little bit, perhaps obliquely, about how gravity does not show aberration due to relative movement the way that light does?

A lot of questions about the speed of gravity come from wondering about presumed propagation delay effects on orbit stability.
 
bahamagreen said:
how gravity does not show aberration due to relative movement the way that light does?
Light is a propagating disturbance of the EM-field, comparable to gravitational waves. Gravity itself is comparable to the Coulomb force, which doesn't show the aberration that light shows.
 
phinds said:
Changes in gravity propagate at c, just as does light, BUT your question is more complex than that because to a body far away from an object there IS no change in the center of mass of the object, as far as the distant body is concerned, as photons or mass leave an object.

SO ... I assume your question is really just "do changes in gravity propagate at c?" and they answer to that is yes.
Why? Is the speed of light by gravity shown by general relativity or einstein field equation? If so, can you tell me?
 
TimeRip496 said:
Why? Is the speed of light by gravity shown by general relativity or einstein field equation? If so, can you tell me?
I don't know what the specific math is that shows that gravity changes propagate at c, but there are lots of posts on this forum discussing it so a forum search will turn something up.

By the way, I slightly misspoke when I said that there is no change in the center of mass of a radiating object as far as a distant observer is concerned. I should have added "until the radiation begins to pass the remote observer" (at which point the COM actually STILL hasn't changed, assuming equal radiation in all directions, but the effects on that observer will start to change).

EDIT: I see that wabbit's post already covered this correction.
 
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bahamagreen said:
When you say "more complex" and refer to the center of mass... are you hedging a little bit, perhaps obliquely, about how gravity does not show aberration due to relative movement the way that light does?

/QUOTE]
No, I was referring to the correction I made in my more recent post (and that was explained also by wabbit, which I didn't notice until after my recent post).
 
A.T. said:
Light is a propagating disturbance of the EM-field, comparable to gravitational waves. Gravity itself is comparable to the Coulomb force, which doesn't show the aberration that light shows.
Right, which is why I said "changes in gravity propagate ... " (AT, I'm pointing this out as additional info for TimeRip, more than as a response to your correct statement).
 

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