I Gravity as geometry vs gravity traveling at c

[Canis Lupus]

Hi,

I am seeking to understand better how this well accepted idea:

"...according to general relativity, gravity is a manifestation of the geometry of spacetime."
(https://en.wikipedia.org/wiki/Loop_quantum_gravity)

is compatible with the equally well accepted idea that gravity travels at the speed of light.

Any help would be appreciated.

 

[phinds]

Hi,

I am seeking to understand better how this well accepted idea:

"...according to general relativity, gravity is a manifestation of the geometry of spacetime."
(https://en.wikipedia.org/wiki/Loop_quantum_gravity)

is compatible with the idea that gravity travels at the speed of light.

Any help would be appreciated.

CHANGES in gravity travel at the speed of light. Gravity itself is a field and is a manifestation of spacetime or, it is, I think, more appropriate to say that gravity IS spacetime geometry.

 

[Canis Lupus]

CHANGES in gravity travel at the speed of light. Gravity itself is a field and is a manifestation of spacetime or, it is, I think, more appropriate to say that gravity IS spacetime geometry.

Thanks for the reply.

 

[rumborak]

A follow-up question: how come for gravity the space-time distortion view is preferred (to my understanding, a hypothetical graviton field would be equivalent), whereas the other forces are preferred to be viewed as fields?

 

[phinds]

A follow-up question: how come for gravity the space-time distortion view is preferred (to my understanding, a hypothetical graviton field would be equivalent), whereas the other forces are preferred to be viewed as fields?

Gravity IS spacetime geometry so it's not really a choice

 

[rumborak]

I may be mistaken, but I thought the graviton point of view does away with space-time distortion.

 

[FactChecker]

A follow-up question: how come for gravity the space-time distortion view is preferred (to my understanding, a hypothetical graviton field would be equivalent), whereas the other forces are preferred to be viewed as fields?

Is there a field theory that changes time?

 

[FactChecker]

Gravity itself is a field

I'm not sure that I understand this if I take it literally. When I interpret a field as a force vector at every position and time, I have to wonder which position and time. If gravity changes space-time, can it really be considered a field? -- or do I need to give up the distortion part to accept it as a field? In that case, I guess the force is also changing motion in time -- which I could accept. Does that make it more of a tensor than a force in the F=ma sense, since the changing motion in time must not depend on its mass?
EDIT: A field is not necessarily a force field where acceleration would need to depend on mass.

 

[Clausen]

Gravity IS spacetime geometry so it's not really a choice

The gravity field and spacetime are one and the same? Is this a new understanding?
I thought that space-time was a coordinate system; a mathematical construct only. A gravity field is more than that as it has the capability to exert a force if a mass is present. Gravitational field intensity has the dimensions of [Force]/[Mass], Same as acceleration. Is this wrong?

 

[phinds]

I'm not sure that I understand this if I take it literally. When I interpret a field as a force vector at every position and time, I have to wonder which position and time. If gravity changes space-time, can it really be considered a field? -- or do I need to give up the distortion part to accept it as a field? In that case, I guess the force is also changing motion in time -- which I could accept. Does that make it more of a tensor than a force in the F=ma sense, since the changing motion in time must not depend on its mass?

I think you're right; it's not a field (that was a poor choice of description --- I did better w/ the last sentence in that post), it's just the geometry inherent in spacetime. What I meant was that it is pervasive and does not travel. It's the changes in gravity that travel.

 

[Canis Lupus]

I think you're right; it's not a field (that was a poor choice of description --- I did better w/ the last sentence in that post), it's just the geometry inherent in spacetime. What I meant was that it is pervasive and does not travel. It's the changes in gravity that travel.

Does this mean it is constantly changing?

 

[phinds]

Does this mean it is constantly changing?

calling @PeterDonis

 

[FactChecker]

Does this mean it is constantly changing?

When the Sun moves through space, the associated change of space-time due to gravity moves with it. The change travels out from the Sun at the speed of light.

 

[Canis Lupus]

When the Sun moves through space, the associated change of space-time due to gravity moves with it. The change travels out from the Sun at the speed of light.

Thanks. That gives me a better idea.

 

[Canis Lupus]

calling @PeterDonis

Sorry, I don't understand this post.

 

[phinds]

Sorry, I don't understand this post.

I'm calling on one of our experts so that you can get a better answer than what I could provide.

 

[Canis Lupus]

I'm calling on one of our experts so that you can get a better answer than what I could provide.

thanks