What is the measure of space-time curvature and how is it calculated?

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Discussion Overview

The discussion revolves around the concept of space-time curvature in relation to mass, specifically questioning where maximum curvature occurs and how it is measured. Participants explore theoretical aspects of curvature, its visual representation, and implications for gravitational forces.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • One participant questions whether the point of maximum curvature is at the center of mass, suggesting that visual representations imply a flat bottomed "dent" which could indicate no curvature at the center.
  • Another participant clarifies that the visual "dent" represents space-curvature, not space-time curvature, and asserts that local space-time curvature is related to tidal forces rather than gravitational attraction.
  • Concerns are raised about how curvature can exist without coordinate acceleration, with a focus on the relationship between gravitational potential and curvature.
  • Some participants assert that space-time curvature increases as one approaches a massive object, while others discuss the concept of constant curvature within a spherical mass.
  • Questions are posed regarding the use of the Ricci scalar as a measure of curvature and its relationship to the stress-energy tensor.

Areas of Agreement / Disagreement

Participants express differing views on the relationship between gravitational potential and curvature, as well as the implications of curvature in relation to mass. There is no consensus on the interpretation of curvature at the center of mass or the nature of truly flat space-time.

Contextual Notes

Participants reference various aspects of curvature, including spatial and space-time curvature, tidal forces, and the significance of metric derivatives. The discussion includes unresolved questions about the definitions and measurements of curvature.

Who May Find This Useful

This discussion may be of interest to those studying general relativity, gravitational physics, or mathematical models of space-time, particularly in relation to curvature and its implications.

Gingermolloy
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Space-Time Curvature Question!

Hi Guys,

A question about the curvture of space-time by mass.

Where is the point of maximum curvature??

Is it at the centre of mass (i.e.. the middle of the body)

The reason I ask, is that when space-time curvature is shown visually it makes out like it is a flat bottomed "dent" in space-time. If this was the case it would mean surely that there is no curvature at the centre of mass.

Where am I going wrong with this thought process.

Thanks

Ginger
 
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1) The "dent" just shows space-curvature, not space-time curvature. Check out:
http://www.physics.ucla.edu/demoweb..._and_general_relativity/curved_spacetime.html

2) The "dent" is not flat. The spatial-curvature is the same everywhere within a uniform massive sphere (the spherical cap at the bottom):

Schwarzschild_interior.jpg


3) The local space-time curvature is connected to tidal forces rather than gravitational attraction. At the center of a massive sphere the gravitational acceleration is zero, but the curvature isn't (unless there is a spherical cavity at the center).
 
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A.T. said:
3) ... At the center of a massive sphere the gravitational acceleration is zero, but the curvature isn't (unless there is a spherical cavity at the center).

How can there be curvature but no coordinate acceleration? If the gravitational potential is net zero, then wouldn't that mean there is no curvature?
 
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nitsuj said:
How can there be curvature but no coordinate acceleration?
It's explained in the part you sniped: The local space-time curvature is connected to tidal forces rather than gravitational attraction

nitsuj said:
If the gravitational potential is net zero, then wouldn't that mean there is no curvature?
The value of the gravitational potential is arbitrary. Its gradient matters, and determines the direction of coordinate acceleration. In the center the gradient or 1st metric derivatives are zero, therefore no gravity pull exists. But curvature or 2nd metric derivatives are not zero, therefore tidal forces exist.
 


I was under the impression that space-time became more curved the closer to a massive object you get. Is this true??

The area of constant curvature? Is that the region of space within the body itself?

And is there such thing as truly flat space-time?
 


Gingermolloy said:
I was under the impression that space-time became more curved the closer to a massive object you get. Is this true??
Yes, outside of it.
Gingermolloy said:
The area of constant curvature? Is that the region of space within the body itself?
Yes, the interior spatial metric is spherical. A sphere has constant curvature.
Gingermolloy said:
And is there such thing as truly flat space-time?
Not in reality. Only regions with negligible curvature.
 


A.T. said:
Yes, outside of it.

Yes, the interior spatial metric is spherical. A sphere has constant curvature.

Not in reality. Only regions with negligible curvature.

A quick pair of questions on the technical side. Are you using the Ricci scalar as a measure of the magnitude of the curvature? And setting it equal to the minus the trace of T_ab (possibly multiplied by some constant)?
 

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