How would you calculate how bodies curve space/time?

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Discussion Overview

The discussion centers around how to calculate the curvature of space-time caused by bodies, particularly in the context of general relativity. Participants explore various equations and concepts related to the Schwarzschild radius, the Einstein Field Equations, and approximations for curvature in weak gravitational fields.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Debate/contested
  • Homework-related

Main Points Raised

  • One participant expresses interest in relativity and mentions the equation for regular space-time involving the Schwarzschild radius and the radius from the center of mass.
  • Another participant suggests that for weak fields, the curvature can be approximated using the formula 1/R = g/c², where g is the Newtonian acceleration.
  • A different participant explains that the curvature of space-time is calculated by solving the Einstein Field Equations and mentions the Schwarzschild metric as a specific solution for non-rotating black holes.
  • Some participants emphasize that the question is complex and not easily answered with simple formulas, suggesting that foundational reading on general relativity may be beneficial.

Areas of Agreement / Disagreement

Participants generally agree that the question of calculating how bodies curve space-time is complex and cannot be resolved with straightforward answers. Multiple approaches and models are presented, indicating a lack of consensus on a singular method or formula.

Contextual Notes

Participants note the limitations of their discussions, including the need for foundational knowledge in general relativity and the complexity of the equations involved. There is also mention of different metrics applicable to various scenarios, such as rotating versus non-rotating black holes.

Who May Find This Useful

This discussion may be useful for individuals interested in general relativity, physics students seeking to understand space-time curvature, and those exploring the mathematical underpinnings of gravitational theories.

zeromodz
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Okay, I am really interested in relativity, but very ignorant in it also. I already know you would divide regular space/time by

√(1 - rs/r)

rs = schwarzschilds radius
r = radius of object from center of mass

How would we define regular space/time in an equation? What units or dimensions do we get the answer in. Thanks in advanced for answering.
 
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zeromodz said:
Okay, I am really interested in relativity, but very ignorant in it also. I already know you would divide regular space/time by

√(1 - rs/r)

rs = schwarzschilds radius
r = radius of object from center of mass

How would we define regular space/time in an equation? What units or dimensions do we get the answer in. Thanks in advanced for answering.

Look at:
http://en.wikipedia.org/wiki/Schwarzschild_metric

Here some visualizations of it:
http://www.relativitet.se/spacetime1.html
http://www.adamtoons.de/physics/gravitation.swf
 
zeromodz said:
Okay, I am really interested in relativity, but very ignorant in it also. I already know you would divide regular space/time by

√(1 - rs/r)

rs = schwarzschilds radius
r = radius of object from center of mass

How would we define regular space/time in an equation? What units or dimensions do we get the answer in. Thanks in advanced for answering.

If you don't need to handle really strong fields, you can just use the approximation that the curvature is 1/R = g/c2 where g is the Newtonian acceleration. That value gives the effective acceleration g = c2/R for something at rest, and also gives the curvature of space, so that if the speed is v perpendicularly to the field there is an extra acceleration of v2/R, and if v=c the total acceleration is twice the Newtonian value.
 
You calculate how matter/energy curve space-time by solving the Einstein Field Equations.

The Swarzchild metric is one exact solution (the first one that was found! Other than the normal flat metric (or sometimes called the Minkowski space)) to Einstein's field equations. This solution is valid for non-rotating, non-charged, black holes (basically the space around a spherical object that just sits there). There are others, such as the Kerr metric for a rotating black hole. And there are even others where the space is not "empty" such as for these solutions, and therefore the stress-energy tensor is non-zero (I'm not sure if we've found any exact solutions to those).

http://en.wikipedia.org/wiki/Einstein_field_equation
 
Zeromodz, this is not a simple question with a simple answer. It's not the kind of thing where people can just give you a couple of formulas and then you'll be all set. You might want to start by reading a good elementary description of general relativity, such as the one in Hewitt's Conceptual Physics, or Relativity Simply Explained by Gardner.
 

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