Endercreeper01 Posted August 2, 2013 Share Posted August 2, 2013 I was just wondering in general relativity how you would be able to calculate how strong gravity is? I know that you can calculate spacetime curvature, but how do you calculate the force of gravity in general relativity? Link to comment Share on other sites More sharing options...
timo Posted August 2, 2013 Share Posted August 2, 2013 What you actually calculate from a given state of an object (position and velocity) and a known spacetime structure is the acceleration on the object. The relevant equation is called the "geodesic equation". The concept of forces as in "F=ma" is mostly used in non-relativistic, non-QM physics. Link to comment Share on other sites More sharing options...
elfmotat Posted August 4, 2013 Share Posted August 4, 2013 In GR gravity isn't actually a force. Geodesic motion is "natural" motion, i.e. the motion that something exhibits if there are no forces around to mess with it. You can find things like "the normal force required to keep an object on the surface of the Earth" through a slightly tedious calculation of proper acceleration by taking the magnitude of four-acceleration. But "force of gravity" has no real meaning in GR. Link to comment Share on other sites More sharing options...
Endercreeper01 Posted August 7, 2013 Author Share Posted August 7, 2013 (edited) But then what would the acceleration be of an object in a gravitational field in general relativity? Edited August 7, 2013 by Endercreeper01 Link to comment Share on other sites More sharing options...
timo Posted August 8, 2013 Share Posted August 8, 2013 But then what would the acceleration be of an object in a gravitational field in general relativity? I did in fact mention the term "geodesic equation" on purpose. Google it, look it up on Wikipedia, check this this text (eq. 31), ... . Link to comment Share on other sites More sharing options...
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