### Re: Is motion of an object affected by its own curvature of space-time?

Date: Thu Feb 7 13:38:17 2002
Posted By: Michael Wohlgenannt, Grad student, Department of Theoretical Physics , University of Munich, Germany
Area of science: Physics
ID: 1011298635.Ph
Message:

Hi Telamon,

you are right, a massive object curves space-time. It will distort space-time along its path. In fact massive objects and energy-distributions are sources for the gravitational field, i.e., they curve space-time. Space-time is described by a metric tensor, which is the solution of the Einstein equation. The curvature of space-time is given by some second derivatives and squares of first derivatives of the metric. The trajectory of a massive particle is given by the socalled time-like geodesic equation. In order to solve this equation you need to know the metric.
If you want to calculate the trajectory of a massive particle, you need to solve this set equations successively. You start by calculating the metric at some (proper) time t with some initial mass and energy distribution. You plug the metric into the geodesic equation and get the position of the particle at a later time t', which is close to t. Again you calculate the metric for the new mass constellation und plug it into the geodesic equation....

Usually the masses of the objects is not large enough to distort space-time considerably. The distortion can be neglected. For example, if you consider the motion of the earth around the sun, you can forget about the distortions of space-time due to the earth. In very massive systems the play a considerable role, e.g., in a binary system consisting of two heavy stars. There a considerable amount of energy is radiated in form of gravity waves, and the stars will eventually collide. This decrease in the period of circulation has been measured in some binaries.

greetings
Michael

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