Spacetime Symmetries and Kepler's Third Law

Feb, 2012
11 pages
Published in:
  • Class.Quant.Grav. 29 (2012) 217002
e-Print:

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Abstract: (arXiv)
The curved spacetime geometry of a system of two point masses moving on a circular orbit has a helical symmetry. We show how Kepler's third law for circular motion, and its generalization in post-Newtonian theory, can be recovered from a simple, covariant condition on the norm of the associated helical Killing vector field. This unusual derivation can be used to illustrate some concepts of prime importance in a general relativity course, including those of Killing field, covariance, coordinate dependence, and gravitational redshift.
Note:
  • 11 pages, 3 figures; minor changes and text improvements; matches version to appear in Class. Quant. Grav
  • vector: Killing
  • symmetry: space-time
  • gravitation: redshift
  • field theory: vector
  • space-time: geometry
  • general relativity
  • covariance
  • orbit
  • curvature
  • gravitation: weak field