PlanetPhysics/Fermat's Principle

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Fermat's Principle

Initially conceived in optics, Fermat's principle was stated as the principle of least time for traveling light [[../CosmologicalConstant2/|waves]], that is the path or paths taken between two points by light which can be traversed in the least time; in an Euclidean space or a flat Minkowski space, this is the straight line defined by a single ray of light. This can be thought as the trajectory of an emitted photon traveling at the universal maximum [[../Velocity/|speed]] $c$ in vacuum. In a Riemannian or Minkowski [[../SR/|spacetime]] this corresponds to the surface of a light cone.

In general relativity, however, a [[../CenterOfGravity/|point particle]] path is a [[../GeodesicEquation/|geodesic]] curve in a Riemannian space that can be curved, for example, by the presence of intense gravitational [[../CosmologicalConstant2/|fields]]. One such effect was observed and reported by modern astrophysicists and is called gravitational lensing .