Named for a

physicist by the name of

Killing, not for the type of action such a

vector might take, a Killing

vector is an important

concept in

General Relativity. It is a

tangent vector to a

trajectory along which the

metric tensor is

invariant. Taking the

inner product of a Killing

vector and a

vector tangent to a

geodesic produces a

constant of motion.

The existence of a timelike Killing vector implies that the spacetime is stationary.