In this article Greek indices
take space-time values 0, 1, 2, 3 and Latin indices
spatial values 1,
2, 3. Cartesian coordinates are assumed throughout and boldface notation is often used for ordinary Euclidean vectors. In
Section 11 upper Latin letters
will refer to tetrad indices 0, 1, 2, 3 with
the corresponding spatial values 1, 2,
3. Our signature is +2; hence the Minkowski metric reads
. As usual
and
are
Newton’s constant and the speed of light.