and the curvature
of the universe; although, of course,
and
are one and the same, so that, as before, it is matter that creates the spatio-temporal universe.
[121] We are assuming that a four-dimensional vector calculus would have been in existence; but this is a purely mathematical question.
[122] We are using the word “Action” to denote what Hamilton called the “Principal Function.” For a more rigorous treatment the reader must refer to standard works on Analytical Dynamics.