The quantum mechanical propagator may also be found by using a path integral.

In the path integral, these are just integration variables and they have no obvious ordering.

To see this, consider the simplest path integral, the brownian walk.

In the same way, the path integral is manifestly relativistic.

This path integral is also called circulation, especially in fluid dynamics.

The analogous expression in quantum mechanics is the path integral.

It is called the path integral or sum over histories approach.

The measure of the path integral is then defined to be:

The first term does not depend on any fluctuating fields, so that it can be brought out of the path integral.

The path integral can be generalized to p-adic time as well.