Excerpt: The Principle of Least Action [...] At first glance, S seems like an arbitrary combination of energies. But it has one remarkable property. It turn

Excerpt: The Principle of Least Action [...] At first glance, S seems like an arbitrary combination of energies. But it has one remarkable property. It turns out that for all possible paths between x0 and x1, there is only one path that gives a stationary value of S. Moreover, that path is the one that nature always takes.