3 Expectation and uncertainty

So far, all we’ve been doing is solving Schr¨odinger’s equation, which is arguably

not very fun. In this chapter, we will look at some theoretical foundations of

quantum mechanics. Most importantly, we will learn how to extract information

from the wavefunction

ψ

. Two important concepts will be the expectation

and uncertainty. We will then prove two important theorems about these —

Ehrenfest’s theorem and the Heisenberg uncertainty principle.