One aspect of quantum mechanics that is very different from the classical world is that particles can be absolutely identical – so identical that it is meaningless to say which is which. This “identicality” has substantial consequences for what states are allowed, quantum mechanically, and in the counting of possible states. Here, we examine this identicality, introducing the concepts of fermions and bosons and the Pauli exclusion principle that lies behind so much of the physics of materials.
13.1 Scattering of identical particles
Suppose we have two electrons in the same spin state,1 electrons that, for the moment, we imagine we can label as electron 1 ...