# The Essence of Quantum Mechanics Part 2: Complex Numbers

In the first article in this series we outlined some basic physical intuition and described some of the ways in which quantum physics diverges from the classical physics of everyday life. The most important difference between classical and quantum physics is that quantum physics tends to resist intuitive understanding and is therefore best understood in terms of an abstract mathematical formalism. Before we can move on to building this formalism, we need to go over some mathematical foundations.