Chapter 1

One normally makes a distinction between quantum mechanics and quantum physics. Quantum physics is concerned with those processes that involve discrete energies, and quanta (such as photons). Quantum Mechanics concerns the study of a specific part of quantum physics, those quantum phenomena described by Schrödinger’s equation.

Quantum physics plays a rôle on small (atomic and subatomic) scales (say length scales of the order of 1 0 9 m) and below. You can see whether an expression has a quantum-physical origin as soon as it contains Planck’s constant in one of its two guises

h = 6 . 6 2 6 1 0 3 4 J s , = h 2 π = 1 . 0 5 5 1 0 3 4 J s . (1.1)

Here we shall shortly review some of the standard examples for the break-down classical physics, which can be described by introducing quantum principles.