Since the classical eld is not real, the corresponding quantum eld is not hermitian.
This is the reason that we have dierent operators b and c appearing in the positive
and negative frequency parts. The classical eld momentum is = L/ = . We
also turn this
2. Free Fields
The career of a young theoretical physicist consists of treating the harmonic
oscillator in ever-increasing levels of abstraction.
Sidney Coleman
2.1 Canonical Quantization
In quantum mechanics, canonical quantization is a recipe that takes
1.2 Lorentz Invariance
The laws of Nature are relativistic, and one of the main motivations to develop quantum
eld theory is to reconcile quantum mechanics with special relativity. To this end, we
want to construct eld theories in which space and time are
0. Introduction
There are no real one-particle systems in nature, not even few-particle
systems. The existence of virtual pairs and of pair uctuations shows that
the days of xed particle numbers are over.
Viki Weisskopf
The concept of wave-particle dualit