

Quantumelectrodynamics describes the interactions
between electrons and photons. 



In 1925, when he was 23 years
old, Dirac started to built on the theories which Heisenberg
and Schrödinger had developed and generalised them.
He also added in relativity and spin for good measure. He
applied his new generalised theory of quantum mechanics
to Maxwell's equations which describe electromagnetic fields.
This was the very first 'Quantum Field Theory.' Despite
formidable calculation difficulties which often generated
infinite results, this theory lead the way to a plethora
of new quantum field theories which are used routinely today
to describe particles and their interactions. One of these,
Quantum Electrodynamics or QED which describes the interactions
between electrons and photons, is a brilliant success and
has been tested successfully to 2 parts in 1 000 000 000
000! 