Light, the universe and everything

Abstract

The issues of localisation and quantisation of light are looked at in some detail. Two particular issues are addressed: how localised classical electromagnetism solutions affected by the famous result of Newton & Wigner (1949) that photons cannot be localised, and in what way can a photon be seen as a limit of a localised classical pulse. The latter result is a well known result due to Glauber: classical states are coherent states of photons and no direct semiclassical limit can be found. A substantial amount of this thesis investigates how the classical aspects of electromagnetism (such as phase and amplitude) show up when no analogs exist in the quantum case. The ability to localise classical systems is shown not to depend on the fact that individual photons cannot be localised.