Relativistic Quantum Mechanics and Quantum Field Theory

Relativistic quantum mechanics can be considered to have begun with a search for wave equations corresponding to each intrinsic spin. However, relativistic quantum physics differs fundamentally from the non-relativistic wave mechanics. It requires a formalism allowing creation and destruction of particles. This gets proper treatment only in a framework called quantum field theory. This article is a semi-historic account of the intriguing new features which emerge as a part of quantum field theory. Such a discussion is impossible without a basic presentation of the formalism itself. Hence some mathematics is included in finer print. The article is directed mostly to those familiar with essential classical mechanics and basic quantum mechanics, though I strive to provide a flavour of the subject to the keenly interested nonphysics reader.