Elementary Particles

Introduction

There have always been close links between physics and astronomy and physics and cosmology. This is to be expected since astronomy and cosmology are fields of science which apply physics in an attempt to understand observations of the cosmos and to comprehend the structure, origin and evolution of the universe. Equally our understanding of physical laws and in particular their apparent universality in space and time, has in a number of instances depended crucially on astronomical data.

In the first half of the twentieth century a number of common areas of interest – relativity theory, nuclear reactions and stellar evolution, and cosmic rays, among others – provided fruitful points of contact between particle and nuclear physics on the one hand and cosmology on the other. After a period of less interaction common interests have increased dramatically over the last 10–15 years in a way which has been highly stimulating for both subjects.

Most fundamentally the development and general acceptance of the Big Bang model implies energy densities during the first instants after the Big Bang which can now be even distantly approached only in high energy particle collisions. On the other hand it is clear that no experiments we can ever do will attain the energies at which we might expect unification of all four forces including gravity (energies ∼ Planck mass ∼ 1019 GeV/c2) or even Grand Unification energies ∼ 1015 GeV, so that the only laboratory for direct study of these phenomena existed in the first instants after the Big Bang.