Lecture 39 - The Big and the Small Unification of Forces

Quests to show that the four basic forces are different manifestations of a single unified force follow a long tradition. In the nineteenth century, the distinct electric and magnetic forces were shown to be intimately connected and are now collectively called the electromagnetic force.

More recently, the weak nuclear force was united with the electromagnetic force. It is natural to suggest that a theory may be constructed in which the strong nuclear, weak nuclear, and electromagnetic forces are all unified. Formulation of such a theory is intricately connected to our understanding the nature of the forces/interactions in the early Universe.

It is now clear that the large-scale behaviour of the universe was determined by the conditions that prevailed when the universe was 10-35 seconds old, when a UNIFIED FORCE described all interactions between the elementary particles. So, this lecture is devoted to a review of the microcosm. Among the greatest achievement in physics in the second half of the 20th century was the construction of quantum theories of three of the four forces of nature – electromagnetism, weak interaction which mediates radioactivity, strong interaction which binds the nucleus together. Then came the great paradigm shift, inspired by the theory of superconductivity. This led to the unified theories of forces. First the Electro-Weak Theory, and then the Grand Unified Theory of Strong, Weak and Electromagnetism. In this lecture, I shall attempt to explain in simple terms the ideas underlying the unified theory of forces.