Unit 2: The Fundamental Interactions

Unit Overview

This unit takes the story of the basic constituents of matter beyond the fundamental particles that we encountered in unit 1. It focuses on the interactions that hold those particles together or tear them asunder. Many of the forces responsible for those interactions are basically the same even though they manifest themselves in different ways. Today we recognize four fundamental forces: gravity, electromagnetism, and the strong and weak nuclear forces. Detailed studies of those forces suggest that the last three—and possibly all four—were themselves identical when the universe was young, but have since gone their own way. But while physicists target a grand unification theory that combines all four forces, they also seek evidence of the existence of new forces of nature.