Introduction

• The full scale of the universe, from the very small to the very big
• The most basic interactions and how they compare
• The quest to unify the fundamental forces

Nature presents us with the macroscopic world, everything we see about us on Earth, but also everything above us, in our solar system and beyond. Nature also presents us with microscopic entities such as atoms, which are made of nuclei and electrons. Nuclei are themselves composed of protons and neutrons. But is this the end of the line? Are protons and neutrons fundamental particles? And what does it mean to be “fundamental” anyway?

We will burrow even more deeply into the atom to see what may lie within the nucleus. We will also begin to take a very, very big step outwards to see how the universe behaves in the realm of galaxies and beyond. Along the way, we will re-examine the basic forces, or fundamental “interactions,” that underlie all of physics. We will examine the similarities and differences between these forces and the ranges over which they operate.

We will also discuss progress to date in the quest to discover one simple theory that rules all of nature. This ultimate pie in the sky could be just within reach. As we have seen, much of the world that surrounds us can be explained by a few simple and elegant theories that have withstood repeated experimental verification. Or, this unification could be a dream that lies forever beyond our grasp.