If you love science, it is probably because you love questions. And you probably love questions because they can lead to discoveries. This book is about one of the most productive questions in the history of science: What is the nature of light?
As you will discover, that question led different scientists to different conclusions. Some, like the great seventeenth-century Dutch scientist Christiaan Huygens, concluded that light was pure energy carried by waves. Disputing Huygens from across the English Channel was England’s Sir Isaac Newton, who had concluded that light was a stream of tiny particles. No one anticipated that it might be both. But, as puzzling as that seems, that is exactly what it is. This book explains how that can be. Understanding Photons is about bundles of pure energy, particles with no mass at all that always zip along at exactly the speed of light.
They weren’t called photons at first. In 1900, when Max Planck proposed such bundles in a formula that explained the spectrum of glowing hot matter, he called them quanta (singular, quantum). He didn’t think quanta were real, but they made his mathematics work.
Five years later, Albert Einstein, in explaining a phenomenon called the photoelectric effect, became convinced that Planck’s quanta actually existed. Before Einstein’s work, scientists had made clear-cut distinctions between waves and particles. The discovery of the photon blurred the difference. Along with the earlier discovery of the electron and the later discovery of the nucleus, it opened the door to a new understanding of atoms and “shed light” on the nature of matter itself.
Thanks to those discoveries, we now know that atoms are swarming with subatomic particles. They absorb photons, produce photons, and would not stay together without photons, yet they don’t “contain” photons in the usual sense of that word.
This book will take you on a journey inside matter and energy. You will follow the questions that led to our understanding of photons. And along the way, you will discover the remarkable technology that our understanding has made possible.