B. H. Fields - Understanding Photons

To Eliana, who can light up the world with her smile

Published in 2016 by Cavendish Square Publishing, LLC
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Copyright 2016 by Cavendish Square Publishing, LLC

First Edition

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Library of Congress Cataloging-in-Publication Data

Fields, B. H.

Understanding photons / by B. H. Fields and Fred Bortz.

p. cm. (Exploring the subatomic world)

Includes index.

ISBN 978-1-50260-544-3 (hardcover) ISBN 978-1-50260-545-0 (ebook)

1. Photons Juvenile literature. I. Fields, B. H. II. Title.

QC793.5.P42 F48 2016

539.7217d23

Editorial Director: David McNamara

Editor: Andrew Coddington

Copy Editor: Cynthia Roby

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Printed in the United States of America

Contents

What Is Light?

Plancks Surprise

Light and Matter

Photons and Modern Technology

I f 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 Englands 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 werent 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 didnt 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 Plancks quanta actually existed. Before Einsteins 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 dont 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.

O ur planet is full of life because it is full of light. Plants use the energy of sunlight to grow, and plants provide food for animals. Humans and many animals use their sense of sight to find their way in the world.

But what is light? That simple question has driven human curiosity throughout history. No question in science has led to more discoveries. It has led not only to understanding that important form of energy, but also knowledge about the nature of matter and the forces that govern the universe.

Light and Color

Among the first to pursue that question were two seventeenth-century scientists who are considered to be among the most important of their time, or of any time: Sir Isaac Newton (16421727) and Christiaan Huygens (16291695).

At Cambridge University in England in the mid-1660s, the young Newton made some important observations about color. Until that time, the prevailing scientific view was that white light was pure, and something had to be added to produce color. Though that theory fit with common sense, Newton discovered that it was wrong.

In a darkened room with a hole in the window shade that allowed a sunbeam to enter, Newton took a piece of glass in the shape of a triangular prism and put it in the beams path. The light emerged from the prism in a different direction, and it spread out much more than it would have without the prism. More important, when the light struck the opposite wall, it was no longer white. Instead, Newton observed a band of colors from red to violet, like those of a rainbow.