We began this book with the observation that most people associate physics with extreme and exotic phenomena: the strange particles brought into fleeting existence in giant particle accelerators, the sudden creation of matter and space-time itself in the Big Bang, the mysterious fate of giant stars that collapse to form black holes. These take places on scales that fire the imagination, with results that defy our everyday intuition of how the world ought to operate.
As we’ve seen through the course of this book, though, the same physics principles that come into play in those extraordinary scenarios also affect extremely mundane activities like getting out of bed and making breakfast before going off to work. Even as basic a fact of our existence as the stability of solid objects turns out to require quantum theory for an explanation: if not for electron spin and the Pauli exclusion principle, any attempt to make a macroscopic object would end in a catastrophic implosion. Everything that we do, no matter how boringly ordinary, is ultimately rooted in quantum physics.
I hope this book has also made clear, though, that this connection goes both ways: that is, exotic quantum physics is ultimately rooted in very ordinary phenomena affecting the behavior of everyday objects. The entire field began with the deceptively simple question, “Why does a hot object glow that particular color?” The changing light from a hot object is so common—whether it’s an electric toaster oven, an incandescent light bulb, or the sun itself—that we almost forget it’s a phenomenon that needs explaining at all. Thanks to the curiosity of the nineteenth-century spectroscopists who decided to study the color carefully, and Max Planck’s brave and bold trick, we were set on the path to the strangest and most powerful theory in physics.
Physicists didn’t jump to strange and counterintuitive theories in a single step, however; rather, we were inexorably led there by a chain of reasoning each step of which begins with a phenomenon that’s readily observable in relatively unremarkable circumstances. Planck introduced the quantum hypothesis to explain black-body radiation, then Albert Einstein used that idea to explain the photoelectric effect, which lead to photon statistics, and then to lasers. Marie Curie dug deeply into radioactivity, which Ernest Rutherford used to discover the nucleus of the atom, which led Niels Bohr to introduce discrete atomic states, which lead to ultra-precise atomic timekeeping. Dmitri Mendeleev introduced the periodic table, which led to the idea of electron shells, which led Wolfgang Pauli to introduce the exclusion principle, which turns out to be essential for just about everything.
The story of quantum physics isn’t a story of people dreaming up bizarre ideas that only apply in unlikely situations; it’s a story of basic curiosity followed through with determination and rigorous logic. And no small amount of courage—the key steps in the process involve bold and startling suggestions from Planck, Einstein, Bohr, Louis de Broglie, and others along the way—ideas that easily could’ve been (and sometimes were) dismissed as flatly crazy, but that stood up to incredibly exacting experimental tests.
So, the connection between quantum physics and everyday activities is a mutual one. A mundane weekday breakfast would not be possible without quantum physics, and quantum physics would not exist without scientists who looked at the glow of a hot object or the attraction between two magnets and said, “I wonder why that happens?”
I hope that, in the end, you’ll take a lesson from both sides of this relationship. I hope the discussion of the physics underlying ordinary reality inspires you to look a little more closely at everyday activities, and appreciate their roots in astounding and exotic physics. And I hope the stories of the development of quantum theory will inspire you to follow your curiosity: to ask questions about the world around you, take those questions seriously, and follow them wherever they lead. Most of the time, it turns out to be somewhere amazing.