If you were to shrink down to the size of an electron, you would enter what physicists call the quantum realm, and things would suddenly get very weird. At this minute scale, there is no “here” here—subatomic particles are, at any given moment, not just here but also there… and there… and over there. “Virtual” particles briefly pop into existence and then vanish just as quickly; this happens so often that space itself seems to seethe like a wind-whipped ocean. Sometimes particles become entangled with one another. When the spin, polarization, or other properties of one particle change, its partner also transforms instantaneously—faster even than light could pass information from one to the other. Albert Einstein called it “spooky action at a distance” (spukhafte Fernwirkung were his exact words). Scientists understand the math of how it works, but they still can’t describe it in words in any really satisfying way.
Strange stuff, indeed, as Brian Greene explains in Quantum Leap, an episode of NOVA’s series based on his book The Fabric of the Cosmos. But though it may flout common sense, quantum theory works spectacularly well—and not just as a mathematical description of the universe. Quantum phenomena lie at the heart of many of the technologies that have transformed modern life.
“If quantum mechanics suddenly went on strike,” Max Tegmark of the Massachusetts Institute of Technology explains in “Quantum Leap,” “every single machine that we have in the U.S., almost, would stop functioning.”
That may seem hard to believe. We are billions of trillions of times bigger than electrons, after all. Why should the bizarre laws that rule the quantum realm affect us?
You can see the answer for yourself if you crack the case of most any machine in your home or workplace. You probably won’t have to dig too deep to find microchips inside it. Examine them under magnification, observes Allan Adams, a theoretical physicist at M.I.T., and you’ll see they rely on diodes, transistors, and other components “that form the basis of information technology, the basis of daily life in all sorts of ways. And why do they work? They work because of quantum mechanics.”
Electrons and other subatomic particles are constrained by quantum rules. For instance, they are restricted to just two kinds of spin and to a distinct set of energy levels, limitations that don’t apply to macroscopic matter. But they also have special quantum powers, such as the ability to tunnel, ghost-like, through thin solid walls. Engineers have found myriad useful applications that exploit these constraints and powers.
My nine-year-old son liked the NOVA episode on the quantum realm so much that he watched it twice, but when I told him that we are surrounded by quantum-powered technology, he was skeptical. “Point to any machine you can see,” I challenged him, as we stood in our family room.
His first selection was a glowing ornament hanging on our Christmas tree. “Aha,” I said, feeling vindicated. “See those little green lights? Those are LEDs—light-emitting diodes—that make light by passing electrons through a semiconductor material that has some extra ingredients mixed into it. As the electrons move from one side of the semiconductor to the other, they drop into a lower energy level and spit out a photon of light. The color of the light corresponds to the amount of energy the electrons lose.”
“So how do you know what color the light will be?” he asked.
“That’s what quantum mechanics is all about: The electrons can gain and lose energy only in specific amounts—’quanta’—so the light can’t take on just any old color. It always has the color that corresponds to the gap between those energy levels.”
“OK, hmm,” he said, spinning around. He pointed at our printer.
“Yep, that’s got quantum technology in it, too,” I said. The control screen on the device is backlit—just like the screens on laptops and smartphones—by a cold cathode lamp, a thin kind of fluorescent bulb. High-voltage electrons bombard mercury gas inside the tube, which then releases photons of ultraviolet light. But that isn’t very useful for illumination, because human eyes can’t perceive ultraviolet colors. So the tube is coated with a mixture of phosphors made from alkaline and rare earth elements, such as strontium, yttrium, and europium. Thanks to quantum mechanical interactions among the molecules in these phosphors, electrons change energy levels and give off visible photons when stimulated by ultraviolet light. So when the printer turns on, it comes to life with a friendly glow to its touchscreen.
And as I thought about it, I realized that Tegmark was right—most every gadget in my house that was invented since the 1930s dips at least a toe into the quantum realm. Both the solar cells on my yard lights and the electric eye on my garage door opener exploit the photoelectric effect, for example. This phenomena, in which incoming light knocks electrons off their atoms, led Einstein to first postulate that light behaves as if it comes in packets of energy. He called them “energy quanta” in a 1905 paper explaining the effect—work for which he was eventually awarded a Nobel Prize.
“What about this?” my son asked, gesturing to a magnetic marble maze in his play room. I nodded as soon as I saw the wire leading to its control box. Like our toaster, our oven, our thermostat and just about every other electronic thing we own, that toy contains microchips without which it cannot operate. Each microchip, in turn, contains thousands or even millions of transistors and diodes that control the flow of electrons by exploiting the rules of quantum physics that create gaps between bands of energy levels that electrons may take on when they are inside semiconductors.
So if all the quantum mechanical machines should decide to take the day off, I wouldn’t be able to go to work. The garage wouldn’t open, and the car wouldn’t start. Clocks, phones, and appliances of every kind would shut down. Computers would get a double-whammy: their processors would be paralyzed and their hard disk drives would become unreadable, for computers rely on a quantum phenomenon called giant magnetoresistance to register the weak magnetic fields that store data in our ever-smaller devices.
“Well, how about that?” My son was now pointing to a stapler.
“You got me there, kid,” I said. On the day of the quantum mechanics’ strike, I could catch up on my backlog of stapling.
For more examples of how quantum physics is at work in everyday life, I recommend James Kaklios’s excellent book The Amazing Story of Quantum Mechanics (Gotham, 2010).