What Is Quantum Mechanics Good for?

Scientific American's John Matson interviewed physicist James Kakalios, author of The Amazing Story of Quantum Mechanics, who wants people to know what quantum physics has done for them lately — and why it shouldn't take the rap for New Age self-realization hokum such as The Secret.

What could be weirder than quantum mechanics? This physics framework is responsible for any number of bizarre phenomena—theoretical cats that are simultaneously dead and alive, particles kilometers apart that can nonetheless communicate instantaneously, and indecisive photons that somehow go two directions at once.

But it is also responsible for the technological advances that make modern life possible. Without quantum mechanics there would be no transistor, and hence no personal computer; no laser, and hence no Blu-ray players. James Kakalios, a physics professor at the University of Minnesota, wants people to understand how much quantum mechanics influences our everyday lives—but to do so people must first understand quantum mechanics.

Kakalios sets out to tackle both tasks in The Amazing Story of Quantum Mechanics (Gotham Books, 2010), an accessible, mostly math-free treatment of one of the most complex topics in science. To keep things lively, the author intersperses illustrations and analogies from Buck Rogers stories and other classic science fiction tales. We spoke to Kakalios about his new book, what quantum mechanics has made possible, and how early sci-fi visions of the future compare with the present as we know it.

[An edited transcript of the interview follows.]

Is the purpose of this book to expose this world of quantum mechanics that people find so mysterious and point out that it's everywhere?

That's right. In fact, the introduction is called, "Quantum physics? You're soaking in it!"

There are many excellent books about the history and the philosophical underpinnings of quantum mechanics. But there didn't seem to be many that talked about how useful quantum mechanics is. Yes, the science has weird ideas and it can be confusing. But one of the most amazing things about quantum mechanics is that you can use it correctly and productively even if you're confused by it.

I present in the introduction what I call a "workingman's view" of quantum mechanics and show how if you accept on faith three weird ideas—that light is a photon; that matter has a wavelength nature associated with its motion; and that everything, light and matter, has an intrinsic angular momentum or spin that can only have discrete values—it turns out that you can then see how lasers work. You can see how a transistor works or your computer hard drive or magnetic resonance imaging—a host of technologies that we take for granted that pretty much define our life.

There were computers before the transistor; they used vacuum tubes as logic elements. To make a more powerful computer meant that you had to have more vacuum tubes. They were big, they generated a lot of heat, they were fragile. You had to make the room and the computer very large. And so if you used vacuum tubes, only the government and a few large corporations would have the most powerful computers. You wouldn't have millions of them across the country. There would be no reason to hook them all together into an Internet, and there would be no World Wide Web.

The beautiful aspect to this is the scientists who developed this were not trying to make a cell phone; they were not trying to invent a CD player. If you went to Schrödinger in 1926 and said, "Nice equation, Erwin. What's it good for?" He's not going to say, "Well, if you want to store music in a compact digital format..."

But without the curiosity-driven understanding of how atoms behave, how they interact with each other, and how they interact with light, the world we live in would be profoundly different.

So, to take one example, how does quantum mechanics make the laser possible?

One of the most basic consequences of quantum mechanics is that there is a wave associated with the motion of all matter, including electrons in an atom. Schrödinger came up with an equation that said: "You tell me the forces acting on the electron, and I can tell you what its wave is doing at any point in space and time." And Max Born said that by manipulating this wave function that Schrödinger developed, you could tell the probability of finding the electron at any point in space and time. From that, it turns out that the electron can only have certain discrete energies inside an atom. This had been discovered experimentally; this is the source of the famous line spectrum that atoms exhibit and that accounts for why neon lights are red whereas sodium streetlights have a yellow tinge. It has to do with the line spectra of their respective elements.

But to have an actual understanding of where these discrete energies come from—that electrons and atoms can only have certain energies and no other—is one of the most amazing things about quantum mechanics. It's as though you are driving a car on a racetrack and you are only allowed to go in multiples of 10 miles per hour. When you take that and you bring many atoms together, all of those energies broaden out into a band of possible energies.

The analogy that I use is you have an auditorium with an orchestra below and a balcony above. That means to go from the orchestra to the balcony you have to absorb some energy to be promoted from the orchestra to the balcony. Now if every seat in the orchestra is filled, and you want to move from one seat to another, you can't go anywhere unless you absorb some energy and are promoted up into the balcony, where there are empty seats and you can move around. What happens in a laser is you have a little mezzanine right below the balcony. You get promoted up to the balcony but then you fall and you sit in the mezzanine. And eventually, as the mezzanine gets filled up, there's a bunch of empty seats in the orchestra, where you came from.

One person gets pushed out of the mezzanine, and because of the way they talk to each other, they all go at the same time. They release energy as they fall back from the mezzanine into the orchestra, and that energy is in the form of light. Because they are all coming from the same row of seats in the mezzanine, all the light has exactly the same color. Since they all went at the same time, they are all coherently in phase. And if you have a lot of them up in the mezzanine, you can have a very high intensity beam of single-color light. That's a laser.

And just as Schrödinger couldn't have had any idea about what his equation would be used for, the same could be said of the laser, which now allows us to have CDs and DVDs and a lot of other things.

The same goes for the transistor. It was first developed to amplify radio signals, and you had transistor radios that replaced the vacuum tubes that were being used. Now they are also used as logic elements, 1s and 0s. If you apply a voltage to a transistor you can basically open or close a gate and allow electrons to flow through or make it very difficult for electrons to flow. And so you have two different current states, high and low, that you can call a 1 or a 0. You can combine them in clever ways to do logic operations with the 1s and 0s. You can encode information. You can develop a language of the 1s and 0s and manipulate them that way.

And again, I don't think that was the first thought of the people that developed the transistor. Look at all the things that it has brought out. There are probably more transistors in a standard hospital than there are stars in the Milky Way Galaxy, when you think about all the computers and all the electronic devices that we use just for medical applications. So it really has transformed life in a very profound way.

The real superheroes of science are a small handful of people who knew they were changing physics, but I don't think they recognized that they were also changing the future.

One of the ways you keep this book lively and accessible is to use anecdotes from early science fiction. How well have those predictions held up?

The main problem is that they believed that there was going to be a revolution in energy, which would lead to jet packs, death rays and flying cars. But what we got was a revolution in information. This information age, of course, came about because of semiconductors and solid-state physics, which were enabled by quantum mechanics.

A lot of these things go back to transistors and semiconductors. Is that in your view the biggest fundamental leap that quantum mechanics allowed us to make?

More than that, even. By discerning what were the fundamental rules that govern how atoms interact with each other and how they interact with light, you also have now a fundamental understanding of chemistry. There is a reason why the atoms are arranged the way they are in the periodic table of the elements, and it comes out naturally from the Schrödinger equation when you add in the Pauli exclusion principle. There is a really deep appreciation for why the world is the way it is.

Can you imagine living in a world before quantum mechanics?

We take all these things for granted. It's like the Louis C. K. YouTube clip—everything is amazing and nobody is happy.

"Quantum" is thrown around a lot as a label for things we don't understand, and we often lump a number of phenomena into the vague category of "quantum weirdness". Is that something that you'd like to see dissipate?

I would. It's used too much as a catchall. Proposing weird and counterintuitive ideas to explain observations, developing the consequences of these ideas and testing them further, and then, if they conform with reality, accepting them is not unique to quantum mechanics. It's what we call physics.

Also, because it has a reputation for weirdness, quantum mechanics is used too much as a justification for things that have nothing to do with quantum mechanics. There is an expression, "quantum woo," where people take a personal philosophy, such as the power of positive thinking or let a smile be your umbrella, and somehow affix quantum mechanics to it to try to make it sound scientific.

And make a lot of money doing so.

Yeah. It kind of seems to me to be at the same level as using mathematical knot theory or topology to justify crossing your fingers when you're making a wish. It has about as much relevance and justification.

--Originally published: Scientific American Online, November 2, 2010