Trespassing on Einstein's Lawn (34 page)

“Wheeler had a tremendous ability to use physical intuition to guess how things behave. The recognition that there's enormous power in that—that had the biggest influence on me. Wheeler made great discoveries using intuition, though ultimately they had to be tested against the mathematics. In my generation, the person who has been most effective in the Wheeler approach is Stephen Hawking. Out of necessity he was unable to do complex mathematics once he lost the use of his hands, so he functions through enormous physical intuition, plus solving problems geometrically and topologically in his head.”

“Do you have any good stories about Wheeler?” my father asked.

“I'll tell you one,” Thorne offered. “Today there's a lot of discussion in string theory about the idea of the landscape of vacua. The particular version of the laws of quantum fields we have in our universe might be different in other universes.” Wheeler, ahead of his time as always, had thought a lot about this issue, Thorne told us. Wheeler called it “mutability,” the idea that the laws of physics don't exist in some Platonic realm outside the universe, but come into being with the universe at its birth and eventually die with the universe at its death. “In 1971 Wheeler was visiting, and Wheeler, Feynman, and I went to lunch at the Burger Continental restaurant here at Caltech. Wheeler
was talking about this idea of mutability and asking, ‘What determines which laws are in our universe?' Feynman turned to me and said, ‘This guy sounds crazy. But he has
always
sounded crazy.' ”

We all laughed. “What are you working on these days?” I asked.

“I'm exploring ways to be creative in other areas,” Thorne said. “I'm working on two science fiction movies in Hollywood and writing an article for
Playboy.
”

My father chuckled loudly and then, realizing that maybe he shouldn't, cleared his throat, furrowed his brow, and tried to be serious. “What inspired you to make that change?”

“Based on my genetic heritage, I'll probably live into my hundreds,” Thorne said. “But I can't continue doing really great theoretical physics for a long time. I decided that this was the appropriate time to move into directions that I can continue with for a few decades. Also, I'm bored.”

“Well, that was kind of a bummer,” I said, as we walked back toward our hotel.

We had been hoping to get some answers, but all we'd gotten were a few verbal shrugs. Thorne didn't see any profound meaning in the boundary of a boundary; he pretty much said that the idea was useless.

Maybe it was. No matter how intriguing it sounded, there was no guarantee that the phrase held any shining truth. Maybe it was nothing more than the desperate, incoherent cry of an aging physicist who knew he was running out of time, or an aging man who didn't know he was running out of wits. Then again, as Feynman had said, Wheeler had always sounded crazy. And more often than not, he had been right.

“At least he told us about Zurek,” my dad said. “That's useful.”

That was true. Thorne had said that Wojciech Zurek, a physicist at Los Alamos, was the world's best living expert on Wheeler's self-excited circuit.

I nodded. “I guess we're going to New Mexico.”

* * *

We checked in to a Pueblo-style bed-and-breakfast surrounded by white adobe walls and hanging ristras of fire-red chile peppers, then spent the day visiting art galleries on Canyon Road and discussing the nature of reality.

The next morning, we drove forty-five minutes to Los Alamos, winding our way up the mountainside to the Pajarito Plateau, seven thousand feet above sea level, to the “town that never was.” Seven decades earlier the government had overtaken the mesa and set up Los Alamos National Laboratory as the top-secret headquarters for the Manhattan Project. Physicists from around the country had left their respective universities and come here to build the atomic bomb in the hopes of putting an end to World War II. Wheeler, who had first developed the theoretical underpinnings of the bomb in his work on nuclear fission with Bohr, was stationed in Hanford, Washington, at the time, working on a nuclear reactor that fed plutonium to Los Alamos. He would come to New Mexico now and then to work and to discuss electrodynamics with Feynman.

In 1944, at the start of his time in Hanford, Wheeler received a postcard from his younger brother, Joe, who was fighting on the front lines in Italy. It contained only two words:
Hurry up.
But it wasn't until the following July, nearly a year after Joe had been killed, that the Manhattan Project completed construction of the bomb. Some two hundred miles south of Los Alamos, in the Jornada del Muerto desert, they tested their plutonium “gadget,” detonating the first nuclear bomb in history. The physicists watched the Trinity explosion from the safety of a base camp ten miles away as the bomb produced a blinding light, intense heat, grumbling shock waves, and a mushroom cloud that swelled more than seven miles overhead, turning one thousand feet of desert sand below to glass. J. Robert Oppenheimer, the lab's director, solemnly quoted the
Bhagavad Gita:
“Now I am become Death, the destroyer of worlds.”

While his fellow physicists were still reeling from the horrors wrought by their involvement with the bomb, Wheeler was living with the guilt of his brother's death and the regret of not having gotten the job done quicker.
“It does little good to second-guess history,” he wrote
in 1998. “But I cannot avoid reflecting on my own role. I could have understood the gravity of the German threat sooner than I did. I could—probably—have influenced the decision makers if I had tried. For more than fifty years I have lived with the fact of my brother's death. I cannot easily untangle all of the influences of that event on my life, but one is clear: my obligation to accept government service when called upon to render it.” So in 1950, when he was asked to work on the hydrogen bomb, Wheeler agreed. He moved here, to Los Alamos, and lived for one year in Oppenheimer's former home.

Driving across the mesa, I found it strange to be steeped in all that tragic history. Strange to think that obscure, abstract ideas like relativity and quantum mechanics—ideas that my father and I had been discussing for more than ten years as nothing more tangible than intellectual puzzles—had such unimaginably real consequences. Not real as in invariant and observer-independent. Real as in blood and fire and grief.

We found our way to the residential neighborhood where Zurek lived. Zurek was a major figure in the science of quantum information. With Bill Wootters, another student of Wheeler's, Zurek had proven what's known as the no-cloning theorem, which says that an unmeasured bit of quantum information can never be perfectly copied. He had also made crucial inroads to understanding the process known as quantum decoherence, which helps explain why the everyday, macroscopic world doesn't seem all that quantum.

Even though you can pretend, as Bohr and his Copenhagen crew did, to draw a distinction between observer and observed, calling half of the world “macroscopic” or “classical” and the other half “microscopic” or “quantum,” you can always push the boundary to larger and larger scales, the observer becoming the observed, the outside engulfed by the inside, the classical swallowed up by the growing gulp of the quantum. Why, then, don't we see the remnants of superpositions—those stripes of interference that show up in the double-slit experiment—when we measure the length of a couch or the height of a child or the position of the Moon? Why, in the world of big stuff, do classical probabilities, which assume that something always has only
one position or another, work so well even though things ought to be described by quantum probabilities, which assume that things are suspended in multiple states simultaneously before we measure them?

The answer, thanks largely to Zurek, is decoherence. The idea was simple enough. Interference patterns form when the wavefunctions describing the two possible states of a system—say, the component of a wavefunction that says an electron went through slit A and the component of a wavefunction that says the electron went through slit B—add together. As the photographic plate registers one electron after the next, each lands at a random spot allowed by the probability distribution encoded in the summed wave, the superposition. The resulting pattern of stripes depends on the relative phases of the waves: dark bands appear where the waves are out of phase and cancel out, the bright bands where they are in phase and amplify. Because the phase difference between the waves remains fixed electron after electron, the superposition is coherent. If, however, the electrons are immersed in a larger environment, like air, they'll end up getting knocked around by the billions of molecules bouncing around as they travel from the slits to the photographic plate. Each time an electron is fired through the slits, its path is thrown off course and the relative phase difference between the two components of its wavefunctions changes from one detection to the next. As the electrons build up on the plate, there's no single, coherent superposition to encode the kind of probabilities that would produce light and dark stripes. Instead, the measurements reflect the probabilities of each individual wavefunction—the exact probabilities you'd expect if the particle were traveling through only a single slit at a time, and not through both simultaneously. The kind of probabilities you'd expect if the particle
wasn't quantum.

By smearing out the coherence of superpositions and rendering quantum probability distributions classical, environmental decoherence makes it look like quantum wavefunctions collapse, transforming hosts of possibilities into single actualities. In reality, the wavefunctions haven't collapsed at all. In reality, the electron gets entangled with every air molecule it hits, its wavefunction superposing with the wavefunction of each molecule. In reality, things are getting
more
quantum.
We just don't notice because we're not measuring the air molecules. If we measured not only the electrons and the detector but also the larger environment, we'd see more bat-shit interference than ever.

Wojciech Zurek and me in Los Alamos, New Mexico
W. Gefter

Zurek greeted us at the door. He was warm and wild-looking, with bushy orange hair, an equally full beard, and a thick Polish accent. We followed him into a large living room, which had a stylish southwestern flair—a stone hearth framed a fireplace at one end of the room, and at the other, floor-to-ceiling windows showcased a sweeping panoramic view of the mountains and the canyons below.

“How did you get to know Wheeler?” I asked as the three of us settled onto the couches.

“I became a graduate student at the University of Texas in 1975 and John Wheeler arrived there a year later,” Zurek said. “I took his class on electrodynamics. One thing that made a lasting impression on me was when John tried to derive something on the board. Sometimes it didn't work and instead of being apologetic he would cross out the attempted derivation and write ‘wrong' in big letters. That freedom to go the wrong way was one of the most important lessons I learned from
him. A year or two later I took his seminar on quantum measurement. There were wild ideas being explored, but also being torn apart. It was like writing ‘wrong.' You can explore wild ideas, but at some point you have to evaluate them honestly. After that, I was thoroughly hooked on Wheeler's way of doing physics and on quantum mechanics. Not just quantum mechanics—something broader. The fascinating thing that comes through in quantum measurement, but is bigger than that, is understanding how we, as observers, as beings that are alive, fit in the universe. How does our existence fit in with physical laws?”

“A lot of your work since then has been focused on understanding how the classical world emerges from the quantum,” I said.

“The superposition principle tells you that if you have two quantum states you can put them together into new states in any proportions,” said Zurek. “Before decoherence, every state—every superposition of every superposition—is legal. And yet the Moon is in one place; cats are either alive or dead. As Einstein pointed out, quantum mechanics of closed systems doesn't provide a reason for that. Decoherence does.”

“Recently you proposed a theory you call quantum Darwinism,” I prompted. I had seen some mention of it in my research but wasn't sure what it was all about.

“Quantum Darwinism goes beyond decoherence. It recognizes that we don't measure anything directly,” Zurek said. “We just find out stuff from the environment. Right now you are looking at me. We are a couple of meters apart. The only reason you know where I am and what I look like is because you intercept a tiny fraction of photons—of the photon environment—that scattered from me. It's clear that there are many more copies of that very same information about me all over the place. For decoherence it's enough that the environment poses a question once. But in real life the environment is boringly asking the same darn question and disseminating the same boring answer all over the place. We grab a small piece of the environment and find out.”