What makes science science? The pious answers are: its ceaseless curiosity in the face of mystery, its keen edge of experimental objectivity, its endless accumulation of new data, and the cool machines it uses. We stare, the scientists see; we gawk, they gaze. We guess; they know.
The defense of science against this claim turns out to be complicated, for the simple reason that, as a social activity, science is vulnerable to all the comedy inherent in any social activity: group thinking, self-pleasing, and running down the competition in order to get the customer’s (or, in this case, the government’s) cash. Books about the history of science should therefore be about both science and scientists, about the things they found and the way they found them. A good science writer has to show us the fallible men and women who made the theory, and then show us why, after the human foibles are boiled off, the theory remains reliable.
No well-tested scientific concept is more astonishing than the one that gives its name to a new book by the Scientific American contributing editor George Musser, “Spooky Action at a Distance” (Scientific American/Farrar, Straus & Giroux). The ostensible subject is the mechanics of quantum entanglement; the actual subject is the entanglement of its observers. Musser presents the hard-to-grasp physics of “non-locality,” and his question isn’t so much how this weird thing can be true as why, given that this weird thing had been known about for so long, so many scientists were so reluctant to confront it. What keeps a scientific truth from spreading?
The story dates to the early decades of quantum theory, in the nineteen-twenties and thirties, when Albert Einstein was holding out against the “probabilistic” views about the identity of particles and waves held by a younger generation of theoretical physicists. He created what he thought of as a reductio ad absurdum. Suppose, he said, that particles like photons and electrons really do act like waves, as the new interpretations insisted, and that, as they also insisted, their properties can be determined only as they are being measured. Then, he pointed out, something else would have to be true: particles that were part of a single wave function would be permanently “entangled,” no matter how far from each other they migrated. If you have a box full of photons governed by one wave function, and one escapes, the escapee remains entangled in the fate of the particles it left behind—like the outer edges of the ripples spreading from a pebble thrown into a pond. An entangled particle, measured here in the Milky Way, would have to show the same spin—or the opposite spin, depending—or momentum as its partner, conjoined millions of light-years away, when measured at the same time. Like Paul Simon and Art Garfunkel, no matter how far they spread apart they would still be helplessly conjoined. Einstein’s point was that such a phenomenon could only mean that the particles were somehow communicating with each other instantaneously, at a speed faster than light, violating the laws of nature. This was what he condemned as “spooky action at a distance.”
John Donne, thou shouldst be living at this hour! One can only imagine what the science-loving Metaphysical poet would have made of a metaphor that had two lovers spinning in unison no matter how far apart they were. But Musser has a nice, if less exalted, analogy for the event: it is as if two magic coins, flipped at different corners of the cosmos, always came up heads or tails together. (The spooky action takes place only in the context of simultaneous measurement. The particles share states, but they don’t send signals.)
What started out as a reductio ad absurdum became proof that the cosmos is in certain ways absurd. What began as a bug became a feature and is now a fact. Musser takes us into the lab of the Colgate professor Enrique Galvez, who has constructed a simple apparatus that allows him to entangle photons and then show that “the photons are behaving like a pair of magic coins. . . .They are not in contact, and no known force links them, yet they act as one.” With near-quantum serendipity, the publication of Musser’s book has coincided with news of another breakthrough experiment, in which scientists at Delft University measured two hundred and forty-five pairs of entangled electrons and confirmed the phenomenon with greater rigor than before. The certainty that spooky action at a distance takes place, Musser says, challenges the very notion of “locality,” our intuitive sense that some stuff happens only here, and some stuff over there. What’s happening isn’t really spooky action at a distance; it’s spooky distance, revealed through an action.
Why, then, did Einstein’s question get excluded for so long from reputable theoretical physics? The reasons, unfolding through generations of physicists, have several notable social aspects, worthy of Trollope’s studies of how private feuds affect public decisions. Musser tells us that fashion, temperament, zeitgeist, and sheer tenacity affected the debate, along with evidence and argument. The “indeterminacy” of the atom was, for younger European physicists, “a lesson of modernity, an antidote to a misplaced Enlightenment trust in reason, which German intellectuals in the 1920’s widely held responsible for their country’s defeat in the First World War.” The tonal and temperamental difference between the scientists was as great as the evidence they called on.
Musser tracks the action at the “Solvay” meetings, scientific conferences held at an institute in Brussels in the twenties. (Ernest Solvay was a rich Belgian chemist with a taste for high science.) Einstein and Niels Bohr met and argued over breakfast and dinner there, talking past each other more than to each other. Musser writes, “Bohr punted on Einstein’s central concern about links between distant locations in space,” preferring to focus on the disputes about probability and randomness in nature. As Musser says, the “indeterminacy” questions of whether what you measured was actually indefinite or just unknowable until you measured it was an important point, but not this important point.
Musser explains that the big issue was settled mainly by being pushed aside. Generational imperatives trumped evidentiary ones. The things that made Einstein the lovable genius of popular imagination were also the things that made him an easy object of condescension. The hot younger theorists patronized him, one of Bohr’s colleagues sneering that if a student had raised Einstein’s objections “I would have considered him quite intelligent and promising.”
There was never a decisive debate, never a hallowed crucial experiment, never even a winning argument to settle the case, with one physicist admitting, “Most physicists (including me) accept that Bohr won the debate, although like most physicists I am hard pressed to put into words just how it was done.” Arguing about non-locality went out of fashion, in this account, almost the way “Rock Around the Clock” displaced Sinatra from the top of the charts.
The same pattern of avoidance and talking-past and taking on the temper of the times turns up in the contemporary science that has returned to the possibility of non-locality. Musser notes that Geoffrey Chew’s attack on the notion of underlying laws in physics “was radical, and radicalism went over well in ’60’s-era Berkeley.” The British mathematician Roger Penrose’s assaults on string theory in the nineties were intriguing but too intemperate and too inconclusive for the room: “Penrose didn’t help his cause with his outspoken skepticism. . . . Valid though his critiques might have been, they weren’t calculated to endear him to his colleagues.”
Indeed, Musser, though committed to empirical explanation, suggests that the revival of “non-locality” as a topic in physics may be due to our finding the metaphor of non-locality ever more palatable: “Modern communications technology may not technically be non-local but it sure feels that it is.” Living among distant connections, where what happens in Bangalore happens in Boston, we are more receptive to the idea of such a strange order in the universe. Musser sums it up in an enviable aphorism: “If poetry is emotion recollected in tranquility, then science is tranquility recollected in emotion.” The seemingly neutral order of the natural world becomes the sounding board for every passionate feeling the physicist possesses.