Spooky Action at a Distance Read online

  Begin Reading

  Table of Contents

  About the Author

  Copyright Page

  Thank you for buying this

  Farrar, Straus and Giroux ebook.

  To receive special offers, bonus content,

  and info on new releases and other great reads,

  sign up for our newsletters.

  Or visit us online at

  us.macmillan.com/newslettersignup

  For email updates on the author, click here.

  The author and publisher have provided this e-book to you for your personal use only. You may not make this e-book publicly available in any way. Copyright infringement is against the law. If you believe the copy of this e-book you are reading infringes on the author’s copyright, please notify the publisher at: us.macmillanusa.com/piracy.

  For Talia and Eliana

  Introduction: Einstein’s Castle in the Air

  When I first learned about nonlocality as a graduate student in the early 1990s, it wasn’t from my quantum-mechanics professor: he didn’t see fit to so much as mention it. Browsing a local bookshop, I picked up a newly published book, The Conscious Universe, which startled me with its claim that “no previous discovery has posed more challenges to our sense of everyday reality” than nonlocality. The phenomenon had the taste of forbidden fruit.

  In everyday speech, “locality” is a slightly pretentious word for a neighborhood, town, or other place. But its original meaning, dating to the seventeenth century, is about the very concept of “place.” It means that everything has a place. You can always point to an object and say, “Here it is.” If you can’t, that thing must not really exist. If your teacher asks where your homework is and you say it isn’t anywhere, you have some explaining to do.

  The world we experience possesses all the qualities of locality. We have a strong sense of place and of the relations among places. We feel the pain of separation from those we love and the impotence of being too far away from something we want to affect. And yet quantum mechanics and other branches of physics now suggest that, at a deeper level, there may be no such thing as place and no such thing as distance. Physics experiments can bind the fate of two particles together, so that they behave like a pair of magic coins: if you flip them, each will land on heads or tails—but always on the same side as its partner. They act in a coordinated way even though no force passes through the space between them. Those particles might zip off to opposite sides of the universe, and still they act in unison. These particles violate locality. They transcend space.

  Evidently nature has struck a peculiar and delicate balance: under most circumstances it obeys locality, and it must obey locality if we are to exist, yet it drops hints of being nonlocal at its foundations. That tension is what I’ll explore in this book. For those who study it, nonlocality is the mother of all physics riddles, implicated in a broad cross section of the mysteries that physicists confront these days: not just the weirdness of quantum particles, but also the fate of black holes, the origin of the cosmos, and the essential unity of nature.

  For Albert Einstein, locality was one aspect of a broader philosophical puzzle: Why are we humans able to do science at all? Why is the world such that we can make sense of it? In a famous essay in 1936, Einstein wrote that the most incomprehensible thing about the universe is that it is comprehensible. At first glance, this statement itself seems incomprehensible. The universe is not a conspicuously rational place. It is wild and capricious, full of misdirection and arbitrariness, injustice and misfortune. Much of what happens defies reason (especially when romance or driving is involved). Yet against this backdrop of inexplicable happenings, the world’s rules glow with reassuring regularity. The sun rises in the east. Things fall when you drop them. After the rain comes a rainbow. People go into physics out of a conviction that these are not just gratifying exceptions to the anarchy of life, but glimpses of an underlying order.

  Einstein’s point was that physicists really had no right to expect that. The world needn’t have been orderly at all. It didn’t have to abide by laws; under other circumstances, it might have been anarchic all the way down. When a friend wrote to ask Einstein what he’d meant by the comprehensibility remark, he wrote back, “A priori one should expect a chaotic world which cannot be grasped by the mind in any way.”

  Although Einstein said comprehensibility was a “miracle” we shall never understand, that didn’t stop him from trying. He spent his entire professional life articulating exactly what it is about the universe that makes it make sense, and his thinking set the course of modern physics. He recognized, for example, that the inner workings of nature are highly symmetrical, looking the same if you view the world from a different angle. Symmetry brings order to the bewildering zoo of particles that physicists have found; entire species of particles are, in a sense, mirror images of one another. But among all the properties of the world that give us hope for understanding it, Einstein kept coming back to locality as the most important.

  Locality is a subtle concept that can mean different things to different people. For Einstein, it had two aspects. The first he called “separability,” which says that you can separate any two objects or parts of an object and consider each on its own, at least in principle. You can take your dining chairs and put each one in a different corner of the room. They will not cease to exist or lose any of their features—size, style, cushiness. The entire dining-room set derives its properties from the chairs that make it up; if each chair can seat one person, a set of four chairs can seat four people. The whole is the sum of its parts. The second aspect that Einstein identified is known as “local action,” which says that objects interact only by banging into one another or recruiting some middleman to bridge the gap between them. Whenever a distance separates us from someone, we know we cannot have any effect on that person unless we cross the distance and touch, talk to, punch—somehow, make direct contact with—that person, or send someone or something to do it for us. Modern technology does not evade this principle; it merely recruits new intermediaries. A phone translates sound waves into electrical signals or radio waves that travel through wires or open space and then get translated back into sound on the other end. At every step of the way, something has to make direct contact with something else. If there is even a hairline crack in the wire, the message gets as far as a scream on an airless moon. Simply put, separability defines what objects are, and local action dictates what they do.

  Einstein captured these principles in his theory of relativity. Specifically, relativity theory says that no material thing can move faster than light. Without such an ultimate speed limit, objects might move infinitely fast and distance would lose its meaning. All the forces of nature must wend their way laboriously through space, rather than leap across it in a single bound, as physicists used to suppose. Relativity theory thereby provides a measure of isolation among separated objects and ensures their mutual distinctness.

  Depending on your frame of mind, relativity theory and the other laws of physics are either a satisfying deep order to the universe or a series of killjoy rules, like an authoritarian parent trying to take all the fun out of life. How great it would be to flap our arms and fly—but sorry, no can do. We could solve the world’s problems by creating energy—oh, physics won’t allow that, either; we can only convert one form of energy into another. And now comes locality, yet another draconian diktat, to spoil our dreams of faster-than-light starships and psychic powers. Locality dashes sports fans’ eternal hope that, by crossing their fingers or bellowing some insightful comment from their armchairs, they might give their team an edge on the playing field. Unfortunately, if your team is losing and you’re serious
about wanting to help, you’ll have to get up and go to the stadium.

  Yet locality is for our own good. It grounds our sense of self, our confidence that our thoughts and feelings are our own. With all due respect to John Donne, every man is an island, entire of himself. We are insulated from one another by seas of space, and we should be grateful for it. Were it not for locality, the world would be magical—and not in a happy, Disneyesque way. As much as sports fans may wish they could sway the game from their living rooms, they should be careful what they wish for, because supporters of the opposing team would presumably have this power, too. Millions of couch potatoes across the land would strain to give their side some advantage, making the game itself meaningless—a contest of fans’ wills rather than of talent on the field. Not just sports games, but the entire world would become hostile to us. In a world without locality, objects outside your body could reach inside without having to pass through your skin, and your body would lose its ability to control its internal condition. You would blend into your environment. And that is the very definition of death.

  * * *

  By focusing on locality as a crucial prerequisite to comprehending nature, Einstein crystallized two thousand years of philosophical and scientific thought. For ancient Greek thinkers such as Aristotle and Democritus, locality made rational explanation possible. When objects can affect one another only by making direct contact, you can explain any event by giving a blow-by-blow account of “this hit that, which in turn knocked into that, which in turn bounced off some other thing.” Every effect has a cause linked to it by a chain of events unbroken in space and time. There’s no point at which you have to wave your hands and mumble, “Then a miracle occurs.” It wasn’t the miracle the Greek philosophers objected to—they weren’t atheists—so much as the mumbling. Even gods, they felt, should exert their power by clear and explicable rules. Locality is essential not just to the types of explanations that philosophers and scientists seek, but to the methods they use. They can isolate objects from one another, grasp them one at a time, and build up a picture of the world step by step. They are not faced with the impossible task of taking it all in at once.

  In 1948, toward the end of his life, Einstein summarized the importance of locality in a short essay: “The concepts of physics refer to a real external world … things that claim a ‘real existence’ independent of the perceiving subject … These things claim an existence independent of one another, insofar as these things ‘lie in different parts of space.’ Without such an assumption of the mutually independent existence … of spatially distant things, an assumption that originates in everyday thought, physical thought in the sense familiar to us would not be possible. Nor does one see how physical laws could be formulated and tested without such a clean separation.”

  Locality has such a pervasive importance because it is the essence of what space is. By “space” I don’t just mean “outer space,” the realm of astronauts and asteroids, but the space between us and all around us, the space that our bodies and everything else occupy, the space through which we swing a baseball bat or stretch a measuring tape. Whether you point your telescope at the planets or at the next-door neighbors, you are peering across space. For me, the beauty of a landscape comes from the giddy sense of spanning space, a sort of horizontal vertigo when you realize the little dots on the other side of a valley really are there and that you could touch them if only your arm were long enough.

  As painters have long recognized, space is not mere absence, but a thing in its own right. What comes between objects on a canvas is as important to a composition as the objects themselves. For a physicist, space is the canvas of physical reality. Almost every attribute of our physical selves is spatial. We occupy a place. We have a shape. We move. Our bodies are intricate choreographies of cells and fluids dancing in space. Our thoughts are impulses zapping along pathways in space. Every interaction we have with the rest of the world passes through space. Living things are things, and what is a thing but a part of the universe that acquires an individual identity by virtue of occupying a certain volume of space?

  Physics is rooted in the study of how things move through space, and space defines practically every quantity that physics deals in: distance, size, shape, position, speed, direction. Other qualities of the world may not appear spatial, but are; color, for example, corresponds to the size of a light wave. Only a very few properties of matter have no known spatial explanation, such as electric charge, and even these betray themselves by deflecting motion through space. When we look at an object, everything about it is ultimately spatial, arising from how its particles are arranged; the particles themselves are the barest flecks. Function follows form. Even nonspatial concepts become spatial in physicists’ minds; time becomes an axis on a graph, and the laws of nature operate within abstract spaces of possibility. No less an authority than Immanuel Kant, whose ideas were a major influence on Einstein, thought it impossible to conceive of the world without space.

  * * *

  What a twist of fate that the greatest champion of locality was also its undoer. Though best known to the wider world for relativity theory, Einstein actually won his Nobel for cofounding quantum mechanics, the theory that describes how atoms and subatomic particles behave. Actually, physicists think quantum mechanics describes how everything behaves, although its distinctive effects are strongest on tiny scales. The theory grew out of Einstein’s and his contemporaries’ epiphany that atoms and particles can’t just be littler versions of the things we see around us. If they were—if they acted according to the classical laws of physics developed by Isaac Newton and others—the world would self-destruct. Atoms would implode; particles would explode; lightbulbs would fry you with deadly radiation. The fact we’re still alive means that matter must be governed by some new set of laws. Einstein welcomed the strangeness; in fact, despite the (unfair) reputation he later acquired as a rearguard defender of classical physics, he was consistently ahead of everyone else in appreciating the alien features of the quantum world.

  Among those features was nonlocality. Quantum mechanics predicts that two particles can become blood brothers. For want of a mechanism to couple them, the particles should be completely autonomous, yet to touch one is to touch the other, as if distance meant nothing to them. The scientific method of divide and conquer fails for them. The particles have joint properties that escape you if you view them one at a time; you must measure the particles together. Our world is crisscrossed by a web of these seemingly mystical relationships. Atoms in your body retain a bond with every person you have loved—which sounds romantic until you realize that you’re also linked to every weirdo who brushed against you while walking down the street.

  Particles on opposite sides of the universe can’t really be connected, can they? The idea struck Einstein as silly, a regression to prescientific notions of sorcery. Any theory that implied such “spooky actions at a distance,” he reasoned, had to be missing something. He figured that the world was in fact local and merely gave the impression of being nonlocal, and he sought a deeper theory that would lay bare the hidden mechanism whereby two particles can act in unison. Try as he might, though, Einstein could never find such a theory, and he recognized that he might be the one who was missing something. There might be no concealed clockwork. The principle of locality—and with it, our conception of space—might not hold. A few months before he died, Einstein reflected on what the dissolution of space might mean for our understanding of the world: “Then nothing will remain of my whole castle in the air including the theory of gravitation, but also nothing of the rest of contemporary physics.”

  What was really spooky was how sanguine most of his contemporaries were. To them, nonlocality was a nonissue. The reasons for their dismissive attitude were complicated and are still debated by historians, but perhaps the most charitable explanation is pragmatism. The questions that vexed Einstein just didn’t seem relevant to the practical applications of quantum theory. Onl
y in the 1960s did a new generation of physicists and philosophers give Einstein’s worries a real hearing. The experiments they did suggested that nonlocality was not a theoretical curiosity, but a fact of life. And even then, most of their colleagues gave it little thought—which is why I practically had to stumble on the topic as a grad student.

  In the past twenty years, though, I’ve witnessed a remarkable evolution in attitudes. Nonlocality has surged into the currents of mainstream physics and swept far past the phenomenon that Einstein discovered. In my career as a science writer and editor, I have had the privilege of talking to scientists from a wide range of communities—people who study everything from subatomic particles to black holes to the grand structure of the cosmos. Over and over, I heard some variant of: “Well, it’s weird, and I wouldn’t have believed it if I hadn’t seen it for myself, but it looks like the world has just got to be nonlocal.” Researchers were like those matching particles on opposite sides of the universe, often not even knowing of one another, yet reaching the same conclusions.

  If Einstein thought nonlocality smacked of sorcery, does the new research lend credence to paranormal claims? Some have thought so. In past decades, a number of scientists speculated that nonlocal links between particles could endow you with psychic powers. For instance, if particles in your brain were entangled with particles in your friend’s, perhaps the two of you could communicate telepathically. At the other extreme, the supernatural intimations of nonlocality have been cause for many physicists to dismiss the whole area of research as hooey. In fact, there’s no connection. None of the evidence for ESP has ever stood up, and the types of nonlocal phenomena under discussion are too subtle to meld minds or sway distant baseball games.

  Some people are disappointed by that. They shouldn’t be. The real magic of the world is that it isn’t magical. For the reasons I discussed earlier, locality is a precondition for our existence. Any nonlocality must remain safely tucked away, emerging only under certain conditions, or else our universe would be inimical to life. What nonlocality gives us is much more impressive than any paranormal phenomenon: a window into the true nature of physical reality. If influences can leap across space as though it weren’t really there, the natural conclusion is: space isn’t really there. The Columbia University string theorist Brian Greene wrote in his 2003 book, The Fabric of the Cosmos, that nonlocal connections “show us, fundamentally, that space is not what we once thought it was.” Well, what is it, then? Investigating nonlocality may clue us in. Many physicists now think that space and time are doomed—not fundamental elements of nature, but products of some primeval condition of spacelessness. Space is like a rug with ragged edges and worn spots. Just as we can look at those frayed areas to see how the rug is woven, we can study nonlocal phenomena to glimpse how space is assembled from spaceless components.