The phenomenon that Einstein thought too spooky and strange to be true
What is entanglement? It's a connection between quantum particles, the building blocks of the universe. Once two particles are entangled, a change to one of them is reflected---instantly---in the other, be they in the same lab or light-years apart. So counterintuitive is this phenomenon and its implications that Einstein himself called it "spooky" and thought that it would lead to the downfall of quantum theory. Yet scientists have since discovered that quantum entanglement, the "God Effect," was one of Einstein's few---and perhaps one of his greatest---mistakes.
What does it mean? The possibilities offered by a fuller understanding of the nature of entanglement read like something out of science fiction: communications devices that could span the stars, codes that cannot be broken, computers that dwarf today's machines in speed and power, teleportation, and more.
In The God Effect, veteran science writer Brian Clegg has written an exceptionally readable and fascinating (and equation-free) account of entanglement, its history, and its application. Fans of Brian Greene and Amir Aczel and those interested in the marvelous possibilities coming down the quantum road will find much to marvel, illuminate, and delight.
|Publisher:||St. Martin's Press|
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About the Author
Brian Clegg is the author of A Brief History of Infinity, The First Scientist: A Life of Roger Bacon, and Light Years: The Extraordinary Story of Mankind's Fascination with Light. He holds a physics degree from Cambridge and has written regular columns, features, and reviews for numerous magazines. His books have been translated into ten languages. He lives in Wiltshire, England, with his wife and two children.
BRIAN CLEGG is the author of Ten Billion Tomorrows, Final Frontier, Extra Sensory, Gravity, How to Build a Time Machine, Armageddon Science, Before the Big Bang, Upgrade Me, and The God Effect among others. He holds a physics degree from Cambridge and has written regular columns, features, and reviews for numerous magazines. He lives in Wiltshire, England, with his wife and two children.
Read an Excerpt
The God Effect
Quantum Entanglement, Science's Strangest Phenomenon
By Brian Clegg
St. Martin's PressCopyright © 2006 Brian Clegg
All rights reserved.
Laws are generally found to be nets of such a texture, as the little creep through, the great break through, and the middle-sized are alone entangled in.
— WILLIAM SHENSTONE, Essays on Men, Manners, and Things
Entanglement. It's a word that is ripe with implications. It brings to mind a kitten tied up in an unraveled ball of wool, or the complex personal relationship between two human beings. In physics, though, it refers to a very specific and strange concept, an idea so bizarre, so fundamental, and so far reaching that I have called it the God Effect. Once two particles become entangled, it doesn't matter where those particles are; they retain an immediate and powerful connection that can be harnessed to perform seemingly impossible tasks.
The word "quantum" needs a little demystifying to be used safely. It does nothing more than establish that we are dealing with "quanta," the tiny packets of energy and matter that are the building blocks of reality. A quantum is usually a very small speck of something, a uniform building block normally found in vast numbers, whether it's a photon of light, an atom of matter, or a subatomic particle like an electron.
Dealing in quanta implies that we are working with something that comes in measured packages, fixed amounts, rather than delivered as a continuously variable quantity. In effect, the difference between something that is quantized and something continuous is similar to the difference between digital information, based on quanta of 0s and 1s, and analog information that can take any value. In the physical world, a quantum is usually a very small unit, just as a quantum leap is a very small change — quite different from its implications in everyday speech.
The phenomenon at the heart of this book is a linkage between the incomprehensibly small particles that make up the world around us. At this quantum level, it is possible to link particles together so completely that the linked objects (photons, electrons, and atoms, for instance) become, to all intents and purposes, part of the same thing. Even if these entangled particles are then separated to opposite sides of the universe, they retain this strange connection. Make a change to one particle, and that change is instantly reflected in the other(s) — however far apart they may be. The God Effect has an unsettling omnipresence.
This unbounded linkage permits the remarkable applications of quantum entanglement that are being developed. It enables the distribution of a secret key for data encryption that is impossible to intercept. It plays a fundamental role in the operation of a quantum computer — a computer where each bit is an individual subatomic particle, capable of calculations that are beyond any conventional computer, even if the program ran for the whole lifetime of the universe. And entanglement makes it possible to transfer a particle, and potentially an object, from one place to another without passing through the space in between.
This counterintuitive ability of entanglement to provide an intimate link between two particles at a distance seems just as odd to physicists as it does to the rest of us. Albert Einstein, who was directly responsible for the origins of quantum theory that made entanglement inevitable, was never comfortable with the way entanglement acts at a distance, without anything connecting the entangled particles. He referred to the ability of quantum theory to ignore spatial separation as "spükhafte Fernwirkungen," literally spooky or ghostly distant actions, in a letter written to fellow scientist Max Born:
I cannot make a case for my attitude in physics which you would consider reasonable ... I cannot seriously believe in [quantum theory] because the theory cannot be reconciled with the idea that physics should represent a reality in time and space, free from spooky actions at a distance.
Entanglement, as a word, seems to have entered the language of physics at the hand of scientist Erwin Schrödinger, in an article in the Proceedings of the Cambridge Philosophical Society. Interestingly, although German, Schrödinger was working and writing in English at the time — and this may have inspired his use of "entanglement" — the German word for the phenomenon, Verschränkung, has a rather different meaning than does his word choice in English.
The English term has subtly negative connotations. It gives a sense of being out of control and messed up. But the German word is more structured and neutral — it is about enfolding, crossing over in an orderly manner. A piece of string that is knotted and messed up is entangled, where a carefully woven tapestry has Verschränkung. In practice, neither word seems ideal. Quantum entanglement may lack the disorder implied by "entanglement," but it is much stronger and more fundamental than the pallid Verschränkung seems to suggest.
For Einstein, the prediction that entanglement should exist was a clear indicator of the lack of sense in quantum theory. The idea of entanglement was an anathema to Einstein, a challenge to his view on what "reality" truly consisted of. And this was all because entanglement seemed to defy the concept of locality.
Locality. It's the kind of principle that is so obvious we usually assume it without even being aware of it. If we want to act upon something that isn't directly connected to us — to give it a push, to pass a piece of information to it, or whatever — we need to get something from us to the object we wish to act upon. Often this "something" involves direct contact — I reach over and pick up my coffee cup to get it moving toward my mouth. But if we want to act on something at a distance without crossing the gap that separates us from that something, we need to send an intermediary from one place to the other.
Imagine that you are throwing stones at a can that's perched on a fence. If you want to knock the can off, you can't just look at it and make it jump into the air by some sort of mystical influence; you have to throw a stone at it. Your hand pushes the stone, the stone travels through the air and hits the can; as long as your aim is good (and the can isn't wedged in place), the can falls off and you smile smugly.
Similarly, if I want to speak to someone across the other side of a room, my vocal chords vibrate, pushing against the nearest air molecules. These send a train of sound waves through the air, rippling molecules across the gap, until finally those vibrations get to the other person's ear, start her eardrum vibrating, and result in my voice being heard. In the first case, the ball was the intermediary, in the second the sound wave, but in both cases something physically traveled from A to B. This need for travel — travel that takes time — is what locality is all about. It says that you can't act on a remote object without that intervention.
All the evidence is that we are programmed from birth to find the ability to influence objects at a distance unnatural. Research on babies has shown that they don't accept action at a distance, believing that there needs to be contact between two objects to allow one to act on the other.
This seems an extravagant assertion. After all, babies are hardly capable of telling us that this is what they think, and no one can remember how they saw the world in their first few months of life. The research technique that gets around this problem is delightfully cunning: babies are made bored by constant repetition of a particular scene, then after many repeats, some small aspect of the scene is changed. The babies are watched to see how they react. If the new movement involves action with visible contact, the babies get less worked up than if it appears to involve action at a distance. If a hand pushes a toy and it moves, the baby doesn't react; if a toy moves on its own, the baby does a double take. The inference that babies don't like the ability to act remotely is indirect, but the monitoring does appear to display babies' concern about action at a distance — the whole business feels unnatural.
Next time you are watching a magician at work, doing a trick where he manipulates an object at a distance, try to monitor your own reaction. As the magician's hand moves, so does the ball (or whatever the object he is controlling happens to be). Your mind rebels against the sight. You know that there has to be a trick. There has to be something linking the action of the hand and the movement of the object, whether directly — say, with a very thin wire — or indirectly, perhaps by a hidden person moving the object while watching the magician's hand. Your brain is entirely convinced that action at a distance is not real.
However, though action at a distance looks unreal, this doesn't rule out the possibility of its truly happening. We are used to having to overcome appearances, to take a step away from what looks natural, given extra knowledge. From an early age (unlike dogs and cats) we know that there aren't really little men behind the TV screen. Similarly, a modern child will have been taught about gravity, which itself gives the appearance of action at a distance. We know gravity works from a great range, yet there is no obvious linkage between the two bodies that are attracted to each other. Gravitation seems to offer a prime challenge to the concept of locality.
This idea of gravitational attraction emerged with the Newtonian view of the world, but even as far back as the ancient Greeks, before any idea of gravity existed, there was awareness of other apparent actions at a distance. Amber rubbed with a cloth attracts lightweight objects, such as fragments of paper, toward it. Lodestones, natural magnets, attract metal and spin around, when set on a cork to float on water, until they are pointing in a particular direction. In each case, the action has no obvious linkage to make it work. The attracted object moves toward the magnet — the floating lodestone spins and the static-charged amber summons its retinue of paper scraps as if by magic.
The Greeks had competing schools of thought on what might be happening. One group, the atomists, believed that everything was either atom or void — and, as nothing could act across a void, there had to be a continuous chain of atoms that linked cause to effect. Other Greek philosophers put action at a distance down to a sympathetic process — that some materials were inherently attracted to each other as one person attracts another. This was little more than a variant on the third possibility open to the Greek mind — supernatural intervention. In effect, this theory said there was something out there that provided an occult nudge to make things happen. This idea was widely respected in ancient times as the mechanism of the long-lasting if scientifically unsupportable concept of astrology, in which supernatural influence by the planets was thought to shape our lives.
Even though, nearly two thousand years later, Newton was able to exhibit pure genius in his description of what happened as a result of one apparent action at a distance — gravity — he was no better than the Greeks in explaining how one mass influenced another without anything connecting them. In his masterpiece, the Principia Mathematica, published in 1688, he said:
Hitherto, we have explained the phenomena of the heavens and of our sea by the power of gravity, but have not yet assigned the cause of this power. This is certain, that it must proceed from a cause that penetrates to the very centres of the sun and planets, without suffering the least diminution of its force; that operates not according to the quantity of the surfaces of the particles upon which it acts (as mechanical causes used to do) but according to the quantity of the solid matter which they contain, and propagates its virtue on all sides to immense distances ...
I have not been able to discover the cause of those properties of gravity from the phenomena, and I frame no hypothesis; for whatever is not deduced from the phenomena is to be called an hypothesis; and hypotheses, whether metaphysical or physical, whether of occult qualities or mechanical, have no place in experimental philosophy. In this philosophy particular propositions are inferred from the phenomena, and afterward rendered general by deduction ... And to us it is enough that gravity does really exist, and acts according to the laws which we have explained, and abundantly serves to account for all the motions of the celestial bodies, and of our sea.
This quote contains one of Newton's best-known lines, "I frame no hypothesis" ("hypotheses non fingo" in his original Latin). The modern translation of Principia, by Cohen and Whitman, points out that fingo was a derogatory term, implying making something up rather than the apparently neutral "frame." Newton was saying that gravity exists, but he wasn't going to provide a nonempirical guess at how it works. Some would continue to believe that gravity had some occult mechanism, on a par with astrology, but mostly the workings of gravity were swept under the carpet until Einstein came along.
One fundamental that came out of Einstein's work was that nothing could travel faster than light. We will revisit the reasoning behind this (and the implications of breaking Einstein's limit) in chapter 5. For the moment, though, relativity sounded the death knell for action at distance. It had been known since 1676 that light traveled at a finite speed, when the Danish astronomer Ole Roemer made the first effective determination of a velocity now set at around 186,000 miles per second. Einstein showed that action could not escape this constraint. Nothing, not even gravity, could travel faster than the speed of light. It was the ultimate limit.
We still don't know exactly how gravity works, but Einstein's limit was finally proved experimentally at the beginning of the twenty-first century — gravity does travel at the speed of light. If the sun suddenly vanished, just as we wouldn't see that it had disappeared for about eight minutes, we also wouldn't feel the catastrophic impact of the loss of its gravitational pull until then. Locality reigns.
Or at least that seemed to be the case, until experiments based on the work of an obscure physicist from Northern Ireland, John Bell, proved the existence of entanglement. Entanglement is genuine action at a distance, something that even now troubles many scientists. Of course, today we have a more sophisticated view of the universe — and have to face up to the fact that the concept of "distance" itself is perhaps not as clear and obvious as it once was. Theorist Berndt Müller, of Duke University, has suggested that the quantum world has an extra unseen dimension through which apparently spatially separated objects can communicate as if they were side by side. Others imagine spatial separation to be invisible — in effect, nonexistent — to entangled particles. Even so, there is a powerful reluctance to allow that anything, however insubstantial and unable to carry information, could travel faster than light.
Although Einstein's objections to quantum theory based on its dependence on probability are frequently repeated (usually in one of several quotes about God not throwing dice), it was the breach of locality that really seemed to wound Einstein's sense of what was right. This is never more obvious than in a series of sharp handwritten remarks Einstein appended to the text draft of an article his friend Max Born had sent to him for comment:
The whole thing is rather sloppily thought out, and for this I must respectfully clip your ear ... whatever we regard as existing (real) should somehow be localized in time and space ... [otherwise] one has to assume that the physically real in [position] B suffers a sudden change as a result of a measurement in [position] A. My instinct for physics bristles at this. However, if one abandons the assumption that what exists in different parts of space has its own, independent, real existence then I simply cannot see what it is that physics is meant to describe.
The phenomenon that challenges locality, that makes action a distance a possibility once more, the phenomenon of entanglement, emerges from quantum theory, the modern science of the very small. To reach the conception of entanglement, we need to trace quantum theory's development from a useful fudge to fix a puzzling phenomenon, to a wide-ranging structure that would undermine all of classical physics.
Max Planck, a scientist with roots firmly in the nineteenth century, started it all in an attempt to find a practical solution to an otherwise intractable problem. Planck, born in Kiel, Germany, in 1858, was almost put off physics by his professor at the University of Munich, Phillip von Jolly. Von Jolly held the downbeat view that physics was a dead-end career for a young man. According to von Jolly, pretty well everything that happened in the world, with a couple of minor exceptions, was perfectly explained by the physical theories of the day, and there was nothing left to do but polish up the results and add a few decimal places. Planck could have been tempted to build on his musical capabilities and become a concert pianist, but instead he stuck with physics.
Excerpted from The God Effect by Brian Clegg. Copyright © 2006 Brian Clegg. Excerpted by permission of St. Martin's Press.
All rights reserved. No part of this excerpt may be reproduced or reprinted without permission in writing from the publisher.
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Table of Contents
A Note About Alice and Bob,
CHAPTER 1. ENTANGLEMENT BEGINS,
CHAPTER 2. QUANTUM ARMAGEDDON,
CHAPTER 3. TWINS OF LIGHT,
CHAPTER 4. A TANGLE OF SECRETS,
CHAPTER 5. THE BLISH EFFECT,
CHAPTER 6. THE UNREAL MACHINE,
CHAPTER 7. MIRROR, MIRROR,
CHAPTER 8. CURIOUSER AND CURIOUSER,
ALSO BY BRIAN CLEGG,