# Quantum Strangeness PDF by George Greenstein

**Download Quantum Strangeness PDF book free by George S. Greenstein** – From Quantum Strangeness: Quantum mechanics is one of the glories of our age. The theory lies at the heart of modern society. Quantum mechanics is one of our most valuable forecasters―a “great predictor.” It has immeasurably altered our conception of the natural world. **Buy from Amazon**

Table of Contents

## Quantum Strangeness PDF

**A physicist’s efforts to understand the enigma that is quantum mechanics.**

Its philosophical implications are earthshaking. But quantum mechanics steadfastly refuses to speak of many things; it deals in probabilities rather than giving explicit descriptions. It never explains. Einstein, one of its creators, considered the theory incomplete. Even now, many years after the creation of quantum mechanics, physicists continue to argue about it. Astrophysicist George Greenstein has been both fascinated and confused by quantum mechanics for his entire career. In this book, he describes, engagingly and accessibly, his efforts to understand the enigma that is quantum mechanics.

The fastest route to the insight into the ultimate nature of reality revealed by quantum mechanics, Greenstein writes, is through Bell’s Theorem, which concerns reality at the quantum level; and Bell’s 1964 discovery drives Greenstein’s quest. Greenstein recounts a scientific odyssey that begins with Einstein, continues with Bell, and culminates with today’s push to develop an industry of quantum machines. Along the way, he discusses spin, entanglement, experimental metaphysics, and quantum teleportation, often with easy-to-grasp analogies. We have known for decades that the world of the quantum was strange, but, Greenstein says, not until John Bell came along did we know just how strange.

## Content – Quantum Strangeness PDF

Contents

Foreword by David Kaiser

Acknowledgments

- The Great Predictor

Background to Bell - Silence
- Half a Theory?
- The Solvay Battles
- Spin
- An Impoverished Language?
- The EPR Paradox
- Hidden Variables

Bell’s Theorem - A Hidden Variable Theory
- Bell’s Theorem
- Stigma

Experimental Metaphysics - Experimental …
- … Metaphysics
- Nonlocality
- Quantum machines
- A New Universe

Appendix 1: The GHZ Theorem

Appendix 2: Further Reading

Index

## Editorial Reviews

### Review – Quantum Strangeness PDF

This is one of the finest books I have read on quantum mechanics: lucid and careful, but also entertaining, honest, and generous. It gets to the core of the matter, exposing the strangeness we perceive withing quantum theory. George Greenstein doesn’t pretend to give you the answers, but he does something more valuable: he reveals the right questions.―**Phillip Ball, author of Beyond Weird: Why Everything You Thought You knew About Quantum Physics is Different**

George Greenstein tried for a long time to develop a clear understanding of why Bell’s inequalities are important, and one day he had, as he says, an epiphany. We must thank him for sharing with the reader the long and difficult path that led him to his final clarification.―**Alain Aspect**, Professor at Institut d’Optique Graduate School, Universite Paris-Saclay

### Review – Quantum Strangeness PDF

George Greenstein tried for a long time to develop a clear understanding of why Bell’s inequalities are important, and one day he had, as he says, an epiphany. We must thank him for sharing with the reader the long and difficult path that led him to his final clarification.―**Alain Aspect**, Professor at Institut d’Optique Graduate School, Université Paris Saclay.

This is one of the finest books I have read on quantum mechanics: lucid, and careful, but also entertaining, honest and generous. It gets to the core of the matter, exposing the strangeness we perceive within quantum theory. George Greenstein doesn’t pretend to give you the answers, but he does something more valuable: he reveals the right questions.―**Philip Ball**, *author of Beyond Weird: Why Everything You Thought You Knew About Quantum Physics Is Different.*

### Review* – Quantum Strangeness PDF

I was very excited to have the mysteries of Quantum Strangeness elucidated by an expert in the field. What I received was a poorly (un?) edited series of tedious anecdotes from an Astrophysicist who never really understood the topic himself.

First, does MIT Press have editors?

Chapter 1 begins “It was many years ago that I first encountered the Great Predictor.”

Chapter 9 begins “It was many years ago that I first encountered the Great Predictor.” and continues with the same 4 paragraphs from chapter 1.

Chapter 16 begins “It was many years ago that I first encountered the Great Predictor.” and continues to repeat the introduction *again* for a page and a half!

A simple search algorithm could have prevented the egregious editing problems in this text.

Second, the substance of this very short (124pgs including the duplicated text) was next to non-existent. It offers some light historical background on the key scientists, John Bell, Einstein of course.. which would be fine if the author ever actually got around to making a concerted effort to provide some depth to the subject matter at hand. Instead the ‘background’ text just feels like padding for content that might make a nice blog post or pop-sci magazine article.

One final quote from the book:

“The astute reader will have noticed that I have not solved the mystery of quantum theory”

Nor has he clarified it’s philosophical implications, described it’s mathematical underpinnings, or brought any more clarity to the subject.

It’s nice that he’s enthusiastic and curious about the implications of Quantum Strangeness… I am too, that’s why I bought the book. But, while enthusiasm and curiosity might make a nice blog post, they aren’t enough to be the foundation of an entire book.

### Review****

This is indeed a strange book. Rather than being an exposition of quantum theory, it is more of a personal journey, recounting the author’s struggle with the weirdness of quantum mechanics. It is focused on one particular puzzle: the startling work of the Irish theoretician, John Stewart Bell (1928-1990).

Bell’s Theorem shows that quantum mechanics predicts correlations between measurements on separated particles which exceed those deduced by straightforward logic based on the natural assumption that (for example) each member of a pair of correlated photons has an actual value of its polarization value while in flight from source to detector. Quantum theory says something different: the polarization values do not exist until the photons hit the detector, and then the correlation depends only on the angle between the detectors, and not any preexisting property of the photons in flight. Bell’s theorem is testable and three decades of experimental work have shown that quantum theory is correct. The commonsense view that things have definite properties before we look at them is demonstrably wrong.

One of the most profound insights into quantum mechanics, Bell’s Theorem is also one of the most misunderstood. Even some senior physicists, who should know better, often state that Bell rules out “hidden variable theories” – physicist-speak for the commonsense idea that things have properties before measurement. This statement that Bell excludes hidden variables is downright wrong.

To quote Bell’s paper: “It is the requirement of locality, or more precisely that the result of a measurement on one system be unaffected by operations on a distant system with which it has interacted in the past, that creates the essential difficulty.” [Bell, JS. On the Einstein Podolsky Rosen Paradox. Physics, 1, 195-200, 1964. The quotation is the fourth sentence of the Introduction.]

Quantum experiments show that our reality is actually non-local. The intuitive idea that things only affect each other if they are adjacent, or at least able to send some kind of message or force between them, turns out to be wrong.

Greenstein’s book gives very little of the overall flavor of quantum theory other than the author’s struggle with Bell’s Theorem. For this reason, it may be unsatisfying, or even confusing, to the beginner. It will be better received by the reader who is already familiar with wave-functions, the uncertainty principle and wave-particle duality through reading some popular books or taking a Modern Physics course at college freshman level.

Part of Greenstein’s problem in understanding quantum phenomena is that he believes in particles. He has a lot of company. But much of the mystery derives from our intuitive, but flawed, idea that particles should have definite properties like position, momentum, energy, etc. When we realize a photon must go through both slits simultaneously in a double-slit diffraction experiment, we have an uncomfortable double-think to cope with. How can an object be in two places at once?

Our best version of quantum theory is Quantum Field Theory, in which there are only waves. “Particles” are just (packets of) waves. Waves can have particle-like properties, such as momentum. Many of the puzzles of the quantum world are much less confronting when we take a wave-only perspective. An accessible account is Jean Bricmont, 2017, Quantum Sense and Nonsense. [Springer; also Amazon Kindle: ASIN: B076XYDKSQ]. At a less technical level: Rodney Brooks, 2010, Fields of Color: The theory that escaped Einstein. [Kindle ASIN: B004ULVG9O].

## Foreword

Physics has more than its share of mind-bending ideas: the slowing clocks and shrinking meter sticks of relativity; enormous coagulations of matter, like black holes, that can rupture space-time itself. Yet the strangest ideas of all are clustered in quantum theory, physicists’ remarkably successful description of matter and energy at atomic scales. Here we find descriptions of objects that seem to act as if they were in two places at once; of particles that can tunnel through walls; of Erwin Schrödinger’s twice-fated cat, trapped in a zombielike state of being both alive and dead. For all that, Schrödinger himself declared one idea in particular, quantum entanglement, to be “the characteristic trait of quantum mechanics, the one that enforces its entire departure from classical lines of thought.” Quantum Strangeness PDF

1 Schrödinger had done so much to contribute to quantum theory; his “wave function,” obeying an equation he first published in 1926, remains central to physicists’ efforts to describe quantum systems quantitatively. Almost a decade later, in 1935, Schrödinger coined the term “entanglement,” though by then his enthusiasm for quantum theory had begun to wane. That same year his friend Albert Einstein teamed up with two younger colleagues, Boris Podolsky and Nathan Rosen, to issue his own, latest challenge to quantum theory. In their famous “EPR” paper (named for the authors’ initials), they described a system involving a pair of entangled particles emitted from a central source. Physicists could perform various measurements on one particle, and thereby learn something about the second particle, far off in the distance. Indeed, the EPR authors concluded, physicists should be able to glean more information about the far-away particle than could be accounted for within quantum theory. Quantum Strangeness PDF

2 Each particle, it seemed self-evident to Einstein and his coauthors, should possess definite properties on its own, independent of what physicists happened to choose to measure. If physicists elected to measure the first particle’s position at a given moment, for example, they would learn about the position of the second particle, which had headed off at the same speed but in the opposite direction from the first particle. Or the physicists might choose to measure the momentum of the first particle, and thereby learn about the second particle’s momentum. But surely the second particle had definite values for these and any other properties the physicists might have chosen to investigate, regardless of what choices the physicists had made. After all, Einstein’s own theory of relativity made clear that no signal or influence could travel faster than the speed of light—so nothing the physicists might have chosen to do to the first particle should have been able to affect the second particle, which had traveled so far away. If relativity really set an absolute speed limit on how quickly A could influence B, then the second particle would need to carry all its own information with it, as it traveled through space; there would be no time to receive an update on what values for various properties it should have, based on the outcomes of measurements on the first particle. Quantum Strangeness PDF

Therefore, the EPR authors concluded with a flourish, there existed “elements of reality”—real, definite properties of that second particle —about which quantum theory offered no description. Quantum mechanics, they argued, was incomplete. 3 Within weeks a response came from Niels Bohr, the Danish physicist who had helped to craft quantum theory and who served as a kind of spokesperson for the emerging work. Bohr’s response to EPR was rapid, but abstruse; to this day, it remains difficult to parse Bohr’s argument. Central to his response, however, was a denial that objects in the subatomic realm really must carry complete sets of properties on their own. Rather, Bohr insisted, a particle might have no definite value of, say, momentum, until subjected to a particular measurement—as if a person had no definite weight until stepping on a bathroom scale. (Years later, Einstein famously asked a colleague if quantum physicists really believed that the moon was only there when someone chose to look.) Most important to physicists at the time, it seems, was that Bohr had responded at all. More recent scholarship has indicated that Einstein and Bohr were largely talking past each other—a series of miscommunications exacerbated by the rise of fascism in Europe, which had driven Einstein to emigrate to the United States, thereby ending the late-night, face-to-face discussions that the two had enjoyed during happier times. Each physicist died, decades later, having failed to convince the other when it came to quantum entanglement. Quantum Strangeness PDF

4 The debate seemed to linger, with no clear resolution, for years. A young physicist from Northern Ireland, John S. Bell, shared many of the reservations about quantum theory that Einstein had expressed. Indeed, Bell had nursed a private concern about the topic since his student days, growing frustrated when students and teachers seemed to parrot Bohr’s responses. Bell was quickly counseled to keep such “philosophical” concerns to himself—by the 1950s, quantum mechanics had moved to the very center of physicists’ expanding efforts to understand everything from nuclear reactions to superconductivity to the properties of little devices like transistors. In every single case, the equations of quantum theory provided a remarkable match to experiments. So why, Bell’s teachers pressed, should they continue to fret over the abstract questions that had distracted old-timers like Einstein and Bohr? 5 Bell dove into mainstream topics for his research in high-energy physics, even as his thoughts kept returning to nagging questions about quantum entanglement. Finally, during a sabbatical in the United States in 1964, Bell brought many of his ideas to fruition. He tweaked the famous EPR thought experiment, focusing on specific combinations of measurements that physicists could perform on each of the two entangled particles. In just a few lines of algebra, Bell demonstrated that Einstein’s pair of assumptions—that particles carry definite properties on their own, prior to and independent of measurement, and that no influence can travel faster than light—necessarily led to a contradiction with quantum theory. Bell identified a quantitative upper limit for how often the outcomes of certain combinations of measurements on the two particles could ever line up, if they behaved in accordance with Einstein’s assumptions. Quantum Strangeness PDF

If, instead, the particles were governed by quantum theory, then the measurements on each particle should be more strongly correlated, surpassing the upper bound that Bell had derived. If quantum theory were true, in other words, then performing a measurement over here really would seem to affect the behavior of some other tiny bit of matter, observed arbitrarily far away. 6 On paper, Bell showed, the contrast was as clear as day: an Einstein-like world limited to one side of the bound; a quantum-mechanical world clearly surpassing that limit. The central question that had absorbed Einstein and Bohr for decades could be posed in a laboratory, not just debated in a smokefilled room. Bell published his paper, and then … nothing. Years went by before he heard so much as a peep of interest from the physics community.Quantum Strangeness PDF

In time, Bell’s elegant paper happened to catch the eye of a few unconventional physicists, who recognized the magnitude of Bell’s achievement. If they followed Bell’s reasoning, and really conducted experiments of the sort he had described, they might be able to learn something deep about how the world works. Pioneering physicists like Abner Shimony, John Clauser, Michael Horne, Stuart Freedman, Alain Aspect, and a handful of others began to realize that by testing Bell’s inequality in a laboratory, they could subject abstract, metaphysical mysteries to experimental investigation. Hence the term used in George Greenstein’s lovely book: experimental metaphysics. 7 For nearly half a century, physicists have subjected Bell’s inequality to experimental test. Every single published result has been consistent with the predictions of quantum theory, showing correlations among measurements on pairs of entangled particles in excess of Bell’s bound. Yet from the start, Bell, Shimony, Clauser, Horne, Aspect, and others have recognized that each of these tests has been subject to one or more “loopholes”: little conceptual escape hatches by which an Einstein-like interpretation could still account for the experimental results. Perhaps the particles, or other elements of the apparatus, had shared information (at or below the speed of light) during a particular series of measurements, thereby arranging for the measurements to line up the way they did.Quantum Strangeness PDF

Or perhaps the detectors that had been used to measure the particles were inefficient, and failed to register any definite outcome some fraction of the time. Then it would be possible, at least in principle, for the strong correlations that showed up in those measurements that were successfully recorded to be but a rare statistical hiccup, some fluke that would have been washed out had all of the particles actually been measured. Or perhaps the striking correlations arose from some common cause, deep in the experiment’s past, which had somehow nudged the selection of measurements to be performed and tipped off the particles in advance. After all, as Schrödinger himself acknowledged back in 1935, one should hardly be surprised when a student aces an examination, if she had received a copy of the questions ahead of time. 8 Experimental groups around the world have tackled these loopholes, usually one at a time, since the early 1980s. 9 Only as recently as 2015 have various groups succeeded in measuring significant violations of Bell’s inequality while closing not one but two of the stubborn loopholes. Quantum Strangeness PDF

10 More recently, my own colleagues and I have conducted experiments to address that strange, third loophole—the one regarding the seemingly random selection of measurements to perform on the entangled particles—by turning the universe itself into a pair of random-number generators. Yet again we have found—as have our colleagues around the world—the strong correlations that Bell had first identified. 11 Why go through all the trouble? Aren’t the dozens of previous experiments sufficient for us to declare the question settled? More than just stubbornness is at stake. In fact, quantum entanglement now lies at the center of a booming field dubbed “quantum information science,” which promises major new devices. Quantum encryption and quantum computers—each of which has progressed well into the beta-testing stage—will function as promised only if entanglement is real. If, for some reason, entanglement were merely an artifact, and the world really were governed by Einstein’s assumptions, then quantum encryption simply would not be secure, and quantum computers would fail to deliver the anticipated exponential speed-up compared to ordinary machines. These days, practical technologies built around quantum entanglement constitute a multibillion-dollar industry—contributing a new set of imperatives to keep testing Bell’s inequality, in addition to the deep, metaphysical questions. Quantum Strangeness PDF

12 Despite all the theoretical progress over the past half century, and the recent experimental advances in addressing various loopholes, we are still left with vexing questions. How could the world really work that way? How could two little specks of matter act in concert, even after they had moved arbitrarily far apart? In recent years, physicists have gone to extremes trying to articulate, in everyday scenarios, what entanglement implies about the world. There have been elaborate fables about cops chasing quantum robbers; quantum soufflés that do or do not rise; tales of twins who order drinks in bars an ocean apart; and so on. 13 Amid all these discussions, George Greenstein’s book is a special delight. With patience and clarity, Greenstein guides readers along this extraordinary conceptual journey. We are neither hushed nor rushed; never reprimanded, as John Bell himself had been as a student, to simply take this or that result on faith. Rather, Greenstein shares his own earnest struggles to come to grips with the ideas, to sit with them, to try to puzzle through what they might imply about the workings of nature at its most fundamental. And he does all this with simple illustrations and virtually no mathematics. Quantum Strangeness PDF

His book is an invitation and a primer for those new to the topic, and a timely reminder to fellow specialists, who have long since grown comfortable with the mathematical formalism of quantum theory, that this central element of physicists’ toolkit retains a beguiling strangeness at its core. David Kaiser Germeshausen Professor of the History of Science and Professor of Physics Massachusetts Institute of Technology October 2018

## Acknowledgments

This book is the product of many minds. Guy Blaylock, Danny Greenerger, David Harrison, David Kaiser, Preston Stahley, and Arthur Zajonc read the manuscript and gave me the immeasurable benefit of their advice. Andrew Fraknoi and John Harte read an earlier article and similarly gave me much help. And over the years I have benefited greatly from—and enjoyed—illuminating conversations with innumerable colleagues and friends: some of them scientists working in the field, others nonscientists who nevertheless had insights that gently prodded me in productive directions. Renate Bertleman, John Clauser, and Jain Wei Pan kindly contributed their own personal photographs of people and equipment. To all my deepest thanks.

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## About the Author

George Greenstein is Sidney Dillon Emeritus Professor of Astronomy at Amherst College. He is the author of *Frozen Star: Of Pulsars, Black Holes, and the Nature of Stars*, *The Symbiotic Universe: Life and Mind in the Cosmos*, *The Quantum Challenge: Modern Research on the Foundations of Quantum Mechanics* (with Arthur Zajonc), and other books.

David Kaiser is Germeshausen Professor of the History of Science, Department Head of the Program in Science, Technology, and Society, and Senior Lecturer in the Department of Physics at MIT. He is the author of *Drawing Theories Apart: The Dispersion of the Feynman Diagrams in Postwar Physics*, and editor of *Pedagogy and the Practice of Science: Historical and Contemporary Perspectives* (MIT Press).