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The MIT Press Essential Knowledge
Quantum Entanglement
An exploration of quantum entanglement and the ways in which it contradicts our everyday assumptions about the ultimate nature of reality.
Quantum physics is notable for its brazen defiance of common sense. (Think of Schrödinger's Cat, famously both dead and alive.) An especially rigorous form of quantum contradiction occurs in experiments with entangled particles. Our common assumption is that objects have properties whether or not anyone is observing them, and the measurement of one can't affect the other. Quantum entanglement--called by Einstein "spooky action at a distance"--rejects this assumption, offering impeccable reasoning and irrefutable evidence of the opposite. Is quantum entanglement mystical, or just mystifying? In this volume in the MIT Press Essential Knowledge series, Jed Brody equips readers to decide for themselves. He explains how our commonsense assumptions impose constraints--from which entangled particles break free.
Brody explores such concepts as local realism, Bell's inequality, polarization, time dilation, and special relativity. He introduces readers to imaginary physicists Alice and Bob and their photon analyses; points out that it's easier to reject falsehood than establish the truth; and reports that some physicists explain entanglement by arguing that we live in a cross-section of a higher-dimensional reality. He examines a variety of viewpoints held by physicists, including quantum decoherence, Niels Bohr's Copenhagen interpretation, genuine fortuitousness, and QBism. This relatively recent interpretation, an abbreviation of "quantum Bayesianism," holds that there's no such thing as an absolutely accurate, objective probability "out there," that quantum mechanical probabilities are subjective judgments, and there's no "action at a distance," spooky or otherwise.
Quantum physics is notable for its brazen defiance of common sense. (Think of Schrödinger's Cat, famously both dead and alive.) An especially rigorous form of quantum contradiction occurs in experiments with entangled particles. Our common assumption is that objects have properties whether or not anyone is observing them, and the measurement of one can't affect the other. Quantum entanglement--called by Einstein "spooky action at a distance"--rejects this assumption, offering impeccable reasoning and irrefutable evidence of the opposite. Is quantum entanglement mystical, or just mystifying? In this volume in the MIT Press Essential Knowledge series, Jed Brody equips readers to decide for themselves. He explains how our commonsense assumptions impose constraints--from which entangled particles break free.
Brody explores such concepts as local realism, Bell's inequality, polarization, time dilation, and special relativity. He introduces readers to imaginary physicists Alice and Bob and their photon analyses; points out that it's easier to reject falsehood than establish the truth; and reports that some physicists explain entanglement by arguing that we live in a cross-section of a higher-dimensional reality. He examines a variety of viewpoints held by physicists, including quantum decoherence, Niels Bohr's Copenhagen interpretation, genuine fortuitousness, and QBism. This relatively recent interpretation, an abbreviation of "quantum Bayesianism," holds that there's no such thing as an absolutely accurate, objective probability "out there," that quantum mechanical probabilities are subjective judgments, and there's no "action at a distance," spooky or otherwise.
4 pages, MP3 CD
First published January 1, 2020
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496 people want to read
About the author
Jed Brody
5 books4 followersJed Brody is Senior Lecturer in Physics at Emory University, where he has taught an interdisciplinary course on quantum entanglement.
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Displaying 1 - 30 of 37 reviews
March 17, 2020
An entry in MIT Press's pocket-sized Essential Knowledge series, this is an attempt to take on one of the strangest and most mind-bending aspects of physics - quantum entanglement - in a new way.
There are several books describing the historical development and implications of quantum entanglement, but what Jed Brody does is take an experimentalist's view and helps the reader understand what is involved in a Bell inequality and how a test of quantum entanglement in this fashion really works.
There are other bits as well - a very rapid introduction and a rather tagged-on feeling bit about quantum theory and relativity, plus a too-brief-to-understand trip into the unlikely world of quantum Bayesianism. But the crucial part of the book, and the reason it gets four stars, is that experimental bit. Specifically what Brody does, something that I have never seen before in any other book on the subject, is give an explanation of a specific Bell inequality that proves why the outcome of a particular measurement runs counter to local realism - that's a real achievement. Usually, the best that can be done is to tell the reader such an experiment will prove the outcome without explaining why.
There is one big proviso. I think this is a great book if you have already picked up the background to quantum entanglement (try The God Effect for this, rather than Brody's 'further reading' recommendations), but it really wouldn't be so useful if you haven't absorbed the context, history and meaning - so if the bits of the review above referring to a Bell inequality, say, don't mean a lot to you, do some background reading first.
Even with that background, some of the later examples that Brody gives involve just too much twisted logic to easily get your brain around - but I still think that the relatively small part of the book that involves working through a basic Bell inequality is well worth laying your hands on it, and make this title unique.
Definitely one of the better additions to this quirky series.
There are several books describing the historical development and implications of quantum entanglement, but what Jed Brody does is take an experimentalist's view and helps the reader understand what is involved in a Bell inequality and how a test of quantum entanglement in this fashion really works.
There are other bits as well - a very rapid introduction and a rather tagged-on feeling bit about quantum theory and relativity, plus a too-brief-to-understand trip into the unlikely world of quantum Bayesianism. But the crucial part of the book, and the reason it gets four stars, is that experimental bit. Specifically what Brody does, something that I have never seen before in any other book on the subject, is give an explanation of a specific Bell inequality that proves why the outcome of a particular measurement runs counter to local realism - that's a real achievement. Usually, the best that can be done is to tell the reader such an experiment will prove the outcome without explaining why.
There is one big proviso. I think this is a great book if you have already picked up the background to quantum entanglement (try The God Effect for this, rather than Brody's 'further reading' recommendations), but it really wouldn't be so useful if you haven't absorbed the context, history and meaning - so if the bits of the review above referring to a Bell inequality, say, don't mean a lot to you, do some background reading first.
Even with that background, some of the later examples that Brody gives involve just too much twisted logic to easily get your brain around - but I still think that the relatively small part of the book that involves working through a basic Bell inequality is well worth laying your hands on it, and make this title unique.
Definitely one of the better additions to this quirky series.
March 16, 2026
In general, the more you read about a topic, the more you understand it would be true. I am not sure if that holds for quantum theory though! Beyond a certain point, there are no incremental gains. Nevertheless, I find our universe fascinating and am always on the lookout for science writers who can explain concepts without getting into too many heavy details.
This book does well to steer clear of complex calculations. In instances where the concept is complex, the author takes to real life analogies. Quantum entanglement violates assumptions of local events and fixed states. This means we assume that events happening at one place do not immediately affect another distant place. At the same time, we take objects to have pre-existing properties, and it is counter-intuitive to think that an object may take on a property when we observe it. There is good explanation of what experiments have revealed about quantum entanglement where particles separated by a distance behave similarly one immediately after the other. There are a few possibilities discussed on how this could be possible with the author’s own views.
I liked the effort which went into simplifying the complexity of the concepts. I would have liked to see some more details of experiments – till date & ongoing, more analogies and possibly some illustrations. Overall, a good book on the subject.
This book does well to steer clear of complex calculations. In instances where the concept is complex, the author takes to real life analogies. Quantum entanglement violates assumptions of local events and fixed states. This means we assume that events happening at one place do not immediately affect another distant place. At the same time, we take objects to have pre-existing properties, and it is counter-intuitive to think that an object may take on a property when we observe it. There is good explanation of what experiments have revealed about quantum entanglement where particles separated by a distance behave similarly one immediately after the other. There are a few possibilities discussed on how this could be possible with the author’s own views.
I liked the effort which went into simplifying the complexity of the concepts. I would have liked to see some more details of experiments – till date & ongoing, more analogies and possibly some illustrations. Overall, a good book on the subject.
July 20, 2024
This is a brief exploration of quantum entanglement and the ways in which it contradicts our everyday assumptions about the ultimate nature of reality. What makes this book different from all the others (which mostly deal with the historical development of quantum physics) is that Brody takes an experimentalist's perspective so that the reader can properly understand what is involved in a Bell inequality and how a test of quantum entanglement really works. Brody presents the experimental evidence that photons are not subject to realism and locality. showing that the Bell equality is violated. From this violation emerges the idea of Quantum Entanglement or as Einstein called it, "spooky action at a distance". Experiments seem to imply entanglement is real, yet we have little or no understanding of why this is so. Brody explains complex concepts, such as as local realism, Bell's inequality, polarization, time dilation, and special relativity, in a relatable manner making use of many examples. Interesting.
April 3, 2021
Short quick read (like other books in the MIT press series). The author presents the experimental evidence that photons are not subject to realism and locality. More than one experiment has confirmed that the Bell equality is violated. From this violation emerges the idea of Quantum Entanglement (or spooky action at a distance). Experiments seem to imply entanglement is real, yet we have little or no understanding of why this is so. Quantum computing relies on this entanglement so I suppose a valid question is whether we can trust all the results from a Quantum computer. The experimental observations make a compelling case, yet I was hoping there would be an equation or two to back up observations. The author hints of a few possible explanations for what is happening. Perhaps as time goes on we will understand the hidden variables that seem to be at play.
February 28, 2021
I thought this would be a sort of dummy’s guide to quantum entanglement, but so much of it remained opaque to me. I initially thought it was just because the author’s examples were distracting and confusing as I find to be the case for many North American STEM professors, as they try to (unsuccessfully) add a little humour to the learning experience. While reading this book, I often had the same sinking feeling I had felt in the mandatory quantum mechanics course I had to take as an electrical engineering student. I surprisingly did not do absolutely horribly in that course, but that’s only because I think all my fellow classmates did equally poorly, and I’m almost certain the professor bell-curved the grades up. All this being said, many of the videos, podcasts, and lectures I looked to in order to better enlighten myself seemed to be equally confusing, and I suspect this is just difficult stuff to wrap my head around.
Quantum entanglement has surfaced in a number of philosophical and theological work I’ve encountered over the past couple years, but I had a very vague sense of what it was, so I thought I should take some time to understand a bit more about it. Not sure how successfully that went here, but it was interesting to encounter Brody mention ‘QBism’ (also known as quantum Bayesianism) which is the interpretation of quantum mechanics that some call the ‘shut up and calculate’ approach. This interpretation eschews any speculation concerning the causality of the correlated behaviour of particles at a distance, leaving that up to philosophers, theologians, poets and science-fiction writers. I suppose that’s the sort of quantum mechanical interpretation that permit theologians like Catherine Keller to elaborate on such matters without feeling the sort of embarrassing bewilderment that I feel when discussing such matters so far beyond my pay grade.
My basic understanding of quantum entanglement at this point is that particles must first become entangled. One photon can be split into two photons by way of crystals composed of something like beta barium borate, and these two photons would be considered entangled. I believe entangled particles can be trapped in some sort of crystal lattice allowing experiments to be carried out with the entangled particles separated by a very large distance, but this aspect is still not very clear to me. Would they not have to be emitted at the same time, to conduct experiments? I’m still very confused whether all experiments require particles to be emitted at a common source or not, and how do you detect said particles at great distances from each other?
Anyway, these particles are basically shot through polarizers (typically a peace of glass or plastic, like the lens of sunglasses) set at certain angles, and photon detectors are set up behind these polarizers, detecting whether the particles pass through the polarizers or are blocked. This is the way they measure the polarization angle of the particles. However, it appears that this way of ‘measuring’ the photon’s polarization angle is actually affecting the behaviour of the photon. It forces the wave function of the particle to collapse. Before the particle reaches the polarizer its precise polarization angle is uncertain, it is in a ‘superposition’, but it collapses when it is forced to ‘choose’ whether it passes through the polarizer or doesn’t. Using words like ‘choose’ always confuses me, because of its deployment of almost anthropomorphic language, but all this is saying is that whether it passes through the polarizer is not preordained. This was not always known to be the case.
Einstein, Podolsky, Rosen had suspected that these particles were always preordained to either pass or not pass through polarizers – that these particles had ‘hidden variables’ or ‘properties’ in them that predisposed them to always behave in the same way. The issue is that we were just too ignorant to know which conditions affected their ‘decisions’ about whether to pass through or not. This concept is undergirded by the intuitive notion of ‘local realism’, which holds at all levels of reality (I believe) except at the level of quantum mechanics. The ‘locality’ aspect of local realism simply means that causality occurs continually in space – that is one thing cannot influence something else instantaneously at a distance, except by affecting other things in the intervening space in between them; therefore this influence is constrained by the speed of light according to Einstein’s theory of relativity, as this action must be propagated through space as light is propagated through space. The ‘realism’ aspect of it is that all objects have definite properties that exist with or without our knowledge of them, and that measuring one object should not affect the properties of another object.
This assumption of ‘local realism’ appears to be violated at the level of quantum mechanics. What seems to occur is that once one entangled particle is ‘measured’ by a polarizer – in other words, its wave function collapses and it is forced to choose a definite polarization angle, its corresponding entangled particle takes on that definite angle as well. This is observed such that every time an entangled particle passes through a polarizer set at some specific angle, its corresponding entangled particle will always pass through some other polarizer if it is set at that exact same angle.
Einstein and company believed that this phenomenon could be explained by ‘hidden variables’ – that is intrinsic properties that the two particles had beforehand that preordained them to either pass through a polarizer or not. This theory by Einstein was later problematized by the Bell inequalities. I’ve tried really hard to understand exactly how this Bell theorem disproves Einstein’s assumption of local realism, trying to work my way through online videos and Oxford physics lectures, but it really is beyond me. It basically uses the mathematics of set theory to demonstrate that the mathematical assumptions of quantum mechanics are not compatible with local realism, by rigorously separating various probabilistic sets of test conditions and outcomes. With this mathematics out of the way, it then becomes possible to run experiments in the real world to see whether the results correspond to the assumption of local realism or the assumptions of quantum mechanics. What all experiments since the 1970s have shown validate the assumptions of quantum mechanics, while violating the constraints set out by Bell’s Inequality that would be required for local realism to be true.
While I have a vaguely better idea what quantum entanglement is about, I’m still fairly clueless about all the logical steps in between that allow one to arrive at such conclusions. This is all very confusing to me still. Maybe one day something will click. Until then, I will settle for the ignorance I still possess now.
Quantum entanglement has surfaced in a number of philosophical and theological work I’ve encountered over the past couple years, but I had a very vague sense of what it was, so I thought I should take some time to understand a bit more about it. Not sure how successfully that went here, but it was interesting to encounter Brody mention ‘QBism’ (also known as quantum Bayesianism) which is the interpretation of quantum mechanics that some call the ‘shut up and calculate’ approach. This interpretation eschews any speculation concerning the causality of the correlated behaviour of particles at a distance, leaving that up to philosophers, theologians, poets and science-fiction writers. I suppose that’s the sort of quantum mechanical interpretation that permit theologians like Catherine Keller to elaborate on such matters without feeling the sort of embarrassing bewilderment that I feel when discussing such matters so far beyond my pay grade.
My basic understanding of quantum entanglement at this point is that particles must first become entangled. One photon can be split into two photons by way of crystals composed of something like beta barium borate, and these two photons would be considered entangled. I believe entangled particles can be trapped in some sort of crystal lattice allowing experiments to be carried out with the entangled particles separated by a very large distance, but this aspect is still not very clear to me. Would they not have to be emitted at the same time, to conduct experiments? I’m still very confused whether all experiments require particles to be emitted at a common source or not, and how do you detect said particles at great distances from each other?
Anyway, these particles are basically shot through polarizers (typically a peace of glass or plastic, like the lens of sunglasses) set at certain angles, and photon detectors are set up behind these polarizers, detecting whether the particles pass through the polarizers or are blocked. This is the way they measure the polarization angle of the particles. However, it appears that this way of ‘measuring’ the photon’s polarization angle is actually affecting the behaviour of the photon. It forces the wave function of the particle to collapse. Before the particle reaches the polarizer its precise polarization angle is uncertain, it is in a ‘superposition’, but it collapses when it is forced to ‘choose’ whether it passes through the polarizer or doesn’t. Using words like ‘choose’ always confuses me, because of its deployment of almost anthropomorphic language, but all this is saying is that whether it passes through the polarizer is not preordained. This was not always known to be the case.
Einstein, Podolsky, Rosen had suspected that these particles were always preordained to either pass or not pass through polarizers – that these particles had ‘hidden variables’ or ‘properties’ in them that predisposed them to always behave in the same way. The issue is that we were just too ignorant to know which conditions affected their ‘decisions’ about whether to pass through or not. This concept is undergirded by the intuitive notion of ‘local realism’, which holds at all levels of reality (I believe) except at the level of quantum mechanics. The ‘locality’ aspect of local realism simply means that causality occurs continually in space – that is one thing cannot influence something else instantaneously at a distance, except by affecting other things in the intervening space in between them; therefore this influence is constrained by the speed of light according to Einstein’s theory of relativity, as this action must be propagated through space as light is propagated through space. The ‘realism’ aspect of it is that all objects have definite properties that exist with or without our knowledge of them, and that measuring one object should not affect the properties of another object.
This assumption of ‘local realism’ appears to be violated at the level of quantum mechanics. What seems to occur is that once one entangled particle is ‘measured’ by a polarizer – in other words, its wave function collapses and it is forced to choose a definite polarization angle, its corresponding entangled particle takes on that definite angle as well. This is observed such that every time an entangled particle passes through a polarizer set at some specific angle, its corresponding entangled particle will always pass through some other polarizer if it is set at that exact same angle.
Einstein and company believed that this phenomenon could be explained by ‘hidden variables’ – that is intrinsic properties that the two particles had beforehand that preordained them to either pass through a polarizer or not. This theory by Einstein was later problematized by the Bell inequalities. I’ve tried really hard to understand exactly how this Bell theorem disproves Einstein’s assumption of local realism, trying to work my way through online videos and Oxford physics lectures, but it really is beyond me. It basically uses the mathematics of set theory to demonstrate that the mathematical assumptions of quantum mechanics are not compatible with local realism, by rigorously separating various probabilistic sets of test conditions and outcomes. With this mathematics out of the way, it then becomes possible to run experiments in the real world to see whether the results correspond to the assumption of local realism or the assumptions of quantum mechanics. What all experiments since the 1970s have shown validate the assumptions of quantum mechanics, while violating the constraints set out by Bell’s Inequality that would be required for local realism to be true.
While I have a vaguely better idea what quantum entanglement is about, I’m still fairly clueless about all the logical steps in between that allow one to arrive at such conclusions. This is all very confusing to me still. Maybe one day something will click. Until then, I will settle for the ignorance I still possess now.
August 5, 2020
This was a good attempt to explain quantum entanglement, but I'm afraid a good part of the book added more confusion to my understanding. I blame how the examples are described, including the confusing figures and long explanations. Most of the examples could be better communicated with improved figures that clarifies each case, rather than adding long paragraphs to a figure that is too simple.
September 11, 2023
A great introduction to Quantum Entanglement written in easy to understand language and (almost) no maths. This book doesn't delve very deeply into the topic but I don't believe that was its intention. Rather it offers really solid foundational knowledge which will help you understand some of the more difficult literature out there. I wish I'd started with this book. Great stuff.
July 7, 2023
"Quantum Entanglement" is a mind-bending and thought-provoking book that delves into the fascinating world of quantum physics and its implications for our understanding of reality. Jed Brody, a physicist and author, takes listeners on a journey through the weird and counterintuitive concepts of quantum mechanics in an accessible and engaging manner.
One of the strengths of the book is Brody's ability to explain complex scientific concepts in a way that is relatable and easy to follow. He breaks down the fundamental principles of quantum mechanics, such as superposition and entanglement, using clear and vivid examples that allow listeners to grasp these abstract concepts.
Moreover, Brody's passion for the subject shines through in the audiobook, making it an enjoyable and immersive experience. His enthusiasm for quantum physics is contagious, and it's evident that he wants listeners to share in his excitement for the mysteries of the quantum world.
Another strength of "Quantum Entanglement" is its integration of real-world applications and implications of quantum mechanics. Brody explores cutting-edge technologies that rely on quantum principles, such as quantum computing and cryptography, and discusses their potential impact on various industries. This adds a practical dimension to the book, making it relevant and engaging for those interested in the future of technology.
The book also raises thought-provoking questions about the nature of reality and our place in the universe. Brody delves into the philosophical implications of quantum mechanics, challenging listeners to reconsider their understanding of cause and effect, determinism, and the nature of consciousness. These philosophical explorations add depth to the book and encourage listeners to ponder the profound implications of quantum physics.
However, the audiobook is not without its limitations. At times, the subject matter can become quite dense and complex, requiring active concentration from listeners to fully grasp the concepts being presented, especially when he starts quoting long mathematical formulae. Some listeners may find themselves needing to rewind and re-listen to certain sections in order to fully understand the material. Additionally, while Brody does a commendable job of simplifying complex ideas, some listeners may still find some of the concepts challenging to comprehend.
Overall, "Quantum Entanglement" is a captivating and illuminating book that will appeal to listeners with an interest in physics, quantum mechanics, and the mysteries of the universe. Brody's ability to make complex concepts accessible and his passion for the subject make for an engaging listening experience. While the book may require some mental effort to fully grasp the intricate concepts, the reward is a deeper understanding of one of the most mind-boggling areas of science. "Quantum Entanglement" is a fascinating journey into the quantum world that will leave listeners with a greater appreciation for the wonders and mysteries of our universe.
One of the strengths of the book is Brody's ability to explain complex scientific concepts in a way that is relatable and easy to follow. He breaks down the fundamental principles of quantum mechanics, such as superposition and entanglement, using clear and vivid examples that allow listeners to grasp these abstract concepts.
Moreover, Brody's passion for the subject shines through in the audiobook, making it an enjoyable and immersive experience. His enthusiasm for quantum physics is contagious, and it's evident that he wants listeners to share in his excitement for the mysteries of the quantum world.
Another strength of "Quantum Entanglement" is its integration of real-world applications and implications of quantum mechanics. Brody explores cutting-edge technologies that rely on quantum principles, such as quantum computing and cryptography, and discusses their potential impact on various industries. This adds a practical dimension to the book, making it relevant and engaging for those interested in the future of technology.
The book also raises thought-provoking questions about the nature of reality and our place in the universe. Brody delves into the philosophical implications of quantum mechanics, challenging listeners to reconsider their understanding of cause and effect, determinism, and the nature of consciousness. These philosophical explorations add depth to the book and encourage listeners to ponder the profound implications of quantum physics.
However, the audiobook is not without its limitations. At times, the subject matter can become quite dense and complex, requiring active concentration from listeners to fully grasp the concepts being presented, especially when he starts quoting long mathematical formulae. Some listeners may find themselves needing to rewind and re-listen to certain sections in order to fully understand the material. Additionally, while Brody does a commendable job of simplifying complex ideas, some listeners may still find some of the concepts challenging to comprehend.
Overall, "Quantum Entanglement" is a captivating and illuminating book that will appeal to listeners with an interest in physics, quantum mechanics, and the mysteries of the universe. Brody's ability to make complex concepts accessible and his passion for the subject make for an engaging listening experience. While the book may require some mental effort to fully grasp the intricate concepts, the reward is a deeper understanding of one of the most mind-boggling areas of science. "Quantum Entanglement" is a fascinating journey into the quantum world that will leave listeners with a greater appreciation for the wonders and mysteries of our universe.
February 8, 2025
Short but not enlightening. Quantum entanglement is, to me, one of the more confusing concepts of quantum physics. So I thought that maybe by reading a book specifically about it that I would be able to grasp it a little better. I was wrong.
That may not be fair, I did get a little clearer understanding, but honestly this book focuses so much on the math that tries to prove quantum entanglement and less on what it actually is. The author doesn’t do so great at explaining the math in a way the average person could understand.
Essentially quantum entanglement is particles that are connected at a subatomic level and once the state of one particle is measured the state of the other is forever fixed. This means one particle can’t be described without the state of the other particle and the distance between the particles doesn’t matter.
One of the best examples of quantum entanglement is the Schrödinger’s cat thought experiment. In it Schrödinger places a cat in a closed box and then states that the cat could be alive or dead and that as long as the cat is in the closed box it exists in both states, alive and dead, simultaneously until the box is opened and the state of the cat is observed. Once observed as alive the world where the cat was dead disappears forever.
Is your brain doing flips yet? Yeah. Well Schrödinger’s cat is potentially the easiest and simplest way to show or explain quantum entanglement. It gets significantly more complicated pretty quickly because there are so many factors that get added to the mix. However, at it’s most basic the point is that any particle could be in any two states at any moment while not being observed but as soon as a particle is observed it must remain that way forever and that truth has some deep consequences to quantum physics.
Anyway. I understand the basics. I get lost as it becomes more complicated particularly as one adds spin, momentum, and polarity to the particles and how they create paradoxes and violate Bell’s inequality, the local realism view of causality, and collapses of wave functions. My brain starts to smoke after a while. This book helped a little but not enough for my liking.
Overall it is short but not enlightening enough to suggest it to anyone. Yet, it feels like something way beneath anyone who is a physicist. So too high brow for average and above average people but too shallow for the brainiacs of the world.
That may not be fair, I did get a little clearer understanding, but honestly this book focuses so much on the math that tries to prove quantum entanglement and less on what it actually is. The author doesn’t do so great at explaining the math in a way the average person could understand.
Essentially quantum entanglement is particles that are connected at a subatomic level and once the state of one particle is measured the state of the other is forever fixed. This means one particle can’t be described without the state of the other particle and the distance between the particles doesn’t matter.
One of the best examples of quantum entanglement is the Schrödinger’s cat thought experiment. In it Schrödinger places a cat in a closed box and then states that the cat could be alive or dead and that as long as the cat is in the closed box it exists in both states, alive and dead, simultaneously until the box is opened and the state of the cat is observed. Once observed as alive the world where the cat was dead disappears forever.
Is your brain doing flips yet? Yeah. Well Schrödinger’s cat is potentially the easiest and simplest way to show or explain quantum entanglement. It gets significantly more complicated pretty quickly because there are so many factors that get added to the mix. However, at it’s most basic the point is that any particle could be in any two states at any moment while not being observed but as soon as a particle is observed it must remain that way forever and that truth has some deep consequences to quantum physics.
Anyway. I understand the basics. I get lost as it becomes more complicated particularly as one adds spin, momentum, and polarity to the particles and how they create paradoxes and violate Bell’s inequality, the local realism view of causality, and collapses of wave functions. My brain starts to smoke after a while. This book helped a little but not enough for my liking.
Overall it is short but not enlightening enough to suggest it to anyone. Yet, it feels like something way beneath anyone who is a physicist. So too high brow for average and above average people but too shallow for the brainiacs of the world.
June 18, 2024
DOES QUANTUM PHYSICS REQUIRE DISCARDING “EVERYDAY ASSUMPTIONS”?
Author Jed Brody wrote in the Preface to this 2020 book, “I read ‘The Tao of Physics’ in high school, and it left me hungry to understand the mathematical rigor that inspired mystical statements about quantum physics. I was equally unsatisfied in college physics courses, which had plenty of mathematical rigor but no mystical statements whatsoever. I wrote a term paper about quantum entanglement, which is mysterious if not quite mystical… but the information sank into my mind no further than the level that handles paraphrasing. One reason I didn’t understand quantum entanglement is that I had never done an experiment with entangled particles… Now that I’ve done experiments with entangled particles, I hope I’m able to explain the phenomenon to anyone who’s curious.” (Pg. ix)
In the first chapter, he explains, “The purpose of this book is to empower you to deeply understand how out common-sense assumptions impose constraints---from which entangled particles burst free. In other words, this book explains what quantum physics is NOT. Our task is to paint the negative space of quantum physics, a space composed of seemingly plausible theories that cannot account for measured results… Does the mathematics of quantum entanglement say something mystifying, or even mystical, about the universe?... should we be mystified by the quantum contradiction of our everyday assumptions? … We will see that our common-sense assumptions impose simple mathematical constraints on measurable quantities. These constraints are violated by both quantum theory and measured data.” (Pg. 1-3) Later, he adds, “By the end of this book, you will understand the reasoning that forces us to discard everyday assumptions, and you will be able to draw your own conclusions.” (Pg. 5)
He states, “People like Einstein were fed up with vagueness, uncertainty, and contradictions… Surely nature itself is not guilty of doublethink. Surely quantum physics can be massaged and refined, retaining its accuracy while eliminating the fuzziness and absurdity. Einstein, uncharacteristically, was wrong.” (Pg. xvii-xix)
He explains, “Einstein insisted on realism to preserve locality: the photons must have shared properties all along---from the moment they are created in a single location. And since these shared properties can’t be predicted with certainty in quantum mechanics must be incomplete… Einstein tirelessly defended our common-sense assumptions, which were shared by many other prominent physicists. But we can no longer accept Einstein’s argument in favor of local realism. Bell showed that local realism imposes constraints that may be either satisfied or violated by experiment. In fact, experimental violates these constraints (Bell inequalities), so local realism is overthrown in the laboratory.” (Pg. 38)
He argues, “There is a way to save realism: we can discard locality… Or, we can discard both realism and locality. This permits an interpretation of quantum mechanics that I find simple and expedient: measurement creates objectively real states… this interpretation is not consistent with realism, which requires measurable properties to exist prior to measurable properties to exist prior to measurement.” (Pg. 83)
He notes, “Spooky action at a distance is consistent with even the strangest consequence of relativity: the chronological order of events may depend on who’s observing. You and I may agree that YOU measure your photon before I measure mine, but someone traveling exceptionally fast may observe, instead, that MY measurement occurs first. The speedy observer sees the measurements occur in the opposite order, but the result is the same: the outcome of the first measurement is random, and the outcome of the second measurement is compelled to be the same.” (Pg. 119)
He observes, “Some physicists have actually proposed that consciousness creates objectively real states. Before registering in someone’s consciousness, the photon is in a fundamentally undetermined and unknowable state---and so is everything it encounters on its way, in an avalanche of indeterminacy! In this view, the computer screen is in some unimaginable combination of showing BOTH MUTUALLY EXCLUSIVE OUTCOMES before the conscious observer comes along.” (Pg. 131)
He concludes, “According to the Qbists, there is absolutely no action at a distance. If I measure the polarization of one entangled photon and find it to be horizontally polarized, I immediately believe with 100 percent certainty that the other photon will also be horizontally polarized… I don’t permanently encamp with the QBists. But on occasion, QBism feels like an invigorating breeze that clears away a cloying miasma of confusion… we step outside of QBist science when we speculate about things that can never be directly observed. What happens to objects that no one’s looking at?... The visible universe does not completely blink out of QBist existence when we close our eyes… QBism preserves our common sense. Quantum mechanics is classified as a prediction took, not a gateway to ultimate reality. QBism sweeps the cobwebby spookiness out of quantum physics … There’s no action at a distance, and there’s no speculation… about what particles are doing when we’re not looking at them. But we can push this idea in a direction unintended by QBist’s inventors. If we really believe that direct observation is the only reality, then, looking at the night sky is a single truth; observer and observed cannot be logically separated. And the quest to preserve locality leads to unification with everything we see.” (Pg. 145-147)
This book will interest those studying creative presentations of quantum mechanics.
Author Jed Brody wrote in the Preface to this 2020 book, “I read ‘The Tao of Physics’ in high school, and it left me hungry to understand the mathematical rigor that inspired mystical statements about quantum physics. I was equally unsatisfied in college physics courses, which had plenty of mathematical rigor but no mystical statements whatsoever. I wrote a term paper about quantum entanglement, which is mysterious if not quite mystical… but the information sank into my mind no further than the level that handles paraphrasing. One reason I didn’t understand quantum entanglement is that I had never done an experiment with entangled particles… Now that I’ve done experiments with entangled particles, I hope I’m able to explain the phenomenon to anyone who’s curious.” (Pg. ix)
In the first chapter, he explains, “The purpose of this book is to empower you to deeply understand how out common-sense assumptions impose constraints---from which entangled particles burst free. In other words, this book explains what quantum physics is NOT. Our task is to paint the negative space of quantum physics, a space composed of seemingly plausible theories that cannot account for measured results… Does the mathematics of quantum entanglement say something mystifying, or even mystical, about the universe?... should we be mystified by the quantum contradiction of our everyday assumptions? … We will see that our common-sense assumptions impose simple mathematical constraints on measurable quantities. These constraints are violated by both quantum theory and measured data.” (Pg. 1-3) Later, he adds, “By the end of this book, you will understand the reasoning that forces us to discard everyday assumptions, and you will be able to draw your own conclusions.” (Pg. 5)
He states, “People like Einstein were fed up with vagueness, uncertainty, and contradictions… Surely nature itself is not guilty of doublethink. Surely quantum physics can be massaged and refined, retaining its accuracy while eliminating the fuzziness and absurdity. Einstein, uncharacteristically, was wrong.” (Pg. xvii-xix)
He explains, “Einstein insisted on realism to preserve locality: the photons must have shared properties all along---from the moment they are created in a single location. And since these shared properties can’t be predicted with certainty in quantum mechanics must be incomplete… Einstein tirelessly defended our common-sense assumptions, which were shared by many other prominent physicists. But we can no longer accept Einstein’s argument in favor of local realism. Bell showed that local realism imposes constraints that may be either satisfied or violated by experiment. In fact, experimental violates these constraints (Bell inequalities), so local realism is overthrown in the laboratory.” (Pg. 38)
He argues, “There is a way to save realism: we can discard locality… Or, we can discard both realism and locality. This permits an interpretation of quantum mechanics that I find simple and expedient: measurement creates objectively real states… this interpretation is not consistent with realism, which requires measurable properties to exist prior to measurable properties to exist prior to measurement.” (Pg. 83)
He notes, “Spooky action at a distance is consistent with even the strangest consequence of relativity: the chronological order of events may depend on who’s observing. You and I may agree that YOU measure your photon before I measure mine, but someone traveling exceptionally fast may observe, instead, that MY measurement occurs first. The speedy observer sees the measurements occur in the opposite order, but the result is the same: the outcome of the first measurement is random, and the outcome of the second measurement is compelled to be the same.” (Pg. 119)
He observes, “Some physicists have actually proposed that consciousness creates objectively real states. Before registering in someone’s consciousness, the photon is in a fundamentally undetermined and unknowable state---and so is everything it encounters on its way, in an avalanche of indeterminacy! In this view, the computer screen is in some unimaginable combination of showing BOTH MUTUALLY EXCLUSIVE OUTCOMES before the conscious observer comes along.” (Pg. 131)
He concludes, “According to the Qbists, there is absolutely no action at a distance. If I measure the polarization of one entangled photon and find it to be horizontally polarized, I immediately believe with 100 percent certainty that the other photon will also be horizontally polarized… I don’t permanently encamp with the QBists. But on occasion, QBism feels like an invigorating breeze that clears away a cloying miasma of confusion… we step outside of QBist science when we speculate about things that can never be directly observed. What happens to objects that no one’s looking at?... The visible universe does not completely blink out of QBist existence when we close our eyes… QBism preserves our common sense. Quantum mechanics is classified as a prediction took, not a gateway to ultimate reality. QBism sweeps the cobwebby spookiness out of quantum physics … There’s no action at a distance, and there’s no speculation… about what particles are doing when we’re not looking at them. But we can push this idea in a direction unintended by QBist’s inventors. If we really believe that direct observation is the only reality, then, looking at the night sky is a single truth; observer and observed cannot be logically separated. And the quest to preserve locality leads to unification with everything we see.” (Pg. 145-147)
This book will interest those studying creative presentations of quantum mechanics.
June 21, 2024
That was actually great.
March 22, 2021
I'm a layperson with no scientific education; I'm just interested in learning the various ways in which science attempts to explain "reality". This book established the concept of local realism well and how it breaks down at the quantum level. The grey area that is resulted allows us to explore various theories and philosophical ideas. In this space we can let our imaginations run wild.
For me, chapter 4, "Rigorous Contradiction of Everyday Assumptions", was a bit over my head with the logic/mathematical examples, but I think it was necessary to have this chapter in order to establish just how local realism breaks down under relative observation.
This book opened my eyes to the funny business of quantum mechanics. That said, I will be looking for additional reading that does a better job of putting this subject matter into words for someone like me whose mind breaks down when mathematical examples are used
For me, chapter 4, "Rigorous Contradiction of Everyday Assumptions", was a bit over my head with the logic/mathematical examples, but I think it was necessary to have this chapter in order to establish just how local realism breaks down under relative observation.
This book opened my eyes to the funny business of quantum mechanics. That said, I will be looking for additional reading that does a better job of putting this subject matter into words for someone like me whose mind breaks down when mathematical examples are used
December 21, 2020
Silly and incomplete
If you did not know what entanglement is before you read this silly book you will be none the wiser after reading it. Instead you will have been treated to fragmentary and incomplete accounts of Bell’s inequality which will also leave you none the wiser. If you are going to go on a spree go the whole hog or don’t waste our time with it. The overall paper tiger being assailed is local ‘realism’. But the level of philosophical naivety if not outright obtuseness is astonishing. A fragmentary discussion of measurement is thrown into the mix just to add to confusion. If direct observation is the only reality ... ugh ... what of the state of the earth for all of those billions of years before humans arrived. Maybe it was kept ‘real’ by hordes of little green men in flying saucers. The whole silliness of the discussion leaves me nauseated.
If you did not know what entanglement is before you read this silly book you will be none the wiser after reading it. Instead you will have been treated to fragmentary and incomplete accounts of Bell’s inequality which will also leave you none the wiser. If you are going to go on a spree go the whole hog or don’t waste our time with it. The overall paper tiger being assailed is local ‘realism’. But the level of philosophical naivety if not outright obtuseness is astonishing. A fragmentary discussion of measurement is thrown into the mix just to add to confusion. If direct observation is the only reality ... ugh ... what of the state of the earth for all of those billions of years before humans arrived. Maybe it was kept ‘real’ by hordes of little green men in flying saucers. The whole silliness of the discussion leaves me nauseated.
March 18, 2023
Reading this book was part of my re-embracing of the interest in physics I had when I was younger. It was at times a difficult read, but in the end I was able to follow it which is a testament to the author.
The counter-intuitive predictions of quantum mechanics are often extrapolated into the service of mystical views of the universe, and the book does not reject those extrapolations, though it does provide an example of how to apply logic to even the more "out there" interpretations of quantum uncertainties.
If you have some comfort with math, or at least rigorous logic, this book is worth a read.
The counter-intuitive predictions of quantum mechanics are often extrapolated into the service of mystical views of the universe, and the book does not reject those extrapolations, though it does provide an example of how to apply logic to even the more "out there" interpretations of quantum uncertainties.
If you have some comfort with math, or at least rigorous logic, this book is worth a read.
February 8, 2025
Jed Brody’s Quantum Entanglement is an accessible and illuminating journey into one of the most mysterious and fascinating phenomena in quantum mechanics. Written for both the curious novice and the scientifically inclined reader, the book strikes a rare balance between clarity and depth, making it a standout work in the realm of popular science.
Brody begins by unpacking the foundational principles of quantum mechanics, offering a clear explanation of concepts like wave-particle duality and superposition. From there, he dives into the crux of the book: quantum entanglement, or what Einstein famously called “spooky action at a distance.” Through engaging analogies and real-world examples, Brody demystifies this mind-bending phenomenon where particles become linked in such a way that the state of one instantaneously affects the other, no matter the distance between them.
What sets this book apart is Brody’s ability to weave complex mathematical ideas into the narrative without overwhelming the reader. While equations are present for those who wish to delve deeper, they are not a barrier to understanding the core concepts. Brody’s writing is crisp, often humorous, and infused with wonder, which keeps the reader engaged even when grappling with the most abstract ideas.
The book also provides historical context, discussing the groundbreaking work of scientists like Bell, Schrödinger, and Bohr, and how their contributions have shaped our understanding of entanglement. Brody highlights the philosophical implications of quantum mechanics, prompting readers to ponder questions about reality, causality, and the nature of the universe itself.
For readers looking for practical applications, Brody touches on how quantum entanglement underpins revolutionary technologies like quantum computing, quantum cryptography, and teleportation experiments. These glimpses into the future help ground the abstract concepts in tangible possibilities.
If there’s any critique, it might be that readers completely unfamiliar with basic physics may need to pause and reread certain sections to fully grasp the material. However, this is more a testament to the complexity of the subject rather than a shortcoming of Brody’s writing.
In Quantum Entanglement, Jed Brody has created a rare gem: a book that is both educational and delightful, inviting readers to peer into the quantum world with awe and curiosity. Whether you’re a science enthusiast, a student, or simply someone intrigued by the mysteries of the universe, this book is an excellent starting point for understanding one of physics’ most mind-bending phenomena.
Brody begins by unpacking the foundational principles of quantum mechanics, offering a clear explanation of concepts like wave-particle duality and superposition. From there, he dives into the crux of the book: quantum entanglement, or what Einstein famously called “spooky action at a distance.” Through engaging analogies and real-world examples, Brody demystifies this mind-bending phenomenon where particles become linked in such a way that the state of one instantaneously affects the other, no matter the distance between them.
What sets this book apart is Brody’s ability to weave complex mathematical ideas into the narrative without overwhelming the reader. While equations are present for those who wish to delve deeper, they are not a barrier to understanding the core concepts. Brody’s writing is crisp, often humorous, and infused with wonder, which keeps the reader engaged even when grappling with the most abstract ideas.
The book also provides historical context, discussing the groundbreaking work of scientists like Bell, Schrödinger, and Bohr, and how their contributions have shaped our understanding of entanglement. Brody highlights the philosophical implications of quantum mechanics, prompting readers to ponder questions about reality, causality, and the nature of the universe itself.
For readers looking for practical applications, Brody touches on how quantum entanglement underpins revolutionary technologies like quantum computing, quantum cryptography, and teleportation experiments. These glimpses into the future help ground the abstract concepts in tangible possibilities.
If there’s any critique, it might be that readers completely unfamiliar with basic physics may need to pause and reread certain sections to fully grasp the material. However, this is more a testament to the complexity of the subject rather than a shortcoming of Brody’s writing.
In Quantum Entanglement, Jed Brody has created a rare gem: a book that is both educational and delightful, inviting readers to peer into the quantum world with awe and curiosity. Whether you’re a science enthusiast, a student, or simply someone intrigued by the mysteries of the universe, this book is an excellent starting point for understanding one of physics’ most mind-bending phenomena.
May 8, 2024
This is a summary of quantum mechanics and the idea of quantum entanglement. The narration is excellent and it starts off strong with some personal stories about the author. Very engaging. However, the narration soon got bogged down in something akin to accounting. The proofs for quantum entanglement are necessarily statistical and while the examples were reasonably simple, it seemed to require pencil and paper to figure things out.
I started to zone out as the explanations became more and more detailed. No matter how simple the author tried to make it, it really did require a chalkboard or the printed page and obviously, neither of these were available via audio.
A much longer but more easily comprehensible explanation for quantum entanglement can be found in the book, "Spooky Action at a Distance: The Phenomenon That Reimagines Space and Time—and What It Means for Black Holes, the Big Bang, and Theories of Everything" by George Musser.
I doubt I will return to this book even though I found the author quite likable.
I started to zone out as the explanations became more and more detailed. No matter how simple the author tried to make it, it really did require a chalkboard or the printed page and obviously, neither of these were available via audio.
A much longer but more easily comprehensible explanation for quantum entanglement can be found in the book, "Spooky Action at a Distance: The Phenomenon That Reimagines Space and Time—and What It Means for Black Holes, the Big Bang, and Theories of Everything" by George Musser.
I doubt I will return to this book even though I found the author quite likable.
July 26, 2022
TLDR: Not a bad book - a light read, but somewhat lacking in depth .
The book explains how some of the early Quantum Entanglement experiments have been performed and why they were set up that way. The simplified examples are visual and easy to follow.
Unfortunately it's somewhat to simplistic, to a point where many times it feels like a dejavu reading the same statements. Progressing from the first experiment to the last there's barely any new information added. Reading about the first one, tells you almost everything about the last one. And if there is something new one could also say it's because it was omitted from the earlier explanations and not because it's exclusive to the later experiments.
It's also missing at least one important experiment - the Delayed Choice Quantum Eraser (Which almost defies not just space but time!)
I am also convinced there is one mistake in the book, but I will need to double check.
The book explains how some of the early Quantum Entanglement experiments have been performed and why they were set up that way. The simplified examples are visual and easy to follow.
Unfortunately it's somewhat to simplistic, to a point where many times it feels like a dejavu reading the same statements. Progressing from the first experiment to the last there's barely any new information added. Reading about the first one, tells you almost everything about the last one. And if there is something new one could also say it's because it was omitted from the earlier explanations and not because it's exclusive to the later experiments.
It's also missing at least one important experiment - the Delayed Choice Quantum Eraser (Which almost defies not just space but time!)
I am also convinced there is one mistake in the book, but I will need to double check.
July 22, 2021
Key Takeaways:
Realism: Everything that has a physical state has a physical state regardless if any one or thing is observing.
Locality: Observing one object has no impact on another.
Local Realism: Objects have physical properties that exist whether or not observed, and they remain unaffected by observed distant objects.
Bell inequality: A constraint on a measurable quantity.
An experiment can test bell inequalities, if proven then the experiment will satisfy local realism, but falsify quantum physics.
If the experiment fails, the opposite occurs.
Over and over, Bell inequalities fail.
Light is an electromagnetic wave
An object's length depends on the speed of the observer
Properties of space and time are not universal, they depend on who is observing.
For discussion questions and more please visit https://ethanaycock.com/book-reviews/...
Realism: Everything that has a physical state has a physical state regardless if any one or thing is observing.
Locality: Observing one object has no impact on another.
Local Realism: Objects have physical properties that exist whether or not observed, and they remain unaffected by observed distant objects.
Bell inequality: A constraint on a measurable quantity.
An experiment can test bell inequalities, if proven then the experiment will satisfy local realism, but falsify quantum physics.
If the experiment fails, the opposite occurs.
Over and over, Bell inequalities fail.
Light is an electromagnetic wave
An object's length depends on the speed of the observer
Properties of space and time are not universal, they depend on who is observing.
For discussion questions and more please visit https://ethanaycock.com/book-reviews/...
December 17, 2025
I thoroughly enjoyed this as someone who hates really theoretical & scientific books. I already shared Brody’s stance before reading this and his arguments out only amplified my original stance. Liked how the final chapter borders on almost philosophy.
Loved the concept of “"In a certain sense then, reality is something that happens in another space than our own, and what we perceive of it are just shadows”.
Loved the concept of “"In a certain sense then, reality is something that happens in another space than our own, and what we perceive of it are just shadows”.
September 15, 2020
This is definately the most I've felt I understood quantum entanglement... though that's not saying much. Generally this is a really interesting topic, and I think the author did a good job of communicating it. I would recommend this book to people who aren't necessarily physics majors, but have a bit of a scientific background (high-school intro physics/chem would help a bit).
October 25, 2020
So you want to crack quantum entanglement? This book provides a solid foundation in an approachable but still theoretically challenging beginners guide format. Do not seek this book if you desire greater mathematical or philosophical depth, this provides a mere introduction to both aspects. I enjoyed the book and will return to it for reference.
August 1, 2024
Quantum Mechanics for the layman
The author made a good attempt to present a broad range of the historical background and current theories in the physics community. If anything, he may be guilty of trying to cover too much in one book. I still recommend it for amateur physicists.
The author made a good attempt to present a broad range of the historical background and current theories in the physics community. If anything, he may be guilty of trying to cover too much in one book. I still recommend it for amateur physicists.
August 7, 2022
I'd give this book a 3.5. There are parts that are well written, while other parts are not so good. I read it twice, stopping two thirds of the way the first time, as the writing style was just confusing. I found that at times the author is repetitive and at the same time not getting to the conclusions in an articulated way. It's short, but because of this, it can take some time to read.
September 9, 2024
Very brief, which is to its credit, but in some places I wanted more. Not sure who the book is targeting though, too simple for experts, maybe not simple enough for amateurs? Probably best for undergraduate physics majors.
January 13, 2025
A succinct summary of quantum entanglement and spooky action at a distance. I would have like a deeper dive into some of the philosophy that it’s inspired, but this ended up being more about the experimental facts.
December 30, 2025
An exploration of quantum entanglement and the ways in which it contradicts our everyday assumptions about the ultimate nature of reality. Quantum physics is notable for its brazen defiance of common sense. Very technical. I didn’t understand most of it but it was great for helping me get to sleep!
June 16, 2021
Poorly written, poorly rendered concept. I'll look elsewhere.
February 20, 2023
An escalating series of mathematical experiments to show why quantum mechanics cannot be measured with any certainty.
May 25, 2023
This would probably be an excellent intro to the subject as a video but a bit hard to follow in this format.
September 30, 2023
Quantums are the smallest particles and entanglements are how these particles react together. They seem to follow physics laws until they don’t. The analogies used with quantum entanglement are 1) how your feet don’t always do what you want them to, and 2) how twins seems to know what the other twin is feeling.
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