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Quantum: Einstein, Bohr and the Great Debate About the Nature of Reality

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For most people, quantum theory is a byword for mysterious, impenetrable science. And yet for many years it was equally baffling for scientists themselves. Manjit Kumar gives a dramatic and superbly-written history of this fundamental scientific revolution, and the divisive debate at its heart.

For 60 years most physicists believed that quantum theory denied the very existence of reality itself. Yet Kumar shows how the golden age of physics ignited the greatest intellectual debate of the twentieth century.

Quantum sets the science in the context of the great upheavals of the modern age. In 1925 the quantum pioneers nearly all hailed from upper-middle-class academic families; most were German; and their average age was 24. But it was their irrational, romantic spirit, formed in reaction to the mechanised slaughter of the First World War that inspired their will to test science to its limits.

The essential read for anyone fascinated by this complex and thrilling story and by the band of young men at its heart.

448 pages, Paperback

First published March 5, 2007

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Manjit Kumar

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Displaying 1 - 30 of 481 reviews
Profile Image for Matt.
752 reviews522 followers
January 16, 2016

Quantum-Theory is a rather complicated matter of which I knew next to nothing prior to reading this book. Of course I heard of some players in this field, like Einstein, Bohr, Schrödinger, or Heisenberg, but it was all very vague and left me standing pretty much in the dark. Manjit Kumar was able to shed at least a little light (some photons if you like) on the topic, and I got a glimpse on this extraordinary achievement of human mind.

Spanning roughly the time between 1900 (Planck's constant) and the mid 1960s (Everett's many world interpretation) this books explains QT/QM in a language that makes it relatively easy for this layman to follow. There's hardly any mathematics in this book and only a few diagrams. The author sets the weight on the essential leaps in developing the theory and adds some intriguing biographical and historical background on the physicists involved.

I suppose everyone heard of "Schrödinger's cat". This thought experiment is explained pretty well, and also why Schrödinger invented it in the first place. Much more interesting to me though was the Einstein-Bohr debate. Apparently Einstein has spend a lot of his energy to refute Bohr's interpretation of QM. Alas, he failed.

For scientists, this book is certainly too superficial, but I think in order to gain an outside perspective on quantum mechanics this is an excellent read.

UPDATE 1/16/16
Dramatis personæ; at the Solvay International Conference on Electrons and Photons, 1927 [click to enlarge and read names]

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Profile Image for Prerna.
222 reviews1,325 followers
July 31, 2021
Twentieth century European physicists have enjoyed an unparalleled degree of fame, recognition and adoration. Physics in its aims has differed very greatly from the other sciences, no other branch will even presume to give a complete description of reality. They're all happy in their niches, but physics, with its grand search for a unified theory has birthed many debates - both productive and caustic, self-criticism, long-standing rivalries and even great friendships.

This book is essentially a history of the development of quantum mechanics and contains stories of both its proponents and opponents. Any good physics student can probably recite the quantum mechanics recipe to you within a minute if asked, and it all comes from the celebrated and widely accepted Copenhagen interpretation. But it's the very nature of this interpretation that Einstein attacked repeatedly, even well into his final years. He couldn't accept that a theory that postulates fundamental uncertainties could actually be complete. There must be hidden variables un-accounted for by quantum mechanics, he argued. But Bohr and his students/followers/posse always constructed counter-arguments that Einstein begrudgingly accepted. Until the infamous Einstein-Podolsky-Rosen paper.

The EPR paper argued that quantum mechanics couldn't be complete, because its description necessitated non-locality. Although Bohr and his team came up with several answers, none of them were truly satisfactory. Even as Copenhagen interpretation was accepted, taught and practiced worldwide, this issue remained unsolved until Bell. We now know, with almost absolute certainty that Bohr was right. Or at least that's what most experimental evidence and Bell's theorem proved. However, there has recently been renewed interest in Einstein's view and physicists as well as philosophers have tried to formulate other theories that would satisfy Bell's inequality while also providing a better description of reality than the Copenhagen interpretation does. The many worlds theory is probably the most famous of them.

I have reduced this book down greatly. Manjit Kumar writes wittily and inspiringly of many, many physicists and traces the development of physics through two world wars, and examines its status at the turn of the last century. I honestly wish I'd read this during my undergrad or at least during my masters.
Profile Image for Max.
343 reviews309 followers
June 7, 2017
I thoroughly enjoyed Kumar’s book. He traces the scientific discoveries leading to quantum theory and the relationships of the scientists with a focus on the Einstein-Bohr debate over the theory’s meaning. I found Kumar’s explanations of complex theories accessible and helpful. I remember in high school and college in the 1960’s always hearing about this strange quantum world that didn’t quite exist unless someone looked at it. Kumar really helps make sense of it. My notes below summarize the science that paved the way for quantum theory, the Einstein Bohr rivalry and the various takes on the Copenhagen interpretation.

Kumar’s history begins with Max Planck’s discovery of the quantum and his eponymous constant. Working to derive a formula to predict the spectral distribution of blackbody radiation in 1900, Planck found that only whole increments of energy worked. At a time when the atom was not a widely accepted theory, this confronted Planck’s belief in the continuous nature of energy and matter. He dodged the issue by saying that only the exchange of energy was quantized, not energy itself.

Along came Einstein who accepted atoms as discrete matter and sources of discrete energy. After reading Planck’s paper Einstein challenged the prevailing wave theory of light, proclaiming light is made up of quanta. Einstein employed his quantum theory of electromagnetic radiation to explain the photoelectric effect in which light precipitates the release of electrons from metals. This was in 1905. Even in 1922 when Einstein was awarded the Noble Prize for his equation explaining the photoelectric effect, the underlying principle of light as quanta was still not widely accepted. Newton had held that light was composed of particles, but Thomas Young’s famous two slit experiment in 1801 showed light to be a wave. After overcoming the implied disrespect to Newton, scientists finally accepted light as a wave and held onto that view as tenaciously as they had held onto the particle view before. Also in Einstein’s Annus Mirabilis he explained Brownian motion with atomic theory gaining the atom much wider acceptance. And in his spare time that year he formulated the special theory of relativity and the famous E=MC2.

In 1913 Niels Bohr conceptualized the quantum atom. Recognizing that J. J. Thomson’s plum pudding model of the atom was inherently unstable Bohr assigned electrons to special orbits in which they could not continuously emit radiation and lose energy. Each orbit had a specific energy level. When an electron moved from one orbit to another an exact amount of energy (quantum) was exchanged which resulted in unique spectral patterns. Amazingly there was no in between. An electron left one orbit and appeared in another instantaneously. The Franck-Hertz experiment in 1914 confirmed that the energy released or absorbed was exactly the difference between the energy levels of the orbits. In 1922 Bohr refined his atomic model with the concept of electron shells. This allowed him to predict the chemical similarities of elements in the periodic table.

Einstein was thrilled with Bohr’s quantum atom as he felt it proved his theory of light-quanta. In 1916, finding time after his ground shattering theory of general relativity was announced in 1915, Einstein theorized that spontaneous emission occurred when an electron jumped to a lower energy orbit. The rub was that in his theory electrons made these jumps at random. His theory employed probabilities to determine the frequency of these jumps. Einstein, now as later, was uncomfortable with chance in physics theories. Einstein’s light-quantum, later to be renamed the photon, was proven in an 1923 experiment by American Arthur Compton who firing x-rays at graphite recorded changed wavelengths in the reflected scattered x-rays. Only a particle would behave this way. Furthermore he found the recoiling electrons that the x-rays had bounced off of. Then a French prince, Louis de Broglie, setting the stage for quantum mechanics, postulated that if a wave could have the values of a particle, why not the reverse? Ascribing wave characteristics to electrons explained perfectly the available orbits for electrons in an atom. Only those orbits that could accommodate whole or half wave lengths were physically possible. Sure enough subsequent experiments showed that electrons diffracted just like light. Wave particle duality was now established for energy and matter.

In 1925 Wolfgang Pauli building on a paper by Edmund Stoner developed the exclusion principle. Stoner determined the number of possible energy states of electrons orbiting an atom. But the three quantum numbers denoting angular momentum, shape of orbit and orientation of orbit only allowed for half of the possible energy states. Pauli developed a fourth quantum number which would later be explained as spin. This quantum spin had two states, up or down, doubling the number of allowable electrons. It also explained the heretofore mysterious splitting of spectral lines known as the Zeeman Effect. The exclusion principle stated that no two electrons in an atom could have the same set of quantum numbers thus limiting the number of electrons.

Werner Heisenberg solved a remaining problem of the quantum atom model. Even though it now explained the frequency of spectral lines, it did not explain the different intensities. Heisenberg decided to discard anything not observable, even that electrons occupied orbits. He needed the help of Max Born who collaborated with one his students, an excellent mathematician named Pascual Jordan, to get the math to support the physical theory. This new quantum mechanics employed a strange form of matrix mathematics in which A times B does not equal B times A, but it successfully calculated spectral line intensities. In England, Cambridge student P. A. M. Dirac also developed a mathematical proof working from a draft of Heisenberg’s paper.

In 1926 Edwin Schrödinger developed a wave function for de Broglie’s electrons which eliminated the incomprehensible electron jumps. It also supported calculations that achieved the same predictive results as Heisenberg’s matrix mechanics. The rub was picturing what the wave represented. Schrödinger claimed it was a cloud of charge that could smoothly and continuously move from one orbit to another. He denied that electrons were particles at all while Heisenberg, committed to particles, opposed the wave theory, putting the two at odds.

Heisenberg trying to settle his dispute with Schrödinger developed the uncertainty principle. This stated that quantum mechanics could not determine both the position and momentum of a particle, specifically an electron. Heisenberg, working as Bohr’s assistant, toyed with the idea that the photon itself that measured the electron interfered with the observation. Heisenberg refused to imply any behavior to an electron that could not be measured. There was no assuming what happened to an electron between two measurements, thus no path at all was held to have been traveled. Basically Heisenberg was saying classical concepts of wave, particle, position, momentum and trajectory had no meaning in the quantum world until observed.

Bohr believed that uncertainty was fundamental to the quantum nature of wave-particle duality. Bohr felt the electron was both a wave and a particle, but that no experiment could measure both at the same time. He called his principle complementarity. Bohr held that observer and observed could not be separated. The way the quantum world was observed determined what was seen. Be it wave or particle, both observations were true depending on the way it was observed. Causality and regular patterns had no meaning. The only prediction quantum mechanics could make was one of probability. No experiment could ever return the deterministic clockwork cosmos of Newton to the quantum world. There was no reality at the quantum level outside of observation. This view became known as the Copenhagen interpretation.

Einstein, while accepting that quantum mechanics was a correct and important theory, did not accept this interpretation. Einstein believed the quantum world was deterministic (“God doesn’t play dice.”) and most importantly real. It was there even when nobody was looking. The stage was set for a lifelong series of challenges to this interpretation by Einstein directed at Bohr, the Copenhagen Interpretation’s champion. At the conferences in Solvay in 1927 and 1930 Einstein offered thought experiments to show quantum mechanics was an incomplete description of reality. Bohr would parry and nothing would be resolved.

After the Nazi’s assumed power in Germany In 1933 Einstein moved to Princeton. Bohr would be able to continue in Copenhagen until the Nazi’s declared martial law in Denmark in 1943. Many Physicists in Germany were Jewish or had Jewish connections. They were leaving and scattering around the world. Despite the turmoil of the 1930’s and 40’s, Einstein and Bohr carried on their quantum chess match. Einstein in 1935 published a paper with help from Princeton assistants known as the EPR paper. This thought experiment proposed measuring the momentum and position of one of a pair of entangled particles to determine the momentum and position of the other. The point was to prove the existence of the other particle independent of direct observation of it. The Copenhagen interpretation denied reality independent of observation. Key to Einstein’s argument was the concept of locality, that nothing faster than the speed of light could affect the other particle. Bohr conceded this but claimed the particles were entwined and thus one system, that a measurement of one was a measurement of both.

Einstein reached out to the sympathetic Schrödinger who came up with his famous cat in a box thought experiment. A tiny radioactive substance is placed in the box. When it decays it will trigger a Geiger counter that will trigger the release of a vial of poison killing the cat. Since the event is not observed, does it happen? In the Copenhagen interpretation of quantum mechanics only a probability wave of the event exists. Schrödinger was trying to appeal to common sense in support of Einstein believing in reality that the cat was either actually dead or still alive. But Copenhagen purists would still say that the cat was both dead and alive until the wave was collapsed by observation. The debate would dominate the minds of Bohr and Einstein over the ensuing years. Bohr last visited Einstein in Princeton in 1954. Einstein died the next year at 76. Bohr died in 1962 at 77. The night before his death Bohr had drawn on his blackboard Einstein’s light box, a thought experiment Einstein proposed at the 1930 Solvay conference in an attempt to prove quantum mechanics an incomplete theory. Over 30 years later Bohr was still refining his argument.

In 1964 John Stewart Bell put forth a theorem to test whether any local hidden variables could be used to explain the behavior of the entangled particles in the EPR thought experiment. Subsequent tests of the theorem supported non-locality between entangled particles and paved the way for today’s experiments with quantum level teleportation. But even though what Einstein called “spooky action at a distance” was proven to exist, his underlying belief that the quantum world also existed even when not measured was not disproven. In 1957 Hugh Everett III found a neat way around the problem with his many worlds interpretation. In this theory all quantum states actually exist simultaneously, obviating the probability wave. This resolved one objection to the Copenhagen Interpretation: Who observed the big bang to collapse the probability wave? God, of course, is one answer. Another issue for quantum mechanics is determining the dividing line between the quantum world and the classical world where reality is the norm.

Despite the overwhelming acceptance of the Copenhagen interpretation in the mid-twentieth century, today while quantum mechanics itself is universally accepted, many physicists don’t believe it is a complete theory. The Copenhagen interpretation has lost its luster. Nobel laurate Murray Gell-Mann said ”Niels Bohr brain-washed a whole generation of physicists into believing that the problem had been solved.” At a 1999 quantum mechanics conference at Cambridge University, of 90 physicists polled, only four accepted the Copenhagen interpretation, thirty believed the modern version of the many worlds theory and most were undecided. Famed British physicist Roger Penrose said “I would, myself, strongly side with Einstein in his belief in a submicroscopic reality, and with his conviction that present-day quantum mechanics is fundamentally incomplete.” So maybe somewhere in the great beyond Einstein is finally winning his argument with Bohr.
Profile Image for India M. Clamp.
212 reviews
June 8, 2022
Einstein---like Feynman---was not so easily discouraged and remained dancing to a beat only they had ears for (despite what others thought about their theories or revelations). His own fellow physicists---youthful and aged---termed him as eccentric or crazy even; some often used the word senile in reference. Einstein remarked “in a world that objectively exists, and which I, in a wildly speculative way, am trying to capture.” Could capture be a form of measurement?

“The fact that all heated objects emit light of the same color at the same temperature was well known to potters long before 1859, the year that Gustav Kirchhoff, a 34-year-old German physicist at Heidelberg University, started his theoretical investigations into the nature of this correlation.”
---Manjit Kumar

For comprehension, basic knowledge of mathematics and science will help you motor like a hummingbird through Kumar's "Quantum: Einstein, Bohr and the Great Debate About the Nature of Reality." Narrative here renders one to full flipping focus imparted by drama, emotion and most skilled writing. When John Wheeler visited Einstein in 1940s (to correct him) about "God playing dice," he still would not concede to Bohr and his big "God" correctness---publicly.
This entire review has been hidden because of spoilers.
Profile Image for Loraine.
253 reviews17 followers
October 24, 2013
Whether the science in this book is light or heavy depends on who you are. For me, the science was heavy, as my fascination with science has always been greater than my knowledge of it. I am not a scientist.
That said, I loved this book. Did I understand all the theories, experiments and discussions? No. But I understood enough to follow the narrative and get excited or saddened by events and to share the passion of these giants and marvel at their tenacity and their genius.
Years ago, When I started my studies in chemistry and physics, my brother thoughtfully gave me a framed copy of the famous Solvay 1927 Conference group photo, the one mentioned in the prologue, as inspiration. Inspire it did, as I gradually learned who these participants were and what they contributed to the understanding of our world. Theirs is such a grand story, I did not need to get every scientific reference in order to love listening to it. I think that is a measure of just how good this book is.
Profile Image for Marta.
996 reviews100 followers
July 4, 2021
Quantum physics seems to me like voodoo - but this book taught me that I am not alone: Einstein himself thought so. “God does not play dice” - he said, being uneasy that quantum theory does not give definite answers to basic questions of reality, in fact it questions the existence of reality itself. This did not jibe with Einstein’s intuition that a theory should be able to answer with yes or no: maybe is not good enough. To the end of his life, Einstein was challenging the validity of quantum theory; and when his challenges were consistently refuted by Bohr, he accepted it but continued to assert that the theory was incomplete. He spent the rest of his life looking for a unified theory that bridges classical and quantum physics.

Manjit Kumar surveys the evolution of quantum theory and the life of its main contributors, with special emphasis on the debate for and con by the two giants of physics: Niels Bohr and Albert Einstein. The Solvey conference of 1927 were packed with the greatest of all time Nobel laureates: Albert Einstein, Marie Curie, Ernest Rutherford, Erwin Schrödinger, Niels Bohr, Werner Heisenberg, etc, etc. Kumar provides insight into their lives, workings, collaborations, and discussions of these great scientists.

Kumar’s gradual explanation enabled me to understand the basic concepts, even though the equations and the details of the thought experiments flew over my head. My notes below are mostly to myself so I can remember later.

The quantum journey begins with Max Planck, who reluctantly added “quantum” as a discreet unit of energy to his calculations while trying to work out the so called “black body problem” that dealt with light waves. Later Einstein expanded the use of quanta to light. He also applied quantum theory to the photoelectric effect in 1905. (Need to go back to look up what this was.)

Niels Bohr came up with “quantum leap” when trying to solve the structure of the atom, and coming up with different energy levels (a.k.a “shells”) for electrons to occupy around the nucleus. Since the electrons can only occupy these levels, when they move between them, they appear instantaniously, with no route between the two: this is called the quantum leap. I bet you did not know that. I didn’t.

While Heisenberg was struggling to work out the math, he realized that measurements of a particle will always change it: at the atomic level, even applying one photon (which is necessary to observe) will change a particle’s position, thus we cannot measure a particle’s position and momentum at the same time - we have to choose. This is the “Heisenberg uncertainty principle”. Unfortunately the math was so complicated that even Heisenberg needed help with it. This is where Schrödinger comes in: he described the quantum events in terms of a wave function, which was much easier to use. The idea that particles can be described as waves was introduced by French physicist and prince (for real!) de Broglie just a couple years before.

There were many more contributors, but by this time the theory was complete enough that the debate could ensue wether it was complete or completely described reality. Niels Bohr expanded on the theory and took it to its conclusions: that we don’t know where a particle is, or whether it even exists, until we observe it. What’s more, it does not even exist until we observe it. This is where Einstein took exception: while he accepted the theory as accurately describing the atomic world, he believed strongly that objective reality exists. Einstein and Bohr spent decades arguing, with many thought experiments involved (details of which I did not get). Schrödinger’s cat was one of these; contrary to popular belief, Schrödinger wrote it to show how ludicrous the theory’s conclusions are when applied to the macro world.

Overall I found the book enjoyable and enlightening, and I even learned from it. (Gasp!). I have listened as I like to listen to popular science books - on audio I tend to enjoy them more than reading, even though I remember less. I guess those cancel each other out. If you want to learn about quantum physics at a popular level, this is a good book. Available on Audible Plus.
Profile Image for Menglong Youk.
401 reviews56 followers
December 12, 2020
4.5/5 stars

If you believe that quantum mechanics is complicated, then, to quote Walter White, you're goddamn right. However, it doesn't mean that quantum mechanics cannot be understood whatsoever. With persistence, patience, and attention, some level of understanding could be reached.

"Quantum: Einstein, Bohr, and the Great Debate about the Nature of Reality" written by Manjit Kumar is a book attempting to guide you through the rich history behind this revolution: from the quantization of energy, which Max Planck considered to be just a magic trick, to Einstein's realization that light is made up of a package of energy called quanta. After the two events, a wave of new generation of young physicists started to emerge including Niels Bohr, Louis de Broglie, Wolfgang Pauli, Weiner Heisenberg, Erwin Schrődinger, Paul Dirac and others.

There were two groups among these men: one, leading by Niels Bohr, believed in Copenhagen Interpretation, while the other one, leading by Einstein, opposed to it. Copenhagen Interpretation states that a physical system does not have a definite property prior to being measured, which means that before being measured, its property is just the cloud of probability. This obscures the nature of reality because nothing is real until observed, and Einstein felt bothered by it. The debate between Einstein and Borh spanned for 3 decades until their death. On the drawing board on the day Bohr died was Einstein's light box which Einstein used to argue with Borh thirty years ago. This, I must admit, made me tear up.

I've read books and watched many documentaries about quantum mechanics before. Yet, each time I re-encounter the contents, my grasp of the subject appears to be pity, miniscule even. The concept of bell theorem is still annoyingly out of reach for me despite my reading about it from various sources many times already. Maybe one day when I have a firm grip and a more stable basic understanding on this subject, all the remaining unreachable concepts would be within my grasp.

If you desire to know more about quantum mechanics, I would totally recommend this book, for it is presented in not-too-technical styles, thus making the probability of your being able to grasp it a bit higher even if you don't have any background of physics or mathematics.


More reviews at https://menglongstarstuff.wordpress.com
Profile Image for Jafar.
728 reviews234 followers
January 23, 2010
I’ve read a few books on Quantum physics and its incredible quirks and its implications about the nature of reality. By comparison, this book is light on the science, but provides an excellent history of quantum physics. There are historical fact that I had never heard of, such as the rivalry between Schrodinger and Heisenberg. Any book on quantum physics makes you think that Schrodinger was one of the pillars of the quantum community, but in fact he was an outsider and at odds with Bohr/Heisenberg/Pauli and closer to Einstein. Einstein’s famous disapproval of the interpretation of quantum physics (“God does not play dice.”) is mentioned in many books, but here you see very well why Einstein, who was the grandfather of quantum, was so uncomfortable with what the Bohr camp was saying, and how he obsessed many years over refuting the probabilistic nature of quantum physics. All in all, a very fascinating book.
Profile Image for Murray Ewing.
Author 13 books19 followers
September 26, 2016
It started with German physicists trying to make a better light bulb, and ended with the collapse of classical physics (if only at the subatomic level). Manjit Kumar’s Quantum is a history of the development of our understanding (if understanding is the right word for something nobody seems to understand) of quantum mechanics, looking into the lives of the key players as much as their discoveries.

The two major players are Einstein and Niels Bohr, who, while agreeing that the equations behind quantum mechanics worked, differed absolutely on what those equations actually meant. Einstein wanted a physics that presented an accurate, realistic model of reality; Bohr believed there was no reality at the quantum level — not until we measured it, at any rate — just a bunch of probabilities, and that no ‘realistic model’ was possible.

Kumar’s biographical approach highlights just how strange the path that led to the ideas of quantum science was — how, for instance, at the early stages, people presented equations that explained experimental results, but that nobody expected to be anything but a stop-gap till a more understandable (and less bizarre) solution came along, only to find that no, their bizarre equations were the best solution, and things were only going to get stranger.

I can’t say I now understand quantum mechanics, or that I followed every theoretical step forward — the actual steps forward are explained quite briefly, without getting too much into technicalities — but I have certainly come to a strong appreciation of what strange materials these genius-level scientists were working with. Plus, it’s a good look into the scientific process generally, how a theory is worked at, and advanced, by many players, how ideas that are later accepted as canonical can be at first ridiculed, and how every step forward in science can raise even more questions.

A good book, it certainly left me wanting to know more.
Profile Image for BetseaK.
78 reviews
December 6, 2014
In this work the author managed to give a superb account of the development of thought about quantum by bringing to life all the great physicists involved (Planck, Einstein, Born, Bohr, Schrödinger, de Broglie, Wien, Pauli, Heisenberg, Dirac, Boltzmann, Compton, Bohm, von Neumann, Bell) through vivid vignettes of their scientific accomplishments, interpersonal relations and the historical background. As it is evident from the title, the aim of the book was to present the clash of philosophical viewpoints between Einstein and Bohr about quantum theory and its interpretation. Without leaning on the equations and the mathematics of quantum theory, Manjit Kumar succeeded to accomplish it through a story that reads like an epistemological thriller. (Needless to say, though ‘the Bell’s Theorem tolled for Einstein’, the ending is still a sort of a cliffhanger.) The quantum concepts are explained with clarity (with a couple of exceptions, but I enjoyed the book too much to be too critical).

As an afterthought: If you are interested in a mystical or religious interpretation of quantum theory, this is not the book.

And also, here’s the link to a review which, in my opinion, captures the feel of this book very well:
Profile Image for Cassandra Kay Silva.
704 reviews280 followers
December 4, 2021
Don't expect to walk away from this book learning anything about Quantum Mechanics. This book is more about the dialogues and interplay between the key players in the development and fleshing out of the theory. About how some of the thought experiments were formed and about the people involved in the debate as it unfolded. For what it was it was an enjoyable narrative.
Profile Image for Roger.
72 reviews14 followers
November 6, 2013
There are a lot of popular science books on quantum theory but this one is different in that its aim is to question what's meant by reality. Manjit Kumar achieves this objective admirably. He also provides what I've found to be the best and most coherent account of the history of the development of quantum theory that I've read, managing, at the same time, to bring alive many of the key physicists and mathematicians involved, and not just Neils Bohr and Albert Einstein who are in the book's title. He also succeeded in explaining many aspects of quantum theory without resorting to mathematics, which is no mean feat. An exception was Bell's Inequality Theorem but I doubt that anyone could explain that in a non-mathematical way - despite having read several accounts by different authors I still have little idea of why this theory should tell us anything about hidden variables, but evidently it does.

Whilst the subject of reality forms the main theme of the book, it's past the half way point before this topic is discussed in any serious way. But then Manjit examines the concept very thoroughly, focussing on the Copenhagen interpretation along with Einstein's objections to this interpretation, based on his belief that quantum theory is incomplete and that probability and non-locality must have some underlying explanation that is still to be discovered.

My only criticism is that I feel the book could have been shorter, perhaps my omitting some of the finer detail when it came to history or by cutting out some of the views expressed by "lesser" scientists. There is quite a lot of repetition but, from my perspective, I found that helpful in reinforcing many of the points raised. However, a reader more familiar with the area might find the repetition irritating.
Profile Image for Nilesh Jasani.
987 reviews135 followers
July 30, 2011
Many good books are written to simplistically explain the theoretical revolutions brought about in The first half of the tweNtieth century. Great biographies are published on the protagonists. But this book is something just different, wonderfuLly different.

Sidestepping relativity is never easy while talking about Einstein. The book manages this. His opposition to Quantum theory is often either trivialised or made ridiculously philosOphical. The book masterfully traverses the landscape.

But the book's biggest achievement is the roles played by so many other luminaries aLong with their background, interpersonal relationShips, rivalries, along with roles played by chance, the sequencing of events that made the era possible as well as the influence of wars.

A must read for anyone interested in either science or scienlists.
Profile Image for Britta Böhler.
Author 9 books1,865 followers
February 10, 2017
A very interesting and detailed account of the development of quantum physics and the decennia-long discussion between Einstein and Bohr about the nature of reality. Not an easy subject but the author manages to make it accessible for non-scientist, (and he kept the mathematicas at a minimum). I listened to the audiobook (ca. 14 hrs), beautifully read by Nat Porter.
Profile Image for D.
504 reviews62 followers
May 14, 2023
The fascinating story of the discovery/development of the theory of quantum mechanics. Very readable, almost no formulas in sight. It is a beautiful example of 'science in action'.

The first use of the term 'quantum' was by Planck who thought the concept just a minor trick to make his theory, about something unrelated, work. Einstein made important contributions, e.g. by insisting that light behaves both as a wave and as a particle (a photon). Many other scientists contributed, and the book devotes some space to their, sometimes surprising, biographies. In the end, the majority settles on at a few complete (and mathematically equivalent) theories. Although very unintuitive (in essence, nature behaves non-deterministically is one such aspect), it appears that the theory unfailingly predicts the outcome of any experiment that one can throw at it.

An interesting subplot concerns the philosophical interpretation of quantum theory. The winning interpretation was pushed none too subtly but successfully by Bohr. This so-called Copenhagen interpretation holds that, in a sense, certain things do not exist independently of their observation. I found it amazing how such a non-realist viewpoint could become the dominant interpretation, at least until recently. Einstein never agreed with the non-deterministic aspect of the theory and spent much of the rest of his life trying to find an alternative deterministic theory. Something that was later, after Einstein's death, proven to be impossible by Bell.

There are 2 useful appendices: a short chronological history of the main events and an index explaining many of the concepts in an intuitive way.
Profile Image for Anna.
1,686 reviews636 followers
June 5, 2017
I’ve ostensibly been reading ‘Quantum’ for nine months. Actually, I got about 70 pages in while on a train then let it sit on my bedside table for three quarters of a year. Then I took it along on another long train journey and got back into it, although it definitely benefits from the lack of distractions in a quiet carriage. The fact is, I am social scientist who hasn’t studied any actual science since I was 16 and only realised while reading this book that the word ‘nuclear’ refers to the nucleus of an atom. Thus I read ‘Quantum’ at a slower pace than I’m used to, in order to get my head around it. The author deserves commendation for making quantum physics gradually comprehensible, on some level, to a layperson. Using the format of a narrative history definitely helps with this. The account of how the Nazis destroyed perhaps the world’s best physics institute with their decree that Jews couldn’t work in universities is especially memorable.

It took me about a hundred pages to get properly involved, but after that I was hooked. Kumar explains the debates between Bohr and Einstein about quantum theory and the very nature of reality with impressive clarity. I certainly feel much closer to understanding and my interest in more recent developments in quantum physics has been piqued. I also appreciated Kumar’s turn of phrase, particularly, ‘In the past, none had emerged unscathed from an attempt to pinpoint what constituted reality’.
Profile Image for Durvasa Gupta.
9 reviews5 followers
June 18, 2018
The title itself is enough to carry away someone who is a quantum nerd. The author presents the biography of not a person but a field of science “Quantum Mechanics” in a most fascinating way. It took over a millennium for people to believe that the Earth was round, not flat. It was a difficult leap for humanity. There was a similar leap needed when the quantum was discovered. All the while when people believed light was a wave and matter continuous they had to take a leap into believing light could be a particle and an atom can have discontinuities. The book not only gives a comprehensive account of the birth of the quantum to the development of quantum mechanics but also in agreement with the title, it gives captivating details of the debate between Einstein and Bohr on the ontology of quantum mechanics. Highly recommended for people passionate about science.
Profile Image for RSJ.
48 reviews5 followers
May 27, 2021
"The aspiration to truth is more precious than its assured possession"
-Gotthold Lessing, German Playwright and Philosopher

As I read this final sentence in the book Quantum, I am left with a mix of emotions that I have never experienced from reading any thriller or philosophical writing. I am being dramatic by saying that a book about Quantum Mechanics touched my heart more that any other fiction out there, but my vindication lies in my personal association with Quantum Mechanics. During my post-graduation in Physics, I failed my quantum mechanics paper. My instructor was astonished at my results and said that I must have deliberately failed because he found it inconceivable that one of his top students failed when everyone else succeeded. I wish I could say I was plagued by the same agony that was felt by the two groups of physicists over the years, one siding with Einstein and Schrodinger, the other with Bohr and Heisenberg. But no, I failed because I lost the forest for the trees, I drowned in obscure mathematical equations and theorems that made no sense and apparently, to me, served no function. Theoretical Physics is not what Hollywood movies make it out to be. I repented my choice in my major for almost 10 years and now I feel some closure as I navigate through the origins of QM and the philosophical transactions between two of the greatest minds and pioneers of new Physics.

In my opinion, this book should be made a mandatory reading for students of Higher Physics. They deserve a chance to fully appreciate the fact that they are dedicating time and effort to study a theory that eventually went against the scientific instincts of one of the greatest minds of the century, Albert Einstein.

The book is beautifully written and while it has some flaws like ambiguous sentence construction and occasional jumps between timelines, they can be excused considering the nature of the subject it deals with. The book's cover, font and pages are amazing, not intimidating in any way for a book in QM. It is hailed by many who love QM so it was not a big surprise that I stumbled into it. The first chapter of the book started with a question that I had, ever since I started studying Modern Physics. Every text starts with Black Body Radiation. Everything seems to start there, but no one ever bothered to explain why. Why was BBR so important? What was the motivation?

Motivation is always political or rather, capitalist. History proves that over and over. In a few short sentences, Manjit Kumar establishes the political aspirations behind the exploration into the study of BBR, which goes beyond scientific curiosity. From there on he follows the same formula to connect science with the political developments in the world at the time. He introduced concepts in a humane fashion, collating the science with the scientist. A timeline of scientific history is essential to appreciate the science. Just imagine, BBR was explained by Planck who at the time frowned upon the theory of atoms! It was a jolting reminder that atom, the first chapter in any science textbook from primary classes, was a late addition to the knowledge. I believe students have a misconception that everything happened in the exact order as they are introduced in his or her textbooks. While this may not seem like a hindrance to understanding the math or the concept, it essentially rips one off a chance to truly appreciate the scientific journey. This is what Manjit Kumar rectifies through his book. He passionately and lucidly explains one of the most difficult theories of all times that enables the curious reader to hold his or her end in any philosophical discussion about QM. Towards the end of the book, it becomes increasingly complicated, but Manjit Kumar iterates the concepts repeatedly just when you are about to lose the thread. That style of writing is a mark of an excellent entertainer who knows the mind of his audience.

This book ended my 10 year-old hatred for a subject which failed me and which I failed, by giving me a precious insight that would now help me patiently traverse the mathematical world of QM. I will forever be indebted to Manjit Kumar and his Quantum for giving me back what I have lost due to an outdated education system and also my laziness.

Perhaps a person who has had no prior experience in QM will find this book pedantic and dry. But with a little bit of effort, patience and interest this book can prove to be an emotional thriller, just like a Jefferey Archer Kane and Abel story. I haven't finished with this book by any means. My physical copy is marked with different coloured pens and crowded with my notes and I need to go back again and again to fix the ideas in my mind, which I think I will absolutely enjoy.

I want every physics student to read this book, so that when asked what is Quantum Mechanics, you have an answer besides a vague "some bras and kets, and oh, matrices and waves and at some point a cat appears dead and/or alive".
Profile Image for Teun Voost.
56 reviews
December 3, 2020
Mandatory, and essential reading material for anyone who dares call himself 'curious'.
Profile Image for Mike W.
59 reviews36 followers
April 3, 2013
This is a good recounting of the historical development of quantum physics. It tells the story through a series of biographies of the major players--Planck, Bohr, Einstein, Schrodinger, etc...

The book contains a lot of interesting information about the confusion felt by these great physicists as they tried to understand the implications of their experimental results and mathematical theories. It became clear over time that the assumptions of classical physics were not valid at the subatomic level, though Einstein, Planck and Schrodinger were never fully comfortable with the rejection of classical determinism and causality.

There had been a long-standing dispute in physics about whether light was a particle or a wave. Ironically, it was Einstein who revived the particle theory of light, arguing that light was emitted in discrete quanta or photons.

For a long time, the dominant interpretation of quantum mechanics espoused by Bohr, Heisenberg and others depicted electrons and photons as having dual particle and wave aspects, but denied that they were either particles or waves unless measured by some observer. This was the famous "Copenhagen Interpretation" in which the wave and particle aspect were "complementary". Moreover, these "particles" were really essentially indeterminate. As Heisenberg showed, it was impossible to estimate their position and momenta with perfect precision, not because of the limits of our knowledge or the imprecision of the measuring devices used, but because this uncertainty or indeterminacy were inherent characteristics of phenomena at a subatomic scale. Until someone took a measurement, it did not make sense to say the particle is at such and such a place. The particles simply were "potentialities", or probabilities. And reality was not really real until someone took a measurement. this prompted Einstein's famous protestation that "God does not play dice with the universe."

But over time, as the book explains briefly in its conclusion, the Copenhagen Interpretation fell out of favor as various rivals challenged it--Bohm's hidden variables, or Everett's many worlds hypothesis for example.

And, while marginalized over the last decades of his life, Einstein might well be vindicated, at least in part. he always believed that there was a deeper theory, a "unified field theory" that would explain the phenomena without resorting to an essential indeterminacy or unreality in nature. Strangely, the book does not mention "String Theory" which might prove to be the "Theory of Everything" than Einstein hoped in vain to discover.

Again, the book tells this story well. It explains clearly the difficult concepts involved in the early debates about quanta, and gives the reader a sense of the personalities involved int these debates. It points out that Heisenberg, who won the Nobel prize for the creation of "matrix mechanics" didn't understand matrices, that Bohr, the champion of the quanta, strangely refused to accept that light too was quantized, that Schrodinger failed to understand his own wave equation, and so on... Such was the confusion into which physicists had plunged.

But in its matter of fact style, the book fails to convey the majesty of the subject, or to explain with sufficient energy the fascination it holds even for intelligent laymen. It's good, but it could have been better.
Profile Image for Mohamed al-Jamri.
174 reviews116 followers
April 7, 2016
عنوان الكتاب: الكمومية - آينشتاين، بور والنقاش العظيم حول طبيعة الواقع
المؤلف: مانجت كومار
عدد الصفحات: 448 - 14 ساعة ونص تقريبًا ككتاب مسموع
سنة النشر: 2008
التقييم: أربع نجوم ونصف

يمكننا اعتبار هذا الكتاب الجزء الثاني أو التفصيلي لكتاب مبدأ اللايقين الذي قرأته قبله بفترة بسيطة، فهو يتناول نفس الموضوع، بل إن العنوان يشبهه إلى حدٍ كبير. هو كتاب تاريخي حول ظهور نظرية الميكانيكا الكمية حيث يتناولها من جذورها وصولًا لرأي العلماء المعاصرين فيها. تمامًا كالكتاب الأول يستخدم الكاتب، وهو صحفي أسلوبًا غاية في التشويق يعجلك تشعر وكأنك تعيش علماء ذلك العصر عندما ظهرت هذه النظرية الثورية.

تبدأ القصة مع الثوري المتردد، ماكس بلانك ومشكلة الجسم الأسود ومن ثم آينشتاين والسنة المعجزة 1905 التي نشر فيها أربع أوراق علمية مهمة جدًا. يتحر الكاتب الخلفيات العلمية لكل من هذه الأوراق. إحدى الأوراق ورقة حول كوانتات الضوء والتي صارت تعرف فيما بعد بالفوتونات، حيث يأخذنا الكاتب لتاريخ النظريات العلمية حول الضوء منذ نيوتن وتوماس يونج وفارادي حتى ماكسويل وكيف كان الضوء يعتبر جسيمًا في البداية ثم موجة. وهكذا بالنسبة للأوراق العلمية الأخرى التي تضمنت النسبية الخاصة والحركة البراونية. ننتقل بعد ذلك لنيلز بور و��لنموذج الذري وإلى آخره من الخلفيات والتطورات العلمية المثيرة التي تصاحب ظهور الميكانيكا الكمية والتي يتعاون فيها عدد كبير من العلماء في ملحمة قلّما تكرر في تاريخ العلم.

بعدها نصل لنقطة الذرة عندما يرفض آينشتاين النظرية النسبية ويتحدى بور في سلسلة من النقاشات المثيرة جدًا والتي تحبس الأنفاس لآخر لحظة.

ما يميز هذا الكتاب هو توسعه في طرح تاريخ كل تقدم يحصل لفهم الميكانيكا الكمية، فهو لا يكتفي بذكر الاكتشافات وسردها وشرحها، بل يذكر الخلفيات وطريقة تفكير العلماء التي توصلهم لهذه الاكتشافات والأخطاء التي يقعون فيها. في نفس الوقت لا يغفل الكاتب الجانب النفسي لحياة العلماء وعلاقاتهم بع بعضهم البعض. هؤلاء الثوريون العباقرة بأخلاقهم العالية يجبرونك على احترامهم وتقديرهم بشدة. يتطرق الكاتب أيضًا لمرحلة الحرب العالمية الأولى ومن ثم معاناة العلماء اليهود من التمييز بسبب انتشار معاداة السامية وصعود الحزب النازي.

باختصار إنه كتاب تاريخي، علمي، عاطفي وسيرة ذاتية مقدم بصورة في غاية الروعة. أي شخص مهتم بالعلم سيجد متعة لا توصف عند قراءته.
Profile Image for Irene.
Author 18 books12 followers
October 15, 2012
Although I study chemistry and I love science, I've never been good at physics. This time I decided to make an exception and read this book. I found it absorbing like a novel, really well written and clear in explaining scientifics notions.

I especially appreciate the way the author combine science, history and scientists personal lives. As a student I often heard Einstein, Bohr, Rutherford, Planck, Shroedinger, Heisenberg, Pauli, but I never stopped thinking about them just as persons.
This book tells us about all the hard work, the passion, the struggles that these scientists experienced. Moreover gives a clear idea about how difficult is to bring new concepts in a well established academic community.

I don't know enough about quantum physics to dwell on scientific explanations that are given in this book. I simply have to trust the author knowledge!
I really recommend this book to everyone who wants to approach this fascinating subject.

422 reviews169 followers
March 24, 2015
Well-written and engaging. Clarifies and explains concepts and events in 20th-century physics in ways that enable the scientific imbecile to better comprehend what the big deal is and why it's (still) such a big deal. Also works to arm said scientific imbecile with ways to humiliate people in the humanities who just love to bullshit about stuff they understand even less than someone who read a pop-science history does.

Oh, and there's fun stuff in here about the personal lives of major figures in 20th-century physics. But that stuff is nowhere near as compelling as the overall drama at the heart of this account.
Profile Image for Gary  Beauregard Bottomley.
977 reviews580 followers
June 6, 2012
"Personality to explain quantum physics"

Uses the personal interaction of the main discovers of quantum physics to understand physics. The book reads very excitingly due to the personalities involved. Even someone who is not fully interested in the quantum physics would enjoy the story.
5 reviews4 followers
March 15, 2018
The book gives a condensed history of the modern physics. Each chapter is dedicated to a scientist starting with Max Plank to Einstein to Bhor to and the final verdicts on quantum mechanics that world now agrees on. The author presents a nice proportionate view of different aspects (childhood, personal, professional) of the life of the scientists without every missing a rudimentary explanation of the physical principles each scientist unfolded with their discoveries of new things and how it eventually led to a weird world of quantum. The personal flaws of each scientist were also subtly pointed out which made them a bit human for me after finishing the book. For anyone who likes or remotely interested in physics, I highly recommend this book. For sure it'll clear up what quantum means when the physics people use it.

The author juggles a lot of different scientists in chapters to make a lot of connections which makes the reading a bit chaotic. So a rating of 4 instead of 5. But I guess the microscopic quantum world itself is chaotic.
Profile Image for Joseph Yue.
112 reviews22 followers
June 23, 2022
This is not a work of genius, but a one of diligence. It sketches an intricate picture of the development of modern quantum physics from not only a scientific perspective, but also a historical and bibliographical one as it narrates the lives of the main contributors of this field. With remarkable lucidity and precision, this book reveals how the wackiest theory of reality known today had been enthroned the scientific orthodoxy, a process originated from apparently 'innocent' yet persistent pursuits for the knowledge of the subatomic world. The title is the only point with which I'm not entirely satisfied. If I were to propose a better main title instead of simply "Quantum", I'd probably use "The Greedy Subatomic Miners and the Unfortunate Awakening of the Quantum Balrog", which is obviously much more fitting for the theme.
Profile Image for Anup Sinha.
Author 3 books6 followers
December 22, 2019
Expertly written review of the development of Quantum Theory from both the scientific and historical perspective. Manjit Kumar did very well to make this a readable narrative that humanized the legendary scientists in describing their work. I have never seen anywhere such a survey of this era in research.

As a chemistry teacher, I drop the names of Bohr, Pauli, Heisenberg, Schrodinger, Einstein, etc. quite often and it’s nice to learn about the men behind the laws and theories.

Much of quantum theory and the debates described are still over my head and I skimmed through portions of the book but I still gained a lot from it.
Profile Image for Rama Rao.
735 reviews103 followers
February 20, 2014
Quantum : Einstein, Bohr and the Great Debate About the Nature of Reality

The great Einstein-Bohr debate about physical reality is interesting not only to physicists, but also to great many readers interested in understanding the nature. This discussion between Bohr and Einstein over the interpretation of quantum theory began in 1927 at the fifth Solvay Conference. The debate over the ability of quantum theory to describe nature was fueled by many leading physicists of the time, some of whom directly contributed to the development of quantum physics, but later found themselves arguing against the theory they helped to create. Notable examples include Erwin Schrodinger, Paul Dirac, and Max Planck; the latter two did not actively participate in challenging the quantum reality. Bohr and Einstein spent many years intensely debating the nature of reality, and their discussions are known for very famous Einstein's comments such as; "God does not play dice,' or "God is slick, but he ain't mean," and Bohr's response was "don't bring God into this (discussion of quantum physics)." Bohr argued vigorously against both deterministic and realistic world, but Einstein was equally adamant to defend these two physical and philosophical concepts. Deterministic philosophy was spurred by Newtonian mechanics; if we know a system and its physical properties (size, color, or position) at one point in time, then at some point in future we can predict the system based on these physical properties. Bohr argued that complete knowledge of the present can result only in a description of what the future most probably will be like, but there is no such thing as certainty in quantum world. This thought is mystified by what is commonly called Copenhagen interpretation, and its strong proponents were Niels Bohr, Werner Heisenberg, and Max Born. Classical reality envisioned by Einstein was supported to a certain level by Schrödinger. Recent historical research shows that Paul Dirac had his own doubts about Copenhagen school of thought (1), and Max Planck, the founding father of quantum physics, lived until 1947 did not participate directly in Einstein-Bohr debate because of his own insecurities about quantum reality. When experimental test for Bell's inequality was conducted by Alain Aspect and others, many thought that Einstein was definitely wrong, but recent advances say, not so fast. Physicist Roger Penrose and many others believe that quantum physics is an incomplete theory (2). Few weeks ago when Large Hadron Collider (LHC) conducted test runs, Stephen Hawking expressed pessimism of finding Higgs Boson in LHC experiments by stating that "I think it will be much more exciting if we don't find the Higgs. That will show something is wrong, and we need to think again. I have a bet of 100 dollars that we won't find the Higgs." In a poll conducted in 1999 at Cambridge University, 55% of physicists polled for none of the existing quantum interpretations are right. This shows that not everything is settled in quantum physics.

History of quantum physics is the best example to understand how scientists work. Their collective efforts to understand the universe we live in through publications, conferences, discussions correspondence and collaborative efforts are essential to scientific advancement. The author describes these things well in the book, but he falls short in certain areas; his current work uses previously published works of Max Jammer (3), Jagdish Mehra and Helmut Rechenberg (4) as his few sources of information, but he could have researched a little more by talking to people who were directly associated with Einstein or Bohr. In a recent book by Louisa Gilder (5), after interviewing a colleague of Boris Podolsky, she reported that Rosen or Podolsky never asked Einstein for his permission when they published the classic Einstein, Podolsky and Rosen paper, 'Can Quantum Mechanical Description of Physical Reality Be Considered Complete." It is also stated elsewhere that Einstein never thought this was going to be a paper; the ideas came out during informal discussions (6). The author discusses the results of crucial experiments such as tests of Bell's theorem, and other work that may have lead to confusions or mistakes.

Many who are familiar with the history of quantum physics think that even though Einstein is unquestionably the best scientist mankind has ever seen but they also believe that he was grumpy old man who did not appreciate new and novel ideas in physics. This is certainly not true according to physicists who knew him. He helped Max Planck in the development of early ideas such as quantized energy levels in quantum physics. Einstein was not against new ideas such as the probabilistic or statistical interpretation of quantum mechanics, but the denial of an independent reality bothered him immensely. This lead to another famous quote from Einstein: "I think that a particle must have a separate reality independent of the measurements. That is an electron has spin, location and so forth even when it is not being measured. I like to think that the moon is there even if I am not looking at it." The author resurrects these ideals of Einstein hastily when he discusses experimental tests of Bell's theorem. He concludes that Einstein's doubts about the completeness of quantum mechanics are vindicated.

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