What Is Real?: The Unfinished Quest for the Meaning of Quantum Physics by Adam Becker (PDF)

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A thorough, illuminating exploration of the most consequential controversy raging in modern science. –New York Times Book ReviewAn Editor’s Choice, New York Times Book ReviewLonglisted for PEN/E.O. Wilson Prize for Literary Science WritingLonglisted for Goodreads Choice Award Every physicist agrees quantum mechanics is among humanity’s finest scientific achievements. But ask what it means, and the result will be a brawl. For a century, most physicists have followed Niels Bohr’s solipsistic and poorly reasoned Copenhagen interpretation. Indeed, questioning it has long meant professional ruin, yet some daring physicists, such as John Bell, David Bohm, and Hugh Everett, persisted in seeking the true meaning of quantum mechanics. What Is Real? is the gripping story of this battle of ideas and the courageous scientists who dared to stand up for truth. “An excellent, accessible account.” –Wall Street Journal “Splendid. . . . Deeply detailed research, accompanied by charming anecdotes about the scientists.” –Washington Post

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⭐What is real by Adam Becker gives an interesting historical overview of the Copenhagen interpretation of Quantum Physics, the Bohr Einstein debates, the double slit experiment, EPR, locality versus nonlocality, entanglement, Bells Theorem and related experiments, and more. The book discusses the problems with the Copenhagen interpretation, the measurement problem, complementarity and the Copenhagen interpretation’s connection to logical positivism. The author introduces several alternatives to the Copenhagen interpretation including Bohm’s pilot wave interpretation, the many worlds’ interpretation, spontaneous collapse theory, and information theoretic interpretations.I am an engineer not a physicist, but I’ve taken several classes in quantum physics and I am interested in the topic. When I took my first class in quantum physics, I encountered the De Broglie wave (quantum wave) for a free electron. The speed of the wave is: [ w = L * f ] (wavelength times frequency) = h/p * E/h (h is the Planck constant, p is momentum, E is energy) = E/p = mv^2 / mv = v/2 (v is the velocity of the electron). Voila, an apparent contradiction. The wave is moving half as fast as the particle. You do a few Galileo transformations, and you see that you can assign the wave any speed that you like. Since, it is the wave packet (indicating an approximation for position as well as velocity) that’s important and the wave packet moves with the particle, it is not a true contradiction, well unless you claim that the wave is a physical object in itself. Add to that the fact that QFT assigns completely different speeds to the individual waves and that Heisenberg’s representation of Quantum Physics did not even include waves, and you will have problems if you claim that the matter waves a la De Broglie and Schrödinger are physical objects in themselves. This is never discussed in the book.None of the interpretations are without issues. The author briefly discusses the information theoretic interpretations on half a page while vaguely invoking Bell’s criticism about it possibly leading to logical positivism and even solipsism, critique I do not understand and do not agree with. Information theoretic interpretations is that the quantum wave represents an observer’s knowledge of the system and is not a physical object in itself. This is my favorite (so far). On the other hand, he extensively discusses and defends and even extols the bizarre many-worlds interpretation (MWI). Basically, every time there is a quantum transition (or anything happens) the Universe is split into several Universes resulting in quintillions times quintillions times quintillions …etc., of Universes being created every millisecond, and they in turn all create many Universes every millisecond, exponentially and virtually infinitely. I should clarify that the many-worlds interpretation is distinct from the multiverse hypothesis, which envisions other universes, born in separate Big Bangs, that have always been physically disconnected from our own. I do not have a problem with the multiverse hypothesis, but I do with MWI.MWI has some advantages, it is a realist, deterministic and local theory (if you consider those to be advantages). However, in addition to being bizarre there are many problems with MWI, one being that the wave function is a physical object, another that the alleged multi-Universes are uncontactable. Other problems include that it muddles the concept of probability and creates a new difficulty in interpreting probabilities in Quantum mechanics (do they exist?). Consciousness is built on experience; how does that work with constantly splitting worlds? Also how does these Universe splits happen and how quickly? A critic of MWI Andrew Peres argued that the “various many-worlds interpretations merely shift the arbitrariness or vagueness of the collapse postulate to the question of when “worlds” can be regarded as separate, and that no objective criterion for that separation can actually be formulated”. Philip Ball another critic of MWI states that MWI “really denies is the existence of facts at all”. He states, “if you say everything is true, you have said nothing.” I don’t have a big problem with nonlocality or indeterminism or putting the observer at the center. The problems that MWI introduce are much worse, which is why I find his infatuation with MWI a hindrance to me liking this book.The author discusses a couple of the objections to MWI, but not in an unbiased way. He is not stating that MWI is his favorite but the way he is approaching the topic shows his bias. While he is shortchanging, for example, the information theoretic interpretations he is clearly promoting MWI. Also updated versions of the Copenhagen Interpretation solve many of its problems (decoherence), so his critique of the 1930’s Copenhagen Interpretation, without mentioning the updates, isn’t fair either. Personally, I wanted more balance in this book. That’s why I am not giving this book a good rating, and I wanted to explain why. I am not giving it a bad rating either since it is discussing an interesting but complex topic in a fairly lucid way (but biased way). Also, the history of quantum physics that he is telling us is interesting reading. So, three stars.

⭐This book is worth while as there is some interesting history presented and is well written and researched. However, the author’s main underlying purpose is to argue for pilot-wave and/or many-worlds interpretations of quantum mechanics (QM), and to argue against the Copenhagen Interpretation (C.I.). Unfortunately, his obvious bias prevents him from articulating fairly what the C.I. actually was or why it existed,… even implying it was incoherent and adopted en masse due to some conspiracy of personalities, particularly Niels Bohr.This is questionable to say the least as it’s not actually confusing as to why the C.I. was adopted en masse; As pointed out to E. Schrodinger at the time, the wavefunction can not be an observable physical entity as he envisioned it, as it evolves in a tensor product space. Therefore, it is quite rational why one would adopt a Born Rule type interpretation of the wavefunction. Both the Born Rule component of the C.I. and the “shut up and calculate” component merely reflects how actual QM experiments must occur. The former on account of the fact that there is only one measurement result despite a possible superposition of states as described via the wavefuncion, and the latter on account of the fact that no one can actually have a wavefunction description of himself and the experimental apparatus. Another rational reason why the C.I. was adopted en masse, was that the standard Hilbert space mathematical foundation of QM with von Neumann’s projection postulate (wavefunction collapse) was able to unify both the matrix mechanics of Heisenberg and the wave formulation of Schrodinger. Certainly a general scientific positivist mentality was a great influence in motivating C.I. at the time as well…. as it should have.”I can well appreciate that, in the early days of quantum mechanics, something of the nature of Niels Bohr’s perspective on the subject was almost a necessity, so that the theory could actually be used, and progress in quantum physics could be made” – Roger PenroseThe author briefly mentions twice that Bohr was influenced by Kant, but remarkably never attempts to explain Kant’s epistemology.Considering Bohr’s interpretational contributions to quantum theory, Abraham Pais, nuclear physicist and renowned biographer and physics historian, stated that Bohr was “one of the most important twentieth century philosophers,…. As such he must be considered the successor to [Immanuel] Kant,…”.Essentially, the C.I. argument was that the measurement problem is epistemic in nature, and therefore not a problem with the theory itself. In other words, the discontinuity between the deterministic evolution of the wavefunction via the Schrodinger equation, and the “collapse” to a measurement result, is on account of the conditions of observability given the nature of mind. Which is to say, we must supply a conceptual form in which the ‘underlying reality’ is to be observed in the first place. In the standard Hilbert space formulation of QM, the Operator and Basis are supplied by the physicist given the particular experimental arrangement and interpretation of results. So, if one is so inclined to imagine a de facto metaphysical ‘underlying reality’, one can see that this supposed reality is projected or conformed to, our a-priori conceptual framework, in order to meet the conditions of observability…. by a mind so constituted, given its evolution to synthesize experience on the macroscopic scale…. i.e. “it” is only a particle or a wave to the extent that those notions are defined by the experimental apparatus and interpretations thereof.And no, an epistemic interpretation does not mean that consciousness ‘reaches out’ as it were and interacts physically with the quantum system to cause collapse of the supposed physical wavefunction. There was some historical confusion on this point. We’re talking about a biological system evolved at the macroscopic scale with it’s own emergent laws, processing experience to form a synthesis for the understanding, which since this mind is NOT omnipotent, must of necessity have conditions for observability to be at all possible. This precludes knowledge of ‘independent reality’ because intellectual artifacts or ‘conceptual forms of thought’ are always implicit in the experimental arrangement, presumptions, and interpretations….“There is no way to remove the observer — us — from our perception of the world, which is created through our sensory processing and through the way we think and reason. Our perception — and hence the observations upon which our theories are based — is not direct, but rather is shaped by a kind of lens, the interpretive structure of our brains.”- Stephen Hawking“The doctrine that the world is made up of objects whose existence is independent of human consciousness [mind] turns out to be in conflict with quantum mechanics and with facts established by experiment.” – Bernard d’EspagnatThe author does not state that the pilot-wave for multiple particles, evolves in a tensor product space, which is to say not in our 3 dimensional space, and therefore is in principal unobservable. Likewise, the many-worlds are in principal unobservable. Despite suggestions to the contrary in the book, this is entirely different from Mach’s view that atoms are metaphysical on account of not observing them,… as in principal, atoms could be observed or rationally hypothesized given observable attributes. Metaphysical entities are precisely those that are intrinsically unobservable, like the pilot-wave or multiverse. In contrast, an epistemic interpretation does not propose unscientific metaphysics, but rather artifacts of thought, which IS in principal investigable as the field of epistemology. It’s just that the problem extends beyond physics, and into a field that is undeveloped. See “John von Neumann’s Cut” to substantiate this point.Since all interpretations of QM are empirically indistinguishable, it becomes a Choice of the theoretician which is to be his guide,… and therefore are epistemic in any case.I don’t feel that the author presents the interpretation of the Bell inequality tests entirely fairly; The empirical failure of the Bell inequalities refutes ‘local realism’, by which is meant that at least one of the following implicit assumptions are refuted,… locality, counterfactual definiteness [Stapp, Eberhard], or no conspiracy condition. The Copenhagen Interpretation was philosophically aligned with the rejection of counterfactual definiteness, …i.e. that elements of reality or attribute values exist independently of measurement,… or more properly, that for statistical purposes it is valid to presume measurements that could be, but have not been performed (this would have been rejected by C.I.). The author seems to imply that no such assumption is made in the Bell tests, despite that it is the very point of the Bell tests to presume this,…. resulting in the conclusion that no such classical presumptions of hidden variables can reproduce the results of quantum mechanics, given Einstein locality. The generalized Bell theorem, however, makes no assumptions with respect to the form of the quantum entity or attributes being measured (particle, wave, spin, polarization, position, momentum, etc).The author is correct to say that philosophy is important in physics as at minimum a guide for theoretical research and interpretation of results. The author is also correct to point out Quine’s thesis that verification or falsification can not be done in isolation, free and clear of any presumptions and interpretations, thus refuting the extremism of logical positivism. However, Quine did not refute scientific positivism nor verification nor falsification as valid and essential guides for physicists,….. as if he managed to crack the door open such that it was then legitimate for metaphysics to infect science. The many-worlds formulation is itself an extremism of mathematical idealism, in that it essentially lets the mathematics of the wavefunction solutions of the Schrödinger equation supplant the work of the theoretician.”As far as laws of mathematics refer to reality, they are not certain; and as far as they are certain, they do not refer to reality” – A. EinsteinNot mentioned in the book as well is that the C.I. has since been revised with decoherence, in the consistent histories interpretation,… “Copenhagen done right”.A few general-reader books by prominent physicists that speak out against metaphysical speculation in physics and cosmology are,…-The Trouble With Physics: The Rise of String Theory, The Fall of a Science, and What Comes Next – Lee Smolin-Fashion, Faith, and Fantasy in the New Physics of the Universe – Roger PenroseAn excellent and fairly unbiased exposition of the various interpretations of QM….Beyond Measure – Jim Baggott

⭐This book, written in a popular style, gives the history of how physics has taken a wrong turn for over 80 years. For centuries, since about 1600, scientists had regarded it as their vocation to study the universe and describe mathematically how it and its contents behave and interact. In effect they were confident that, even if the whole of humanity were obliterated, the universe would continue to exist, obeying the same laws.At the outset of the twentieth century scientists investigating the microphysics of the world found that they were no longer able to understand the universe in this fashion. Quantum mechanics (QM), the best mathematical formalism available, was complicated and ad-hoc. It was superb in predicting the results of laboratory experiments (to many decimal places) – but attempting to discover the reality behind these results seemed to force one into paradox.It was here that the appalling mistake was made. From about 1927, under the leadership of charismatic Niels Bohr, a prominent group of physicists (the ‘Copenhagen’ school) insisted that the failure of understanding of that era was to be elevated into an eternal principle: the microphysical could only ever be understood in terms of laboratory experiments. Outside of this piddlingly limited context, we could never know anything. By making this grandiose (metaphysical) claim of eternal ignorance, these physicists abandoned the quest to understand the realities of the universe – some denied that there were any. Worse, this powerful group did their utmost to ensure that anyone who had the temerity to try to understand the micro-world was subject to personal abuse, to having their arguments ignored and their careers ruined. The book describes the history of this dominant group and those who dissented from them: how the latter were misrepresented – and still are to this day.Einstein, together with colleagues Podolski and Rosen (EPR), described a simple physics experiment, and agreed that QM correctly predicted its results. But what followed from these results? EPR carefully and explicitly (1) set out a sufficient condition for an objective (real) physical property to exist and (2) defined a locality condition stating that the universe is such that systems are isolated from one another if they are space-like separated. EPR began by supposing that the universe satisfied this locality property. The experiment and its (undisputed) results then implied that subatomic particles must have real physical properties which determine both their position and momentum simultaneously; moreover these physical properties must be deterministic. EPR concluded that – if one accepts the locality condition – then QM must be incomplete and in need of supplementing by deterministic hidden physical properties. Bohr’s response was a model of obscurity, and there is still no consensus as to what he was trying to convey.David Bohm arrived at a straightforwardly realistic model of the world in which particles have definite positions and velocities at all times. A feature of this theory is that it is explicitly non-local. The experimental predictions of this theory are identical to those of QM. When someone presented Bohm’s model at a seminar in Princeton his ideas were rejected as “juvenile deviationism”, he was denounced as a Trotskyite, and Oppenheimer closed the meeting by suggesting that “if we cannot disprove Bohm, then we must agree to ignore him”.John Stewart Bell took up EPR’s ideas and developed them so that they became experimentally testable. He showed that, if locality is true, then the experimental results on two isolated systems (involving particles originating from a common source) must satisfy a certain inequality – Bell’s inequality. Clauser was first to test this and Aspect later performed an improved experiment in which the choice of experimental arrangement in each of the target locations was not made until after the particles had left the source. Both experiments violated the Bell inequality, demonstrating that our universe is non-local.Even today quantum mechanics is mistaught and false assertions made – even at the most prestigious universities. Here are just some of the myths about the Aspect experiment:1) Einstein rejected QM and its experimental results because he was wedded to determinism. Einstein accepted all the result of QM – it was the irrealism and vagueness of Copenhagen QM that he objected to. Determinism for some physical properties is a logical consequence of accepting locality as the EPR paper shows.2) The Aspect experiment proves that no deterministic account can be given of microphysical behaviour. This is false as Bohm’s model shows.3) The Aspect experiment proves that QM gives a complete picture of the universe. This is false as Bohm’s model shows.4) Einstein was mistaken in assuming that the universe is local. This is technically true but highly misleading. Einstein was the first to see that Copenhagen QM implied that the world was non-local. He explicitly put locality into the EPR paper as a hypothesis. It is perfectly honourable for a scientist to make a plausible, explicit, testable proposal that is later shown to be wrong. By these standards Bohr’s response to EPR was “not even wrong.”5) The Aspect experiment’s proof of non-locality was predicted by and thus vindicated Copenhagen QM. In fact, nonlocality (under the name “entanglement”) was first discussed by Schrödinger, a critic of the Copenhagen school. Its experimental discovery was the joint work of Copenhagen dissidents EPR, Bell, Clauser and Aspect. This, the most bizarre feature of the quantum world, was initially greeted with astonishment, but almost immediately accepted (one might say purloined) with complacency by Bohr and company.The later part of the book describes how new and realistic versions of QM are coming into acceptance – at least as *respectable candidates* for rationally describing the world as it actually is. Any realistic QM must describe micro- and macro-entities in the same terms, obeying the same laws. Ghirardi, Rimini and Weber (GRW) have developed a stochastic “spontaneous collapse” model in which, as with the case of Bohm, the macroscopic world of commonplace objects arises smoothly and in an understandable manner from the quantum subatomic world. GRW’s predictions differ very slightly from QM, but no experimental test has so far been proposed that would distinguish them. Everett’s “Many Worlds” interpretation is popular, especially among cosmologists. This still has a major problem in that experimental probabilities cannot be derived in a principled way from the alleged splitting of the universe. (My suspicion is that, because of this lack, “Many Worlds” will not prove to be tenable as a description of reality.)This is an excellent popular-science book. It certainly won’t teach QM, but it makes one realise the extent to which lowness of nature stalks the jungles of academe. It is very well referenced; perhaps most valuable are interviews with various scientists, some conducted by the author. This book introduces the hero of realism John Stuart Bell to a general audience. He is a wonderful, underrated scientist and philosopher whose papers are witty – in the senses of being down-to-earth, erudite, apt and also laugh-’til-it-hurts funny.

⭐A solid overview of the problems in the quantum foundations (via a historical approach), from a pluralistic perspective. The author takes the reader on a fascinating journey from the beginnings of QM until our days, covering the most important events in the evolution of our understanding of QM, including some crucial developments in the philosophy of science relevant to the subject (the problems with the old positivism of Mach, the fall of logical positivism and the rise of realism, the problems with falsificationism in front of Duhem-Quine criticism and so on), finally explaining well why the current generation of physicists hold philosophy in low esteem and how they are wrong.I liked the clarity of the explanations, I read quite many books on QM before and I witness I was surprised by the simplicity of the descriptions and analogies used, very easy to understand even for people who know relatively few things on the subject. In short an easy to read book but which offers nonetheless a solid understanding of the subject [here I mean the foundational aspects of quantum mechanics, by the way the author never claim to teach the formalism of quantum mechanics]. Sure there is not a great depth but it is more than enough to have a clear overview of the facts (for example the fact that the author does not stress that Bohr tried to undermine the definition of what constitute an element of reality in EPR paper changes little)..Anyone who has not decided yet (entirely subjectively I would say) that Science can only be cumulative (at least at limit) or that we already have clear cut criterions to make a difference, once and forever, between Science and pseudo-Science will be sympathetic with the approach of Becker. I certainly am. Without falling in (quasi)relativism though, too much postmodernism is harmful despite the undeniable social dimension of the scientific quest (but Becker is not guilty of that).Finally, to paraphrase Popper if I am not wrong, ‘if we are told again and again that something is impossible or meaningless even the most obvious connections may go unnoticed’. Let’s not be too authoritarian here, what if a (contextual) nonlocal realist ‘hidden variables’ theory is there, waiting to be discovered (giving us at least a glimpse of reality at quantum level)? Even superdeterminism is still viable I’d say, anyways counterfactual definiteness should not be a ‘sacred cow’, in spite of the fact that is of ‘bon sens’ to accept it (I agree that physicists are entitled to use it in the assumptions; as much as a healthy fallibilism is still there of course).Now one can argue that not all existing interpretations of QM are on equal foot if we look beyond the mere empirical aspect (albeit all have problems) but I don’t think this is enough to claim that there is a winner at this time (as some would like, usually arguing pro Copenhagen); no interpretation has the important edge which to make it irresistible from a rational standpoint (maybe in the future). Besides we must never forget that even seemingly degenerative research programs can, sometimes, become extremely successful later, when the ‘background assumptions’ are prepared for them. Fallibilism should always be there. Becker’s approach is definitely sound.

⭐I really enjoyed reading this book. When I first learnt about quantum mechanics, well over 40 years ago, we were taught the Copenhagen Interpretation as if it was the only permissible way to think about quantum mechanics. At the time it disturbed me. The Copenhagen Interpretation has been described as ‘shut up and calculate’. Of course, you have to calculate whatever interpretation you follow, so really this interpretation just means ‘shut up’. In other words quantum reality is too complicated for your little mind, so don’t think about it.Adam Becker’s book dispatches the Copenhagen Interpretation for good. Not because it’s wrong, but because it is not so much a theory as a prohibition on theories. Thank goodness it’s gone. Now the physicists can get to work devising alternative theories and experiments to test between them.Becker’s book is a pretty effective hatchet job on Neils Bohr too, who comes over as a stereotypically patriarchal, rather stupid, male — incapable of understanding anyone else’s point of view except in the sense of coopting it as a defence of his own. One of the real strengths of the book is the bibliographic detail. I’d recommend the book even to people who are not interested in physics. Who could fail to be interested in the personality clashes described here.I would say that Becker’s hero is John Bell, who devised the inequality that bears his name. When his inequality was first shown to me in the late 1970s, it was presented as a proof that hidden variable theories do not work. Becker shows that this presentation, though common, is completely wrong. The Bell inequality is about locality, and applies just as much to the Copenhagen Interpretation as to any other theories, including hidden variables. Becker claims that non-locality does not apply to Many Worlds theories, though he does not include a justification of this claim.Becker describes a few of the candidates to a theory of quantum reality: Many Worlds, including the effects of decoherence; Pilot Wave theories; Spontaneous Collapse theories, including Roger Penrose’s related gravitational collapse theory. He presents all these theories seriously and fairly, without implying a preference between them. As well as dismissing Copenhagen, Becker dismisses all those rather silly new-age theories that present quantum mechanics measurement as being related to consciousness or even parapsychology. Good for Becker.For my money, the winning theory will be the one whose predictions match experiment. Experiments such as Aspect’s, which prove the Bell inequality, have already ruled out any interpretations that preserve locality. It is easy to imagine experiments that would be able to test spontaneous collapse theories (though perhaps not so easy to implement the experiments!). Any theory must not only work for the microscopic quantum world but also scale to larger sizes, and show why classical behaviour appears to be the limit.Perhaps in 50 years time, experiments will have disproved all but one of the ‘interpretations’, which will then have the status of Theory. Future readers of this book will look back on the times of Copenhagen ‘shut up and calculate’ as a bizarre wrong-turn in science, rather like Creationism or Phlogiston.———– edit ———–I was interested in the reasons why Becker claims that non-locality does not apply to Many Worlds theories, so I read some papers online. Consider the simple case of two entangled particles which are measured by Alice and Bob — for the sake of argument, say they are photons, and Alice and Bob can both vary the angle they test the polarisation of the photons. Interpretations of quantum mechanics that consider Alice and Bob to be purely classical have a problem with non-locality because the ‘collapse’ or ‘measurement’ that Alice makes affects the results that Bob sees and vice versa. Interpretations that allow Alice and Bob themselves to enter superpositions of states do not suffer from this problem. Alice and Bob each enter entangled states with the photon that they measure. This can happen as slowly as you like — Alice and Bob do not have to be in the same ‘world’ as each other. Some time later, Alice and Bob meet for a coffee and to discuss their results. When this happens, they enter an entangled state with each other, and only then can you think of them as being in classical worlds together, both having made correlated observations.So if we postulate that the breach of special relativity implied by non-locality is impossible, which interpretations of quantum mechanics pass the experimental tests carried out so far, such as Aspect’s experiment? Certainly not the Copenhagen interpretation, where both Alice and Bob are strictly classical. Nor does Bohm’s hidden variables scheme. Many Worlds clearly passes the test, but so do a number of other interpretations. In the experiments performed so far, Alice and Bob are photon detectors connected to computers: the entangled non-classical states are matters of electron positions in a few transistors. Thus as well as Many Worlds, the experiments performed to date allow interpretations of quantum mechanics where collapse/measurement is a function of mass (Roger Penrose), consciousness (von Neumann and Wigner), non-linearity (Pearle, Weber, Ghirardi, and Rimini).It would be very difficult to experimentally disprove all of these alternatives to Many Worlds, but it would be possible to enhance Aspect’s experiment to push their thresholds further from the microscopic world. For example, Alice and Bob could be human experimenters, who are isolated from each other at the time of the experiment and later compare results. This would test the consciousness-causes-collapse theories, at least if we discount non-physical communication such as telepathy. If Alice and Bob have substantial mass, which is displaced differently in their different quantum states, this would test Roger Penrose’s ideas.

⭐A somewhat polemical account of the Quantum Interpretation Wars of the 20th century (and since). Bohr plays the villain, Einstein and Bohm the misunderstood heroes.What does Quantum Mechanics tell us about the nature of reality – is the wavefunction “real” or is it just a useful mathematical model of something more fundamental? Can we know and does it matter?It’s nice to see these questions coming back into vogue, after having been dismissed as an unnecessary or unproductive avenue for a while. I think the lack of a convincing explanation for why QM allows us to predict the behaviour of the subatomic world (albeit only probabilistically) is a clear sign that it is an unfinished theory.This book isn’t really trying to answer the question that the title poses, but it does want to challenge the idea that Bohr won the debate, or that the question is not worth asking.

⭐This books is a well written, a clear and understandable review of the various interpretations of quantum mechanics through a mainly historical lens.Look deeper though and between the lines you will find a social constructivist flavoured thesis on the nature of reality and the practice of science, as well as everything you need in order to understand how and why this is meaningful.I really enjoyed the book on both levels, and I personally had a number of “aha”moments as I recall wrestling with quantum mechanics, in general, as a student- mainly because none of it made any sense to me then (and now? you ask -much more so) . The “science” is really well explained, at a suitable level, I would say, for the sophisticated amateur (like me) and illustrated, and brought to life through stories concerning the lives and personalities of the key players. This is a really amazing story of the birth of a physics that has had huge practical implications and yet explanation how it maps to reality causes continued controversy.

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