What Is Real?: The Unfinished Quest for the Meaning of Quantum Physics

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.

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 is probably the most accessible telling of the quantum story I have come across, & certainly one of the most engaging & useful. The author discusses his whole subject with us, & reading it a chapter at a time (as I did) is like attending a high quality evening class. Having just finished it, I could write reams more appreciation, but perhaps I had better just say it's a landmark, & recommend you enjoy it for yourself.