The Emergent Multiverse: Quantum Theory according to the Everett Interpretation by David Wallace (PDF)

Description

The Emergent Multiverse presents a striking new account of the “many worlds” approach to quantum theory. The point of science, it is generally accepted, is to tell us how the world works and what it is like. But quantum theory seems to fail to do this: taken literally as a theory of the world, it seems to make crazy claims: particles are in two places at once; cats are alive and dead at the same time. So physicists and philosophers have often been led either to give up on the idea that quantum theory describes reality, or to modify or augment the theory. The Everett interpretation of quantum mechanics takes the apparent craziness seriously, and asks, “what would it be like if particles really were in two places at once, if cats really were alive and dead at the same time?” The answer, it turns out, is that if the world were like that–if it were as quantum theory claims–it would be a world that, at the macroscopic level, was constantly branching into copies–hence the more sensationalist name for the Everett interpretation, the “many worlds theory.” But really, the interpretation is not sensationalist at all: it simply takes quantum theory seriously, literally, as a description of the world. Once dismissed as absurd, it is now accepted by many physicists as the best way to make coherent sense of quantum theory.David Wallace offers a clear and up-to-date survey of work on the Everett interpretation in physics and in philosophy of science, and at the same time provides a self-contained and thoroughly modern account of it–an account which is accessible to readers who have previously studied quantum theory at undergraduate level, and which will shape the future direction of research by leading experts in the field.

User’s Reviews

Editorial Reviews: Review “The Emergent Multiverse is the most extensive, careful, and wide-ranging discussion of Hugh Everett’s so-called Many Worlds interpretation of quantum theory in existence (at least on our branch of the multiverse), and is certain to become the locus classicus for all future discussions of the theory…. You won’t find a better discussion of both foundational issues and far-flung consequences of the theory anywhere.”–Tim Maudlin, Nous”As those who have read Wallace’s articles will expect, [this] is an excellent book, and should be required reading for anyone interested in the foundations of quantum mechanics.”–Peter J. Lewis, Notre Dame Philosophical Reviews”This book is an outstanding achievement. It presents the current state of the art in the Everett interpretation to a depth and level of sophistication that will be appreciated by the leading experts in the foundations of quantum theory (of whom Wallace is one) — and will educate them, and should chasten most of them.”–David Deutsch, Centre for Quantum Computation, The Clarendon Laboratory, University of Oxford About the Author David Wallace was born in San Rafael, California, in 1976, but has been resident in the UK since 1977. He studied theoretical physics at Oxford University from 1994-2002, but upon realising his research interests lay mostly in conceptual and foundational aspects of physics, he moved across into philosophy of physics. For the last six years he has been Tutorial Fellow in Philosophy of Science at Balliol College, Oxford. He holds PhDs in physics and in philosophy, and his research interests span a wide range of issues on the boundary between philosophy and physics: symmetry and the gauge principle, the direction of time, the structure of quantum field theory, and of course the interpretation of quantum mechanics.

Reviews from Amazon users which were colected at the time this book was published on the website:

⭐David Wallace is a philosopher of physics who teaches at the University of Southern California; he previously taught at the University of Oxford.He wrote in the Introduction to this 2012 book, “The basic thesis of this book is that there is no quantum measurement problem… Quantum theory describes reality just fine… What I mean is that there is actually no conflict between the dynamics and ontology of (unitary) quantum theory and our empirical observations… [Hugh] Everett was the first to really see clearly, in outline, how this worked, hence the term ‘Everett interpretation of quantum mechanics. But really the ‘Everett interpretation’ is just quantum mechanics itself, read literally, straightforwardly—naively, if you will—as a direct description of the physical world… [Bryce] DeWitt stated explicitly the shocking fact which Everett only hinted at in publications… [In fact, so oblique are Everett’s mentions of ‘many worlds’ in his published work that for many years it has been controversial whether he really saw his own interpretation in many-worlds terms…Examination of Everett’s unpublished work, however, has recently made it quite clear that he understood the many-worlds implications of his view, and that he refrained from making them clearer essentially for political reasons.]…” (Pg. 1-2)“In this book, I aim to give a detailed cohesive account of quantum mechanics, when it is interpreted as a literal theory of the world… I should probably note right away that Everettian quantum mechanics really is both a many-worlds and a many-minds theory, in the sense that it entails that there are a great many versions of myself, living in surroundings much like my own and interacting with other versions of YOURself, elsewhere in physical reality. The other worlds, and their inhabitants, are not abstracta, or fictions, or mere unrealized possibilities: if Everettian quantum mechanics is true, they are as real as I, you, and our mutual surroundings.” (Pg. 2-3)He explains, “quantum mechanics… is the most powerful, most accurate, most fruitful theory that physics has ever devised… Yet, at least at first sight, it is impossible to understand quantum mechanics as telling us objective facts about the world… At worst, it seems to be telling us plain nonsense, claiming that somehow things can be in two places at once, and that cats can be alive and dead simultaneously. This, in brief, is the ‘measurement problem’ of quantum mechanics… some have argued that it gives us reason to abandon the picture of science as describing an observer-independent world, and to replace it with one where notions of ‘measurement,’ ‘observation,’ and perhaps even ‘consciousness’ play a central role. Others with so … reject quantum mechanics itself, replacing it with some new theory… This book, by contrast, takes an extremely conservative approach to quantum mechanics… the unmodified quantum theory can be taken as representing the structure of the world just as surely as any other theory of physics… quantum mechanics can be taken literally. The only catch is that, when we do take it literally, the world turns out to be rather larger than we had anticipated: indeed, it turns out that our classical ‘world’ is only a small part of a much larger reality.” (Pg. 13)He adds, “One might … object… but we don’t observe the Universe as being in superpositions of containing live cats and containing dead cats, any more than we observe cats as being in superpositions of alive and dead. But it is not at all clear that we DON’T observe the Universe in such superpositions… the Universe is a very big place… and we inhabit only a very small part of it, and it will not do to claim that it is just ‘obvious’ that it is not in a superposition… If the correct way to understand such superpositions is as some sort of multiplicity, than our failure to observe that multiplicity is explained quite simply by the fact that we live in one of the ‘worlds’ and the other ones don’t interact with ours strongly enough for us to detect them.” (Pg. 37-38)He asserts, “It is simply untrue that any entity not directly represented in the basic axioms of our theory is an illusion. Rather, science is replete with perfectly respectable entities which are nowhere to be found in the underlying microphysics… The generic philosophy-of-science term for entities such as these is ‘emergent’… A basic claim of this book is that worlds, in the Everettian interpretation, are likewise emergent entities—and that this… puts Everettian worlds on a part with all manner of unmysterious, scientifically respectable entities.” (Pg. 47-48)He outlines, “We [can now] … answer one of the most commonly asked questions about the Everett interpretation: how much branching happens?… there are basically three kinds of these processes: 1. Deliberate human experiments: Schrödinger’s cat, the two-slit experiment, Geiger counters, and the like. 2. ‘Natural quantum measurements,’ such as occur when radiations causes cell mutation. 3. ‘Classically chaotic’ processes: that is, processes governed by Hamiltonians whose classical analogues are chaotic… the [last] two are ubiquitous. Chaos… is everywhere… and where there is chaos, there is branching (the weather, for instance, s chaotic, so there will be different weather in different branches)… we will eventually reach a point where interference between branches ceases to be negligible, but there is no precise point where this occurs As such, the question, ‘How many branches are there?’ does not, ultimately, make sense.” (Pg. 99-100) He continues, “asking how many worlds there are is like asking how many experiences you had yesterday… It makes perfect sense to say that you had many experiences… but it is a non-question to ask ‘how many’.” (Pg. 102)About the objection that “there’s no possible way to observe one of [these worlds],” he replies, “Our best current theory of physics (a) predicts that they exist and (b_ explains why we can’t normally see them… We can’t directly observe a dinosaur, or a quark, or a quasar… but that doesn’t stop us taking them seriously… if we were properly situated in the multiverse we’d be able to see other worlds… My best theory of physics tells me so.” (Pg. 104)Of the Schrödinger’s Cat thought experiment, he says, “There’s nothing illusory or indefinite about the dead cat’s death: he’s dead… It’s just that there’s another cat, elsewhere in physical reality, that’s alive. I can’t rule out that hypothesis by checking the dead cat, any more than I can rule out… the hypothesis that the neighbor’s cat is alive.” (Pg. 108)Of the ‘I just find the Everett interpretation unbelievable” objection, he responds, “That’s an interesting psychological observation… empirically that’s false: plenty of people (me for a start) seem to manage. But I think what you’re saying is: it’s so weird that we SHOULDN’T take it seriously… I’d like to hear an argument as to why weirdness is a criterion in rejecting scientific theories…. let’s suppose you’re right. That still doesn’t amount to any kind of argument.” (Pg. 109)He suggests, “Once we recognize the semantic implications of the branching Universe hypothesis, we realize that the statement ‘Either A of B will occur, but not both, and I don’t know which’… becomes a perfectly rational thing for someone to say… Everettian quantum mechanics has no difficulty in explaining why experimenters are entirely justified when, as they routinely do, they express ignorance as to the outcome of their experiments.” (Pg. 290)He observes, “in Everettian quantum mechanics we have a rather precisely constrained theory of a multiverse, generating detailed … predictions, and arguably allowing us to directly detect multiple Universe in certain cases.. For instance, it is not infrequently suggested that the value of the charge of the electron… can be understood by postulating a multiverse in which all conceivable values, and noting that most of them are barren of life. To make such a story work using an Everettian multiverse, we would require some underlying quantum theory in which the charge of the electron was dynamically determined in such a way as to take different values in different branches; such a theory would, presumably, make other concrete and testable predictions.’ (Pg. 368)He concludes, “This is not to say that most physicists—even most physicists who accept universal unitarity—believe in the literal existence of many worlds. Plenty do, of course; plenty more don’t, or are agnostic. Buta pretty large fraction recognize that what the theory MEANS is.. that those worlds exist. Beyond that, it’s a free country…” (Pg. 423)Whether or no one accepts the MWI, Wallace’s explanations and arguments are frank and clear, and this bok will be of great interest to anyone studying the Many Worlds Interpretation.

⭐This is the definitive book for anyone interested in the Everett, or Many-Worlds, formulation of quantum theory. David Wallace is a leading philosopher of physics, with an incredibly deep understanding of the underlying physics.It isn’t a popular-level book; this is a scholarly work, aimed at professional philosophers, physicists, and students. Wallace gives a thorough discussion of the main issues confronting the contemporary Everettian: decoherence, the emergence of classical worlds, pointer states, the origin of the Born Rule for probability, and time-asymmetry. The style is uniformly clear and engaging. Readers will certainly come to the work with a wide variety of opinions on the plausibility of Many-Worlds, but everyone should get a lot out of reading this book.

⭐I suspect that this is THE book to read if you want to understand multiverse (or many worlds) theory. Wallace is thorough, precise, technical, and formal. And the subject matter is fascinating.Hugh Everett was a Princeton Physics PhD student when he developed the “Everett Interpretation” of quantum mechanics, now known as the multiverse theory, or the many worlds theory. Despite support from John Wheeler, Everett got a cold reception from the physics world for his published papers and actually left academic science for a commercial career after completing his PhD.In more recent years, the Everett Interpretation has gained credibility in the physics world, and Wallace’s treatment gives some good answers to account for its resurgence.The traditionally dominant Copenhagen Interpretation of quantum theory has a problem with realism. It’s not even a sophisticated philosophical problem. It just doesn’t seem to render what’s really going on at the quantum level understandable, at least not in conceptual or visualizable terms. Even theorists we commonly associate with quantum mechanics, like Schrödinger, or more recently Richard Feynman, have said as much.Wallace’s account of the Everett Interpretation aims to restore realism to quantum theory. Wallace, who has very enviable facility in both theoretical physics and philosophy of science, undertakes two daunting tasks — a detailed mathematical elaboration of the Everett interpretation itself, and a defense of realism at the quantum level when understood by that interpretation.I should say before I go on that I’m not a physicist. My academic background is in philosophy, and, although I have certainly studied philosophy of science, a lot of this is new and uncomfortable to me. So I’m sure my account (of both Wallace and Everett) will have mistakes — hopefully they will be quibbles, not howlers. I’ll try to stick to my most solid ground.Everett’s core idea is actually fairly straightforward. Schrödinger’s wavefunction provides successful mathematical tools for calculating and predicting behaviors of particles at the quantum level.But it does so in terms of probabilities — the attributes of particles are expressed as objective probabilities. We cannot say what a particle’s spin or momentum or position, for example, is, only what possible values those attributes may have, and what weights or probabilities to attach to those possible values.It’s not until a measurement is made that those attributes take on determinant values. Upon measurement, the quantum wavefunction “collapses” to a determinant state.Wallace stresses, as has traditionally been maintained in the Copenhagen and other interpretations, that the indeterminacy prior to measurement is not epistemic, it is objective. It’s not that the particle’s spin is unknown, for example, but that the particle’s spin is objectively undetermined until the measurement takes place.That leads traditionally to what is called the “measurement problem.” Why would a measurement determine the values of a particle’s attributes, and what becomes of all the possible but unrealized values the attributes had prior to measurement?On Wallace’s account, the Everett Interpretation doesn’t solve the measurement problem, it eliminates it. All of the possible values for the particle’s attributes are realized. The measurement changes nothing.The catch of course is that while all of the values are realized, they are realized in different “worlds” (or “universes”). Each possible value represents a branching of reality upon its realization. If a particle’s spin has possible values of up and down, both are realized in subsequently different branches of reality.Straightforward but mind-boggling. We’ve rid ourselves of the nasty measurement problem, but we got the multiverse in trade.Some readers, like some physicists, will bail at this point. Wallace, following Everett, has posited the existence of an indefinitely large number of universes (the terms “universe” and “world” are kind of awkwardly used interchangeably) — indefinitely large given that our reality is after all quantum reality, and the branchings are going to take place and compound upon one another on a literally countless scale.Those universes do not interact, or technically may do so only very minimally. For all intents and purposes, there are countless independently existing universes, following their own courses, themselves producing new branchings and new universes.You and I exist in countless of those universes, as branchings happen from the universe we are currently in. We experience only one — we are “branch-bound” in Wallace’s term, but we are instances among countless instances of ourselves across the multiverse.Wallace says, “The ‘actual physical Universe’ is the multiply branching structure generated by unitary evolution under the Schrödinger equation. The branch weights are physical features of the structure; they are represented mathematically with the quantum wavefunction.”It’s critical to Wallace’s argument that what Everett offers is a “literal” interpretation of quantum mechanics, in some sense the simplest interpretation. He even balks at the term “interpretation,” preferring its use restricted to such accounts as the Copenhagen Interpretation that add something to quantum mechanics (to Schrödinger’s wavefunction) rather that taking it “literally” as he believes the Everettian quantum theory does.I would have liked to hear a little more discussion from Wallace of what constitutes a “literal” interpretation of a mathematical equation like Schrödinger’s, especially given how central the claim is to his argument.That is the core idea, and the remainder of Wallace’s book is elaboration and defense of the Everett Interpretation. The longest treatment is a formal construction of the notion of “probability” in an Everettian universe, in which Wallace claims advantages for Everettian theory over the Copenhagen and other interpretations, as well as over classical physics itself.Throughout, Wallace’s strategy is to show that what may appear paradoxical or weird about quantum theory as a whole is mitigated by Everettian multiverse theory, and that any apparent paradoxes or weirdness generated by Everettian physics itself dissolve under scrutiny or at least pale by comparison to alternatives.Of course, there’s still the elephant in the room (or the many elephants in many rooms). That idea of “many worlds” or the “multiverse.”I can’t even come close to presuming to pass judgment on Everettian theory, or on Wallace’s account of it, but here are some areas I’m left puzzling about. I know this review is going to get long, so I’ll try to be brief, especially since I don’t have answers, just questions.Ontology:Occam’s Razor tells us that “entities should not be multiplied beyond necessity.” But Occam’s Razor doesn’t always cut cleanly. Wallace would have it that the Everett universe has the advantage in that it doesn’t require the existence of unrealized probabilities, but it does so, arguably, at the cost of multiplying entities indefinitely, across its “many” worlds. I don’t think there’s a clear winner on the Occam scale.Maybe more importantly, I’m unsure what to make of the notion of an Everettian “world.” In keeping with his emphasis on realism, Wallace treats the branched worlds of Everettian physics as physical, not logical worlds. The very physical world we live in right now is one of those Everettian worlds. To ask “where” the others places a pretty severe stress on the word “where” since they aren’t anywhere in our universe.Wallace asks us though to consider that the Everett universe is not so strange after all. For example, the extension of reality into “many worlds” is not so different from the expansion of our concept of space — once we considered the solar system to be the universe, but now we’ve expanded that concept to encompass countless solar systems in countless galaxies.But the extension that the Everett universe requires is of a different kind — it’s not an expansion of the concept of physical space, it’s an uncontrolled multiplication of discrete, non-interacting physical spaces.Personal Identity:Each of us experiences continuous existence in only one Everettian world — we are, as Wallace says, branch-bound.But there are indefinitely many worlds in which “I” also exist, alongside the one I experience. And, as time goes along, with more branching, there will be more and more “me’s” populating them. All of those “me’s” will continue a first person experience, in multiple branches of the future, but first person experience itself is singular, not multiple, so only one of those branches will be experienced by (this) me.Our branch-boundedness guarantees that nothing really changes in terms of our singular first person experience. As Wallace says, “Despite appearances, the branching structure of Everettian quantum mechanics has few or no consequences for our everyday beliefs and actions.”It is only from a “God’s eye view” that there are multiple me’s in multiple branches, with their own first person experiences.Some ethical questions struggle to rise up. What are my responsibilities to those branched versions of myself, or the branched versions of other persons? Once branched, each is responsible for its own future, but, in the future branchings, my actions now have consequences for all of my branched selves and the branches selves of everyone I affect in my present world.Testability:Since the many worlds of Everettian physics don’t interact and aren’t directly detectable (see exception below), there is no sense in which we can detect the presence of other worlds than our own, or detect effects events in our own world could have on those others. We don’t directly observe branchings, and once branched, other worlds continue separately and independently.Testability — some way in which we can observe and test whether the branching actually happens — is a core element of scientific method. I wouldn’t be the first to point out this weakness in multiverse theory.This is where Wallace’s insistence that Everettian theory is a literal interpretation of quantum mechanics needs to bear weight. He, I think, would have it that the burden of proof lies not on Everettian theory but on other interpretations of quantum mechanics that add such features as wavefunction collapse or hidden variables. As he says, “. . . the Everett interpretation just is quantum mechanics. If you’re after some experiment to distinguish Everett-interpreted quantum mechanics from an operational interpretation of quantum mechanics [i.e., a non-realist interpretation], then sure, I haven’t got anything to offer.”Given that, according to Wallace, Everettian theory is a literal interpretation of quantum mechanics, all tests of quantum mechanics are for him tests of Everettian theory. Therefore, Everettian theory is testable, despite our inability to directly detect the presence of the many worlds it predicts.The one exception to the indetectability of other Everettian worlds, by the way, is discussed by Wallace in Chapter 10, specifically in a discussion of David Deutsch’s work on neutron interference. I admit I wasn’t fully able to follow that discussion. More homework for me.Probability:Remember that this is an attempt to construct a “realist” interpretation of quantum theoryPart II of the book is an extensive construction of probability in an Everett universe.I won’t (and couldn’t reliably) go into the detail. The gist is that Wallace believes that Everettian quantum theory can not only make proper sense of the probabilities of events, but do so in a way that is in some respects superior to classical physics or non-Everettian quantum theory.Intuitively, I can see it arguable that, since all non-zero probabilities are realized in the Everettian universe, there is a superior sense to the ‘reality” of those probabilities than for a universe in which some of those non-zero probabilities are not realized and simply vanish.The suspicion I had about probability going into Wallace’s discussion was this: Schrödinger’s wavefunction contains weights assigned to potential attributes of a particle, awaiting realization by measurement. If we interpret those weights as probabilities (e.g., that the spin of a particle will be measured with one value rather than another), as is normally done (and as Wallace does under Everettian quantum theory), what effect do those probabilities have on branching? For example, do higher probability outcomes produce more worlds with that outcome that lower probability ones?But Wallace has ruled out, for reasons I won’t go into and don’t fully understand, counting worlds — thus there is no sense in which there are “more” worlds with higher probability outcomes than lower probability ones.So the problem, phrased in the way that I just did to anticipate some such resolution, is a pseudo-problem.What becomes of probability in an Everettian universe is exactly what one would want to become of it — for any observer, the weights in the wavefunction can be interpreted as the likelihood that that observer will obtain the relevant value for the particle’s attribute when measured. The existence of other branched observers subsequent to the measurement is irrelevant to that observer’s own experience.Measurement:The dissolution of the measurement problem is one of the chief advantages that Wallace sees with Everettian theory. No wavefunction collapse, no magic happening when a measurement takes place, because all possible values of the measurement are realized, just in branched worlds.Fine. But I’m still left with a question. Does the branching take place when measurement takes place? If so, although the measurement doesn’t generate a wavefunction collapse, it does seem to generate branching.I may be misunderstanding the relationship between measurement and branching, so the gap here may be my own.I’ve gone on for a long time. This is obviously a fascinating, provocative book. I’d dare anyone to read it and not be challenged by it.I can’t say Im convinced — after all, my understanding of what I would be convinced of has a lot of gaps. But I won’t stop thinking about this.I should mention that there are more accessible treatments of Everettian theory out there. See Sean Carroll’s Something Deeply Hidden for example. Wallace’s book is challenging not only conceptually but technically — his treatment is formal and mathematical.

⭐I have been looking for a book that explains Everett’s Many Worlds Interpretation of Quantum Mechanics in a way that is authoritative, thorough, rigorous, and understandable to a person like myself who is a scientist in a different field. This is it. Wallace uses a combination of mathematics, and verbal explanation of both physics and philosophy to make all the issues accessible. He writes very clearly and precisely, summarizes as he goes along and does not avoid (in fact, faces squarely) the common criticisms of MWI. This is by no means light reading, but rewards the careful reader with a much improved understanding of what MWI is and is not.

⭐This book is more technical than I expected and is requiring me to revisit largely forgotten parts of quantum theory. It is carefully argued and to me very convincing. A most valuable work resulting from many years study. Not for the faint-hearted!

⭐This book defends the controversial idea that when certain events happen, like the decay of a radioactive atom, the world divides into branches where in one the atom has decayed and in the other it hasn’t. A person observing the decay in a Geiger counter also branches into copies of him or herself, each observing a different decay result.The author justifies this idea, first propounded by Hugh Everett III in his PhD thesis, against a multitude of alternative proposals for explaining what happens without calling upon branching. The author insists that the Everett approach is not just an interpretation of quantum theory, but IS quantum theory without any need for embellishment. It helps reading the book to have some knowledge of quantum theory, decision theory, and the philosophy of science. Nevertheless, I found it possible to skip over most equations and appreciate the scholarship of the author and the profound consequences of Everett’s ideas — figuring out what to do with trillions of lives.

⭐Excellent. Although the rendering is technical at times the explanations are amply focused and self explanatory. Highly recommend it for anyone interested in this fascinating story.

⭐Depuis la fin des années 1990 et les travaux de Deutsch, Saunders, Wallace et quelques autres, l’interprétation d’Everett est considérée par de nombreux philosophes analytiques comme une des interprétations les plus élaborées et les plus crédibles de la mécanique quantique. Malheureusement, les adversaires de cette interprétation ignorent la plupart du temps ces derniers développements et basent leurs critiques de la théorie à partir d’une vision assez naïve de ce qu’est une théorie physique en générale, et d’une vision caricaturale de ce qu’est la théorie d’Everett en particulier. C’est particulièrement vrai en France, ou même les rares défenseurs de cette interprétation n’ont souvent pas suivi les développements de leurs collègues d’Oxford, et ne prennent pas en compte l’importance de la décohérence et l’intérêt des approches de la théorie de la décision pour résoudre les deux plus gros problèmes qui se posent à la théorie d’Everett, à savoir le problème dit de la base préférée et celui des probabilités.Le livre de Wallace est le livre qu’il faut avoir lu pour pouvoir juger de la consistance de la théorie d’Everett. On ne peut aujourd’hui tout simplement pas en rester aux travaux originaux d’Everett ou à ceux de Brice DeWitt pour pouvoir l’évaluer.Pour défendre sa thèse, Wallace propose un cadre interprétatif fonctionnaliste des théories physiques et des rapports entre différents niveaux de descriptions théoriques, basés sur la notion d’instanciation, qui a un grand intérêt en soi (c’est à dire au delà des problèmes d’interprétation de la mécanique quantique) notamment sur les questions d’émergences et du réductionnisme, qui évite à la fois l’écueil des versions trop simplistes du réductionnisme tout en ne tombant pas dans cette forme de mysticisme qui apparait si souvent entourer certains discours obscurs en faveur de l’émergentisme.Le livre n’est pas très difficile, et est raisonnablement accessible aux personnes qui ont un bagage assez solide en mécanique quantique standard, niveau master 1. Les chapitres les plus difficiles, qui concernent les preuves rigoureuses données à ses résultats sur le problème des probabilités peuvent être sautés sans dommage car l’auteur propose en amont d’autres preuves moins rigoureuses, mais plus intuitives et moins formelles, qui donnent déjà une idée précise de comment l’auteur parvient à résoudre le problème.Excellent livre.

⭐

⭐Good intro to Quantum Mechanics

⭐量子力学の多世界解釈、もちろん1957年のエヴェレット論文を出発点とする。しかし、20世紀の終盤からこの解釈が脚光を浴び始めたことの、少なくとも一因は、David Deutschによる量子コンピューターの研究にある。あまり他人との交流に積極的ではない彼の共同研究者となったのが、本書の著者David Wallaceである。主として彼の学会その他での活動により、二人の共同研究は広く知られることになった、とコリン・ブルース「量子力学の解釈問題」（和田純夫訳、講談社BB、2008）は注意を喚起している。この本、500ページを超える大著だが、全体の筋書きは第3章のなかばまでと、第4章の始めのほうを拾い読みすれば容易にわかる仕掛けになっていてありがたい。いまだに数学や物理学の数式にビビりまくる日本の「科学哲学者」たちと違って、物理学と哲学の二つの学位を持つこの著者は、量子力学の計算を厭わず、数式もふんだんに出てくるが、全体の筋を掴んで難しいところは飛ばし読みしても、十分に楽しめる（？）はずである。日本では和田純夫さんの著書などで知られてきた多世界解釈の要点は、次の二つとなろう。（１）量子力学のシュレーディンガー方程式は決定論的であって、（２）個々の量子系ではなく世界全体に適用されるべし。そうすると、これまでの標準的な解釈で前提されていた（３）波束の収縮は不要となり、また、（４）量子力学内部に「確率」が入る余地もない。さらに、（５）非局所的な作用のない物理学が可能となる。もちろん、以上のようなメリットが得られることの代償として、（a）多くの枝分かれし、共存する世界が生まれることをどう説明するか、（b）統計的、確率的予測の成功で支えられてきた量子力学を「確率」抜きでどのように弁護しうるのか、あるいは「確率」の使用を、この解釈でどのようにして導入できるのか、という問題を解決しなければならない。これ以上内容を紹介するのは控えるが、どちらの点でも読み応えのある力作であることはマチガイない。日本にも「量子論の哲学」の専門家は何人かいるはずなので、しっかり読んで検討していただきたい。そして、これに負けないだけの大著を早く出してもらいたいものだ（筋が通っておれば、小著でも良しとしよう）。

⭐

Keywords

Free Download The Emergent Multiverse: Quantum Theory according to the Everett Interpretation in PDF format
The Emergent Multiverse: Quantum Theory according to the Everett Interpretation PDF Free Download
Download The Emergent Multiverse: Quantum Theory according to the Everett Interpretation 2014 PDF Free
The Emergent Multiverse: Quantum Theory according to the Everett Interpretation 2014 PDF Free Download
Download The Emergent Multiverse: Quantum Theory according to the Everett Interpretation PDF
Free Download Ebook The Emergent Multiverse: Quantum Theory according to the Everett Interpretation