QBism: The Future of Quantum Physics by Hans Christian von Baeyer (PDF)

Description

Measured by the accuracy of its predictions and the scope of its technological applications, quantum mechanics is one of the most successful theories in science—as well as one of the most misunderstood. The deeper meaning of quantum mechanics remains controversial almost a century after its invention. Providing a way past quantum theory’s paradoxes and puzzles, QBism offers a strikingly new interpretation that opens up for the nonspecialist reader the profound implications of quantum mechanics for how we understand and interact with the world.Short for Quantum Bayesianism, QBism adapts many of the conventional features of quantum mechanics in light of a revised understanding of probability. Bayesian probability, unlike the standard “frequentist probability,” is defined as a numerical measure of the degree of an observer’s belief that a future event will occur or that a particular proposition is true. Bayesianism’s advantages over frequentist probability are that it is applicable to singular events, its probability estimates can be updated based on acquisition of new information, and it can effortlessly include frequentist results. But perhaps most important, much of the weirdness associated with quantum theory—the idea that an atom can be in two places at once, or that signals can travel faster than the speed of light, or that Schrödinger’s cat can be simultaneously dead and alive—dissolves under the lens of QBism.Using straightforward language without equations, Hans Christian von Baeyer clarifies the meaning of quantum mechanics in a commonsense way that suggests a new approach to physics in general.

User’s Reviews

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⭐QBism, short for Quantum Bayesianism, is a new interpretation of quantum theory based on the probability theorem of the eighteenth-century Presbyterian minister and mathematician Thomas Bayes. Drawing from Bayesian law, Christopher Fuchs, the primary developer of QBism, has put forth the most promising understanding of the meaning of quantum theory, eclipsing earlier models such as the Copenhagen interpretation developed by the early founders of quantum mechanics such as Niels Bohr, Werner Heisenberg, and Max Born. Hans Christian von Baeyer, the author of this book, first learned of QBism in 2002 and was immediately impressed. Von Baeyer is well versed in quantum mechanics having taught it at the university level for fifty years and over that time, through books, lectures, and interviews, has attempted to bring the subject to the general public. But like many of his colleagues, he had always felt a sense of unease about its meaning. As the Nobel Lauret, Richard Feynman once proclaimed, “No one understands quantum physics.” But once von Baeyer understood the deep implications of QBism, it brought him a sense of relief. He says, “When I began to understand QBism and realized that by simply switching to a better definition of probability I could finally stop puzzling over the meaning of the collapse of the wavefunction, I felt a sense of liberation bordering on exhilaration.” QBism’s insightful departure from the Copenhagen interpretation of reality involves the theory’s rejection of non-locality and the replacement of the mysterious wavefunction with Bayesian probability, while making a strong case for an observer-dependent universe. The author states: “The principal thesis of QBism is simply this: quantum probabilities are numerical measures of personal belief.” An example of this would be the quantum wavefunction that describes the cloud-like distribution of the electron around the nucleus of an atom. But in reality, the wavefunction does nothing of the sort; it describes, instead, the probability of finding the electron when one looks based on previous experimental results. In fact, the electron has no reality-based location before an observation. Once the observation takes place the belief of the agent or observer changes from uncertainty to certainty. No collapse takes place, only a change in the knowledge of the observer. Classical physics hinges on two tenants, locality and realism, both of which Einstein and two colleagues Nathan Rosen and Boris Podolsky attempted to rescue from the onslaught of quantum mechanics with their celebrated EPR paper in 1935. Einstein thought that he had rid nature of Newton’s spooky action at a distance with his general relativity theory which didn’t require some mysterious force propagating across empty space. Yet, quantum theory and experiment seemed to revive nonlocality in cases of quantum entanglement. Even more upsetting to Einstein, was the proposition that quantum mechanics violated realism, the assumption that the observer interacts with nature in a way that influences the outcome of experiments. Certainly, Einstein said, the moon must be there even if no one looks. Von Baeyer details an experiment conducted in the laboratory by Anton Zeilinger and his team in 2000, involving the measurements of electrons that were put in a state of entanglement. The results of the experiments proved Einstein half-right; locality was not shown to be violated, but realism, “the assumption that objects have physical properties that are unaffected by measurement, observation, and even thoughts and opinions, was indeed violated” as the QBists’ interpretation predicts. QBism doesn’t deny an external world, but rather, through experiments, has suggested we live in a participatory universe in which laws are invented to reflect our recurrent experiences of nature.In his book, QBism: The Future of Quantum Physics, Hons Christian von Baeyer has succeeded in bringing the QBists’ interpretation of quantum theory to the general public. This book has re-invigorated my quest to understand the nature of reality.

⭐Interpretations of quantum mechanics (QM) that are observationally equivalent to QM can be important if they lead to novel explanatory models based on extending the range of the interpretation to new phenomena. Think, for instance, of the Hamiltonian formulation of Newtonian mechanics. Otherwise, there is no scientific basis for preferring one interpretation over another.There is currently no scientific basis for preferring one interpretation of QM (including QBism) over another. People who say one is right and another is wrong are just emoting. I will have none of it.Of course, some interpretations may be preferred on metaphysical grounds, whatever that means. If there is a candidate for rejection on metaphysical grounds, QBism is it. The interpretation rests on the rejection of a frequency interpretation of probability in favor of a Bayesian (subjective) interpretation. In fact, there are several different notions of probability in the scientific literature, and both frequency and subjective models are valid under different conditions. But the frequency interpretation is perfectly valid for QM, and the subjective interpretation is simply outlandish. Can one really believe there was no spectrum to the hydrogen atom until someone saw such a spectrum? Do QM electron ic devices work because of human subjectivity? Or quantum computing? Outlandish is the subjective interpretation in these cases.The book devotes a shoddy chapter to the critique of frequency models. It starts by observing that you can’t tell if a roulette wheel is “fair” by observing one outcome (e.g., the ball lands on slot 11). It then says that 100 trials of flipping a coin can be represented by a roulette wheel with 2 to the power 100 slots. You can’t tell if the wheel is fair by the outcome because all outcomes are equally likely. This is true. But suppose before I spin this wheel i assert that the probability that the outcome will have between 45 and 55 ones. This will be correct with very high probability. If the outcome has five ones, the wheel is unfair with probability close to one. This is the basis of all of statistical mechanics. The book’s critique is simply wrong.The book is well writien and fun to read, although quite unconvincing.

⭐Extremely helpful review of concepts and theory in Quantum Mechanics and extremely informative for readers whom have yet to be exposed to QB principles. This text has a lot of personality and the author knew one of the founders of QBism, Chris Fuchs, personally; therefore, the information conveyed in this book is all very accurate and detailed.

⭐”Shut up and calculate,” reveals a fundamental truth about quantum mechanics: the mathematical machinery is flawless but the world the machinery describes is far from clear. QBism avoids the ontological conundrum by treating the machinery as a device used by an observer to calculate the probability of a future observation. This much is clearly true. Problems arise if you go on to ask “How must the world be for this machinery to work so well?” QBism does not try to answer this question and as a result avoids all the problems introduced by the wave-particle story. The author treats QBism in a wonderfully clear and engaging way. Anyone who who has wrestled with trying to picture the world “described” by quantum mechanics will discover an elegant solution to the muddle. Those committed, like Einstein and Schroedinger, to “picturing” the world will doubtless not be satisfied. A great read. I recommend it highly.

⭐I greatly enjoyed this book! If I didn’t have a strong background and understanding of Bayesian and Frequentist statistics, along with prior readings in Philosophy of Science, this would have been a much more difficult read. Considerable pain experienced as an undergraduate taking Modern Physics was quite helpful as well.

⭐Decent quick description of this relatively new way to think about quantum mechanics, but skimpy on technical details.

⭐In hindsight, I was probably expecting too much from this, based on some rave reviews.I found the rather breathless style rather irritating, and the presentation of the actual ideas (which are extremely interesting) was much sketchier than I was expecting. I was dismayed to find that the latter part of the book is largely devoted to what can only be described as crackerbarrel philosophy: given that the author makes a big deal of the supposedly very grand philosophical consequences of QBism, he seems to know less than one might hope about the philosophy of science in general. Indeed, he seems to be implying that QBism is really the One True Theory. and all that remains is to tease out the beautiful consequences. Science doesn’t really work like that.Specifically, I was disappointed that he doesn’t make a better fist of discussing the “no hidden variables” problem. The thing about that is that it’s not that there are aspects of reality which we cannot describe with quantum mechanics, but that such aspects do not in fact *exist* (unless you accept instantaneous action at a distance.) Given that Baynesianism as a philosophical position (as opposed to a mere statistical technique) implies that probability measures the degree of our ignorance of how things are, there seems to me to be a philosophical difficulty there if there is underlyingly nothing there to be ignorant *of*. But the author instead interprets the philosophical implications of Baynesianism as solving all the problems. I may very well have radically misunderstood all this, but it seems reasonable to expect of book of this kind not to airily dismiss such problems.

⭐Il libro è in genere ben scritto, ma, come avviene sempre per i testi di meccanica quantistica che non contengono formule, è veramente comprensibile solo da chi quelle formule le conosce già.L’interpretazione della funzione d’onda come probabilità soggettiva tende a demistificare e sdrammatizzare il fenomeno della cosiddetta azione a distanza. Altri misteri, quello dello strano modo di muoversi degli oggetti quantistici (esperimento della doppia fenditura) però permangono. Alla fine del libro l’autore parla di una certa legge quantistica della probabilità totale. Ma questa ahimè non la conoscevo già e non ho capito di cosa si tratta.Nonostante i suoi limiti, il libro può costituire una piacevole lettura.

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⭐A very good book that explains the Qbism approach to science and knowledge acquirement from each individual’s perspective. This also has the benefit that it removes the current conceptual foundational problems associated with Quantum Mechanics.You will be required to look at the way we understand ‘doing science’ by a 180 degree turn around in perspective.This is in vast contrast to the way Science has been done during the past 450 years or so. There is an objective Nature out there. Scientist are like Gods tinkering about with Nature to try to understand her mathematical truths. When probing nature any information expelled is deemed to have left the realm of Nature and has past into a separate world before arriving through the senses and into the scientist brain. The Scientist senses and brain are not associated with the experiments themselves as they are not deemed part of the experiments. Here we attempt to describe Nature in the absolute.A phrase that helps see the different Qbism perspective is; “The Map is not the Territory”.The ‘territory’ is Nature as she truly is – A mathematical construct. Nature is real.This construct includes ‘Agents’. Agents within this mathematical construct have memories, senses (sensing nature) and processing power. There is a range to the sophistication of these agents. The most sophisticated agents have highly developed sensors, a large memory and significant processing power. Many of these more sophisticated agents have united together and processing the information they have gained from their senses have develop an accurate ‘map’ of ‘nature’ – Science. They share this map of nature that they have developed which can be accessed through memory devises like books, lectures and computers. Each agent has his/her own private map that they use to make predictions about the future. This is a survival advantage. Each agent is continually updating their map as they take on and process new information. Bayer’s statistical Law.Because the agents map is only a map (a highly optimised compression of the description of Nature) there can never be a 100 % correspondence with reality (nature herself). So only predictions of future outcomes are possible ranging from just above 0 to almost 1.Ongoing processing and updating of the map means the map approaches a more accurate description of Nature. But you can never be 100 % confident that the map (in your Brain) describes Nature completely. Only a Bayesian Statistical description is possible.Certainly, an interesting topic. When reading this book, I definitely had the feeling the book has come out in the 21st century. A lot to ponder.

⭐A gentle introduction to QBism. Written in a very accessible manner. Wish there was a more technical followup book on this subject.

⭐Its good to a book which takes the statistical aspects of quantum physics seriously it clears up so many pseudo problems all bought about by the popular misconception that the solution to Schrodinger’s equation is akin to a real wave. QBism along with Ballentine’s statistical interpretation dissolves the pseudo problems by admitting that the solution to Schrodinger’s equation is a means to generating the correct probability density function for a given situation, nothing more nothing less. The so called collapse of the wave function is really only akin to the updating of a Bayesian prior.To take 2 simple examplesa) The so called Schrodinger’s Cat experiment. The cat is alive or dead before the box is open all the superposition is is a superposition of possibilities reflecting the lack of knowledge of the observer as to whether or not the cat is alive or dead before heshe opens the box 50% of the time the cat will be alive and 50% of the time the cat will be dead but in order to get the correct statistics the experiment has to be repeated a number of times. There is no way that the observer can predict what will happen on a given occasionb) Similarly with the Aspect experiment and the violation of the Bell inequalities. Here much confusion has reigned in the popular literature by confusing a time like event with a space like event. Prior to a measurement observer A and observer B can only guess a probability that they will detect a given electron with spin up or down. Suppose A makes a measurement then A will know instantaneously due to the conservation of angular momentum that B’s measurement will be the exact opposite of A’s, However B will still not know what he will measure until either B makes a measurement or he obtains information as the result of A’s. But again the results of a given measurement will not be known only that it has a 50% chance of having spin up or spin down. This does not involve any superluminal signalling as more popular accounts would have us believe.So by taking a purely statistical interpretation of the wavefunction as QBIsm does all the main problems in the interpretation of quantum mechanics disappear.If I have a caveat it is this, I’m not sure one needs to invoke Bayesianism to get a purely statistical interpretation of quantum physics the formalism of quantum mechanics is able for a given situation to give any observer the probabilities of a given situation. It is not true as the author claims that quantum mechanics is about nothing. What tends to be missed in any popular account of quantum mechanics is the obtaining of the Hamiltonian which via the formalism is able to predict the correct probability amplitude. It is that which governs the physics of a given situation not the wavefunction as such. The Hamiltonian essentially summarises the properties of the particles and how they interact with each other.Getting the correct type of particle and their interaction is where the physics is at as has been demonstrated by the successful application of quantum physics to explain the properties of solids atoms and molecules over the past 90 years, By focusing on the wave function as most books on the interpretation of quantum mechanics do the actual physics is likely to be missed,Hopefully this book by helping to demystify the wave function will do something to remedy the rather farcical situation that prevails in the interpretation of quantum physics and people will be able to restore some sanity to the more and more wacky ideas that are currently prevailing

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