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QBism: The Future of Quantum Physics
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.
253 pages, Kindle Edition
Published October 3, 2016
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July 13, 2017
Physical reality gets personal
In this book, the authors have suggested alternative interpretations of quantum reality contrasting the well-known Copenhagen interpretation for the results of quantum physical measurements in the double-slit experiment. This experiment is a demonstration that light and matter can display characteristics of both classically defined waves and particles (wave-particle duality). In addition, it displays the fundamentally probabilistic nature of quantum physical phenomena.
The following brief summary could help us understand how QBism described in this book interprets quantum reality: Physical reality we experience in this universe is due to operation of the laws of physics on matter (and energy) in a four dimensional spacetime. The fabric of reality is made of space and time fused together to form a unified spacetime in four dimensions, and speed of light is a part of this fabric. In the basic energy/force equations of classical physics, relativistic physics and quantum physics, time does not appear. Hence laws of physics allows physical reality to operate from past to future or future to past. In addition, our perception of the reality, of what is “now” (present tense) is not absolute, but only relative. Space and time looks differently for different observers in the universe, since the speed of light is a part of the fabric of reality. This speed is a universal constant for all observers, and matter/energy cannot travel faster than the speed of light (according special relativity.) As a result, for example, for inhabitants of a planet 4.5 billion light years away from us, solar system doesn’t even exist, let alone see human beings. Because light takes 4.5 billion years to reach them from us and hence in their “reality” we don’t exist (Solar system is exists for the last 4.5 billion years.) The speed of light is packaged into the fabric of reality, and this speed limit constrains only the motion of matter/energy, and not to the motion of space. Space can expand much faster than speed of light, and it has done that at about 13.7 billion years ago. Space or spacetime is also not a continuous fabric as we understand physical reality, but it also curves, bends, rips, repairs the rips and connects distant parts of the universe through bridges (cosmic worm holes).
Physics thus far helps in describing the objective external world: fundamental particles, waves, fields, atoms, molecules, biomolecules, and biological systems. How waves/particles change in time; and how they give rise to the different forms of matter, the life-forms, machines, planets, stars and galaxies make the universe. This world makes itself known to each of us through our own perceptions. Yet physics has ignored one other critical factor of reality, the consciousness. Classical and relativistic physics say that reality exists as they appear to us and we are mere observers of its presence. But the laws quantum physics that operate at the microscopic scales on matter and energy, like electrons and photons, deny objective reality, determinism, free will or our understanding that cause must precede an effect. Quantum properties like entanglement, uncertainty principle, quantum gravity (bending of spacetime in presence of matter), vacuum energy, quantum bubbles, black holes, spacetime ripples (also called gravitational waves), etc. deny common sense arguments since spacetime at the most fundamental level is not clearly understood. Hence this has given rise to a wide range of conjectures that suggest that reality could be an illusion or the universe is a two dimensional hologram that contains information for our existence in three dimensional space. Some physicists also suggest that space is real and time is an illusion; others say, time is an illusion and space is real. We have taken for granted for too long that space and time is a non-interactive fabric of reality. But this is turning out be a major error. In fact spacetime may be discontinuous and exists in discrete quanta or units and how this works at subatomic scales is still unclear.
According to wave mechanics, the quantum reality of a physical system is described in terms of a wave function. Matter in most fundamental form, like an electron, exists in both wave and particle forms (wave-particle duality). The shape of the wave function derived from wave mechanics describes wave’s existence in terms of probabilities. It could exist anywhere in the universe with a given (calculated) probability. When physical measurements are made on this system by an observer, this “act” would “collapse the wave function” to a physically identifiable particle form. This explanation is referred to as Copenhagen interpretation of quantum reality. There are other interpretations to account for this result such as many world’s interpretation and Bohmian interpretation, etc. All of them have something in common. They treat the wave function as a description of an objective reality shared by multiple observers. QBism, on the other hand, treats the wave function as a description of a single observer’s subjective knowledge. Q is for quantum and B is for Bayes¬ian; a view of probability that includes an agent who makes bets and updates odds. In this new interpretation of quantum reality, the wave function does not describe the world, but it describes the observer. The wave function’s probabilities are described as Bayesian probabilities, which is nothing but the subjective degrees of “belief” about a system. It is like gambling by placing bets on measurement outcomes, and bets are updated as new data emerges. According to QBism, the wave function’s “collapse” is simply the observer updating the personal beliefs after making a measurement. And quantum entanglement (two particles entangled quantum physically), which is another strange property of quantum physics is when one observer’s measurement of a particle at position 1 collapses the wave function of its entangled particle somewhere else in the universe at position 2. QBism says that the measurement at position 1 simply provides information for the observer 1, who can use to bet on the state of the distant entangled particle at position 2. But how does his/her measurement at one place affect the outcome of a measurement of a second observer at position 2? In fact, it doesn’t. Since QBism wave function doesn’t belong to the physical system being observed, but to the observer himself. Hence, observer 1’s wave function doesn’t have to align with observer 2. This argument circumvents several shortcomings of Copenhagen interpretation of quantum reality. But fails to answer numerous bigger questions that confronts reality, and possible existence of multiverse.
Physicist Niels Bohr once said that the purpose of science was not to reveal “the real essence of the phenomena” but only to find “relations between the manifold aspects of our experience”. His idea still holds pretty well. QBism is a shortcut to understand the quantum phenomenon that is played out on a larger screen, but we are taking a narrow look at one end of the spectrum. I am not too enthusiastic about this interpretation of our physical reality. But nevertheless, it is an interesting alternative idea which I recommend to readers interested in quantum physics and physical reality.
In this book, the authors have suggested alternative interpretations of quantum reality contrasting the well-known Copenhagen interpretation for the results of quantum physical measurements in the double-slit experiment. This experiment is a demonstration that light and matter can display characteristics of both classically defined waves and particles (wave-particle duality). In addition, it displays the fundamentally probabilistic nature of quantum physical phenomena.
The following brief summary could help us understand how QBism described in this book interprets quantum reality: Physical reality we experience in this universe is due to operation of the laws of physics on matter (and energy) in a four dimensional spacetime. The fabric of reality is made of space and time fused together to form a unified spacetime in four dimensions, and speed of light is a part of this fabric. In the basic energy/force equations of classical physics, relativistic physics and quantum physics, time does not appear. Hence laws of physics allows physical reality to operate from past to future or future to past. In addition, our perception of the reality, of what is “now” (present tense) is not absolute, but only relative. Space and time looks differently for different observers in the universe, since the speed of light is a part of the fabric of reality. This speed is a universal constant for all observers, and matter/energy cannot travel faster than the speed of light (according special relativity.) As a result, for example, for inhabitants of a planet 4.5 billion light years away from us, solar system doesn’t even exist, let alone see human beings. Because light takes 4.5 billion years to reach them from us and hence in their “reality” we don’t exist (Solar system is exists for the last 4.5 billion years.) The speed of light is packaged into the fabric of reality, and this speed limit constrains only the motion of matter/energy, and not to the motion of space. Space can expand much faster than speed of light, and it has done that at about 13.7 billion years ago. Space or spacetime is also not a continuous fabric as we understand physical reality, but it also curves, bends, rips, repairs the rips and connects distant parts of the universe through bridges (cosmic worm holes).
Physics thus far helps in describing the objective external world: fundamental particles, waves, fields, atoms, molecules, biomolecules, and biological systems. How waves/particles change in time; and how they give rise to the different forms of matter, the life-forms, machines, planets, stars and galaxies make the universe. This world makes itself known to each of us through our own perceptions. Yet physics has ignored one other critical factor of reality, the consciousness. Classical and relativistic physics say that reality exists as they appear to us and we are mere observers of its presence. But the laws quantum physics that operate at the microscopic scales on matter and energy, like electrons and photons, deny objective reality, determinism, free will or our understanding that cause must precede an effect. Quantum properties like entanglement, uncertainty principle, quantum gravity (bending of spacetime in presence of matter), vacuum energy, quantum bubbles, black holes, spacetime ripples (also called gravitational waves), etc. deny common sense arguments since spacetime at the most fundamental level is not clearly understood. Hence this has given rise to a wide range of conjectures that suggest that reality could be an illusion or the universe is a two dimensional hologram that contains information for our existence in three dimensional space. Some physicists also suggest that space is real and time is an illusion; others say, time is an illusion and space is real. We have taken for granted for too long that space and time is a non-interactive fabric of reality. But this is turning out be a major error. In fact spacetime may be discontinuous and exists in discrete quanta or units and how this works at subatomic scales is still unclear.
According to wave mechanics, the quantum reality of a physical system is described in terms of a wave function. Matter in most fundamental form, like an electron, exists in both wave and particle forms (wave-particle duality). The shape of the wave function derived from wave mechanics describes wave’s existence in terms of probabilities. It could exist anywhere in the universe with a given (calculated) probability. When physical measurements are made on this system by an observer, this “act” would “collapse the wave function” to a physically identifiable particle form. This explanation is referred to as Copenhagen interpretation of quantum reality. There are other interpretations to account for this result such as many world’s interpretation and Bohmian interpretation, etc. All of them have something in common. They treat the wave function as a description of an objective reality shared by multiple observers. QBism, on the other hand, treats the wave function as a description of a single observer’s subjective knowledge. Q is for quantum and B is for Bayes¬ian; a view of probability that includes an agent who makes bets and updates odds. In this new interpretation of quantum reality, the wave function does not describe the world, but it describes the observer. The wave function’s probabilities are described as Bayesian probabilities, which is nothing but the subjective degrees of “belief” about a system. It is like gambling by placing bets on measurement outcomes, and bets are updated as new data emerges. According to QBism, the wave function’s “collapse” is simply the observer updating the personal beliefs after making a measurement. And quantum entanglement (two particles entangled quantum physically), which is another strange property of quantum physics is when one observer’s measurement of a particle at position 1 collapses the wave function of its entangled particle somewhere else in the universe at position 2. QBism says that the measurement at position 1 simply provides information for the observer 1, who can use to bet on the state of the distant entangled particle at position 2. But how does his/her measurement at one place affect the outcome of a measurement of a second observer at position 2? In fact, it doesn’t. Since QBism wave function doesn’t belong to the physical system being observed, but to the observer himself. Hence, observer 1’s wave function doesn’t have to align with observer 2. This argument circumvents several shortcomings of Copenhagen interpretation of quantum reality. But fails to answer numerous bigger questions that confronts reality, and possible existence of multiverse.
Physicist Niels Bohr once said that the purpose of science was not to reveal “the real essence of the phenomena” but only to find “relations between the manifold aspects of our experience”. His idea still holds pretty well. QBism is a shortcut to understand the quantum phenomenon that is played out on a larger screen, but we are taking a narrow look at one end of the spectrum. I am not too enthusiastic about this interpretation of our physical reality. But nevertheless, it is an interesting alternative idea which I recommend to readers interested in quantum physics and physical reality.
November 29, 2019
Aunque he intentado resistirme y ser escéptico (como lo debemos ser todos frente a las soluciones "fáciles" para los más difíciles problemas de la ciencia) ¡creo que he sucumbido al encanto del CuBismo!
Este librito ameno, bien escrito y muy claro es ahora el único culpable de ello.
No sé si me arrepentiré cuando el CuBismo caiga en desgracia (espero que no lo haga), si tendré que borrar toda huella de mi simpatía hacía él, incluyendo tal vez esta reseña (¡es broma!) Lo cierto es que, como el autor, ¡estoy encantado con la idea!
Había oído hablar de esta "curiosa" interpretación de la mecánica cuántica, que nació apenas hace poco mas de 15 años, por algunas referencias en blogs y artículos de corte filosófico en los arXiv (http://arxiv.org.)
No había sin embargo profundizado mucho, pensando justamente que se trataba de otro intento de arreglar un problema que tiene más de 70 años, a saber el problema de que la mecánica cuántica funciona, pero su significado profundo es todavía desconocido por los físicos.
Recientemente, y animado por el deseo de escribir un pequeño blog sobre "el asunto cuántico" me decidí a leer más sobre el CuBismo. Que mejor manera para empezar a hacerlo que con un texto divulgativo (sí, lo admito; a los profesionales también también nos tienen que explicar primero las cosas con "plastilina.")
No pude ser mas acertada mi elección.
El libro esta impecablemente organizado (y tal vez es por ello que logra su cometido) como no esperaría menos de un profesional de la física con una larga experiencia enseñando esta disciplina. A veces la física es tan difícil de enseñar y de aprender, que el buen profesor debe saber organizar las ideas de modo que no haya manera de acercarse a ellas sin creer al final que se entienden un poco (aunque muchas veces sea una ilusión.)
El libro comienza por un repaso de las primeras ideas de la teoría cuántica (la radiación de cuerpo negro, el efecto fotoeléctrico y el átomo de Bohr.) Temas todos muy trillados en la divulgación pero que el Prof. Von Baeyer aborda de manera amena y original. Así por ejemplo, su explicación de la solución de Planck al problema de la radiación de cuerpo negro es bastante original y creo que la seguiré usando en todas mis charlas y cursos.
A continuación aborda los temas más interesantes y profundos de la mecánica cuántica, aquellos donde nacen justamente los problemas que tienen a los físicos en serios embrollos: el papel del observador, el colapso de la función de onda, la incertidumbre cuántica, ¿función de onda o matrices?, la paradoja de la tortuga de Schrödinger (me niego a sacrificar un gatico para esto), el problema de Wigner, etc.
Me encantó en particular la manera como describe la función de onda más simple de todas, es decir aquella de un qubit, y la forma en la que usa esta función de onda en el resto del libro para explicar las cosas mas extrañas de la mecánica cuántica y las soluciones del CuBismo.
A continuación aborda el tema más novedoso del CuBismo: la concepción Bayesiana de la probabilidad.
Para aquellos a los que, como yo, disfruten lecturas agradables sobre probabilidad y estadística encontrar las páginas dedicadas al tema en este libro muy entretenidas y claras.
Para quiénes no hayan oído hablar del "enfoque Bayesiano" de la estadística, Von Baeyer nos recuerda que fue este el enfoque original de la teoría de la probabilidad, incluso aquella desarrollada por el padre de la teoría Pierre Simon de Laplace.
En muy pocas palabras, lo que el Bayeniasismo enseña es que las probabilidades que asignamos a eventos individuales o muy simples (p.e. la probabilidad que en el lanzamiento de una moneda obtenga cara o sello o la probabilidad de que el spin del electrón tenga una determinada orientación en un experimento), no son "objetivas" (tienen una existencia independiente del observador), ni se pueden deducir con principios racionales. Al contrario, se basan en las "creencias subjetivas" con las que los agentes que estudiamos el mundo juzgamos los fenómenos. Muchas probabilidades "derivadas" de ellas si siguen reglas matemáticas rigurosas (justamente las de la teoría de probabilidad) pero se basan primero en consideraciones heurísticas.
He allí la clave del CuBismo: las probabilidades cuánticas y la función de onda, que en la interpretación convencional de la mecánica cuántica está asociada con ella, no son tampoco objetivas; no tienen una existencia independiente del experimento o el "observador." Se construyen en el momento en el que se realiza el experimento y pueden cambiar dependiendo de cómo, de quién haga el experimento pero más importante de si cambian o no las condiciones de un sistema (una propiedad que resuelve magistralmente el problema del colapso de la función de onda y de la no-localidad cuántica.)
Este enfoque, contrasta con el convencional enfoque "frecuentista", tanto de la estadística como de la probabilidad cuántica (y que se puso de moda en estadística apenas en el siglo xx aunque parece que sus días están contados.) Según este enfoque las probabilidades son una propiedad objetiva de los fenómenos aleatorios que pueden "medirse" realizando experimentos (reales o ficticios) y contando "casos favorables y casos posibles".
Si no entienden una palabra de lo que digo ¡es obvio! ¡lean el condenado librito! (y empiecen por las decenas de artículos en línea - incluyendo wikipedia, que explican el enfoque Bayesiano con muchos ejemplos.)
En la última parte procede a resolver los problemas abiertos de la mecánica cuántica, usando los más sencillos argumentos y razonamientos, soportados justamente en lo que presento en todas las secciones anteriores.
El resultado es impresionante. El CuBismo resuelve algunos de los problemas más delicados de la mecánica cuántica: el colapso de la función de onda (el más difícil de todos a mi parecer) o el problema de Wigner (que esta de alguna manera emparentado con la paradoja del gato de Schrödinger.)
Al final se extiende aún más lejos hasta especular en la posibilidad de que el CuBismo (o cualquier cosa que se derive de su enfoque heurístico del problema) podría acercarnos a resolver el problema de la conciencia, la naturaleza de la indagación científica e incluso a una unificación entre la física y la psicología.
¡Parecen ideas locas! Algo sacado de algún libro de nueva era o de un documental de History Channel.
Pero no lo es.
Si bien el CuBismo no cuenta todavía con una gran fanaticada entre los expertos (creo que porque todavía no lo conoce todo el mundo), la idea nació en el seno de la escuela de pensamiento del grandioso John Wheeler, el "padre intelectual" de Richard Feynman y ha sido desarrollado por profesionales de la física primer nivel.
Lo que soy yo, como físico, no volveré a pensar en estos problemas de la misma manera. He sido "tocado" por el CuBismo y por su llamado de que volvamos a los viejos tiempos en los que la filosofía jugaba un papel central en el desarrollo de las ideas de la física.
Prueben a ver si a ustedes les pasa lo mismo.
Este librito ameno, bien escrito y muy claro es ahora el único culpable de ello.
No sé si me arrepentiré cuando el CuBismo caiga en desgracia (espero que no lo haga), si tendré que borrar toda huella de mi simpatía hacía él, incluyendo tal vez esta reseña (¡es broma!) Lo cierto es que, como el autor, ¡estoy encantado con la idea!
Había oído hablar de esta "curiosa" interpretación de la mecánica cuántica, que nació apenas hace poco mas de 15 años, por algunas referencias en blogs y artículos de corte filosófico en los arXiv (http://arxiv.org.)
No había sin embargo profundizado mucho, pensando justamente que se trataba de otro intento de arreglar un problema que tiene más de 70 años, a saber el problema de que la mecánica cuántica funciona, pero su significado profundo es todavía desconocido por los físicos.
Recientemente, y animado por el deseo de escribir un pequeño blog sobre "el asunto cuántico" me decidí a leer más sobre el CuBismo. Que mejor manera para empezar a hacerlo que con un texto divulgativo (sí, lo admito; a los profesionales también también nos tienen que explicar primero las cosas con "plastilina.")
No pude ser mas acertada mi elección.
El libro esta impecablemente organizado (y tal vez es por ello que logra su cometido) como no esperaría menos de un profesional de la física con una larga experiencia enseñando esta disciplina. A veces la física es tan difícil de enseñar y de aprender, que el buen profesor debe saber organizar las ideas de modo que no haya manera de acercarse a ellas sin creer al final que se entienden un poco (aunque muchas veces sea una ilusión.)
El libro comienza por un repaso de las primeras ideas de la teoría cuántica (la radiación de cuerpo negro, el efecto fotoeléctrico y el átomo de Bohr.) Temas todos muy trillados en la divulgación pero que el Prof. Von Baeyer aborda de manera amena y original. Así por ejemplo, su explicación de la solución de Planck al problema de la radiación de cuerpo negro es bastante original y creo que la seguiré usando en todas mis charlas y cursos.
A continuación aborda los temas más interesantes y profundos de la mecánica cuántica, aquellos donde nacen justamente los problemas que tienen a los físicos en serios embrollos: el papel del observador, el colapso de la función de onda, la incertidumbre cuántica, ¿función de onda o matrices?, la paradoja de la tortuga de Schrödinger (me niego a sacrificar un gatico para esto), el problema de Wigner, etc.
Me encantó en particular la manera como describe la función de onda más simple de todas, es decir aquella de un qubit, y la forma en la que usa esta función de onda en el resto del libro para explicar las cosas mas extrañas de la mecánica cuántica y las soluciones del CuBismo.
A continuación aborda el tema más novedoso del CuBismo: la concepción Bayesiana de la probabilidad.
Para aquellos a los que, como yo, disfruten lecturas agradables sobre probabilidad y estadística encontrar las páginas dedicadas al tema en este libro muy entretenidas y claras.
Para quiénes no hayan oído hablar del "enfoque Bayesiano" de la estadística, Von Baeyer nos recuerda que fue este el enfoque original de la teoría de la probabilidad, incluso aquella desarrollada por el padre de la teoría Pierre Simon de Laplace.
En muy pocas palabras, lo que el Bayeniasismo enseña es que las probabilidades que asignamos a eventos individuales o muy simples (p.e. la probabilidad que en el lanzamiento de una moneda obtenga cara o sello o la probabilidad de que el spin del electrón tenga una determinada orientación en un experimento), no son "objetivas" (tienen una existencia independiente del observador), ni se pueden deducir con principios racionales. Al contrario, se basan en las "creencias subjetivas" con las que los agentes que estudiamos el mundo juzgamos los fenómenos. Muchas probabilidades "derivadas" de ellas si siguen reglas matemáticas rigurosas (justamente las de la teoría de probabilidad) pero se basan primero en consideraciones heurísticas.
He allí la clave del CuBismo: las probabilidades cuánticas y la función de onda, que en la interpretación convencional de la mecánica cuántica está asociada con ella, no son tampoco objetivas; no tienen una existencia independiente del experimento o el "observador." Se construyen en el momento en el que se realiza el experimento y pueden cambiar dependiendo de cómo, de quién haga el experimento pero más importante de si cambian o no las condiciones de un sistema (una propiedad que resuelve magistralmente el problema del colapso de la función de onda y de la no-localidad cuántica.)
Este enfoque, contrasta con el convencional enfoque "frecuentista", tanto de la estadística como de la probabilidad cuántica (y que se puso de moda en estadística apenas en el siglo xx aunque parece que sus días están contados.) Según este enfoque las probabilidades son una propiedad objetiva de los fenómenos aleatorios que pueden "medirse" realizando experimentos (reales o ficticios) y contando "casos favorables y casos posibles".
Si no entienden una palabra de lo que digo ¡es obvio! ¡lean el condenado librito! (y empiecen por las decenas de artículos en línea - incluyendo wikipedia, que explican el enfoque Bayesiano con muchos ejemplos.)
En la última parte procede a resolver los problemas abiertos de la mecánica cuántica, usando los más sencillos argumentos y razonamientos, soportados justamente en lo que presento en todas las secciones anteriores.
El resultado es impresionante. El CuBismo resuelve algunos de los problemas más delicados de la mecánica cuántica: el colapso de la función de onda (el más difícil de todos a mi parecer) o el problema de Wigner (que esta de alguna manera emparentado con la paradoja del gato de Schrödinger.)
Al final se extiende aún más lejos hasta especular en la posibilidad de que el CuBismo (o cualquier cosa que se derive de su enfoque heurístico del problema) podría acercarnos a resolver el problema de la conciencia, la naturaleza de la indagación científica e incluso a una unificación entre la física y la psicología.
¡Parecen ideas locas! Algo sacado de algún libro de nueva era o de un documental de History Channel.
Pero no lo es.
Si bien el CuBismo no cuenta todavía con una gran fanaticada entre los expertos (creo que porque todavía no lo conoce todo el mundo), la idea nació en el seno de la escuela de pensamiento del grandioso John Wheeler, el "padre intelectual" de Richard Feynman y ha sido desarrollado por profesionales de la física primer nivel.
Lo que soy yo, como físico, no volveré a pensar en estos problemas de la misma manera. He sido "tocado" por el CuBismo y por su llamado de que volvamos a los viejos tiempos en los que la filosofía jugaba un papel central en el desarrollo de las ideas de la física.
Prueben a ver si a ustedes les pasa lo mismo.
January 16, 2020
2.5/5.0
November 15, 2019
I like the QBism model but not this book...
September 6, 2021
There's a wealth of fascinating material in this slim book. von Baeyer is a fine popular science writer. The subject of this book is quite abstruse. What von Baeyer does exceptionally well is set up the problem: what the proper interpretation of quantum theory is. What he could only do so well was nail the solution -- in part because this is exceedingly complex stuff and the lack of a sophisticated mathematical understanding (par for the course in a popular treatment) can only get a lay reader so far; in part, because the Qbist explanatory approach to which he's wedded is anything but intuitive. Qbism may, per the author's reasoning, address quantum physics' 'locality' problem. But regardless how much the author asserts that Qbism addresses quantum physics' 'reality' problem, as well, I couldn't quite make the conceptual leap with him. I'm entirely receptive to the possibility that a Qbist interpretation is the correct one, perhaps that it's even THE correct one. But I'd hardly call von Baeyer's case (in this book at least) airtight. Even for a lay reader like myself, von Baeyer's treatment fails to answer some very basic (yet profound) questions about what 'reality' in fact is. Nonetheless, Qbism (not von Baeyer's brainchild; the book is a reporting of others' ideas, faithfully attributed throughout) does seem to have much going for it. I'll be fascinated to see whether it grows in popularity -- and explanatory power -- in the future.
October 2, 2021
QBism isn’t an interpretation of quantum mechanics—at least, not as presented here. It is instead an entire worldview, a way of seeing the universe that one can apply to QM. One could also apply it to, say, chemistry, if one so chooses, or biology, or picking up your daughter from daycare. What is your ‘degree of belief’ that she will be holding her backpack or wearing it when you arrive?
Von Bayer explains probability in a way that disparages the frequentist interpretation; I wasn’t previously familiar with interpretations of probability but he certainly turned me into a frequentist in his attempt to do the opposite. The problem with Bayesian interpretations of probability is its vocabulary: that the numerical results of Bayes’s Theorem represents the ‘degrees of belief’ that a particular event will occur. This is absurd on its face. Von Bayer alludes to the fact, though very specifically does not say, that this can only be true of a Rational Actor. And the only possible rational actor is an android—people are not rational (just ask any economist).
Despite von Bayer’s continual mention of the external world, it’s quite apparent that no external world is actually necessary in QBism. It is fundamentally solipsistic, despite its proponents’ assertions to the contrary. I’m not saying it’s WRONG; it may well be accurate. But von Bayer, perhaps, was not the best scholar to communicate its ideas.
Von Bayer explains probability in a way that disparages the frequentist interpretation; I wasn’t previously familiar with interpretations of probability but he certainly turned me into a frequentist in his attempt to do the opposite. The problem with Bayesian interpretations of probability is its vocabulary: that the numerical results of Bayes’s Theorem represents the ‘degrees of belief’ that a particular event will occur. This is absurd on its face. Von Bayer alludes to the fact, though very specifically does not say, that this can only be true of a Rational Actor. And the only possible rational actor is an android—people are not rational (just ask any economist).
Despite von Bayer’s continual mention of the external world, it’s quite apparent that no external world is actually necessary in QBism. It is fundamentally solipsistic, despite its proponents’ assertions to the contrary. I’m not saying it’s WRONG; it may well be accurate. But von Bayer, perhaps, was not the best scholar to communicate its ideas.
February 5, 2024
A very good book on the quantum and how to interpret it using QBism (quantum bayesianism). The author wrote very clearly and explained quantum concepts well. Perhaps I needed more academic details, but I didn’t quite understand how QBism solved the many paradoxes of QM. Just stating that probabilities are subjective and the wavefunction is personal doesn’t really explain it. Though I feel deep down that this interpretation is probably the “most correct” one, I am very thankful for the notes the author collected at the end of the book pointing to the actual papers by Fuchs, one of the main architects of QBism. I’ll be sure to read these papers for the details. (Fun fact: I was friends with Chris Fuchs in grad school at UNC Chapel Hill for a few years when he briefly studied general relativity, before leaving to another grad school to study the quantum, become famous, and change the world! Yes, he was clearly brilliant back then too!!)
February 5, 2020
This book provides a description of the QBism interpretation of the quantum realm by walking through the "spooky" aspects of quantum mechanics and explicating the QBist defense for each one. However, it's not a far reaching concept (actually an age old metaphysical idea), so for people familiar with philosophy it may feel a bit less revolutionary than the book purports. For people who aren't as familiar with quantum mechanics (me) it was a great introduction to why the field requires interpretation in the first place. The writing can get a bit tedious and over-explanatory at times, while much too succinct at others. Definitely recommend supplementing the read with other sources of QM information.
January 17, 2021
An introduction to Qbism which provides the tools to understand John Wheeler‘s ‘it from bit’ quote. Qbism is a theory that posits information as a fundamental element of the universe, and it provides the theoretical constructs for a participatory universe which is created from our observations and beliefs.
April 22, 2022
อย่างที่รู้กันว่ากลศาสตร์ควอนตัม นับตั้งแต่สมัยก่อร่างสร้างฐาน ก็สามารถตีความ mathematical formalism ได้หลากหลาย อาทิ ฟังก์ชั่นคลื่นยุบตัวแบบ Copenhagen หรือฟังก์ชั่นคลื่นไม่ยุบ แต่เอกภพแยกออกเป็นหลาย ๆ เอกภพตามจำนวนผลลัพธ์ที่เป็นไปได้ แบบ many-worlds interpretation หรือที่มากกว่าการตีความนิดหน่อยอย่าง spontaneous collapse theories หนังสือเล่มนี้พูดถึงการตีความแบบหนึ่งที่คล้าย ๆ กับ Copenhagen แต่จะไม่พูดว่าฟังก์ชั่นคลื่นยุบตัว เพราะสำหรับ QBist นั้น ฟังก์ชั่นคลื่นไม่ใช่เหตุการณ์ทางกาพจริง ๆ ความน่าจะเป็นที่คำนวณมาจากฟังก์ชั่นคลื่น ไม่ได้มีลักษณะเป็น objective ไม่ใช่ frequentist แต่เป็นแบบ subjective Bayesian ฉะนั้น แทนที่จะพูดว่าฟังก์ชั่นคลื่นยุบตัว เขาก็จะพูดว่ามีการอัพเดทความน่าจะเป็นหลังจากที่ได้รับข้อมูลใหม่ ทำให้การถามคำถามว่าแมวเป็นหรือแมวตายก่อนเปิดกล่องจึงไร้ความหมาย ตามคำของ Asher Peres คือ "ไม่มีผลลัพธ์จากการทดลองที่ไม่ถูกทดลอง" (Unperformed experiments have no results.) ...
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April 19, 2024
An excellent introduction to the Bayesian Statistics Interpretation of Quantum Physics, as a paradigm shift from the Copenhagen, Many World, Pilot Wave and Spontaneous Collapse interpretations.
Very interesting in its approach, this interpretation reframes the collapse of the wave function as a simple update of probabilities. Interesting, makes you want to dig more into the theory.
Very interesting in its approach, this interpretation reframes the collapse of the wave function as a simple update of probabilities. Interesting, makes you want to dig more into the theory.
August 17, 2025
The entry of QBism into quantum theory is delightful. However, this book left me repeating the old advertising phrase, "Where's the beef?" The promise of QBism is delivered to an extent, but then not paid off. Perhaps a later edition will deliver more substance. (?) In the meanwhile, I suppose one should follow Chris Fuchs' publications.
January 2, 2020
Un libro bien escrito y de los pocos que hacen divulgación de la interpretación bayesiana de la mecánica cuántica (de hecho, traducidos al castellano solo conozco éste).
Las referencias en el apéndice también son buenas.
Las referencias en el apéndice también son buenas.
July 11, 2021
Simplemente impresionante! cómo el autor logra con este corto libro de divulgación, acercar a la gente de forma simple una de las ideas más impresionantes del último siglo.
Una interpretación Bayesiana de la mecánica cuántica, la probabilidad del colapso se encuentra en la mente del agente.
Una interpretación Bayesiana de la mecánica cuántica, la probabilidad del colapso se encuentra en la mente del agente.
May 10, 2020
Excellent and clear-eyed explanation.
August 7, 2023
Excellent writing style, very accessible framing of the story of quantum physics so far. Not great at illustrating why QBism itself is a useful model.
February 26, 2020
Interesting take on quantm physics. Sure makes a lot of sense to me.
February 22, 2017
Bad exposition of a potentially interesting interpretation of QM. Does not clearly answer basic questions for people interested in Qbism. Ok we like Bayes, but then where does the quantum weirdness some from? If wave functions are not real what is doing the interference? And don't get me started on mind and consciousness stuff. Physicists and mathematicians should leave consciousness talk to neuroscientists and philosophers, and stop embarrasing themselves with romantic mysterian ideas.
September 24, 2016
The book itself was well written and the ideas well presented, but I was left feeling vaguely dissatisfied at the end.
Qbism as described in this book strikes me not so much as a new interpretation of quantum physics as a new interpretation of the wave function. By including the observer in the probabilities associated with the wave function (rather than just having those probabilities associated with the system under study), it appears to suggest that each of has our own reality dictated by the information available to us and this reality is updated as new information becomes available. An important insight but one that still doesn't address the why of "quantum weirdness" like the double-slit experiment and wave-particle duality.
More meta-physics than physics. I'm glad I read it but not quite what I was hoping for.
Qbism as described in this book strikes me not so much as a new interpretation of quantum physics as a new interpretation of the wave function. By including the observer in the probabilities associated with the wave function (rather than just having those probabilities associated with the system under study), it appears to suggest that each of has our own reality dictated by the information available to us and this reality is updated as new information becomes available. An important insight but one that still doesn't address the why of "quantum weirdness" like the double-slit experiment and wave-particle duality.
More meta-physics than physics. I'm glad I read it but not quite what I was hoping for.
January 7, 2025
I'm a QBist. A convert.
Intuitively, it makes sense. Even so, the book was a bit boring, and didn't fully explore the philosophical implications of the theory for the first 200 pages. I wish there were more books on the topic. Or better yet, that this were taught in schools as part of a physics education, at least at the graduate level. Perhaps I will read the original white paper authored by the theory's co-founder Chris Fuchs to better understand the theory.
Intuitively, it makes sense. Even so, the book was a bit boring, and didn't fully explore the philosophical implications of the theory for the first 200 pages. I wish there were more books on the topic. Or better yet, that this were taught in schools as part of a physics education, at least at the graduate level. Perhaps I will read the original white paper authored by the theory's co-founder Chris Fuchs to better understand the theory.
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