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Quantum Ontology: A Guide to the Metaphysics of Quantum Mechanics
Metaphysicians should pay attention to quantum mechanics. Why? Not because it provides definitive answers to many metaphysical questions-the theory itself is remarkably silent on the nature of the physical world, and the various interpretations of the theory on offer present conflicting ontological pictures. Rather, quantum mechanics is essential to the metaphysician because it reshapes standard metaphysical debates and opens up unforeseen new metaphysical possibilities. Even if quantum mechanics provides few clear answers, there are good reasons to think that any adequate understanding of the quantum world will result in a radical reshaping of our classical world-view in some way or other. Whatever the world is like at the atomic scale, it is almost certainly not the swarm of particles pushed around by forces that is often presupposed. This book guides readers through the theory of quantum mechanics and its implications for metaphysics in a clear and accessible way. The theory and its various interpretations are presented with a minimum of technicality. The consequences of these interpretations for metaphysical debates concerning realism, indeterminacy, causation, determinism, holism, and individuality (among other topics) are explored in detail, stressing the novel form that the debates take given the empirical facts in the quantum domain. While quantum mechanics may not deliver unconditional pronouncements on these issues, the range of possibilities consistent with our knowledge of the empirical world is relatively small-and each possibility is metaphysically revisionary in some way. This book will appeal to researchers, students, and anybody else interested in how science informs our world-view.
228 pages, Hardcover
Published July 12, 2016
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Displaying 1 - 5 of 5 reviews
September 19, 2016
What does quantum mechanics tell us about the fundamental nature of the world? This certainly sounds like a philosophical question, and I remember complaining to Simon Evnine a couple of years ago that more philosophers should be taking an interest. I didn't have to wait long: one of his colleagues has just published this book, which OUP kindly sent me last week. The author has a well-organized and sensible approach, which starts with empirical facts rather than theories. Let's look at the good old double-slit and EPR experiments. What do we learn from them?
In the double-slit experiment, you let light go through two slits and hit a screen. You see an interference pattern on the screen, which traditionally is explained by saying that light is waves, and the two sets of waves are interfering with each other. But, very mysteriously, the same thing happens even when you turn down the intensity of the light so that only one photon at a time is coming out of the light source. You'd think the photon would have to go though either one slit or the other, so there could be no interference. But that's not so: the single photon somehow appears to have gone through both slits and interfered with itself, since you still see interference! Even more mysteriously, the same thing happens when you do the corresponding experiment with electrons, letting them diffract through a crystal lattice. A single electron can also interfere with itself.
In the Einstein-Podolsky-Rosen (EPR) experiment, you create two charged particles in such a way that they are guaranteed to have opposite directions of spin. You can do this so that you are sure about the spins being opposite, but you don't know anything else. You leave the particles undisturbed and let them move until they are separated by a good distance; then you measure the spin on one of them. Quantum mechanical spin is different from our usual ideas of what spin is, and you measure spin in a given direction by letting the particle pass through a magnetic field. Say the magnetic field is vertical; it turns out that the particle will always go either up or down by a fixed amount, so you say the spin is "up" or "down". If you turn the magnet 90 degrees so that it's horizontal, the particle goes left or right by the same fixed amount. Physicists don't now say that the particle's spin is "left" or "right", as one would expect. Instead, it fits the facts better to change the way you use language. You still say it's "up" or "down", but this time in the horizontal direction; in the first case, you say it's "up" or "down" in the vertical direction. The reason for the odd terminology, and the general weirdness, comes out when you look more closely at the details. If spin were what we're used to thinking it is, then a particle which was measured as having spin "up" in the vertical direction wouldn't have any spin in the horizontal direction. But in the quantum world, not so! You find it will be "up" or "down" in the horizontal direction, with equal probability of both outcomes.
Going back to the two particles in the EPR experiment, if you measure spin vertically on one particle and find it's "up", then it turns out that if you measure spin vertically on the the other, you are sure to get "down". And the same if you measure spin horizontally: if one particle is measured as horizontally "up", then the other is always measured as horizontally "down". But how does the second particle know what to do? It seems as though there are only two possibilities. Either a magic, invisible signal has passed between the two particles, or they had opposite spins all along; since the first explanation is impossible, the second must be correct. Again, the quantum world is not the world we're used to. We assume intuitively that there must be some fact of the matter about whether the first particle has its spin oriented vertically "up" or not, and it's a question of finding out what's going on. But the evidence shows that there is no fact of the matter until you actually carry out the spin measurement. Bell's Theorem, proved back in the 60s and explained here, establishes that there is no consistent way to assign spins to the original particles in accordance with ordinary logic, which takes for granted the idea that a particle has its own identity and its own properties. So in fact neither of the common-sense explanations works: the particles didn't start off with specific opposite spins, but there is no magic signal either! The solution requires a completely new idea, "entanglement". Before you measure the spins, the two particles are "entangled", and you can't talk about the state of one without at the same time talking about the state of the other. They've got opposite spins, and that's the end of the story.
These two paradoxical experiments, double-slit and EPR, have passed into the folk literature and been interpreted in many imaginative ways. For example, in Charles Harness's SF short story The New Reality, a version of the double-slit experiment so confuses a photon that it slows down, somehow destroying the universe; in Michel Houellebecq's novel Les particules élémentaires, EPR is used as a metaphor to suggest (I think) that Western civilization's attitude to sex will either result in its downfall or in its transformation to a post-sexual society; in Bernard Haisch's The Purpose-Guided Universe, EPR proves that the universe is the product of the universal mind and that we all are God; and in Jim Jarmusch's film Only Lovers Left Alive, EPR ("spooky action at a distance") has some connection, I'm not exactly sure what, with relationships between semi-immortal vampires.
This is fun, but it's obviously nonsense. Quantum physicists, who tend to be more interested in mathematics than in vampires, long ago figured out how to write equations that make correct predictions about what's happening in these cases. You represent the world as a "wave-function"; you represent the process of making a measurement as an "operator" on that wave-function; the details are complicated, but it all works well enough to do things like building hydrogen bombs and microprocessors. But what is the "wave-function"? What, if anything, does it have to do with the traditional notion of "reality"? Is it the wave-function that's real, rather than the things we normally think of as real? What happens to other traditional notions like "causality" and "individual"?
That's basically what this book is about. Lewis rarely claims to be giving you answers - when he did, I often felt I disagreed with him. Rather, as a good philosopher should, he confronts you with the questions and forces you to think about them. He makes you feel they're pretty important questions; in fact, for people who enjoy thinking about fundamental philosophical issues, it's hard to imagine anything that could be more important. If you're that kind of person and don't already have a thorough grasp of the philosophy of quantum mechanics, you might want to take a look at Quantum Ontology. The world is even weirder than you thought it was.
In the double-slit experiment, you let light go through two slits and hit a screen. You see an interference pattern on the screen, which traditionally is explained by saying that light is waves, and the two sets of waves are interfering with each other. But, very mysteriously, the same thing happens even when you turn down the intensity of the light so that only one photon at a time is coming out of the light source. You'd think the photon would have to go though either one slit or the other, so there could be no interference. But that's not so: the single photon somehow appears to have gone through both slits and interfered with itself, since you still see interference! Even more mysteriously, the same thing happens when you do the corresponding experiment with electrons, letting them diffract through a crystal lattice. A single electron can also interfere with itself.
In the Einstein-Podolsky-Rosen (EPR) experiment, you create two charged particles in such a way that they are guaranteed to have opposite directions of spin. You can do this so that you are sure about the spins being opposite, but you don't know anything else. You leave the particles undisturbed and let them move until they are separated by a good distance; then you measure the spin on one of them. Quantum mechanical spin is different from our usual ideas of what spin is, and you measure spin in a given direction by letting the particle pass through a magnetic field. Say the magnetic field is vertical; it turns out that the particle will always go either up or down by a fixed amount, so you say the spin is "up" or "down". If you turn the magnet 90 degrees so that it's horizontal, the particle goes left or right by the same fixed amount. Physicists don't now say that the particle's spin is "left" or "right", as one would expect. Instead, it fits the facts better to change the way you use language. You still say it's "up" or "down", but this time in the horizontal direction; in the first case, you say it's "up" or "down" in the vertical direction. The reason for the odd terminology, and the general weirdness, comes out when you look more closely at the details. If spin were what we're used to thinking it is, then a particle which was measured as having spin "up" in the vertical direction wouldn't have any spin in the horizontal direction. But in the quantum world, not so! You find it will be "up" or "down" in the horizontal direction, with equal probability of both outcomes.
Going back to the two particles in the EPR experiment, if you measure spin vertically on one particle and find it's "up", then it turns out that if you measure spin vertically on the the other, you are sure to get "down". And the same if you measure spin horizontally: if one particle is measured as horizontally "up", then the other is always measured as horizontally "down". But how does the second particle know what to do? It seems as though there are only two possibilities. Either a magic, invisible signal has passed between the two particles, or they had opposite spins all along; since the first explanation is impossible, the second must be correct. Again, the quantum world is not the world we're used to. We assume intuitively that there must be some fact of the matter about whether the first particle has its spin oriented vertically "up" or not, and it's a question of finding out what's going on. But the evidence shows that there is no fact of the matter until you actually carry out the spin measurement. Bell's Theorem, proved back in the 60s and explained here, establishes that there is no consistent way to assign spins to the original particles in accordance with ordinary logic, which takes for granted the idea that a particle has its own identity and its own properties. So in fact neither of the common-sense explanations works: the particles didn't start off with specific opposite spins, but there is no magic signal either! The solution requires a completely new idea, "entanglement". Before you measure the spins, the two particles are "entangled", and you can't talk about the state of one without at the same time talking about the state of the other. They've got opposite spins, and that's the end of the story.
These two paradoxical experiments, double-slit and EPR, have passed into the folk literature and been interpreted in many imaginative ways. For example, in Charles Harness's SF short story The New Reality, a version of the double-slit experiment so confuses a photon that it slows down, somehow destroying the universe; in Michel Houellebecq's novel Les particules élémentaires, EPR is used as a metaphor to suggest (I think) that Western civilization's attitude to sex will either result in its downfall or in its transformation to a post-sexual society; in Bernard Haisch's The Purpose-Guided Universe, EPR proves that the universe is the product of the universal mind and that we all are God; and in Jim Jarmusch's film Only Lovers Left Alive, EPR ("spooky action at a distance") has some connection, I'm not exactly sure what, with relationships between semi-immortal vampires.
This is fun, but it's obviously nonsense. Quantum physicists, who tend to be more interested in mathematics than in vampires, long ago figured out how to write equations that make correct predictions about what's happening in these cases. You represent the world as a "wave-function"; you represent the process of making a measurement as an "operator" on that wave-function; the details are complicated, but it all works well enough to do things like building hydrogen bombs and microprocessors. But what is the "wave-function"? What, if anything, does it have to do with the traditional notion of "reality"? Is it the wave-function that's real, rather than the things we normally think of as real? What happens to other traditional notions like "causality" and "individual"?
That's basically what this book is about. Lewis rarely claims to be giving you answers - when he did, I often felt I disagreed with him. Rather, as a good philosopher should, he confronts you with the questions and forces you to think about them. He makes you feel they're pretty important questions; in fact, for people who enjoy thinking about fundamental philosophical issues, it's hard to imagine anything that could be more important. If you're that kind of person and don't already have a thorough grasp of the philosophy of quantum mechanics, you might want to take a look at Quantum Ontology. The world is even weirder than you thought it was.
September 7, 2017
A well written explication of the possible philosophical implications of the three main theories of Quantum mechanics. I've found it difficult to find books in this area that don't present themselves as either offering definitive answers, or flying off into some sort of anthropological magical fantasy, but this book is well grounded, and of a different class. It leaves one with a better appreciation of the limits of what we can draw conclusions from, on subjects we know so little about.
July 14, 2024
4 stars for effort on a difficult subject. To be read as a start not as a conclusion.
January 29, 2019
Learned some math.
Displaying 1 - 5 of 5 reviews