Consistent Quantum Theory by Robert B. Griffiths | (PDF) Free Download

Description

Quantum mechanics is one of the most fundamental yet difficult subjects in physics. Nonrelativistic quantum theory is presented here in a clear and systematic fashion, integrating Born’s probabilistic interpretation with Schrödinger dynamics. Basic quantum principles are illustrated with simple examples requiring no mathematics beyond linear algebra and elementary probability theory. The quantum measurement process is consistently analyzed using fundamental quantum principles without referring to measurement. These same principles are used to resolve several of the paradoxes that have long perplexed physicists, including the double slit and Schrödinger’s cat. The consistent histories formalism used here was first introduced by the author, and extended by M. Gell-Mann, J. Hartle and R. Omnès. Essential for researchers yet accessible to advanced undergraduate students in physics, chemistry, mathematics, and computer science, this book is supplementary to standard textbooks. It will also be of interest to physicists and philosophers working on the foundations of quantum mechanics.

User’s Reviews

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

⭐This is a very interesting, clearly written introduction to the consistent histories (CH) interpretation of quantum mechanics that addresses many of the short-comings of the traditional Copenhagen interpretation. The book is self-contained and should be easy to understand for anyone with some prior exposure to quantum physics, linear algebra, and probability. While people curious about quantum mechanics and its interpretations could read this book by itself, physics students should read it as a supplement to standard textbooks.After laying out the basic principles of quantum theory, Griffiths introduces consistent families of quantum histories and illustrates how they can be applied to quantum phenomena. He argues convincingly that applying CH principles avoids the confusion that many people feel when learning quantum mechanics. He then introduces a key principle called the “single-framework rule” which prohibits combining conclusions from inconsistent families of histories. The second half of the book discusses measurements in the context of quantum physics and explores many of the famous paradoxes of quantum theory, showing that they all result from violations of the single-framework rule.One of the strengths of the CH interpretation is that it addresses the measurement problem of quantum mechanics in a way that applies the same quantum principles to all physical processes including measurements. Griffiths interprets the so-called “collapse” of the wave function introduced by von Neumann as a mathematical procedure for calculating probabilistic correlations rather than as an actual physical phenomenon. This approach avoids non-local effects and eliminates the need to assign any special role to conscious beings.One thing did bother me about the CH approach: in many situations a physicist can select multiple incompatible frameworks of consistent histories to describe physical phenomena and derive contradictory conclusions from them. While Griffiths argues that incompatible frameworks cannot lead to contradictory results if they share the same initial data, a physicist is free to ignore some or all of the initial data available to him (via measurements) when constructing a family of consistent histories. The CH interpretation could benefit from some additional rules that would restrict the choice of frameworks.Despite this objection, I enjoyed this book very much and encourage everyone interested in quantum mechanics to read it.

⭐This book deals with the inconsistencies and puzzles in quantum mechanics. It should be required reading for all physicists.

⭐I always had difficulties with the “Copenhagen-Bohr” interpretation of Quantum Mechanics, which presents a bewildering view on how a quantum system develops and is influenced by observations.The way Griffiths treats the material, plays with toy models en clears all sorts of paradoxes is most reassuring and facilitates the acceptance of this wonderful piece of science.An up to date knowledge of physics at graduate level and an interest in QM is sufficient to read and understand the book.

⭐This book is not so much about doing practical quantum mechanical calculations as with the interpretation of quantum theory. As Griffiths says, you can’t use it alone as a primary text to learn quantum mechanics: you’ll need a separate text to cover blackbody radiation, the photoelectric effect, atomic spectra, the hydrogen atom, harmonic oscillators, perturbation theory, and the like.When quantum mechanics was developed, it gave such good results that people often overlooked the difficulties with connecting the theory to physical reality. Reality to them consisted of actual measurements. And so the notion grew that measurements were an integral part of the theory, and that measurements affected what was thought of as physical reality, even non-locally. When students looked puzzled, their teachers merely reminded them that reality is weird! Well, sure, reality is a little strange, but there is never a need to describe reality in a self-inconsistent manner.The problems came with concepts such as “collapse of the wavefunction.” That is, we’d measure a property (say, the x-polarization) of some particle. And the nature of a faraway linked particle would appear to change, instantly. That’s a non-local effect: it travels faster than light. And if that effect were genuine, it would permit sending signals backwards in time.The associated problem was with measurement: the existence of an observer appeared to change reality.Worse, these complaints struck right at the core of quantum mechanics, whose proponents boasted about the importance of “looking at the fundamental laws” in a way “which makes their self-consistency obvious” (quoting from Dirac’s quantum mechanics book).Those of us who read the excellent text, “The Feynman Lectures on Physics,” were taught that the following statement is false: “you can not alter the physical nature of” (faraway) “photons by changing the kind of observation you make on your photons.” And that just did not help. In some sense, that statement must be not false, but true, to avoid the problems we just stated.Part of the reason for the confusion is that in most cases, making a measurement on a particle really does change the state of that particle. But not always: repeated measurements of x-polarization simply verify the state rather than changing it.Now we have a book that explains how to make quantum theory self-consistent so we can avoid these problems. It explains that wave function collapse is simply a calculational device, rather than a physical effect produced by a measurement. It explicitly solves many famous quantum mechanics “paradoxes,” including the “Schrodinger cat,” the “Einstein-Podolsky-Rosen paradox,” the “delayed choice paradox,” and the “Hardy paradox.” It discusses Bell’s inequalities, showing that actual quantum mechanics is indeed a local theory (yay!) while “hidden variable” alternatives are non-local!The key concept Griffiths introduces is the “consistent quantum framework” or “consistent quantum family.” The idea is that there are multiple such frameworks, but accurate statements can be made only by choosing one of them and staying with it.Griffiths explains that the following are true both of classical and quantum mechanics: measurements play no fundamental role in either, both are local theories, and both are consistent with the notion of an independent reality. However, there are some differences as well. Quantum theory shows that physical objects never have completely precise positions or momentums. The theory is stochastic, not deterministic, so we can’t infer a unique future or past from the present. And finally, and most important, there is no unique exhaustive description of a physical system or process. “Instead, reality is such that it can be described in various alternative, incompatible ways, using descriptions which can not be combined or compared.”This is a valuable book for every physics graduate student.

⭐The product arrived a day late but in good condition.

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