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The Physical Basis of the Direction of Time
The asymmetry of natural phenomena under time reversal is striking. Here Zeh investigates the most important classes of physical phenomena that characterize the arrow of time, discussing their interrelations as well as striving to uncover a cosmological common root of the phenomena, such as the time-independent wave function of the universe. The description of irreversible phenomena is shown to be fundamentally "observer-related". Both physicists and philosophers of science who reviewed the first edition considered this book a magnificent survey, a concise, technically sophisticated, up-to-date discussion of the subject, showing fine sensivity to some of the crucial philosophical subtleties. This new and expanded edition will be welcomed by both students and specialists.
188 pages, Paperback
First published June 23, 1989
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Displaying 1 - 2 of 2 reviews
May 6, 2025
Hardest book I ever read. In the end I think I got something out of it, but the minute details of the calculations I skipped. Still obviously a thourough read, and happy I did. Wondering which audience will get new insights from this book though, it seems like a mixed bag. Too detailed for a lay audience, and probably nothing innovative for the experts. He seems like a good physicist though, that takes his work and his audience seriously; I'd trust his judgement in difficult matters.
Whoever recommended this book to me on a forum: it is appreciated and feels like a must read at a certain level, to check your level of understanding. But not for the faint-hearted.
Whoever recommended this book to me on a forum: it is appreciated and feels like a must read at a certain level, to check your level of understanding. But not for the faint-hearted.
January 25, 2016
From my blog post on time here:
Zeh is prominent as the physicist who first proposed the theory of “decoherence” to explain the transition from the quantum to the classical world. His 2002 (Second Edition) book on decoherence is a joint product with E. Joos and others, Decoherence and the Appearance of the a Classical World in Quantum Theory. His time book is an attempt, as implied in the title, to give a “physical” explanation for the arrow of time. He finds not one, but six arrows of time:
Radiation
The Second Law
Evolution
Quantum Mechanical Measurement
Exponential Decay
Gravity
Zeh’s books are not for the timid. He seems to assume that his audience has at least an undergraduate degree in physics. If you are not familiar with the “Dirac notation” of, for example, T|p>=|-p> or that combined with integral calculus (|p>=(2π)^(-1⁄2)∫dq (e)^(-ipq) |q>) you had better become familiar or you will soon be lost. A typical quote: “Other (more or less physical) compensating symmetry operations are known (See Atkinson 2006). For example, the time reversal symmetry of the Schrodinger equation is restored by complex conjugation of the wave function. This can be described by Wigner’s anti-unity operation T which leaves the configuration basis unchanged, Tc|p>=c*|q> for complex numbers c.” Got that?
But what does he think about time? Truth is, I am not completely sure, but I note that in his epilog he repeats a story about Einstein, which is also quoted in Lee Smolin’s book, Time Reborn:
“According to Carnap (1963), ‘Einstein said that the problem of the Now worried him considerably. He explained that the experience of the Now means something special for man, something different from the past and the future, but that this important difference does not and cannot occur within physics. That this experience cannot be grasped by science seemed to him a matter of painful but inevitable resignation.'”
Cannot occur within physics? Smolin certainly doesn’t agree. But if true, does that really matter to us humans? Zeh has an answer:
“Memories, in particular, have to be stored in physical form, and are then correlated with sources in their past (they are ‘retarded’). This drastic asymmetry may be sufficient to explain the apparent flow of time once there is a psycho-physical parallelism based on a presumed local moment of awareness. Only this (not necessarily asymmetric) concept of local present is fundamentally subjective, while the asymmetry between past and future directions is part of objective reality. What we usually call the preserved identity of a person (who changes considerably during a lifetime) is ‘in reality’ nothing but a particularly strong and robust ‘causal’ correlation between different local physical states which represent the individual carriers of a subjective present. As pointed out by Einstein and Carnap, it is the here-and-now subjectivity as the center of all awareness that goes beyond objective reality, while it must severely affect our perception of the ‘real world’.”
Well, at least he thinks he has proven that the arrow of time is “part of objective reality.” And if my “retarded” experience of my “center of awareness” is just “subjective” isn’t that what we mean by subjective!
Zeh is prominent as the physicist who first proposed the theory of “decoherence” to explain the transition from the quantum to the classical world. His 2002 (Second Edition) book on decoherence is a joint product with E. Joos and others, Decoherence and the Appearance of the a Classical World in Quantum Theory. His time book is an attempt, as implied in the title, to give a “physical” explanation for the arrow of time. He finds not one, but six arrows of time:
Radiation
The Second Law
Evolution
Quantum Mechanical Measurement
Exponential Decay
Gravity
Zeh’s books are not for the timid. He seems to assume that his audience has at least an undergraduate degree in physics. If you are not familiar with the “Dirac notation” of, for example, T|p>=|-p> or that combined with integral calculus (|p>=(2π)^(-1⁄2)∫dq (e)^(-ipq) |q>) you had better become familiar or you will soon be lost. A typical quote: “Other (more or less physical) compensating symmetry operations are known (See Atkinson 2006). For example, the time reversal symmetry of the Schrodinger equation is restored by complex conjugation of the wave function. This can be described by Wigner’s anti-unity operation T which leaves the configuration basis unchanged, Tc|p>=c*|q> for complex numbers c.” Got that?
But what does he think about time? Truth is, I am not completely sure, but I note that in his epilog he repeats a story about Einstein, which is also quoted in Lee Smolin’s book, Time Reborn:
“According to Carnap (1963), ‘Einstein said that the problem of the Now worried him considerably. He explained that the experience of the Now means something special for man, something different from the past and the future, but that this important difference does not and cannot occur within physics. That this experience cannot be grasped by science seemed to him a matter of painful but inevitable resignation.'”
Cannot occur within physics? Smolin certainly doesn’t agree. But if true, does that really matter to us humans? Zeh has an answer:
“Memories, in particular, have to be stored in physical form, and are then correlated with sources in their past (they are ‘retarded’). This drastic asymmetry may be sufficient to explain the apparent flow of time once there is a psycho-physical parallelism based on a presumed local moment of awareness. Only this (not necessarily asymmetric) concept of local present is fundamentally subjective, while the asymmetry between past and future directions is part of objective reality. What we usually call the preserved identity of a person (who changes considerably during a lifetime) is ‘in reality’ nothing but a particularly strong and robust ‘causal’ correlation between different local physical states which represent the individual carriers of a subjective present. As pointed out by Einstein and Carnap, it is the here-and-now subjectivity as the center of all awareness that goes beyond objective reality, while it must severely affect our perception of the ‘real world’.”
Well, at least he thinks he has proven that the arrow of time is “part of objective reality.” And if my “retarded” experience of my “center of awareness” is just “subjective” isn’t that what we mean by subjective!
Displaying 1 - 2 of 2 reviews