The Physical Basis of The Direction of Time

by H. Dieter Zeh

Four previous editions of this book were published in 1989, 1992, 1999, and 2001. They were preceded by a German version (Zeh 1984) that was based on lectures I had given at the University of Heidelberg. My interest in this subject arose originally from the endeavor to better understand all aspects of irreversibility that might be relevant for the statistical nature and interpretation of quantum theory. The quantum measurement process is often claimed to represent an amplification of microscopic properties to the macroscopic scale in close analogy to the origin of classical fluctuations, which may lead to the local onset of a phase transition, for example. This claim can hardly be upheld under the assumption of universal unitary dynamics, as is well known from the example of Schrodinger's cat. However, the classical theory of statistical mechanics offers many problems and misinterpretations of its own, which are in turn related to the oft-debated retardation of radiation, irreversible black holes with their thermodynamical aspects, and last but not least the expansion of the Universe. So the subject offered a great and exciting interdisciplinary challenge. My interest was also stimulated by Paul Davies (1977) book that I used successfully for my early lectures. Quantum gravity, that for consistency has to be taken into account in cosmology, even requires a complete revision of the concept of time, which leads to entirely novel and fundamental questions of interpretation (Sect. 6. 2). Many of these interesting fields and applications have seen considerable progress since the last edition came out."

Genres: Physics, Science

241 pages, Hardcover

First published June 23, 1989

Reviews

[Albert-Jan Jorna · Rating 3 out of 5]

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.

[Randal Samstag · Rating 3 out of 5]

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!