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Decoherence and the Appearance of a Classical World in Quantum Theory

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If you are looking for a single source to learn about "environmental decoherence" this is probably the best you can do. Review papers and many other books are often loaded with jargon and don't span a wide range of topics. This volume allows you to start at the beginning and go as far as you want. It is NOT a book for the general public. You will need a background in undergraduate level quantum mechanics.

One of the problems addressed by this book has concerned me ever since I was a graduate student: how the spreading of wave packets might be limited over the course of time. That is, if you imagine an electron wave packet traveling though free space, quantum dispersion mandates that it must become broader and broader as it goes from one point to another (see Phase Space Picture of Quantum Mechanics: Group Theoretical Approach (World Scientific Lecture Notes in Physics) by Kim & Noz for a detailed exploration of this topic).

The discussion of quantum coherence in this volume, in the section authored by Joos, develops the theory that ambient scattering of other particles off of this wave packet, be they massive particles, photons, or otherwise (e.g. neutrinos), increase the local entropy and limit the spreading of the wave packet. It is also argued that ambient scattering and its entropic influence decrease the intensity of diffraction effects. Joos argues that free particles might go on spreading more and more if it were not for ambient particles or radiation bouncing off of the wave packet. He notes that even in deep space starlight and the 3-degree Kelvin black body radiation left over from the Big Bang should limit the spreading of wave packets. Joos also discusses the interference between two moving wave packets as a function of the degree of coherence (pp.66-68), a problem that is equivalent to the double slit diffraction experiment, as each wave packet can be thought of as emerging from one of the two slits. Joos also addresses the contribution of friction to decoherence (pp. 79-81), and the time dependence of entropy (pp.73-75; 125-134).

Zeh makes a brief mention (p.276) of complex potentials as "the absorption of the projectile into other reaction channels" resulting in the possibility of "different histories" as "in the Everett [i.e. many worlds] interpretation." This mention of complex potentials, however, brings to mind a topic near and dear to my heart, that of inelastic scattering. I was somewhat disappointed that inelastic scattering was not explicitly mentioned as contributed to decoherence. Although this book does not have an index, it has a list of all papers referenced, and Bethe's papers on inelastic scattering are not listed. For a discussion of inelastic scattering see Intermediate Quantum Mechanics by Bethe and Jackiw. For a treatment of inelastic scattering as applied to coherence in high-resolution (i.e. atomic scale imaging) transmission electron microscopy see Z. L. Wang's book Elastic and Inelastic Scattering in Electron Diffraction and Imaging (NATO Asi Series).

It is also worth noting that all of the six contributors to this volume live and work in Germany. Giulini and Kiefer are at Univ. Freiburg. Stametescu and Zeh are at Heidelberg. Kupsch is at Univ. Kaiserslautern and Joos is at Schenefeld.