Monday, March 26, 2018

Quantum Mechanical Interpretations

Woit reviews a new book discussing the different prevailing interpretations of quantum mechanics (Copenhagen, Many World, Bohmian, etc.) and in the process does something even more useful. He refers us to an arXiv pre-print, which he finds to be a better treatment of the subject, in addition to being shorter and free and instantly available. He describes the article this way:
For a . . . recent serious take on the issues involved, I’d recommend reading something by Wojciech Zurek, for instance this article, a version of which was published in Physics Today. Trying to figure out what “interpretation” Zurek subscribes to, I notice that he refers to an “existential interpretation” in some of his papers. I don’t really know what that means. Unlike most discussions of “interpretations”, Zurek seems to be getting at the real physical issues involved, so I think I’ll adopt his (whatever it means) as my chosen “interpretation”.
The article opens in this way:
Quantum principle of superposition decrees every combination of quantum states a legal quantum state. This is at odds with our experience (Fig. 1). 
Decoherence selects preferred pointer states that survive interaction with the environment. They are localized and effectively classical. They persist while their superpositions decohere. Decoherence marks the border between quantum and classical, alleviating concern about flagrant and manifestations of quantumness in the macroscopic domain. 
Here we consider emergence of ‘the classical’ starting at a more fundamental pre-decoherence level, tracing the origin of preferred pointer states and deducing their probabilities from the core quantum postulates. We also explore role of the environment as a medium through which observers acquire information. This mode of information transfer leads to perception of objective classical reality.
The arXiv says this about the eight page long pre-print:

Quantum Darwinism, Classical Reality, and the Randomness of Quantum Jumps

Tracing flows of information in our quantum Universe explains why we see the world as classical.
Comments:This manuscript, after cuts and edits to comply with Physics Today limits and style, was published last October. It may have some rough edges, but it also contains technical elaborations omitted from the published version for lack of space that may be of interest to some readers. Thus, while the essence is the same, but there are differences (starting with the title and abstract)
Subjects:Quantum Physics (quant-ph)
Journal reference:Physics Today, vol. 67, pp. 44-50 (2014).

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