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In the paper

Zeh, H. D. The Wave Function: It or Bit? In Science and Ultimate Reality, eds. J.D. Barrow, P.C.W. Davies, and C.L. Harper Jr. (Cambridge University Press, 2004), pp. 103-120. arXiv:quant-ph/0204088

does Zeh state the classical world is an illusion or that our sense of locality in the classical world is an illusion? Is he correct?

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3 Answers

There's a misleading urban myth spreading around virulantly these days. It says decoherence shows how the classical world can emerge and solve the measurement problem.

Decoherence doesn't do anything of this sort! Note careful thinkers always use the word quasiclassicality instead of classical in this context. Interference may be exponentially suppressed after coarse graining, but the superposition still remains! Exponentially small off diagonal terms are still there, and there's still the problem of definite outcomes!

The classical world is an illusion! Quasiclassicality is the best we can do! We're all Wigner's friend!

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To my knowledge, on most models coherences are killed at a rate of $e^{-\frac{t}{t_{deco}}}$ or $e^{-\frac{t^2}{t^2_{deco}}}$ with a decoherence time $t_{deco}$ of order $10^{-10}$s at best, so quantitatively there is nothing wrong with saying that coherences vanish. Still, you are right when stating that the outcomes are still undefined (apart from the basis selection), apart from Everett's multiverse interpretation I don't know any way of selecting one between the possible ones. –  Learning is a mess Jan 25 '13 at 11:33
    
decaying you are right, –  lee hudson Jan 25 '13 at 18:04
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First of all one should define what illusion means.

1)

a) obsolete : the action of deceiving

b) (1) : the state or fact of being intellectually deceived or misled : misapprehension

(2) : an instance of such deception

2)

a) (1) : a misleading image presented to the vision

(2) : something that deceives or misleads intellectually

b) (1) : perception of something objectively existing in such a way as to cause misinterpretation of its actual nature

(2) : hallucination

(3) : a pattern capable of reversible perspective

If one uses the "deceptive" part of these definitions, the answer is yes, the classical world is an "illusion".

BUT, when one starts being philosophical about our perception of the world one should keep in mind that everything that defines our existence can then be called an illusion. All information we have about the world around us reaches us through successive levels of proxies.

By level of proxies for example: we observe the world through our five senses, they depend on a level of cells organized to send information and store it, and that level depends on the organization of atoms and molecules, which depends on the quantum mechanical substratum of protons and neutros, which protons and neutrons depend on the substratum of quarks.

Another example: when we walk, we sense the earth beneath our feet as solid. It is an illusion because it is composed by a level of atoms which are mostly empty space as far as mass goes, and those atoms are composed by protons and neutrons .....

Nevertheless we do manage to walk, and are sure we exist because we ride as a biological pattern supported by forces over a complex stratum also supported by forces we have studied utilizing all these "illusionary" levels;we have also acquired an understanding of this in depth.

This happens because, as Vladimir concisely says, the everyday world is emergent from the complex levels of matter and forces beneath the dimensions we can measure every day compatible with our size : millimeters or at most microns for length, seconds, or at most microseconds for time. It is when our focus goes to smaller dimensions that the concept of "illusion" pertains.

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anna, so the classical world is only an illusion in the way, that we cannot sense what is going on at the lower levels? –  lee hudson Jan 13 '13 at 21:56
    
a laymans response please :) –  lee hudson Jan 13 '13 at 22:00
    
Yes. The classical world emerges from a number of sublevels. In this sense it is an illusion, an illusion of continuity and impermeability etc. The mathematical formulations we use to describe the physics have to change when we reach down to microscopic levels. –  anna v Jan 14 '13 at 5:45
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Classical world is an inclusive picture with a certain time resolution. In this sense it is an illusion since made of sets of bits of information.

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time and space resolution. Since the quantum mechanical world comes to our senses through classical proxies, the illusion permeates everything. :) –  anna v Jan 12 '13 at 19:43
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vladimir your comment makes no sense, what is a time resoultion and why does the classical world have a certain one and quantum not? –  lee hudson Jan 12 '13 at 20:59
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One dot (pixel, bit of information) is supplied by QM behavior. One dot in two-slit experiment, for example. you need a certain exposition period to collect enough dots to speak certainly about it, but not too much in order to avoid piling up all images together. Think of movie frames. –  Vladimir Kalitvianski Jan 12 '13 at 21:01
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"this is getting me very depressed. is reality an illusion? please help" lee, could you mail me at the email address in my profile? I am interested in the phenomenon of non-physicists who read some of the extreme and contradictory things which are said to be implied by physics, and become troubled about the nature of reality... –  Mitchell Porter Jan 13 '13 at 4:11
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@lee hudson, the idea that seems to horrify you now, is as old as humanity. It exists across times and cultures, from Plato's Cave (en.m.wikipedia.org/wiki/Allegory_of_the_Cave) to Hollywood movies like The Matrix (en.m.wikipedia.org/wiki/Matrix_movie). It is nothing to worry about. Look for help around you, don't get depressed. Enjoy this beautiful illusion of life, where there is room for knowledge, love, science, sex, music, pizza... –  Eduardo Guerras Valera Jan 26 '13 at 15:00
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protected by Qmechanic Jan 25 '13 at 13:02

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