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I Quantum Darwinism and Consciousness (?!)

  1. Jun 26, 2016 #1
    I've red the paper from the father of decoherence W. Zurek called "Quantum Darwinism, Classical Reality, and the Randomness of Quantum Jumps"

    In his conclusion he mentions this "Quantum Darwinism shows why only such redundantly recorded pointer states are accessible to observers|it can account for perception of `quantum jumps'. However, full account of collapse involves `consciousness', and may have go beyond just mathematics or physics. "

    I simple don't understand it, why does he have to invoke consciousness and what sense does it make when his decoherence program was the one of the first abandonments of the old-fashioned "consciousness causes collapse" interpretations. Can anybody explain what does he mean?
     
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  3. Jun 26, 2016 #2

    Paul Colby

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  4. Jun 26, 2016 #3
  5. Jun 26, 2016 #4

    Paul Colby

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    I probably shouldn't comment since I disagree with the very first sentence in this paper. My guess is invoking consciousness is an effort to "make sense" of the concepts developed in the paper. Atoms decay without the help and independently of observation. If someone claims I clearly don't understand the decoherence approach, I'd be forced to agree with them.
     
  6. Jun 26, 2016 #5

    Zafa Pi

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    The first sentence of the paper is:
    "Quantum principle of superposition decrees every combination of quantum states a legal quantum state." Most authors support that principle.
    Can you you give an example where you disagree?
    To give an example to see if we are on the same page: A superposition of the two pure states |00> and |11> is the entangled state √½|00> + √½|11>.
     
  7. Jun 26, 2016 #6

    Paul Colby

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    My bad. It was in fact the sentence that follows; "This is at odds with our experience (Fig. 1)." If one observes a member of a quantum ensemble one finds it in an eigenstate of the observable. This is in fact what people always experience and it is consistent with the rules and holds even for the dreaded cat example. Most of what's written on this topic glosses over the fact that the state prior to measurement is not an observable. Hence, the endless confusion.
     
  8. Jun 27, 2016 #7

    Zafa Pi

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    The sentence "This is at odds with our experience." I agree with, because it leads to the kind of superposition I gave in my previous post #5, which in turn leads to the Bell inequality paradox. However the sentence "This is at odds with our experience (Fig. 1)." convinces me that he is talking about what you are talking about and I agree with you, though I do have a problem with state |live cat>. What's its Hilbert space vector?
     
  9. Jun 27, 2016 #8

    ShayanJ

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    Here you're either using collapse or a non-collapse interpretation. But the whole point of decoherence or other suggestions by Zurek and others, is to explain what happens in a measurement independent of any interpretation, at least as much as possible.
    Its a two state system, dead or alive. So its Hilbert state is the same as any other two state system, e.g. a spin-1/2 particle.
    Till now, decoherence only explains how superposition disappears at the level of system and how a basis set of states is distinguished as a preferred basis. The part that decoherence can't still solve, is why do measurements have outcomes at all? i.e. How does an improper mixed state ## \sum_k c_k |k\rangle \langle k| ## evolves to ## |m\rangle##(where ## |m\rangle \in \{|k\rangle\} ##)? For now, this needs either consciousness or a non-collapse interpretation to be solved.
     
  10. Jun 27, 2016 #9

    atyy

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    Decoherence cannot solve the need for "consciousness causes collapse" or "classical measuring apparatus causes collapse". In short, decoherence alone cannot solve the measurement problem. However, if additional assumptions are used such as hidden variables, then decoherence helps to solve the measurement problem (in some domains of quantum mechnics, eg. non-relativistic quantum mechanics).
     
  11. Jun 27, 2016 #10
    But how would "consciousness" contribute to the fact that we get outcomes at all? We see definite outcomes so our consciousness influenced nature? Its a pretty bizzare way to look at things.
     
  12. Jun 27, 2016 #11

    ShayanJ

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    I don't like it too and actually its not a serious opinion among physicists. Nevertheless it was something that was put forward in the first years of QM.
     
  13. Jun 27, 2016 #12

    Paul Colby

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    What ever it is, the cat state space isn't spanned by a two dimensions. However, in this approximation a particular cat (as an element of an idealized quantum ensemble of non-interacting identically prepared systems) is seen as alive or dead by the rules of QM. This is exactly what is experienced in all cases. In fairness this sentence is quoted from the paper intro which is trying to set the tone and expectations of the work. What the author is trying to do is drop the Born rule in hopes of replacing it with a reduced set of QM + macroscopic complexity. By dropping the Born rule as fundamental the author must provide meaning to the remaining rules. Hence non-sensical (and incorrect) statements like the one quoted.
     
  14. Jun 27, 2016 #13
    Yes, I noticed that. That's why I was surprised why an author like Zurek had the need to even mention it in the context of collapse.
     
  15. Jun 27, 2016 #14

    Paul Colby

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    Your statement sounds "true" in the sense that either ##A## is true, or ##\bar{A}## is true. This surely follows provided ##A\cup\bar{A}## is the set of all possibilities. In fact a "collapse interpretation" spans a rather large set of possibilities and assumptions which themselves contain many wrong or inaccurate views and statements. The very same can be said for the so call "non-collapse" interpretations. What I'm doing is quoting the QM rules and pointing out the rules are exactly how such an experiment unfolds. Accepting this makes the sentence "This is at odd with our experience" appearing in the first paragraph of the paper a false statement thus setting the tone for what follows.
     
  16. Jun 27, 2016 #15

    Zafa Pi

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    Why not spin 1? I agree with Bohr that Copenhagen doesn't demand the cat be in a superposition. Try running it through an interferometer and you'll see.
     
  17. Jun 28, 2016 #16

    ShayanJ

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    If you mean that a cat is too complicated to be described by only a two dimensional Hilbert space, then I agree. But it doesn't mean that no two dimensional Hilbert space is used in its description and its not an approximation. Its just like an electron. Sure its complicated to describe but it has some aspect to it that has only two base states, its spin. Its wave-function is complicated in the sense that its a member of the tensor product of several Hilbert spaces with different properties including different dimensionalities and one of them is a two dimensional Hilbert space to describe its spin.
    Its the same with the cat. It has many properties that can have different number of base values and one of them is whether its alive or dead and that has only two base states. Surely it can have different colors and patterns on its fur and that's too vast and probably needs an infinite dimensional Hilbert space but that's only one of the Hilbert spaces among all the ones present in the tensor product Hilbert space needed to describe the cat.

    If by rules, you mean collapse, then OK. That was part of the rules in the past. But nowadays people don't want it to be a fundamental rule!
    Because there are three base states for spin-1 but two for spin-1/2.
     
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