Quantum Theory and Philosophy

Discussion in 'Physics & Math' started by Human001, Sep 24, 2010.

  1. Human001 Registered Senior Member

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    Question from a Non physicist:

    COnsidering the most famous Quantum experiment, the double slit exp., I am wondering what the current thinking is on the "observer" in such that senario.

    As in, the electron beam chooses a slit if-and-only-if an "observer is there to observe it go through a slit. My fisrt question (as I'm sure everyone's first question) is, what is an observer? Is it just an eyeball connected to a bundle of nerve and brain tissue? A person makes an observation which is important in QT, but a person is surely just an organized collectionof atoms. Philosophically, what is it that connects an observer to the quantum world? I wanted to aske physicist, not philosophers.

    As I said in another thread, I recently read Kaku's Physics of the Impossible, which mentions this sort of conundrum. In his usual hyperbolci style Kaku saidsome quantum physicists think that there must be a "consciousness" pervading the univese to observe quantum events.
     
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  3. temur man of no words Registered Senior Member

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    What I was taught (as an undergrad in physics), an observer in quantum mechanics is a system large enough to obey classical mechanics. But from what I have heard here and there, it has not been proven rigorously within quantum mechanics that the wave function of a particle will collapse upon interacting with large systems. So the wave function collapse must be taken as an axiom.

    Edit: Upon reflecting, it seems simply not possible to get exact wave function collapse within quantum mechanics because of the unitarity of quantum evolution. So one needs to have approximate collapse or more radically some kind of modification of basic laws of quantum mechanics.
     
    Last edited: Sep 24, 2010
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  5. Neverfly Banned Banned

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    The link (Or description, rather) is not perfect but then... it is a wiki. Here goes:
    http://en.wikipedia.org/wiki/Relational_quantum_mechanics

    I won't touch the topic at hand at the moment but rather, since these threads are new - Post a warning.

    This is ground where things are unknown for certain.

    It's crucial to keep that in mind.

    This is not a thing where, "Scientists say this IS such and such."
    It's where scientists say "It could be this way. Observations supports this possibility." Or, "We've determined this interpretation from our results."

    Temur hit your question.

    But for me, given the nature of both threads I saw this morning and your WAY of asking them, I think it's important that you examine quickly (first) just how these concepts are being expressed.

    Now...
    Again, not a perfect article but more than sufficient for now...:
    http://en.wikipedia.org/wiki/Double-slit_experiment#Copenhagen_interpretation
     
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  7. Pandaemoni Valued Senior Member

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    Many other physicists are content with the notion that quantum decoherence causes a wave function interacting with a complex system to appear to have collapsed, and that that serves as an adequate basis for our intuitions regarding the natural world...and replaces the need for an observer for the world to behave in accordance with our common sense. This is not an "actual" collapse, which troubles some people, but it would make sense why the universe would appear as we tend to perceive it.
     
  8. Green Destiny Banned Banned

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    Consciousness has nothing to do with it, thankfully, because that would have made quantum physics almost incomprehensible, in my eyes.

    Thankfully, we have a conceptual basis for such measurements, and our role, and it is said that the collapse of the wave function is a type of weak-coupling to the system. Before a measurement, there is no coupling, or zero probability, and until during the measurement, the probability has a value of one.

    However, we are not important in the sense that a collapse of the wave function can occur just from our side alone when measurements are performed. The identity of an observer in physics takes a new description called Decoherence... well... newish.

    Since collapses can occur without our involvement, the term ''observer'' can apply not only to biological entities, but also atoms. The act of observation therefore is not unique to consciousness or awareness.
     
  9. Green Destiny Banned Banned

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    Decoherence therefore is the result of such a coupling in a thermally-abundant environment.
     
  10. Green Destiny Banned Banned

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    Why do people get confused by this?

    If by definition, only we can collapse the wave function, then by all means, yes... decoherence is not a collapse in the wave function; but in all reality, it's really no more different. It's the reducing of quantum statistical probabilities in the act of a general coupling, whether weakly coupled or strongly coupled.

    Decoherence is a special case of the measurements we perform. In contrast, it's a strong coupling, meaning that it involves continuous observation on the state of a particle due to its environment - it's wave function is therefor contained in a particular state over brief periods of time. This is how the Zeno Effect works.
     
  11. Human001 Registered Senior Member

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    I'm thinking carefully about what everyone said. Thanks for replying. I also followed the wiki links. Thanks!

    Just to give you one quote from Kaku's book:
    Most PhD physics textbooks religiously adhere to the ... Copenhagen School, but many research physicist have abandoned it...

    ...At present there is no consensus on how to resolve this issue, which strikes at the very heart of modern physics. At conferences, many theories heatedly compete with others. One minority point of view is that there must be a "cosmic consciousness" pervading the universe. Objects spring into existence when measurements are made, and measurements ar emade by conscious beings. Hence there must be cosmic consciousness that pervades the universe determining what state we are in. Some like Nobel leareate Eugene Wigner, that this proves the existence of God...


    I highlighted the bold part, as this is probably the part where people get wires crossed. It seems like this is a sweeping statement to make by Kaku.

    Just out of interest, this may be a stupid question, but it's been niggling me. If I were to set up the apparatus for a double slit experiment (DSE) and instead of measuring things myself I programmed a robot to make random measurements and left the room, returning an hour later to see what happened, would it make any difference to a standard DSE? Why did I do that? Well, if the particle (electorn, photon etc) doesn't "know" if its being observed then what will it do? And it can't "know", since it is observed randomly (I'm assuming I can find a way to program a purely random number generator). And then, since a robot isn't conscious it isn't making observations anyway, is it? Even if it is a stupid question, I'd appreciate any answers.
     
    Last edited: Sep 25, 2010
  12. temur man of no words Registered Senior Member

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    What is decoherence?
     
  13. Green Destiny Banned Banned

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    Decoherence temur, is when a particles wave function is collapsed when the environment, ie. others atoms or particles interfere with it - or in other words, atoms act like observers on another particle in an attempt to deflate their wave functions. Decoherence is the natural wave function collapse, obsolete of any conscious observers.
     
  14. Green Destiny Banned Banned

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    I cannot make comments on quantum consciousness. I suppose its possible, but it's still a theory, a wild and postulative one at that.

    Are you asking, can cold technology collapse the wave function? If the apparatus you use has a camera that is observing the particle, then the wave function would collapse, just as the observations of a bare eye would collapse the wave function, if it were possible. The actions of observation is simply ''cutting down'' any multiple possibilities. A non-conscious camera can do this. Even atoms around a particle, can do this.
     
  15. Green Destiny Banned Banned

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    sorry, wrong thread lol
     
  16. temur man of no words Registered Senior Member

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    So it is just another name for wave function collapse? Do you know if it is possible to show that decoherence occurs in quantum mechanics?
     
  17. Green Destiny Banned Banned

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    Well, as my memory accounts, Alain aspect and his team of french scientists observed Decoherence in the lab in the year 1998. It has been, I guess you could say, experimentally-varified.
     
  18. temur man of no words Registered Senior Member

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    It is not about whether or not observer must have consciousness (this can be avoided by saying observer is a system that obeys classical mechanics), but I think the separation of observee and observer has difficulty when you think of the whole universe as the observee.
     
  19. temur man of no words Registered Senior Member

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    I was asking if it is possible to mathematically derive decoherence from basic laws of quantum mechanics, of course without using the wave function collapse axiom.
     
  20. Green Destiny Banned Banned

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    To my feeble mind, I do believe it is capable; but, I don't believe personally there is any difference truely.
     
  21. temur man of no words Registered Senior Member

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    What difference are you talking about? Difference between experimental verification and mathematical derivation, or difference between wave function collapse and decoherence?
     
  22. Neverfly Banned Banned

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    You'll find alphanumeric to be a very knowledgeable person to listen to on this subject.

    Yeah, it was!
    Then again, it's not his first and one of many reasons why I have difficulty taking him seriously.


    Nope.
    It can't "know" in any case.

    MY Own personal little take on this is that the observation is the observer. It creates the effect to itself, which we misapply to that which is observed.

    I'm really going to have to open a notepad and think out how the heck I'm going to explain that coherently so don't be surprised if I'm posting again in a couple hours with an extension

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    I also need to hit a couple of books on the shelf, cuz I'm not even sure I know that what I'm trying to say makes sense when compared with the actual application...
     
  23. Green Destiny Banned Banned

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    Decoherence... see... it's just as I said. You deflate the wave function of a particle continuously (as a strong coupling to the system) then you have effectively simply a collapse of the wave function.

    I guess it is like having your quantum wave function captive by the actions of other particles around you, except, not by a single observation, but by multiple cases of it. An atom can define another atoms angular momentum, just by observing it, just as much as all the other properties can be defined, by external thermal or dynamical objects interfering with their wave states.
     

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