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Does the electron disappear?

  1. Mar 21, 2006 #1
    small and easy question !!

    in any quantum system, harmonic oscillator, atom, or any other we know the electron can be found on a specific orbits or shells, and can't be found between them right?

    how does it go from a shell to another when it's excited for example? does it disappear from the one and appear in the next one? or it moves normally until it reaches the next shell like me when i go from my room to the house door (that's impossible as quantum says)? what then? how does it change it's position? lol !! that's magic !!

    Anyone can explain?
     
  2. jcsd
  3. Mar 21, 2006 #2

    DaveC426913

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    The electron orbital does not define where the electron is, it defines where the electron will likely be when we go looking for it. When we find it, there it is. Quantum theory insists that we cannot know anything about it, and indeed, it is meaningless to ask, while we are not looking at it.

    This is the crux of the weirdness that is QM. Scaled up, it means that the Moon does not necessarily exist when we are not looking at it.
     
  4. Mar 21, 2006 #3
    Dave, wouldnt' an equally ridiculous interpretation of QM state that the Moon is anywhere in the sky within a certain range, and it just 'appears' in a certain spot when we look at it? :)
     
  5. Mar 21, 2006 #4

    chroot

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    LnGrrrR:

    No. The moon is not a quantum-mechanical object. It's a macroscopic object, subject to decoherence by many billions of interactions with other objects (photons, charged particles, etc.).

    It's silly to expect a macroscopic object to behave quantum-mechanically.

    - Warren
     
  6. Mar 21, 2006 #5
    Chroot,

    Read what Dave wrote ("scaled up") and I think you'll get where I'm coming from.
     
  7. Mar 21, 2006 #6

    chroot

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    LnGrrrR:

    I get where you're coming from. You want to equate the moon to an electron, and therefore ascribe the electron's behavior to the moon. Sorry, it ain't that easy. Dave's comment is pretty inaccurate.

    - Warren
     
  8. Mar 21, 2006 #7
    Chroot,

    I think he was being facetious, as was I. :) I don't think either of us were being serious, just pointing out that our 'normal' mode of thinking doesn't really work for QM.
     
  9. Mar 21, 2006 #8

    ZapperZ

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    You'd be surprise. Just look at the thread on the "tunneling" possibility of a tennis ball. People are arguing that it is possible! Yet, when I ask for evidence or theoretical derivation of such a thing, people point to me tunneling of electrons, as IF this is the same beast.

    Whenever I see a discussion like this, my first inclination is to point to Phil Anderson's famous motto: MORE IS DIFFERENT! Just because an object is made up of a gazillion electrons, or atoms, doesn't mean that it is governed by the same rules as those individual electrons and atoms.

    Read up on emergent properties, folks!

    Zz.
     
  10. Mar 21, 2006 #9
    Zapperz,

    Yup...that's some sort of logical fallacy as well, though I can't remember the name of it. (For instance, no human can see atoms with the naked eye, and everything is made up of atoms...therefore, no one can see anything with the naked eye. :)
     
  11. Mar 22, 2006 #10
    In a sentence like this one, it is important to mention what specific quantum property you are refering to, for otherwise its claim will be wrong, as the very existence of macroscopic objects is a quantum event.

    Regarding the OP, the conclusion that the electron desappears would only be valid if, in a given instant t, the whole wave function of the electron vanish. The transient states between two stationary states (eigen functions of the Hamiltonian) are all non zero functions of amplitude of probability in space.

    Unitarity of time evolution may be used in this discussion, too, in order to prove the preservation of the norm of rho(t) (density matrix).

    Best Regards,

    DaTario
     
  12. Mar 22, 2006 #11

    ZapperZ

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    Can you tell me what specific quantum property is relevant for something as large as the moon?

    Zz.
     
  13. Mar 22, 2006 #12

    DaveC426913

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    OK, I was being a bit sensationalist, and that is a disservice to the OP.

    The Moon not being there is a concept - much like the idea that all the air in a room might suddenly gather in one corner.

    These phenomena happen on the atomic scale, but the effect scales inversely to the number of atoms involved. An object of ANY macroscopic scale will take a time scale on the order of the age of the universe (or more - way more) to have this happen.

    However, my point was that, in principle, the concept is valid. QM teaches us that the things we consider stable objects, the things we can count on - a chunk of rock sitting on the table is really a chunk of rock sitting on the table - are slipperier than we thought.

    Nonetheless, withdrawn.
     
  14. Mar 22, 2006 #13

    vanesch

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    Too bad you withdraw your statement :-)

    There is a strange thing going on with quantum theory, and people are induced to say all kinds of weird things in order for the moon to be there!

    If I say that the moon is there in 3-dim Euclidean space and is attracted by the earth, then everybody says "horray"...

    If I say that the moon is tracing out a 4-volume on a spacetime manifold, of which we happen to observe a space-like slice, and is in fact following a geodesic on a 4-dim manifold, then everybody says "horray"...

    But if I dare to say that the moon is described by a component of a vector in Hilbert space, then many people go saying "booh"!

    Now, you'd think that those same people just think that quantum theory has limited validity. But if you ask them if quantum theory is a universally valid theory, then they say "yes".
     
  15. Mar 22, 2006 #14

    vanesch

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    Isn't this similar to asking what specific general relativity property is relevant for something as light and slow as the moon ? And to say that the moon is NOT something that ought to be described by general relativity, but by Newtonian gravity ?

    Just for the sake of clarity: of course it is *ridiculous* to go use quantum theory, or general relativity, to describe something like the moon, because you make the practical problem way too hard, and Newtonian theory is by far adequate.

    But I find it strange that people jump up and down when one wants to make the thought experiment of describing a macroscopic object using quantum theory - while they don't do that when one uses general relativity for a relatively light object.
     
    Last edited: Mar 22, 2006
  16. Mar 22, 2006 #15

    ZapperZ

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    No, it is not similar, because they both converge at some scale.

    I haven't seen QM properties being formulated to include a gazillion particles and converge to form the behavior of a moon.

    Have you?

    Zz.
     
  17. Mar 22, 2006 #16

    vanesch

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    Isn't this essentially what decoherence theory tries to do ? To derive the appearance of a classical world in complex enough quantum interactions ?
    Now, it is of course easier to establish the relationship between the GR and Newtonian case, because in both cases, the point-particle approximation is made and we deal only with a few degrees of freedom (accepting this approximation of saying that the moon is a point particle!). So the calculations can be done more explicitly.
    Nevertheless, I appreciate Zeh and Co's approach in decoherence to arrive - in most cases - at rather classical situations. But again, the "demonstrations" are much rougher, because of the number of degrees of freedom involved. Nevertheless, I find this sufficiently encouraging to believe that the basic tenet of the decoherence programme is correct and to understand, from that, that Newtonian physics is a good approximation to the quantum solution in this case.
     
  18. Mar 22, 2006 #17

    ZapperZ

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    I think you are twisting the issue here.

    Many-body physics IS quantum mechanics, but being applied at a large number scale. I am NOT arguing this and you should know better than that.

    But the theoretical convergence of SR/GR with classical newtonian physics is something we do not have with QM and classical physics. I can set v<<c and I get convergence to newtonian physics from SR in all aspect of mechanics. Do you see this in QM? Can I set n=LARGE and get ALL the classical dynamics of a tennis ball, dispite the so-called convergence in quantum SHO?

    Since we care so much about the theoretical argument here, then let's consider this. There is this 50,000 lbs ugly cow sitting right in front of everyone that is being ignored here. There is STILL zero ability to "see" such emergent phenomena when you write down, with all your ability and expertise, the Hamitonian incorporating all the microscopic detail of the interactions. No matter how much you argue, that still hasn't changed. It is why superconductivity was not predicted, and it is why fractional quantum hall effect was not predicted. They are simply not there to be found. And as far as I know, NONE of the currely-accepted emergent phenomena were ever predicted out of such microscopic reductionist approach. Zilch! This is a huge ugly cow. Until someone can get this ugly cow to disappear, I see no convincing evidence to assume the contrary.

    Zz.
     
  19. Mar 22, 2006 #18

    ZapperZ

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    But note what "decoherence" is. It isn't the study of ONE particle interacting with a gazillion external degree of freedom. It is the study of a many-body system being systematically "induced" into a classically random interaction! Example: interaction with a heat bath!

    So already you assume you know how to handle the emergent property of a large number of particles into a simple form, and THEN, make that system interact with an external classically induced interaction. Don't you see how many levels of ad hoc stuff are introduced here? I can put stuff in by hand easily to account for many things. Is this what is necessary to be convincing?

    Zz.
     
  20. Mar 22, 2006 #19

    Physics Monkey

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    I'm not sure what you mean here, ZapperZ. These phenomenon certainly weren't predicted, but that doesn't mean that they aren't contained in a microscopic Hamiltonian. It simply means we weren't clever enough to see it with our crude methods of analysis. The same is true of QCD, for example, where we have this stunningly beautiful Lagrangian that contains so much rich physics which is nevertheless hidden from simple view by the complexity of the problem. I could see someone arguing that very little is to be gained, at the present time, by examing these complicated many body states from first principles, but I do think it is possible in principle. Do you agree?
     
  21. Mar 22, 2006 #20

    ZapperZ

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    Actually, I don't.

    The Hamiltonian for superconductivity and fractional Hall effect starts off with a many-body ground state. In BCS-theory, for example, you already start off with a Fermi-Liquid state that has renormalized all of the weak-coupling electron-electron interaction into a many one-body problem. This is not the "microscopic Hamiltonian".

    In case you didn't read Laughlin's Nobel Prize speech, he assigned this to his students in a graduate quantum class, i.e. starting from the microscopic interaction at the individual particles and then try to "derive" superconductivity. It can't be done. It was a trick question.

    Zz.
     
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