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Macro superposition

  1. Dec 15, 2013 #1
    My question preferibily if sci advisors could answer this as objects get bigger does the radius or space of its superposition become smaller to the point at which it is so miniscule its hard to notice. Wheras smaller objects like atoms have huge superpositions and can be in california and new york at the same time. On the other hand the superposition of a pencil is so small that its the microscopic size of a Angstrom.

    Any help is appreciated
     
  2. jcsd
  3. Dec 15, 2013 #2
    you can manipulate to be precise,
    more spread momentum, less spread position.
     
  4. Dec 16, 2013 #3
    I dont understand can you clarify please and adress whether there is a diffrence in superposition size between macro and micro objects.
     
  5. Dec 16, 2013 #4

    bhobba

    Staff: Mentor

    The wavelength of the 'wave-packet' of large objects is so small its virtually impossible to detect its quantum character.

    Thanks
    Bill
     
  6. Dec 16, 2013 #5
  7. Dec 16, 2013 #6

    ZapperZ

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    Look at what they needed to do to "detect" it.

    Size isn't the issue. It's the ability to maintain coherence over space and time! It gets progressively more difficult to maintain such coherence as the object gets bigger, and thus, makes it more difficult to detect such quantum effects.

    Zz.
     
  8. Dec 16, 2013 #7

    bhobba

    Staff: Mentor

    That's exactly it. Left to itself a wave-packet will naturally spread. What keeps it from doing that is its decohered by the environment.

    In the linked article they spent a lot of effort removing the environment. That's very hard to do, but not impossible. But when its done some very strange effects appear even for macro objects.

    Nowadays we know fairly well the reason we have a classical world is its constantly being entangled with its environment and decohered. For example a few stray photons from the CBMR is enough to decohere a dust particle and give it a definite position.

    Thanks
    Bill
     
  9. Dec 16, 2013 #8
    Then why does the double slit experiment with a laser pen forexample display an interferance pattern in highschool class experiments since in the classroom the enviorment has not obviously been removed yet we can see superposition on the backboard.
     
  10. Dec 16, 2013 #9

    ZapperZ

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    It is because photons do not interact that much with the air environment. That's why we use photons in many EPR-type experiment - they maintain coherence longer in time and distance!

    Zz.
     
  11. Dec 16, 2013 #10
    Does this only apply to photons
     
  12. Dec 16, 2013 #11

    ZapperZ

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    Does what apply only to photons?

    Zz.
     
  13. Dec 16, 2013 #12
    I think he means "does interference only apply to photons" in which case I think the answer is no, you can observe decoherence and constructive and destructive interference with just about any lepton.
     
  14. Dec 16, 2013 #13
    My real question is it only photons that we can see macro superposition IE double slit interferance without isolating the particles from the outside world.Are photons "special" in this regard.
     
    Last edited: Dec 16, 2013
  15. Dec 16, 2013 #14


    No. The double slit experiment has been carried out without isolating single electrons from their 'environment'(whatever that means quantum mechanically!) or isolating them from interacting with the slits(electrons somehow do not seem to care about interaction with the plate that houses the slits so no decoherence there).

    http://physicsworld.com/cws/article/news/2013/mar/14/feynmans-double-slit-experiment-gets-a-makeover


    BTW, if you want a real understanding of what is going on, a 'bare' decoherence theory will only get you half-way at most.
     
    Last edited: Dec 16, 2013
  16. Dec 16, 2013 #15
    is this true in refrence to electrons, I feel there is a contradiction between entanglment forming a classical world and the double slit exhibiting superpositions of diffrent particles
     
    Last edited: Dec 16, 2013
  17. Dec 16, 2013 #16


    What do you mean? The link I posted was about an experiment done with electrons.

    All quantum particles can show interference effects, it's just that the bigger the object, the harder it is for quantumness to be observed(massive accelerated particles display almost classical behavior). What is it that you are asking?
     
    Last edited: Dec 16, 2013
  18. Dec 16, 2013 #17
    What Im asking is the double slit experiment the only example of superposition in the macro world without isolating the particles from the external enviorment and are there other examples other than the double slit. The sci advisors in the above posts said that when a particle interacts with the outside world it loses its quantum properties "entanglment occurs" and collapses yet the double slit contradicts this. I am very confused at this point also the link I posted earlier about the metal paddle its superposition or eigenstates must be very small or miniscule correct.

    Any answers from mentors or sci advisors would be greatly aprreciated.
     
    Last edited: Dec 16, 2013
  19. Dec 16, 2013 #18


    No. Bigger objects do tend to lose their coherence very fast and there have been experiments with double slits and more massive objects where special measures were taken to avoid decoherence. With single free electrons decoherence plays much lesser role.



    That paddle is almost a classical object and in no way comparable to single electrons or photons. It's huge and massive.
     
    Last edited: Dec 16, 2013
  20. Dec 17, 2013 #19
    But can someone other than maui explain how we live in an entangled world which is always collapsed by the enviorment but at the the same time the double slit expeirment can be performed with particles IE electrons not isolated by the enviorment and not collapse. There is an inconsistinsy here.
     
  21. Dec 17, 2013 #20

    bhobba

    Staff: Mentor

    There is no inconsistency.

    Entanglement, and decoherence is a form of entanglement, requires interaction. If things are arranged so the interaction is weak, and hence negligible, then interference effects can occur.

    Crystal diffraction, which demonstrates the quantum nature of electrons, I believe is done in a vacuum. Not likely to be much interaction there.

    Like I said I am pretty sure its done in a vacuum. Valves for example need a reasonably good one to have an electron stream to even work.

    Thanks
    Bill
     
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