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Single-Particle Interference for BIG objects-what does it mean for a lay person?

  1. Sep 21, 2007 #1
    Hi All,

    I am a new member and not a physicist. A long time back a physicst friend of mine told me about the single particel inteference experimnet and I was fascinated.

    Today I learnt that this exist even for macroscopic objects. http://www.physorg.com/news78650511.html

    Whay could this mean for the layperson.....that we can exist in two places at once!? That we are waves too? So teleporting can actually be a reality??

    Please excuse me if my questions are stupid (the last time I did physics was in highschool)

    Please enligtem me, your explainations will be greatly appreciated!

  2. jcsd
  3. Sep 21, 2007 #2
    Any one able to help me out please ?

  4. Sep 21, 2007 #3


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    There is a HUGE difference between what quantum particles can do, and what you and I (classical objects) can do. If such quantum behavior are that easy to occur, we would have seen it easily by now, and it would not be so strange.

    It also means that many pseudoscience and mystical claims using quantum mechanics as a justification are also bogus, because no such connection has been established.

    So don't worry yourself over such things. Just look at your world. Nothing has changed.

  5. Sep 21, 2007 #4
    but a Silicon dot is BIG.....it is 10 million times bigger than a quantum object.
    Please don't burst my bubble...:-) I am so happy thinking what all would be possible after this great discovery!

    if it applys to a big macroscopic object...why wouldn't it apply to us?
  6. Sep 21, 2007 #5


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    Then would you like to try tunneling through a wall, or interfering with yourself?

  7. Sep 21, 2007 #6
    Tuneeling through a wall would be a great idea:-)
  8. Sep 21, 2007 #7

    Yes, macroscopic objects can exist in two places at once. Or they can be in a superposition of two very different states, such as "alive" and "dead" states of the famous Schroedinger cat. However, this state superposition exists only before the measurement is done. When we actually measure things we find them either "here" or "there" and we find them either "alive" or "dead". We never find them in the superposition state.

  9. Sep 21, 2007 #8
    Thanks Eugene,

    I dont understand what you mean by 'before' measuremnet is done. Before measurement is done, there are infinite possibilities where an object can be because we don't even know.

    But apparently in this particular experimnet, they showed tghat particels exist in 2 places after measurement was done. Isn't it?

    I apologise if my questions seem too stupid.

  10. Sep 21, 2007 #9
    That's right. We don't even know. That's why there is nothing mysterious in quantum-mechanical superposition.

    I can't comment about this particular experiment with droplets. I would need to read beyond this press-release to understand what was actually done there. However, in the classic double-slit experiment with electrons or photons the particles never exist in 2 places after the measurement. Each particle hits the scintillating screen or the photographic plate in one place. So, the measurement of the particle position is unambiguous. The entire "controversy" is about what the particle was doing while we were not watching. Did the particle pass through one slit or through both slits? These are metaphysical questions, because they ask about something we did not observe. As you correctly pointed out, one can answer "I don't know" or "I don't care" and be done with it.

    Last edited: Sep 21, 2007
  11. Sep 21, 2007 #10

    Thanks again. Do you guys believe in metaphysics?
    Have you seen the movie, "what the bleep do we know?" (a very very badly amde film, but the content of it was very interesting nevertheless).

    What do you physicits tink of such stuff?

  12. Sep 21, 2007 #11

    Doc Al

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    It's crap. Almost pure nonsense. Including a very misleading presentation of quantum mechanics.
  13. Sep 21, 2007 #12
    But ALL of them were scientist and doctors , some from Harvard and Stanford.
  14. Sep 21, 2007 #13
    In my opinion, physics is an experimental science. The role of theoretical physics is to predict results of experiments. We really shouldn't ask for more than that. We shouldn't give too much credence to our theoretical models and "mechanisms" which go beyond observable effects and try to say what the system is "actually" doing while we are not watching. Such models and "mechanisms" can be successful mathematical tools, but it would be unwise to assign any physical meaning to them.

    For example, the most precise and comprehensive description of quantum effects is provided by state vectors and Hermitian operators in the Hilbert space. However, nobody can seriously believe that the Hilbert space is a physical entity.

  15. Sep 21, 2007 #14

    Hans de Vries

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    This experiment shows that classical physics can produce effects which we usually
    expect only from quantum mechanical systems. A particle (a 1 mm oil droplet) diffracted
    via it's wavefunction. Quite interesting though.

    Regards, Hans
    Last edited: Sep 21, 2007
  16. Sep 24, 2007 #15


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    Only one of them was a quantum physicist. What he said was OK. But it was not directly related to the rest of the movie.
  17. Sep 24, 2007 #16


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    I would!
    To show that the interpretation of QM I adopt is correct.
    (That physical objects, both microscopic and macroscopic, are not their wave functions.)
    Last edited: Sep 24, 2007
  18. Sep 24, 2007 #17
    Throwing a baseball in the air is quantum mechanics, and so is eating a sandwich. When we are children we learn to generally understand a lot of these particular experiments in quantum mechanics. What we did not notice as children is that there are certain behaviors that are very subtle in high energy experiments (like throwing a ball or eating a sandwich) which become more clear when we do low energy experiments (like slowly rotating a dish of super cold helium or noting the individual photons striking a detector).

    Classical mechanics is an estimate of the average behavior of a lot of low-energy interactions acting in unison. The total energy is high, but each separate interaction is low energy. We see that the low energy interactions don't follow that "average" behavior described by classical mechanics.

    Any experiment demonstrating a behavior of quantum mechanics that seems odd to us (because we didn't notice it as children) will involve very low energy. There are some experiments that produce results that can be seen with the naked eye, so to speak. Quantum vortices, and interference patterns of individual particles, are two examples. So no matter how clever your contraption (and we've no idea how to make one yet), the only way to take advantage of, for example, quantum tunneling on a macroscopic scale (cause tunneling to work in unison for a lot of particles) would be to cool all the particles in the entire experiment WAY down. Next, we'd have to somehow individually associate every particle in the subject to be transported with a position in the destination. Then we'd have to figure out a way to cause all the particles to tunnel at the same time. In other words, it ain't gonna happen real soon.
  19. Sep 24, 2007 #18

    Did you not mean "macroscopic physics"?
    Since I understood from this paper that quantum behaviour was observed for a macroscopic object, but I think it was not classical physics.

    Or maybe I did not understand correctly this article, as I think it was not very clear.
  20. Sep 24, 2007 #19


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    You understood correctly, the paper deals with a quantum macroscopic object. It is "classical" only in the sense that at such large macroscopic scales one naively expects classical behavior.
  21. Sep 24, 2007 #20

    Hans de Vries

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    This experiment is entirely classical physics: A 1 mm oil droplet which bounces on
    a liquid surface because the liquid bath is vibrating vertically. The bouncing droplet
    creates a circular wavefunction. When the droplet + wave function are sent through
    a split then a diffraction pattern appears which is similar to what we see in quantum

    Regards, Hans

  22. Sep 24, 2007 #21
    Dear people....thanks for all your replies..but did you forget that I am a layperson :-)
  23. Sep 25, 2007 #22
    I guessed correctly that I need to better understand this paper.
    However, I expect it now to be a kind of analogy, probably just as deep as the wave equation of this system.
    I wonder how the particle-side of the duality has been introduced in the interpretation of this experiment.

    If I buy a copy, I will specially read about the differences between this system and quantum system, as mentioned in the abstract.
    After all, if there are such differences, why would this system be in any way relevant for quantum mechanics?
    Waves have never been a conceptual problem in quantum mechanics ... only the duality is difficult for our macroscopic nature.
    Or would this be the key for a real understanding of quantum mechanics?

    I just found that this paper is freely available: http://docto.ipgp.jussieu.fr/IMG/pdf/Couder-Fort_PRL_2006.pdf
    Last edited: Sep 25, 2007
  24. Sep 29, 2007 #23
    This is a beautiful experiment. Probably the most beautiful I've seen on the subject of interference patterns. I'm still reading it and it very well may be key to understanding what REALLY happens when photons, electrons, etc pass through slits, as opposed to "wavefunction collapse" hoopla. One thing to note as you read is the difference between the waves being discussed. Particularly:
    - The droplet is always a particle
    - It interacts with it's environment through the wave-like disturbance
    - It's interaction with it's environment determines it's trajectory
    - It's path through the slit determines where it ends up on the detector
    - Not all paths have the same probability, with the probabilities matching the classical single slit diffraction pattern.
    - knowing the path of the particle does not in any way affect the result!
    - The particles are localized throughout the experiment

    The results of this paper are frightfully close to Randell Mills' explanation of the double slit experiment in his CQM theory.
    Last edited: Sep 29, 2007
  25. Sep 29, 2007 #24


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    Very interesting and inspiring experiment. Thanks for renewing this thread, mn4j. I'd have nearly missed it. I'm wondering if this can be related to multi-particle wave functions. Too bad they didn't explain the math of their simulations a bit more. I hope this can be found in their references.
  26. Sep 29, 2007 #25


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    I think nobody's afraid of a comedian...
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