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I Quantum tunneling questions

  1. Jun 15, 2016 #1
    Hello guys,

    I have few questions about the well-known quantum tunneling.

    I'll start off with the animation from wikipedia

    So question #1 why doesn't the barrier collapse the wave function, is that even possible? What's the difference between the barrier and the measurement screen in double slit experiment which collapses it when the behavior of the particle is clearly similar (moving towards the object)

    Question #2: the wavefunction of any object has a small component on the other side of a barrier that it classically cannot pass. So for instance, theoretically, there's a non zero chance that some object from my room instantenously appears in the other room. What would happen with some object on the other side which before the tunneling act was in a location x which the tunneling objecg would occupy during the act of tunelling, how would the "spatial overlap" of those 2 objects be avoided?

    Thanks in advance.
    Last edited: Jun 15, 2016
  2. jcsd
  3. Jun 15, 2016 #2


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    Staff: Mentor

    The explanation depends on which interpretation you choose. The easiest approach, by far, is to select an interpretation in which there is no collapse so then there's nothing to explain. However, if you do want to use a Copenhagen-like interpretation that includes collapse, the explanation is that screen is a classical object so the von Neumann cut goes below it. (If you don't like that explanation, that's OK. There's something not to like about every interpretation).
    Kinda sorta.... But there's also a non-zero chance that all the randomly moving air molecules underneath my chair will, by random chance, happen to all be moving upwards at the same time. This would blast me and the chair through the roof like a rocket. That's not going to happen.... and it's enormously less improbable than what you're describing. Also take a look at this Insights article: https://www.physicsforums.com/insights/you-will-not-tunnel-through-a-wall/
    If there's an object present on the far side of the barrier, it will contribute to the Hamltonian in ways that may either increase or decrease the probability of the tunnelling particle being found in the vicinity of the object. You'd have to specify the exact conditions and then solve Schrodinger's equation for those boundary conditions - the wikipedia animation you posted will no longer describe the situation.
  4. Jun 15, 2016 #3
    That sounds logical and intuitive. My question was directed to the hypotethical case where the concept of instanteneous tunelling would actually occur and the object in question would tunnel to a location where it would neccessary have to push out another object because it would, in a lack of better phrase, took its spot. So considering that, would the pushing out of the mentioned object and tunneling of our original object happen instanteneously and not in order original object tunnels to location x (cause)
    -> object that was at location x gets pushed out (effect).
    I hope I am being clear regarding the problem. Any suggestions are welcome.
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