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Quantum interference. Really. Really?

  1. May 10, 2014 #1
    If leptons can stack up on top of each other and not interfere than how can a single lepton do so in the two split experement?
     
  2. jcsd
  3. May 10, 2014 #2

    Simon Bridge

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    The lepton is not what is doing the interfering.
     
  4. May 10, 2014 #3
    Leptons cannot stack on top of each other. They are fermions.
     
  5. May 10, 2014 #4
    Thinking out loud though. Is the interference pattern common between fermions and bosons?
     
  6. May 10, 2014 #5
    There is no such a thing as a "two split experement". May be you mean a double slit experiment? The wave function does the interfering.
     
  7. May 10, 2014 #6

    Cthugha

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    First order (single particle) interference: Yes.
    Higher order (multi-particle) interference: No.

    Mathematically speaking, the difference between fermions and bosons becomes apparent in different commutation relations. These do not occur when evaluating first-order interference. Loosely speaking, processes, where several indistinguishable bosons will end up in the same state, become enhanced by constructive interference of probability amplitudes (consider stimulated emission), while they are prevented from happening by destructive interference of probability amplitudes for fermions (in accordance with the exclusion principle).
     
  8. May 11, 2014 #7
    My faux pa it was late. But to say that two split experiment does not exist I can only say this was not my terminology I used. And to say that it is the wave function does the interfering I must refer you all to the June 2013 issue of Scientific American. See the cover. My questions are the result of things said by peer reviewed Physicists and not pulled from my bum.
     
  9. May 11, 2014 #8
    Just an afterthought. Mathematics can imply or define reality but has no causal effect.
     
  10. May 11, 2014 #9

    bhobba

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    I think you need to see a correct analysis of such experiments:
    http://arxiv.org/pdf/quant-ph/0703126

    Indeed it has nothing to do with anything interfering with itself, but sometimes people are a bit loose with terminology.

    So exactly what is your point?

    Thanks
    Bill
     
  11. May 11, 2014 #10

    bhobba

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    It models realty - whatever that is. It's just like good old Euclidian geometry you learnt about at school. If it implies something and that doesn't reflect observation it's a bad model - otherwise you tend to trust it - just like surveyors trust geometry and actuaries trust probability.

    Thanks
    Bill
     
  12. May 11, 2014 #11

    Simon Bridge

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    Can you provide a reference to that terminology?

    The June 2013 edition:
    http://www.ebook3000.com/Scientific-American---June-2013_196461.html
    ... appears to show pictures of phytoplankton, but one of the cover-features of that edition is:
    Can Quantum Bayesianism Fix the Paradoxes of Quantum Mechanics?
    ... the article stresses the weirdness of quantum mechanics but does not actually cite any peer-reviewed literature supporting statements like "particles appearing to be in two places at the same time" or "particles interfering with themselves" etc. The author is misrepresenting the weirdness for the purpose of illustration - don't take it literally.

    Anyway - the thrust of the article is actually that particles don't interfere with each other in the double slit experiment (if the article mentions any "two split" experiment, I missed it.)

    Note: Scientific American is not, itself, a peer-reviewed journal. It is a regular magazine which reports on material already published and peer-reviewed elsewhere.

    When an article is about something peer-reviewed, you have to be very careful to identify what is actually being supported: the citations seldom support every single claim in the article - journalists like to make things seem more sensational than they are. But at least you didn't take your ideas from Discovery Channel or something ;)

    @Bhobba: the Marcella article should be read in conjunction with:
    http://arxiv.org/abs/1009.2408
    ... Feynmans treatment is still best, but longer.
     
    Last edited: May 11, 2014
  13. May 11, 2014 #12

    bhobba

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    Last edited by a moderator: May 6, 2017
  14. May 11, 2014 #13

    Simon Bridge

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    That's what I like to stress ... the "interference" at slits is a description of the maths for working out the resulting detection probabilities. It is not a literal interference as with water waves at a barrier. The similarity is because the schrodinger equation governing wavefunctions is a form of the helmholtz equation governing general wave behavior.

    There is a tendency to take the calculation in physics a tad literally - especially by journalists.
    This gets picked up by enthusiasts and students, which it hat post #1 looks like.

    All we really know is that a particle started at some point A and got detected at some point B ... we know nothing about what happened to that particular particle in the middle - but we do know something if what may have happened, which is how we can do a calculation.

    There is a feeling that the maths should arise from some physical process so we can say we know how B was arrived at from A. Attempts to make QM like that tend to lead to arguments. In fact, the SA article pretty much makes that point ...

    wildee44 may benifit from watching Feynman's iconic lectures on QED.
    http://vega.org.uk/video/subseries/8
     
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