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Double slit experiment and Interaction

  1. Mar 27, 2015 #1
    "An interaction is required to manifest physical reality because it creates distinctions."
    my friend referring to the double-slit experiment, is it true?
    He said that the physical world, in order to exist, we need to interact (with our senses) lol
     
  2. jcsd
  3. Mar 27, 2015 #2

    phinds

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    No this is not true. It is a misinterpretation of the Copenhagen Interpretation of Quantum Mechanics and it is basically just silly. Put another way, the moon is there whether anyone is looking at it or not.

    The double-slit experiment DOES require an interaction (but not a human) to destroy the wave pattern but that has nothing to do with reality existing.
     
    Last edited: Mar 27, 2015
  4. Mar 27, 2015 #3

    bhobba

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    All this is tied up with interpretations of QM. But I don't know if anyone would express it that way - in fact I cant really say I understand it.

    No.

    That's tied up with an old idea (conciousness causes collapse) that is a very fringe idea these days. It was introduced for reasons that further research showed wasn't really the issue it was thought. Nowadays there is no reason at all to believe there is not an objective world out there independent of if its being observed or not.

    Thanks
    Bill
     
  5. Mar 27, 2015 #4

    Strilanc

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    The double split experiment gives the same result whether or not there's someone in the room watching.

    Decoherence is explained with math, not consciousness. Even in the Copenhagen interpretation, where decoherence and measurement are simplified into just collapse, collapse happens when a quantum system interacts with any classical system. If collapse only occurred when systems were observed by brains, we would be able to tell. The timing of collapse has measurable effects on how things interfere. The double-slit experiment would play out differently based on whether someone was in the room or not.

    Does that answer your question?
     
  6. Mar 27, 2015 #5

    phinds

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    Another way to respond to this kind of inanity is with simple logic: If the existence of the universe were dependent on human consciousness, or ANY consciousness, then it could not exist because for consciousness to form the universe has to be there first.
     
  7. Mar 27, 2015 #6
    Thanks for the answers!! Last question, about Quantum Erasers..
    there are people that claims that it almost proves that "human knowledge" is required for the experiment .. they say that the electron paths were manipulated in such a way that it removes doubt that human "knowledge/observation" has a role".. Human Knowledge? wtfff
    (sorry my ignorance, I just hate mumbo-jumbo)
     
  8. Mar 27, 2015 #7

    Nugatory

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    Even more wrong than the rest of the mumbo-jumbo. The best execution of a delayed choice erase experiment so far has no human awareness of the paths taken by any of the particles.
     
  9. Mar 27, 2015 #8
    THANKS! It's good to read from REAL physicists.
     
  10. Mar 27, 2015 #9

    Strilanc

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    Note that posters may not be physicists. I am not a physicist. I just took a course in university, and read some books.

    (It's unfortunate that posters aren't tagged with their expertise like they are in the askscience / askphysics sub-reddits, instead of relying on the physicists to call out errors by the likes of me.)
     
  11. Mar 27, 2015 #10
    I'm sure there are people in the room while such experiments are done, so I don't quite follow your conclusion... interference results.

    What makes a system classical? Isn't in principle all systems quantum?
     
  12. Mar 27, 2015 #11

    bhobba

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    The deep reason - interaction with the environment.

    Einstein once quipped to Bohr do you really believe the moon not there when no one is looking? The answer is - its being looked at all the time by its environment. Even a few stray photons from the CMBR is enough to decohere a dust particle so you can say it has a definite position (yes Stevie I know we have apparent instead of actual collapse issue - which is why I used the word say):
    http://www.fisica.ufmg.br/~dsoares/cosmos/10/weinberg-einsteinsmistakes.pdf

    Einstein had many debates with Bohr and it's generally believed Bohr won them. The interesting thing is from our vantage they were both wrong - but Bohr's error was quite minor:
    http://motls.blogspot.com.au/2011/05/copenhagen-interpretation-of-quantum.html

    Also it needs to be said Einstein eventually accepted QM as correct - but in his view incomplete.

    To the OP exactly how the classical world emerges is a deep subject books have been written about and is an area of active research:
    https://www.amazon.com/Decoherence-Classical-Transition-Frontiers-Collection/dp/3540357734

    I have a copy, and its my bible on such matters. It is highly technical but the bottom line is this. Virtually all the issues have been answered - a couple remain but they are thought to be of the crossing t's and dotting i's variety. But they thought the same thing at the turn of last century and look what happened, So one never really knows.

    If you would like to pursue it further at the lay level here is a good book:
    https://www.amazon.com/Understanding-Quantum-Mechanics-Roland-Omnès/dp/0691004358

    He explains it all as well as touching on some of those dotting i's and crossing t's issues such as the lack of certain key theorems.

    Thanks
    Bill
     
    Last edited: Mar 27, 2015
  13. Mar 27, 2015 #12
    StevieTNZ,
    I've read one of the comments from a guy who did the experiment without being in the room.

    "just do the double slit experiment without taking the reading.
    first do the regular one without the detectors.
    then put detectors that interact like normal detectors, but do not show you anything, do not be inside the room or in any way observe whats inside.
    you still get the same results.
    Woo disproven!"
     
  14. Mar 27, 2015 #13

    bhobba

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    Same here - but I am qualified in applied math so my background is such getting to grips with highly technical texts is made easier - I already know the math - well often anyway.

    Thanks
    Bill
     
  15. Mar 27, 2015 #14

    bhobba

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    The double slit is often done with photographic plates. You preach quite an absurd position if you believe collapse occurs when the plate is developed, maybe even decades later. It gets even worse if you imagine it recorded to computer memory, millions of copies taken, and one of those copies read centuries later.

    Just as an aside collapse isn't really part of QM - but that requires another thread.

    Thanks
    Bill
     
  16. Mar 27, 2015 #15
  17. Mar 27, 2015 #16

    bhobba

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    Sorry mate - don't know about that approach.

    We do however have quite a few highly knowledgeable physicists that post on this forum so if you do a separate post about it you may get more information.

    It does speak about coarse graining which is part of a very modern approach to QM called consistent histories:
    http://quantum.phys.cmu.edu/CHS/histories.html

    Its interesting because it doesn't even have observations - for them QM is the stochastic theory of histories which are always coarse grained.

    Thanks
    Bill
     
  18. Mar 27, 2015 #17
    So here you will see no interference, if I understand correctly. Strictly speaking, all that happens is the system interacts and becomes entangled with the detector, and if you erase the 'which-way' info, you see two interference patterns emerge by doing correlations (much like what happens with the quantum eraser experiment proposed by Scully et al.).
     
  19. Mar 27, 2015 #18
    Glad you have put apparent collapse.

    Have Omnes 'Quantum Philosophy' book, which I suspect is similar in material to 'Understanding Quantum Mechanics'.
     
  20. Mar 27, 2015 #19
    The Leggett-Garg inequality rules out certain non-local realistic interpretations of Quantum Mechanics. I don't think, from what I've read, it is suitable for ruling out Bohmian Mechanics.
     
  21. Mar 27, 2015 #20

    atyy

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    Hmmm, I'm not sure I agree exactly with the common sense point of view above, so I would like to give a reference that Rajkovic can read to see why quantum mechanics is sometimes presented in this bizarre way. The Copenhagen interpretation is consistent with common sense - but it is like no other theory of physics before it - and requires an external observer. If we believe the external observer is also governed by laws of physics, then we are challenged to include the observer in the laws of physics, which in the case of quantum mechanics seems to either require presently unobserved hidden variables or many worlds. So there is a measurement problem, which is sometimes presented in a bizarre way to highlight it. An example is given in Zurek's http://arxiv.org/abs/quant-ph/0306072, where the picture on p22 shows Wheeler's evocative depiction of the measurement problem, as the universe observing itself. Zurek is of course perfectly aware of all that decoherence can do, yet in a recent essay http://arxiv.org/abs/1412.5206 he writes, "Quantum Darwinism shows why only such redundantly recorded pointer states are accessible to observers - it can account for perception of 'quantum jumps'. However, full account of collapse involves 'consciousness', and may have go beyond just mathematics or physics." Witten also has very interesting comments on the strange relation between consciousness and quantum mechanics: http://www.preposterousuniverse.com/blog/2015/03/05/the-big-questions/.
     
    Last edited: Mar 28, 2015
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