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B Double slit experiment -- consciousness and information

  1. Feb 2, 2017 #1
    I am not a physicist but I am interested in the double slit experiment and would like a definitive answer, from a physicist, to my question as follows:. If the which path is just detected by a detector, without it flashing and bleeping at the same time, and without the detections being recorded for future reference, and without a consciousness observing these detections, will a two bar pattern still appear on the target screen?
     
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  3. Feb 2, 2017 #2

    phinds

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    There is zero requirement that there EVER be a conscious observer. That's a mistaken point of view that was abandoned about 100 years ago but persists in pop-sci presentations. ANY white-path detection destroys the interference.
     
  4. Feb 2, 2017 #3

    DrClaude

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    Hi Viopia,
    :welcome:

    You will have to post your questions in the proper forum. This one here is only for introducing yourself. But I can tell you already that no, consciousness is not needed. You will find many threads discussing this. For instance, at the bottom of this page, you will find a list of "Similar Discussions."
     
  5. Feb 2, 2017 #4

    phinds

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    OOPS. Didn't realize when I responded that this was in the intro section.
     
  6. Feb 2, 2017 #5
    Thanks for the info. This being the case why is there so much current confusion over this, as demonstrated by the following YouTube link? I believe you are right, but the researchers who actually conduct the experiments also seem to be unsure about whether the which path information has to be recorded or not. Even Jim Al-Khalili's YouTube video shows the detector "flashing and bleeping" while detecting. Why does it need to "flash and bleep" if conscious observation is not required? Please take particular notice 6 minutes from the start of the video to see the complete confusion. Do you also know the answer to the first part of my question?
     
  7. Feb 2, 2017 #6

    phinds

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    As I said in my post, the "confusion" ONLY persists in the minds of pop-science demonstrators. Physicists dumped the notion a century ago. The REAL question is, why don't pop-sci folks pay attention to actual science?
     
  8. Feb 2, 2017 #7

    Mentz114

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    Good question. It does not. A silent, black body detector would have the same effect. Polarizers in each path also affect the pattern. If they are wholely opposed there is no pattern.
     
  9. Feb 2, 2017 #8

    Nugatory

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    Stuff like this is the reason why Physics Forums has its rules about acceptable sources. You won't find this confusion in the peer-reviewed literature where the real work is going on, and you won't find it in the first-year QM textbooks that aim to teach the real thing to people who are preparing to do real work in the field.
     
  10. Feb 2, 2017 #9
    Thanks. So the answer to the first part of my question is the which path detectors only have to detect without recording the information for future reference for a two bar pattern to appear.
     
  11. Feb 2, 2017 #10

    Nugatory

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    In fact just about any substantial interaction will do the trick - it's an accident of history that we use the words "observation" and "detection" to describe these interactions.

    Although not allowed sources under the PF rules (that is, you can't cite them as an authoritative source about what quantum mechanics really says - for that there is no substitute for a real textbook with the math and everything) there are two books that you may find more helpful than the random internet video:
    Giancarlo Ghirardi: Sneaking a look at God's cards
    David Lindley: Where does the wierdness go?
     
  12. Feb 2, 2017 #11
    Thanks for that. Perhaps the two Texas A&M PHd research physicists should also read these books, as well as the ex NASA physicist Tom Campbell. Also, do you think Professor Jim Al-Khalili should alter his YouTube video because the detectors do not need to flash and bleep and showing them flashing and bleeping gives people the impression that consciousness is required when it really is not.
     
  13. Feb 2, 2017 #12
    Just one last question. (It is easier for me to ask you than spending hours plowing through a text book). There seems to be a consensus among physicists that detection "interaction" causing probability waves to become particles is very strange, especially in the delayed choice quantum erasor experiment where the particles historic pathway is created at the same time. Does the Quantum Field Theory address these issues by ignoring wave particle duality and suggesting that there are no particles, only waves. If so, does all the weirdness now have an explanation and is QFT part of mainstream science?
     
  14. Feb 2, 2017 #13
  15. Feb 2, 2017 #14
    Actually wave-particle duality is an outdated concept and as such it's "ignored" by every field of physics.
     
  16. Feb 2, 2017 #15

    bhobba

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    It was outdated at the end of 1926 when Dirac came up with his transformation theory which generally goes under the name QM today. Here is the history:
    http://www.lajpe.org/may08/09_Carlos_Madrid.pdf

    The wave particle idea was just an incorrect stepping stone to Schrodinger's wave equation (he even made a mistake in its derivation I will give a link about at the end) which later morphed and was combined with Matrix Mechanics by Dirac and others. It also included other ideas around at the time such as Dirac's Q numbers that Heisenberg described as much better than his own.

    Here is the paper explaining what Schrodinger did, his mistake, and the modern view:
    https://arxiv.org/abs/1204.0653

    But please understand its purely of historical interest.

    Thanks
    Bill
     
    Last edited: Feb 2, 2017
  17. Feb 2, 2017 #16

    bhobba

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    Post the peer reviewed literature of those people, and experts here will be only too happy to explain whats going on - its likely popularization's which, how to put it, are often way oversimplified to the point of downright lies for a lay audience.

    But we cant comment until you post what they say, its source and just what concerns you.

    It must also be said well respected textbooks are of course suitable references here, and some of the beginner ones of those sail close to - again how to put it - not quite kosha. But you must give the source and what worries you if we are to comment.

    Thanks
    Bill
     
  18. Feb 2, 2017 #17

    bhobba

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    Opinions on if its strange or not varies. This is hardly surprising since 'being strange' is an emotional response. You don't need QFT to explain it.

    To understand the 'real' fundamental issue(s) in QM you need to consult modern textbooks on interpretations, especially those dealing with whats called decoherence. The issue is, colloquially, why we get any outcomes at all, but that's by the by. I cant explain it at the lay level. THE standard text is:
    https://www.amazon.com/Decoherence-Classical-Transition-Frontiers-Collection/dp/3540357734

    Its advanced however.

    At your level I suggest the following textbook that has kindly been put out there for free. It uses math, but explains it as it goes along:
    http://quantum.phys.cmu.edu/CQT/index.html

    It has a whole chapter devoted to the delayed choice experiment, but you must take the time to read the entire book.

    But its just a start. Once you start learning QM you never really stop.

    Thanks
    Bill
     
    Last edited: Feb 2, 2017
  19. Feb 2, 2017 #18

    bhobba

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    That video is trash - discontinuity in reality - I mean - really. The possibility of collecting information - if a tree falls in forest does it make a sound if there is no one to hear it. Of course it does regardless of what people may prattle on about in an introductory philosophy class. If the detector doesn't record the information - same thing. QM is a theory about observations that occur in a common-sense classical world where observation is a very general thing.

    I will not go into how consciousness entered this quantum thing - suffice to say it was due to a mistake made by the very great polymath Von-Neumann (he made a couple - but that in no way diminishes his greatness) in his classic - Mathematical Foundations Of QM. It was excusable at the time but we know more now and can easily see the mistake. Start a new thread if you want to delve into it.

    Be very wary about the writings of the early pioneers such as Von-Neumann. They are of course acceptable sources, but things have moved on a lot.

    To cut to the chase all the quantum eraser experiment does is show in simple cases decoherence can be undone. Its a matter of definition if decoherence so simple it can be undone is a real observation - normally its so complex it cant be undone. But as you probably have guessed I don't care about semantics - take any view you want - who cares - the answer is the same.

    Thanks
    Bill
     
    Last edited: Feb 2, 2017
  20. Feb 2, 2017 #19
    Even Eugene Wigner, who at one point was perhaps the most prominent proponent of the idea that consciousness causes collapse, eventually abandoned it after he learned of H. Deiter Zeh's pioneering 1970 paper on decoherence.
     
  21. Feb 2, 2017 #20

    bhobba

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    Indeed. I have zero doubt so would have Von-Neumann if he was still alive.

    In relation to this these days a measurement is considered to have occurred after decoherence. Its purely quantum, nothing recorded etc etc. Even a dust particle can be decohered to have an actual position by a few stray photons from the CBMR. It can be interpreted as having position regardless of if anyone observes it, records it etc etc. We have made a lot of progress in understanding the measurement problem and why there is an objective reality out there in the common-sense everyday classical world.

    Thanks
    Bill
     
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