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If im not measuring its not there?

  1. Jan 8, 2016 #1
    Without getting too deep into the physics or philosophy of quantum mechanics, and I'm NOT talking about theory (no 'what the equations say') but if I'm not looking at my couch does that it mean at the moment it doesn't exist? Or if I'm not looking at my dad he isn't there but in the form of a wave?
     
  2. jcsd
  3. Jan 8, 2016 #2
  4. Jan 8, 2016 #3
    That is the idea I get when I read about some of the interpretations. I'm just a little confused that's why I asked the question.
     
  5. Jan 8, 2016 #4
    Real quantum theories are ultimately about statistics and only are usefully applicable to things and events on subatomic scale.
    The chances of the couch you are sitting on suddenly disappearing are so low that it's unlikely to happen within the lifespan of the Universe.
     
  6. Jan 8, 2016 #5

    bhobba

    Staff: Mentor

    No. Its being looked at all the time by the environment. A few stray photons from the CBMR, for example, is enough to decohere a dust particle and give it a definite position.

    Thanks
    Bill
     
  7. Jan 8, 2016 #6
    I see basically everything is observing everything, so it is all there but in an isolated system things would work differently
     
  8. Jan 8, 2016 #7

    bhobba

    Staff: Mentor

  9. Jan 8, 2016 #8
    That is cool, so they basically cooled the thing down until there was no or close to zero vibrations left and it all went into superposition. when it is in superposition, what is the material like? do you think it still has mass? can it be moved?

    Also when something is being measured for example Atom 1 measures Atom 2. is the measurement continuous or an on off sequence, so is atom 2 continuously jumping in and out of superposition at a very fast rate.
     
  10. Jan 8, 2016 #9

    bhobba

    Staff: Mentor

    I know no more detail that what the article says. But yes it would still have mass and can be moved.

    Its got to do with decoherene. At the lay level here is the book to get:
    https://www.amazon.com/Where-Does-W...p/B001S2QNLO/ref=mt_kindle?_encoding=UTF8&me=

    Thanks
    Bill
     
    Last edited by a moderator: May 7, 2017
  11. Jan 8, 2016 #10
    Last edited by a moderator: May 7, 2017
  12. Jan 8, 2016 #11

    bhobba

    Staff: Mentor

    Without reading what he says, I can assure you in QM time definitely exists.

    Thanks
    Bill
     
  13. Jan 8, 2016 #12
    Yes, that website is legit so you can take information from it. I've had email correspondence with Erich Joos some time ago.
     
  14. Jan 8, 2016 #13

    bhobba

    Staff: Mentor

    I suspect he is as well, but some things he says such as time doesn't exist are rather controversial to say the least. I am pretty sure what he means is not quite what the prosaic language he uses suggests.

    Time most definitely exists in QM - eg the Schroedinger equation wouldn't make any sense without it.

    He also says:
    Decoherence can not explain quantum probabilities without (a) introducing a novel definition of observer systems in quantum mechanical terms (this is usually done tacitly in classical terms), and (b) postulating the required probability measure (according to the Hilbert space norm).

    That's roughly true - but the devil is in the detail. It's also very interpretation dependant eg it isn't really true of BM which doesn't require a quantum definition of observation - it takes it on board but doesn't require it because objects have properties independent of observation.

    Thanks
    Bill
     
  15. Jan 8, 2016 #14
    @bhobba
    this is what it said
    "explains also how the Schrödinger equation of general relativity (the Wheeler-DeWitt equation) may describe the appearance of time in spite of being time-less

    There is no time at a fundamental level"
    @StevieTNZ
    thanks. I think ive still got a lot to learn before I can understand anything from that website without misinterpreting it.
     
    Last edited by a moderator: May 1, 2017
  16. Jan 8, 2016 #15
    oh I posted my comment before reading yours Bhobba ignore it lol.

    I belive most of my understanding of quantum mechanics is probably wrong because most of the time I don't understand what people actually mean when they try and explain something. I'm always misunderstanding
     
  17. Jan 8, 2016 #16

    bhobba

    Staff: Mentor

    I suspect its this Block-world stuff. Its off-topic here, and rightly so IMHO. I think its basically BS - but Google is your friend, and you can make up your own mind.

    Thanks
    Bill
     
    Last edited: Jan 9, 2016
  18. Jan 8, 2016 #17
    I'd like to believe time does exist, otherwise how would we experience any changes in the universe.
     
  19. Jan 9, 2016 #18
    If everything is being looked at (measured) all the time by its environment, why does the wave pattern show in the double slit before a measuring device is used? Why is the environment not causing the wave to collapse? Thanks in advance!

    Isnt the OPs opening question the same as Einsteins comment about the moon?
     
  20. Jan 9, 2016 #19
    I remember being told that the double slit experiment Is conducted in way where there is no interference from the environment with the electrons until they are measured but some of the other guys know more than me maybe they can give more detail
     
  21. Jan 9, 2016 #20
    Not sure how that could be done, but you would think Einstein would not make the moon statement if that were the case. He would know it was just a lack of interaction that caused the results of the DS. And isnt that still being debated, and the reason for multiple interpretations? No one is still certain what the cause of waveform collapse is?
     
  22. Jan 9, 2016 #21

    bhobba

    Staff: Mentor

    It works because photons interact weakly with the environment.

    Thanks
    Bill
     
  23. Jan 9, 2016 #22

    bhobba

    Staff: Mentor

    It is true that Einstein knew QM very well carrying Dirac's classic text with him at all times - it was basically his bible on it. Also it is incorrect to say Einstein didn't think QM correct. There was a famous exchange between Einstein and Bohr where Einstein bought his last and most devastating attack on QM. Long into the night Bohr laboured to defeat it - which he finally did. He presented his refutation and Einstein tipped his hat, literally, to Bohr. From that point on he never questioned it was correct - but to his dying day believed it incomplete.

    But knowledge of decoherence was not well developed in those days. In fact both Einstein and Bohr were wrong:
    http://scitation.aip.org/content/aip/magazine/physicstoday/article/58/11/10.1063/1.2155755 [Broken]

    Collapse is not part of QM - only some interpretations. And in those that have it its a mystery for some (eg some versions of Copenhagen) and trivial for others (eg GRW).

    What decoherence has done is for many interpretations morphed collapse to the problem of outcomes ie why we get any outcomes at all. Its a mystery for some (eg Copenhagen or Ignorance Ensemble) and trivial in others (eg BM an MW).

    Thanks
    Bill
     
    Last edited by a moderator: May 7, 2017
  24. Jan 9, 2016 #23
    Sorry to be such a pain but would you mind giving me a run down of what decoherence is, just in brief
     
  25. Jan 9, 2016 #24

    bhobba

    Staff: Mentor

    It converts a superposition to a mixed state. In a mixed state we have definite outcomes but but do know know which outcome will occur. Basically you can say collapse has occurred - but we don't know the actual outcome - just there is one.

    I really cant explain it any better at the lay level, so if you want further detail I will have to leave it to others.

    I have tried in the past and it just leads to long threads with the lay person never quite getting it.

    Please read the book I suggested.

    Thanks
    Bill
     
  26. Jan 9, 2016 #25
    Why would they react to a measuring device then?
     
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