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The meaning of HUP

  1. Jul 14, 2011 #1
    Greeting to everyone. This is my first time here (A bit nervous)

    According to many sources, many books, "Heisenberg uncertainty principle" tells us that it is impossible to measure anything exactly. I agree as the proving equation does not apply any measuring instrument at all which means that even the best measuring instrument will never gives us exactly measuring.

    Now comes to the problem. Does the HUP only applied when there is measuring ?
    I have two opinion about this:
    1. We can not measure anything exactly which means nothing is certain at all.
    2. Although we can not measure/predict anything exactly, everything is certain.

    Thank you very much.
     
  2. jcsd
  3. Jul 14, 2011 #2

    Drakkith

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    I was JUST thinking about asking this myself. I believe the mainstream view is that no particle has a 100% definite position and momentum at any point in time, but I really don't know why that is believed to be the case.
     
  4. Jul 14, 2011 #3
    Thank you very much for fast reply

    "no particle has a 100% definite position and momentum at any point in time"
    I'm not sure about this (need some more explanation)

    All I've read, HUP only told me that we can't measure two values exactly at the same time. So if we don't measure momentum, we can know the exact position. Or if we don't measure position, we can know the exact momentum of the particle. So there might be exact position OR momentum for the particle depends on how we measure.

    Is my understanding wrong ?
     
  5. Jul 14, 2011 #4

    WannabeNewton

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    I don't know if this is the very reason why (i.e. the deeper physical meaning) but it comes in part from the incompatibility/ non - vanishing commutator of the momentum and position operators. If you make a position measurement then the system will collapse to a certain position eigenstate but there will still be multiple eigenvalues possible for the momentum operator. If you then immediately try to make a momentum measurement while the system is in that state it will collapse to a certain momentum eigenstate but now you have multiple eigenvalues possible for the position operator.
     
  6. Jul 14, 2011 #5
    If you measure the position of a particle, the wave function collapses into a spike. It's then possible to measure to the momentum of the particle, however, it will collapse again into a defined wavelength but the position you first measured won't be the same!

    There is, however, a way to make it so when you measure the momentum you won't disturb the particle but I can't remember it off the top of my head
     
  7. Jul 14, 2011 #6
    This might be the answer. I forgot to think about wave function. Thank
     
  8. Jul 14, 2011 #7

    Drakkith

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    I'm not asking for some deeper understanding, I'm asking why we accept that particles simply don't have a defined position and momentum. I've read a little bit on QM, but I have no idea how to even do most of the math to figure this stuff out, which is probably why I don't really understand most of it. For example, I have no idea what a commutator is. Nor what eigenstates and eigenvalues are. Heck, I don't even know how to do a function.
     
  9. Jul 14, 2011 #8
    That comes from when you make the change from a particle, to a wave function, and when you do that you start to use a thing called Born statistical interpretation! It pretty much says what's the probability of finding the particle between two points at a certain time given the wave function. Really all you can do with QM is find POSSIBLE results, since QM just gives us statistical information.
     
    Last edited: Jul 14, 2011
  10. Jul 14, 2011 #9

    Drakkith

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    Alright. Now, I understand that the measurement of a particle can't determine position and momentum 100% accurately, but why the leap from there to the belief that a particle simply doesn't ever have it ?
     
  11. Jul 14, 2011 #10
    I don't have the time at this very moment to answer that (going to sleep). However, tomorrow I will have an answer to post (assuming no one else answers it)! Pretty much saying, good question :P and I have to think about it in the morning.
     
  12. Jul 14, 2011 #11

    rcgldr

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    Even though measurement can't be made directly, wouldn't it be possible to describe the position, velocity, acceleration, momentum, ..., of a particle as functions with respect to time, based on a known (possibly calculated) initial state and/or final state and the characteristics of the environment?
     
  13. Jul 14, 2011 #12

    Drakkith

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    I don't think so, as we cannot know those initial states. It's all about probabilities.
     
  14. Jul 15, 2011 #13

    rcgldr

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    I was also thinking along the line of a final state, such as an electron's collision being detected after going through some type of accelerator. Assuming the accelerator was programmed so there was only a tiny window of opurtunity for any one of a number of electrons initially injected into the accelerator that would end up being accelerated and colliding with some target, and based on the time of impact, could math be used to describe the electrons path as it went through the accelerator?
     
  15. Jul 15, 2011 #14
    hup is consequence of de broglie hypothesis....so first one need to understan de broglie n if you do u can derive it quite simply
     
  16. Jul 15, 2011 #15

    Drakkith

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    Care to enlighten us?
     
  17. Jul 15, 2011 #16
    About Pilot Wave ?

    I found this on wikipedia. http://en.wikipedia.org/wiki/Pilot_wave#Principles

    So is my second hypothesis right ?
    "Although we can not measure/predict anything exactly, everything is certain."

    Still not sure about this correctness from wikipedia.

    Thank in advance for many replies.
     
  18. Jul 15, 2011 #17

    Drakkith

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    I don't think the pilot wave is viewed as the most accurate model though.
     
  19. Jul 15, 2011 #18
    It's a fourier transform thing. The same thing happens with classical waves, eg. sound. Here is a good example:
    http://scienceblogs.com/builtonfacts/2010/03/hearing_the_uncertainty_princi.php [Broken]
    https://www.physicsforums.com/showthread.php?t=383906

    RE: pilot wave. It uses the same math so it is as accurate as any other interpretation.
     
    Last edited by a moderator: May 5, 2017
  20. Jul 15, 2011 #19
    its not that easy to enlighten anyone on a website....u search the net or text books u will find it...
    U can easily understand through the names
    see de brogle HYPOTHESIS it is hypothesis

    and HUP is not hypothesis it is derived using de brogle hypo only
     
  21. Jul 15, 2011 #20

    Drakkith

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    Got it. I'll have to do some reading.
     
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