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Unceartianity and virtual pions.

  1. Jul 9, 2011 #1
    Hi, I'm 11 so I probably will not understand your answer if you use alot of math without explaining it. I heard that Heisinburg's unceartianity principle was what made people belive Yukawa(spelled right?) that there are such things as virtual mesons that can be pulled out of a vaccum, you CAN create something out of nothingness. I always thought the universae had definite boundries and E=mc2 ruled over the subatomic world. But how does Unceartianity prove this is correct? as far as I can tell, unceartianity just proves you can make a laser beam wider by making it shorter. is it that the photons that make up the wide-ness of the laser come from the vaccum? thats impossible because your laser beam will keep going till the battery dies.
    ~Brainguy
     
  2. jcsd
  3. Jul 9, 2011 #2
    You might want to learn to spell words first and then deal with the physics and QM is too advanced for your age. About the 'something out of nothingness', the initial singularity (before the Big Bang) was created due to quantum fluctuations. And according to some theories there are billions of virtual particles spawning out of vacuum which annihilate themselves very quickly.
     
  4. Jul 9, 2011 #3
    You haven't really answered my question. Sawree ubawt mai splngg, it haz binnn complimentiedx in othurr posttttz but I guess unceartianity is too long a word for me. :( if this is still recent enough for anyone to notice, please reply. Thanks!
     
  5. Jul 9, 2011 #4

    Drakkith

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    Staff: Mentor

    As far as I understand, not being an expert in Quantum Mechanics, virtual particles were originally developed as an idea to help people visualize what was going on during their calculations and such. Somehow it has become widespread that they ARE actually there, when the reality is that they are simply mathematical constructs. (Made up to help make the math easier to understand) Again, I am not an expert on QM, so I could be completely wrong. That is simply what I have heard and read about a bit.

    The uncertainty principle means that you cannot know exactly where a particle IS and where it WILL BE. They usually mean that when you measure the position of a particle more and more accurately, the momentum (Kind of like speed) of it is less known. When you measure the momentum, the position is less accurately known. It it usually taken further to mean that the particle NEVER has an exact position AND exact momentum at the same time. Your laser beam example isn't really applicable, as the "beam" is a collection of trillions of photons. At that scale quantum effects aren't observable. However, please be aware that the photons in your laser beam ARE real. They are not virtual.
     
  6. Jul 10, 2011 #5
    https://www.physicsforums.com/showpost.php?p=3240965&postcount=86"and check out Lisa Randall out on what goes on with those 'virtual' particles. She is one of the world's leading high energy physicists and wrote a popular book from which the quote is.

    As an introduction and since you are just 11 years old I think that's an ideal place to start.

    As you might have heard quantum mechanics is weird, their are those 'unspeakable' things happening between measurements. We can express them in mathematical formulas, but they do not make too much sense for our brains which are trained in a classical, non quantum physical world.

    Quantum field theory, which is the theoretical framework where those 'virtual' particles arise, takes into account quantum mechanics and special realtivity, so that you have relativistic quantum physics, and thus describes Nature more acurate than quantum mechanics. The quantum weirdness is still all there, but in addition this theory is conceptual deeper and mathematically much more difficult to handle.

    But let's take quantum mechanics. Say you measure the position of a single particle. Now even if you would know all about the forces acting on that particle, you only can give probabilities where that particle will be found some moments later. What that particle does between your two measurements is totally crazy and unspeakable, though we can write it down in mathematics which then give us the right probablity predictions for our measurements.

    Now switch to relativistic quantum physics, where due to E=mc^2 we can convert energy into mass. That means that if we clash particles with very high energy, out of this collision might come different particles which are heavier or larger in number.

    But much the same as in quantum mechanics (nonrelativistic quantum physics) you only can give probabilities of what you will measure (what particles will come out of the collision and in which angle). Also again, what goes on between measurements is complete quantum weirdness and unspeakable. In addition, as I said earlier, the mathematics that describe what goes one between the measurements and which give the probabilities prediction for the measurements are much harder.

    Many physicists interpret from one calculation scheme that works very well, that in those crazy and weird intermediate states between measurements there exist 'virtual' particles. Many others don't. But the majority, I believe, accepts it as an interpretational issue.


    Whether those 'virtual' particles, which are by definition not directly measureable, are part of a physical reality or mathematical constructs or just convenient visualizations is for you to decide after you learned some quantum field theory.

    I do think they are part of physical reality.

    But yes, truth is, that many physicists in the end do not bother too much about it and see it more as a philosophical question, fascinating as it is.
     
    Last edited by a moderator: Apr 26, 2017
  7. Jul 10, 2011 #6
    ThAnks alot! I got two conflicting answers, but I understand that it's sort of just a Philosophical debate. But if some people don't believe in mesons, how do they explain vaccum fluctuations in QED?
     
  8. Jul 10, 2011 #7

    Drakkith

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    Staff: Mentor

    Just to clear things up, Mesons ARE real particles. VIRTUAL mesons are not.
     
  9. Jul 10, 2011 #8
    Ok, thanks. I'll go google the definition of a virtual particle now, thanks!
     
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