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Seeking Point Particle Explanation

  1. Aug 5, 2009 #1
    Seeking "Point Particle" Explanation

    Ahoy,

    For some time I've been reading through various topics in theses Forums as a Guest, but decided to move beyond that. I'm unfortunately not adept with Science or Mathematics (I'm more adept in Language and in Words), but I've always found them fascinating to me nonetheless and try my best understand them as well as I can. So I thought I would preface my question with the hope respondents keep my general inexperience and lack of knowledge in mind.

    I'd like some explanation on the concept of Point Particles--- dimensions, size, the lack-thereof, etc (analogies would be splendid---as I mention, language and words are more my forte).

    Thanks ahead of time to those who respond and take the time to explain!


    --Andy
     
  2. jcsd
  3. Aug 5, 2009 #2
    Re: Seeking "Point Particle" Explanation

    andy - wikipedia is often a good place to start with this kind of question. a point particle has no spatial dimensions, ie, it occupies no volume. electrons and quarks are considered to be point particles, thus everything which we perceive as matter is composed of particles which have no volume - very fun, huh?
     
  4. Aug 5, 2009 #3
    Re: Seeking "Point Particle" Explanation

    I'm not sure if thinking of particles as points is very useful in quantum mechanics.
     
  5. Aug 5, 2009 #4
    Re: Seeking "Point Particle" Explanation

    The apparent volume of matter comes from the interaction of the electromagnetic, strong nuclear and weak nuclear force through mediating force carrier bosons. Not from purported zero dimensional point particles.
     
  6. Aug 5, 2009 #5

    ZapperZ

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    Re: Seeking "Point Particle" Explanation

    So what is the volume of, say, the free particle when you start solving the free particle Schrodinger equation at the beginning of a QM course?

    Zz.
     
  7. Aug 5, 2009 #6
  8. Aug 5, 2009 #7

    DrChinese

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    Re: Seeking "Point Particle" Explanation

    Please remember that the Heisenberg Uncertainty Principle (HUP) is at play with quantum particles. A fundamental particle (say an electron) has no constituent structure and behaves "as if" it is a point particle. (Theory gives us that as well.)

    You could say it has no volume (because you can confine it to any arbitrarily small volume of space). Or you could say it has a large volume (because it has a precise momentum). But quantum particles most definitely exist, by the usual meaning of the word.
     
  9. Aug 5, 2009 #8

    ZapperZ

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    Re: Seeking "Point Particle" Explanation

    Maybe you should turn things around and ask yourself "what do I mean when something has a volume?"

    Do you think in classical ways in which an object has definite boundary of occupation in space? Think about it! It certainly looks that way with your eyes, but what if you look at it using an electron microscope? Or what about using an atomic force microscope? Do those "definite boundaries" look definite anymore? So what "volume" are we talking about then?

    You are trying to force a square object through the round hole. Rather than looking at the square object, you are complaining about the round hole. Same thing here. Maybe your concept of a "volume" really has no meaning at that scale. So trying to force it down to where it doesn't belong can easily be the problem!

    Zz.
     
  10. Aug 5, 2009 #9
    Re: Seeking "Point Particle" Explanation

    "Do you think in classical ways in which an object has definite boundary of occupation in space? Think about it! It certainly looks that way with your eyes, but what if you look at it using an electron microscope? Or what about using an atomic force microscope? Do those "definite boundaries" look definite anymore? So what "volume" are we talking about then?"
    ZapperZ
    But isn't that indefiniteness a result of our technical inability rather than an objective trait of the object? If an object has an actual indefinite boundary would that not mean... well.. suppose I draw a line and have a particle that we call A. Then A would be on one side of the line and also the other. I realize that this has similarities to QM but that still leaves QM as something that cannot be understood. By understood I mean this; if I create a geometry based on the principle of a square circle and am able to make predictive computations with that geometry can I really be said to know what a square circle is?
     
  11. Aug 5, 2009 #10

    ZapperZ

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    Re: Seeking "Point Particle" Explanation

    So you think an atom has a definite boundary, and that the "fuzziness" is simply due to our technical inability?

    Zz.
     
  12. Aug 5, 2009 #11
    Re: Seeking "Point Particle" Explanation

    Or is QM not about "whats out there" but how we can get what we want from reality? We want to be able to make predictions and if we do, it does not matter if the model violates logic . I am asking a question about QM that has bothered me for quite some time. Does QM tell us anything about reality or is it only about making predictions. I realize that "making predictions" says something about reality (future reality) . But to me its like knowing how to do math without knowing why the math works.
     
  13. Aug 5, 2009 #12

    ZapperZ

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    Re: Seeking "Point Particle" Explanation

    Aren't you in the wrong thread to ask these questions? Did you forget where you were? Thread hijacking isn't exactly allowed.

    Zz.
     
  14. Aug 5, 2009 #13
    Re: Seeking "Point Particle" Explanation

    On a personal level I'd love to understand something that violates normal logic. I have even heard about paraconsistent logic. But I have also heard what to me are contradictory claims. 1. There is nothing fantastic* about QM and 2. That A does not necessarily = A.
    * By fantastic I mean anything beyond human understanding.
     
  15. Aug 5, 2009 #14
    Re: Seeking "Point Particle" Explanation

    You don't have to get angry. So you are saying that asking if QM describes reality or is only a system for predicting results belongs in the philosophy section? This is directly related to the point particle concept.
     
  16. Aug 5, 2009 #15

    ZapperZ

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    Re: Seeking "Point Particle" Explanation

    I said "wrong thread", not wrong sub-forum.

    This thread has a specific topic. You are trying to derail it with a different topic.

    Zz.
     
  17. Aug 5, 2009 #16
    Re: Seeking "Point Particle" Explanation

    I think that "trying to derail it" is a bit strong. I was trying to respond to your question," So you think an atom has a definite boundary, and that the "fuzziness" is simply due to our technical inability?" Basically, I was asking is the 'fuzziness' actually there or only a useful model that aids calculations.
     
  18. Aug 5, 2009 #17

    ZapperZ

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    Re: Seeking "Point Particle" Explanation

    You did not answer my question. Do you think an atom has definite boundary or not the way you see the volume of a block of wood?

    Zz.
     
  19. Aug 5, 2009 #18
    Re: Seeking "Point Particle" Explanation

    I would say that if an atom does not have any clear boundaries then in that "fuzziness" area one could say that yes this area is part of the atom and not part of the atom. A is A and not A. Of course I am not saying that that is not the way it is. I am only saying that if a lack of boundaries is an objective fact ( and not the result of our technical inadequacies) then it is something that we humans cannot conceive of.
     
  20. Aug 5, 2009 #19

    ZapperZ

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    Re: Seeking "Point Particle" Explanation

    Er... You HAVE seen the wavefunction for, say, the hydrogen atom before you wrote this, haven't you?

    For example, look at the s-orbital. Where do you think it "ends"? And where do you think the "boundary" of that atom is? And where is the "technical inadequacies" here?

    And in case you missed it the first time around, here is our https://www.physicsforums.com/showthread.php?t=5374". Pay particular attention to our policy on speculative post.

    Zz.
     
    Last edited by a moderator: Apr 24, 2017
  21. Aug 5, 2009 #20
    Re: Seeking "Point Particle" Explanation

    So, if an object does not have a clear boundary then there are parts of it that are part of the object and not part of the object? So you are saying in the example you gave "there are parts of the wavefunction that are part of the wave function and at the same time not part of the wave function? "If you say "NO" to that then you are saying," at every point in the area under viewing it is clear that that point is part of the object or is not a part of the object. That is a clear boundary. Yes, even when looking at a photo I have difficulties telling if the photo is blurred ( technical difficulties) or that the object does not have clear boundaries. But that is a red herring or at least I do not know why you mentioned it. As for speculation, so no new ideas or new questions allowed?
     
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