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Position of elementary particles

  1. Mar 23, 2007 #1
    My teacher told me that elementary particles don't have position. Well, I don't understand this; it's like an oxymoron to me. Anyone with a easy-to-understand explanation?
  2. jcsd
  3. Mar 24, 2007 #2
    What your teacher is talking about is something called the uncertainy principle. What that says is that for a subatomic particle (uncertainy of location X uncertainy of momentum) >= constant. In other words, you can't know the exact location or momentum of a particle. And as the uncertainy of momentum goes down, the uncertainy of location goes up and visa versa.

    This means that we can't peg a subatomic particle at exactly one location. There is a limit of uncertainy that can't be passed. Sure they have position, but the position is smeared.
  4. Mar 24, 2007 #3


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    Actually, we need to be careful with this. Your teacher is describing the uncertainty principle, which is often misunderstood. The reason why I say this is because many elementary particles, such as an electron, CAN have a definite position. When an electron hits a screen, it makes a DOT, and you have already determined that the electron had that position.

    The uncertainty principle indicates our ability to PREDICT the relevant measurement under identical conditions. It doesn't say that a particle doesn't have a "position". It does. It is just how well we can tell the position measurement would turn out if we happen to know its momentum before hand.

  5. Mar 25, 2007 #4
    Your teacher told you that the particles in QM (every particle, not only elementary) are fields and therefore in general have infinitely many positions. As interested_learner and ZapperZ explain to you, in the specific physical situation it may be just a single point in space(position). Today experimenters may show to you the detailed picture of the single electron/photon with any precision you will require.

    Last edited: Mar 25, 2007
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