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HUP and the effects of measuring a particle

  1. Jul 7, 2012 #1
    If I want to measure the position of a particle, and to do so I bombard it with a photon. What attributes of the particle will this interaction affect?

    I would think that it could affect both the particle's direction and its mass, which in turn would have an effect on both its position and its momentum. But what I'm not certain of is whether it would affect the particle's speed. I wouldn't think so, but I'm not sure

    As far as HUP is concerned, what are the important attributes that the interaction would affect. Direction? Mass? Speed? Anything else?

    Any information would be appreciated.

  2. jcsd
  3. Jul 7, 2012 #2
    For the first part of your question: it's a tough one, since it depends on how idealized the situation is you're describing. I presume you're talking about non-relativistic quantum theory? In that case the (rest) mass and spin (the total spin, not the projection) of a particle is invariable. Also the charge cannot change. For the rest I cannot think of any quantities that definitely won't change, but maybe I haven't given it enough thought just yet. On first sight I would characterize all the variables that can change as those kinematical in nature.

    As for the HUP: although it is often said, it's never been theoretically argued that the HUP has anything to do with the measuring process itself, i.e. the uncertainty in momentum is not due to the the fact that the momentum of a particle changes when undergoing a position measurement, although it is often claimed in wishy washy books. The HUP is actually a statement about the wavefunction. I'm not saying that in a roundabout way the HUP can't be linked to what you're implying, I'm just saying I have never seen it done (again, in a non-wishy-washy way).
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