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A question about Heizenberg uncertainty.

  1. Feb 23, 2013 #1
    In some QFT books they say:If we consider momentum p of particle being very great,then the physics is at short scale.Then how can we apply Heizenberg uncertainty principle when the momentum p of particle having a certain value?What do they imply when they say that?
     
  2. jcsd
  3. Feb 23, 2013 #2

    mfb

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    p is not an exact value, but for large p (as distribution, if you like) this can be negligible.
    Consider a particle, confined in a space of 1cm: It has a corresponding minimal momentum uncertainty of ~0.1 meV. If the particle has a momentum of 1 MeV (10 billion times more than this uncertainty), you just don't care.
     
  4. Feb 23, 2013 #3
    Is there any relation between great value p and great value of uncertainty in p?This(relation) explains why with the great p we have short scale physics as they say.
     
  5. Feb 23, 2013 #4
    Great value of p is necessary for the great uncertainty in p.

    Let's say, we have a particle with the well-known p, scuttering on the target (also well-known p).
    Therefore there is a big uncertainty in x

    But, after the scuttering, x may get well measured (xspace by affecting the lattice, xtime by energy dissipation), thus p should get big uncertainty.

    In case of almost elastic scattering, xtime remain uncertain, and p uncertainty rely mostly on the angle uncertainty (ptime → E≈const ; px2+py2+pz2≈const)
     
    Last edited: Feb 23, 2013
  6. Feb 24, 2013 #5
    By the way,are there any difference between particle and quantum of field?Do the value of field coincide with the wave function or not?
     
  7. Feb 24, 2013 #6

    mfb

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    Particles are excitations of fields in quantum field theory, but I don't see the relation to the original question.
     
  8. Feb 24, 2013 #7
    Is that correct if I say c[itex]^{+}[/itex]exp{p.x}/vacum> is the value of field of representation of a quantum of field.This quantum corresponds with a particle having the mean value of momentum equalling p.
     
  9. Feb 24, 2013 #8
    I mean a well defined momentum of a quantum of field corresponds with uncertainty of momentum of a particle having that momentum.
     
  10. Feb 25, 2013 #9
    I was wrong!Each ''quantum field value'' corresponds with a plane wave of particle!
     
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