Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Structure of the electron

  1. Apr 8, 2007 #1
    I ve got a small question. As I have learnt so far, the electron is a particle with negative charge and it is homogenouus, i mean there's no concept of structure inside an electron. But electrons have spin .. so they must have certain structure ?
  2. jcsd
  3. Apr 8, 2007 #2
    No :smile:
    Point particle fermions must have half-integer-spin, as imposed by the Pauli exclusion principle and the Spin-statistic theorem

    In fact, the measure of the electron magnetic moment if one of the most succesful precision tests of quantum electrodynamics. The proton and neutron on the contrary have a magnetic moment which is not the one of a point particle, this being an early indication of their compositeness.

    So far, we have no experimental clue whatsoever indicating that the electron is not a fundamental point particle.
  4. Apr 14, 2007 #3
    Yes and no. Physics usually reserves the word structure to mean, "the properties of an object can be accurately predicted by assuming it to be composed of a collection of more fundanmental entities".

    Under this definition the electron does not have structure, it's a point particle. But I think you are using the word structure within the broader context, "this object has an interesting property (i.e. spin) and so must have some form of inner complexity". In this very general sense I suppose the answer is yes.

    It's probably true to say that at the very deepest level we do not know the origin of spin.
  5. Apr 14, 2007 #4
    I would rather disagree with this statement, sorry :smile:
    We know very well what the representation of the Poincare group are, and this does not involve quantum field theory, just quantum mechanics. As Weinberg once pointed out (in his QFT books perhpas), if quantum field theory turned out to be wrong, that would be a sensation, but if quantum mechanics turned out to be wrong, that would be a catastrophe.
  6. Apr 14, 2007 #5
    I personnally find it amazing that electrons around atoms absorb and emit photons and yet are still considered to be a fundamental particle. I mean, exactly how could a particle interact with light in such a maner without being made out of it? I predict that electrons are fundamentally bundles of photons that share the same world line.
  7. Apr 15, 2007 #6

    Meir Achuz

    User Avatar
    Science Advisor
    Homework Helper
    Gold Member

    Take a course in QFT. Then predict.
  8. Apr 15, 2007 #7
    Sorry, no. :rolleyes: Photons carry no electric charge !
  9. Apr 15, 2007 #8


    User Avatar
    Science Advisor
    Homework Helper

    Humanino, are you aware of the fascinating results for the apparent statistics of spin-0 and spin-2 particles? Lubos Motl verified by calculation some numerical results in this paper:

    See section 4 page 20. The short version is that the spin-1 and spin-1/2 particles behave nicely with the expected statistics, but the spin-0 and spin-2 particles end up with what Lubos calls "Tripled Pauli Statistics".

    Two differences show up. The first is that they are Fermi statistics instead of Bose. The second is that they are triply redundant in terms of number of states, but still get filled by only a single object.
  10. Apr 12, 2008 #9
    In other words a bundle of non-charged particles, will not result in a particle with a relative charge of -1. An electron is fundamental, this would leave me to believe that it had no internal structure. But hey, 3 years ago I was being taught atoms were fundamental. What is responsible in determining a particles spin? Is there a field that governs this symetry?

  11. Apr 12, 2008 #10
    No specific field. All field obey the same symmetry principle. Lorentz symmetry namely.

    But you can already understand where spin comes from if you study carefully enough the rotation group in 3 dimensions, called SO(3).
  12. Apr 13, 2008 #11


    User Avatar
    Science Advisor
    Homework Helper

    I thought spin for fermions come from SO(2)?

    BTW I remember that I posted here yesterday, I mentioned scattering to a guy who was writing loads of speculations. Was that deleted in some way?
  13. Apr 13, 2008 #12
    Yeah so do I, it must have been removed.
  14. Apr 13, 2008 #13


    User Avatar
    Science Advisor
    Homework Helper

    Maybe because the guy i replied was deleted or similar.. I dont know
  15. Apr 13, 2008 #14
    you mean SU(2) ?
  16. Apr 13, 2008 #15


    User Avatar
    Science Advisor
    Homework Helper

    So the determinant does not have to equal 1?
  17. Apr 13, 2008 #16
    Le me gather my thoughts : SO(2) is the group of rotations in the 2D (real) plan, preserve distances, and have indeed det=1
    SU(2) is the group of special unitary complex matrices, and also have det=1
  18. Apr 13, 2008 #17


    User Avatar
    Science Advisor
    Homework Helper

    Ok, great:-) Thanx!
  19. Apr 13, 2008 #18


    User Avatar
    Science Advisor
    Homework Helper

    btw: Does anyone know what happened to my post I wrote yesterday?
  20. Apr 13, 2008 #19
    Mine also has vanished.
  21. Apr 19, 2008 #20


    User Avatar
    Science Advisor

    Lost one too.

    Basically, I noted that QED, with self energy and vertex corrections, and so forth, require the electron to have structure -- bare vs. dressed. But 1. we don't know how to compute the details of the structure, and 2. we know that a point electron works quite nicely in practice. So, whatever structure there is, is rather subtle.
    Reilly Atkinson
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook