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How do we know all electrons are the same?

  1. Nov 15, 2009 #1
    Today I was reading for my Modern Physics class and something I read struck me in a way. The author claimed that all electrons are identical; they have the same measured mass, electric charge and magnetic dipole moment. This statement bothers me, and I haven't been able to stop thinking about it. So I come to you for some closure.

    How do we know that all electrons are the same?

    I understand that electrons are measured to have the same characteristics, but without infinitely precise measurements we can only be sure to a certain degree.
     
  2. jcsd
  3. Nov 15, 2009 #2

    mgb_phys

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    True, it's more an article of 'faith' that Occam's razor works - with no evidence that electrons differ we assume they are the same just because the universe would be annoyingly complex if they were different.
     
  4. Nov 15, 2009 #3
    We can never prove that something (like a different mass eletron) doesn't exist.

    I suppose particle physics tells us that all fits into a nice grid. If electrons were different we would have to abandon the nice symmetrical model. But usually scientists are successful in assuming that laws of physics should be nice and simple at its core.
     
  5. Nov 15, 2009 #4
    I think the question of “are electrons identical” is a metaphysical question.
     
  6. Nov 15, 2009 #5

    A.T.

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    Electrons are the same per definition. They are part of human made model of reality. And this model says they are the same.
    How is this different from anything in physics?
     
  7. Nov 15, 2009 #6
    We can only be sure of anything to a certain degree. We haven't observed an electron with different mass, charge, magnetic dipole moment, etc. in thousands of experiments carried out in the last few centuries, which all obey the known laws of physics. We have no reason to believe that electrons with different properties exist. Are you asking out of curiosity about the merits of this statement, or because you see a reason why some electrons should be different?
     
  8. Nov 15, 2009 #7

    Vanadium 50

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    I am going to take a different direction. Both thermodynamics and quantum mechanics treat identical particles differently from non-identical particles. If there were two kinds of electrons, that were otherwise very similar in properties (so similar that we can't tell with today's technologies) we'd still know this from the periodic table - helium would be a fairly reactive metal and oxygen would be an inert monatomic gas.

    Since this is not what we observe, we can draw the inescapable conclusion.
     
  9. Nov 15, 2009 #8

    D H

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    Vanadium raised a very good point here. The Pauli Exclusion principle explains why the periodic table is the way it is and explains why elements discovered since 1929 fit in this scheme. If all electrons were not indistinguishable, would the exclusion principle still apply?
     
  10. Nov 15, 2009 #9
    I protest; electrons cannot be identical. I once found an electron in stairwell at 5th and Broadway. Some moments later there was another two floors down. They could not have been identical, but distinct. They differed in position. Not only that, the first was moving a tad bit faster.
     
  11. Nov 15, 2009 #10
    Thank you Vanadium, this is the kind of thinking I am looking for.

    Could you go into some detail about how you arrived at this. I'm afraid I do not know very much on the subject.
     
  12. Nov 16, 2009 #11

    Vanadium 50

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    Because there would be no Pauli exclusion principle between "Type A" and "Type B" electrons, atomic orbitals can hold twice as many electrons. So, helium, instead of having a full shell, would have a half-full shell.

    My description Oxygen includes a mistake. Today it has a full shell + one shell that's missing two electrons. (2+6). It would instead have a full shell + a half full shell and would have chemical properties more similar to carbon. The inert gas would have an atomic number of 4+16 or 20, so it would be calcium.

    The noble gasses would be beryllium, calcium, and halfnium.
     
    Last edited: Nov 16, 2009
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