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Exact Description of Properties: Spin, etc.

  1. Nov 30, 2015 #1
    I'm looking for a description of properties such as colour and spin.

    Because we are warned these words do not describe the reality of the particles. i.e. an electron is not 'spinning' up or down.

    They are just handy words. Labels. So quarks are not 'up' or 'down'.

    When I read that electrons moving through a particular magnetic field are deflected either up or down then I understood all that I wanted to know.

    I'm looking for similar simple explanations of what experimentalists have found that led them to eventually give these labels.

    Do I make myself clear? I realise I maybe don't. I just want that little bit more background or explanation of things.

    Is there a place where I can read that?
  2. jcsd
  3. Dec 1, 2015 #2


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    While you're at it, you can also ask for more everyday properties like mass and charge !

    This isn't to give you a corny answer: if you realize that the properties you mention do not really differ fundamentally from those more familiar ones, you gain an insight: properties are assigned to help us describe behaviour in nicely compact formulas. No more, no less.

    :smile: disappointed ? or enlightened ?
  4. Dec 1, 2015 #3
    Not disappointed except in myself. I am a poor communicator and I've demonstrated it once more. I don't put my questions correctly.. Always reminds me of the old saw "Know the answer? I don't even know the question."

    I'll try putting it this way:

    What did the experimenters observe that gave rise to knowledge labelled as, for instance 'Up quark', 'Down quark', 'Strange quark' ?

    Not to confuse things but to try to further elucidate:

    In the same way as experimenters observed the branching of a flow of electrons through a special kind of magnetic field so's they collected at two locations, one above the other - giving rise to the notion of 'spin up' and 'spin down'.

    And then an explanation could go further by describing how the 'spin' idea itself is based on an analogy of spinning particles having a magnetic field etc... culminating perhaps in describing how this is actually not a valid analogy... but all beyond what I'm asking for. Just the first bit would do me.

    p.s. mass and charge I can just about figure out for myself, I think. Kick a rock like Sam Johnson or just touch my own body, there's mass. Generate electricity and note the varying strengths of the electricity generated, there's charge. Similarly I've been familiar all my life with magnets, haven't we all, so there's magnetic field and force.
  5. Dec 1, 2015 #4


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    Well, now that you yourself have come up with a nice link between the 'spin' quantum number and the perception of a spinning particle (that, for all we know has size zero...):

    In another century the appearance of more and more kinds of 'elementary' particles led to the emergence of the notion of isotopic spin as " 'not spin' and not an angular momentum, but describable with a similar formalism". Beautiful models with symmetries (and -breaking), multiplet structures, conservation laws (with their violations, of course) and what have you.

    And nowadays the 'up' and 'down' quark names remind us of all that. But I don't think there is much 'up'-ness to the up quark, or 'down'-ness to the down quark! And sure enough, when hadronic particles appeared that didn't fit this, that was strange ! Another quantum number saw the light!
    By the time up, down and strange were not enough any more, physics was in need of new names for the new flavours and didn't bother too much about analogies with acrobatics of spinning billiard balls.

    I grant you that what I'm describing is an experimenter's view, so I hope to be corrected by folks in the know:
    we haven't got a clue what it actually is that we are describing so exactly, but describe it we we sure can, and most of the time darned accurately!

    And your communication skills are just fine :wink: as far as I can estimate.

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