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B The cause of mass

  1. Jan 1, 2017 #1
    hey guys,

    what is the cause of mass?

    in my understanding the elementary particles directly derive their mass from the higgs-field, and protons and neutrons get their mass from the (potential?) energy in between the up and down particles chained up within the protons and neutrons. my question is: a. how much of this is correct
    b. I need some sources on this, where can I find them
    c. if this is correct does that mean that I'm heavier when I'm running than when I'm standing still?
    d, and if c is true does that mean that mass is relative since there should not be a preferred frame of reference for things like velocity etc.
    (I know there is such a thing as rest mass but what I mean is, if I measured the mass of something, and someone who is going at 0,1C relative to the measured object measures the mass of something, would they measure a difference?(

    thanks!
    -ganoash
     
  2. jcsd
  3. Jan 1, 2017 #2

    ZapperZ

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  4. Jan 2, 2017 #3

    bhobba

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    Actually I will refer you to Landau's classic:
    https://www.amazon.com/Mechanics-Third-Course-Theoretical-Physics/dp/0750628960

    Here he shows its a result of the principle of least action.

    At a deeper level its related to symmetry (specifically local SU(2) symmetry of so called Dirac spinors), Higgs and all that. The following explains it (see page 139)
    https://www.amazon.com/Physics-Symmetry-Undergraduate-Lecture-Notes/dp/3319192000

    But best to read Landau first.

    Thanks
    Bill
     
    Last edited by a moderator: May 8, 2017
  5. Jan 4, 2017 #4
    I think this popular description is in fact incorrect. It basically says that binding energy of proton is positive. But binding energy of any bound system is negative.

    I'd say that quarks acquire a bit of mass from Higgs (just like electron does), and additionally about 350 MeV of mass from QCD vacuum condensate. When uud quarks combine into a proton, they lose a bit of mass (as they should, since any bound system has negative binding energy).
     
  6. Jan 4, 2017 #5

    Orodruin

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    I think one has to be very careful with such generalisations. "Binding energy" usually refers to the energy required to separate the constituents, which is a meaningless concept in QCD.
     
  7. Jan 4, 2017 #6
  8. Jan 5, 2017 #7
    "Increases the mass" of what? There is no such object as "bare u quark with ~3 MeV mass".
     
  9. Jan 5, 2017 #8
    Last time I checked, we can't fully correctly calculate QCD yet.

    For a long time it was long thought that quarks are asymptotically free, that their interaction strength goes to zero with energy increase (= decrease in distance), but recently lattice QCD results become sufficiently precise and they seem to indicate that at short distances, quark interaction strength tends to a small but nonzero value. And IIUC this is not a problem, actually. Past theories based on asymptotic freedom hypothesis don't actually need it to tend to exactly zero.

    Do we know for sure that energy of proton goes to infinity if you pull its quarks apart? It seems to me that a large but finite value would work too, in practice this would cause the same hadronization as in infinite case, matching observed experimental results.
     
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