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Need help with understanding a Weinberg article

  1. May 2, 2010 #1
    Hello !

    In an article (Einstein's mistakes) published in 2005 in "Physics Today" by Steven Weinberg,

    he says:

    even so, einstein would still probably be unhappy with today's theories, because they are not unified with gravitation and because matter - electrons, quarks and so on - still has to be put in by hand

    Can anyone tell me what the physicist meant with "matter still has to be put in by hand" ?

    I'm not a physicist.

  2. jcsd
  3. May 2, 2010 #2


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    Welcome to PF!

    Hello fsoica! Welcome to PF! :smile:

    Physicist would prefer a theory that predicts what the masses of the elementary particles will be, and also various other constants.

    For example, theories predict that the electric charge of an electron is the same as that of the proton, but they do not predict what the mass of the electron is, compared with the mass of the photon.

    For another example, the "fine structure constant" is approximately 1/137, for no appparent reason.

    In other words, the ratio of charges of the electron and the proton (ie, 1) come out of any theory of physics, but the ratio of masses of the electron and the proton, and that figure of 1/137, have to be "put in by hand" into any theory … there is no reason why a theory should have any particular value for them. :wink:
  4. May 3, 2010 #3
    Tks. a lot tiny-tim.

    It's nice for me to be here and it's a nice feeling to know that there's a place where people are eager to help you clarify such ideas...
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