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What accounts for invariant mass' confinement to less than c motion?

  1. Apr 19, 2010 #1
    Hi, hopefully this isn't a dumb question. I've read essentially that in the center of mass/momentum frame an object has invariant mass, and that the system's total mass will be composed of the constituent particles' masses and any other kinetic and potential energies within the system. I also think I know that these various forms of rest mass are interconvertible with kinetic photon energies that can be radiated away from the system should the particles be annihilated. I guess what I'm trying to ask is, what's the mechanism that determines a particle having rest mass and, hence, occupying space and time sublight.

    Anyway, I hope this is phrased correctly and is factually meaningful. Thanks for any answers!

  2. jcsd
  3. Apr 19, 2010 #2


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    In SR, particles have this attribute we call mass which we can ascribe a number to and we can see how these particles move. The question of why particles have mass is not asked in SR. This question is a question asked in the Standard Model of quantum mechanics.

    The currently best accepted model is the Higgs mechanism. Perhaps you will enjoy a read in wiki: http://en.wikipedia.org/wiki/Higgs_mechanism

    The Higgs boson which mediates this mechanism has not yet been detected...its detection is one of the primary goals of the LHC.
  4. Apr 19, 2010 #3


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    In SR there is no reason for or origin of mass.

    SR is based on a certain SO(3,1) symmetry structure of spacetime. The same symmetry applies to energy E and momentum p. Due to that symmetry the "length" E² - p² = m² is invariant, that means it has the same value in all reference frames.

    This means that for each particle both energy E and momentum p are velocity-dependent (that means relative as they depend on the velocity of the particle measured in a certain reference frame), but nevertheless that this invariant "length" characterizes the particles uniquely. Measured in the rest frame and using the well-known relation E = mc² one finds that this invariant is nothing else but the particle's rest mass.

    But SR only requires that this m² is invariant; neither does the theory fix its value nor does it explain its origin.
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