
 Restless Mass 
  This is consistent with the previous result, i.e., the rest mass of two particles in equal and opposite motion about the center of the configuration is simply the sum of their (transverse) relativistic masses, i.e., the sum of their energies. 
  However, it does not follow that the components of its energymomentum vector are all zero, because the Minkowskian norm is not positivedefinite. 
  The Minkowski norms of each of these vectors individually are zero, but the sum of these two vectors is [2E, 0, 0, 0], which has a Minkowski norm of 2E. 
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