.... Thus
energy (and energy density) go up without mass or mass density changing at
^^^^^^^^^^^^^^^
all. This allows mass to be a scalar invariant of relativity theory
and energy to be one component of the relativistic energy-momentum vector.
....
Please excuse the error. As several posters have noted, of course mass
density goes up by a factor of gamma by Lorentz contraction of the volume.
The line above should read "Thus energy (and energy density) go up without
mass changing at all." ...
A. R. Marlow E-MAIL:
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