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Re: [Phys-L] On 4-velocity, 4-momentum, and E=mc^2 (Was: how Einstein discovered E=mc^2)

Moses wrote:
" . . . Finally, and perhaps most important, [1] is, in turn, corollary of E(v)=m(v)c^2. In other words, these two equations are mathematically equivalent. Therefore, if we accept [1], we cannot discard E(v)=m(v)c^2 as generalized mass-energy equivalence, with mass m(v) being the measure of object's inertia experimentally determined by its acceleration under given force transverse to instantaneous 3-velocity. For those who prefer abstract-mathematical formulations, it may be more convenient to define the rest mass as a numerical factor converting 4-velocity into 4-momentum, whereas the relativistic mass is a factor converting 3-velocity into 3-momentum. As far as we regard 3-velocity and 3-momentum as important physical observables, and want to be consistent, we must attribute the same status to relativistic mass. "
Moses Fayngold,NJIT
Moses, I applaud your cogent observations regarding the usefulness of the relativistic mass concept. The belittling of alternate conceptual interpretations of mathematical models should be anathema in physics discussions - it smacks of the tactic of demonizing opposing views - common in political wrangling. Let us acknowledge the possibility of alternate views and practice the "de gustibus . . ." which we are wont to preach. I find the concepts of time dilation, length contraction and relativistic mass very useful conceptual interpretations of our mathematical models.

Bob Sciamanda
Physics, Edinboro Univ of PA (Em)