A short survey of Mass & Energy

. . . . relativistic mass rather than rest mass should be considered as the successor to mass in classical pre-relativistic mechanics.

. . . . the m in E=mc2 represents relativistic mass and not rest mass. If one sees this m as rest mass an incorrect idea emerges from the relation E=mc2. A professor at Leiden University who sees this m as rest mass wrote in his lecture text (see page 11):
"Mass is energy in the rest frame. Energy is conserved, mass is not. Mass can come into existence and can perish."
This quotation states that mass and energy are not equivalent. Yet numerous text books state that mass and energy are equivalent. This contradiction disappears when m is seen as the relativistic mass.

. . . . statements such as "mass can be converted into energy" are incorrect. The liberated energy has exactly the same mass as the mass that seems to have disappeared. See for example page 27 up to and including page 30, including footnotes.

. . . relativistic mass obeys Newton's three laws, so Newtonian and relativistic dynamics appear to be one and the same, once we accept that fields also have relativistic mass. See page 27 up to and including 34, including footnotes.

. . . . Some physicists confuse rest mass and rest mass sum. At the same time, they say that only rest mass has to be seen as mass, while relativistic mass is a misleading (or a confusing or even a wrong) concept, because rest mass is a relativistic invariant whereas relativistic mass is not. However, rest mass sum is not a relativistic invariant. See page 69 and 70. Thus, by referring to "rest mass" when they actually mean rest mass sum, they render the premise of their argument for not using relativistic mass invalid (on top of the fact that the logic of their argument is flawed).

. . . the centre of mass can be used in relativistic mechanics as a useful notion. Until now it has taken French leave with the coming of relativistic mechanics. See page 53 to 64.

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