A short survey of **Mass & ***Energy*

In this article I demonstrate that ...

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

. . . . the *m* in *E=mc*^{2} represents relativistic mass and not rest mass. If one sees this *m* as rest mass an incorrect idea emerges from the relation *E=mc*^{2}. 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.

"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

. . . . 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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