[Still off-top] Physics [was Requests author discusses MentalHealthError exception]

[Marko Rauhamaa]

Oscar Benjamin <oscar.j.benjamin at gmail.com>:

> The mass is carried by the new particles. The new particles may have a
> total *rest mass* which differs from the total rest mass of the
> previous particles. However the total mass is the rest mass plus the
> mass associated with the "kinetic energy" of the particles.
>
> [...]
>
> Mass and energy are not interchangeable in the sense that you can
> exchange one for the other with e=mc^2 giving the exchange rate.
> Rather mass and energy are *the same thing*. Although they are
> different concepts defined in different ways and having different
> dimensions and units they are inseparable: e=mc^2 gives us the
> proportion in which the two appear together.

A physicist mentioned to me that the word "mass" has replaced the term
"rest mass" in modern Physics lingo. That's why you say a photon is
"massless" even though every observable photon has a relativistic mass.
It's all in the terminology.

As for the existence of a negative mass, it is interesting to note that
the (rest) mass of an alpha particle is less than the sum of the (rest)
masses of its constituents. About 1% of the mass is "missing."


Marko