Re: [Phys-l] Rest mass again?

[John Denker <jsd@av8n.com>]

On 10/20/2010 06:42 PM, Derek McKenzie wrote:

> I would be interested to know if my thinking is confused on either of
> these points, but at the moment I'm wondering if plain old vanilla
> 'mass' would be a better term.

Mass is undoubtedly the preferred term.


> ...... the term 'invariant mass' seems to me to conflict
> with a genuine geometric model of spacetime. In particular we must
> ask 'invariant with respect to what?'. Presumably, the invariance is
> with respect to a particular class of coordinate systems, but mass
> transcends these coordinate systems.

Like mass itself, the notion of Lorentz invariance transcends any 
"particular class of coordinate systems" ... so I think we are 
entirely safe when we say things like
 -- Mass is Lorentz invariant.  
 -- Mass is a Lorentz scalar.

I don't see any conflict with a fully geometric approach to special
relativity.

It is shorthand to say "mass is invariant" ... but usually it is
obvious from context that Lorentz invariance is intended.  If this
is not obvious from context, for instance if something unusual 
like isospin invariance is being discussed, I would hope that 
authors would have enough sense to avoid this kind of shorthand.