> Just a comment on one point in Ingvar's last note:
>
> On mass:
>> 3. You write: "and in middle school we learn that each kind of such
>> particles has a mass which can be computed as the sum of the mass of
>> its constituents." Not EACH kind of particle. Photons and neutrinos
>> have no mass.
>>
> Photons have relativistic mass, though no rest mass; neutrinos actually
> have
> a very small rest mass (according to the latest info I have). The "mass"
> we
> measure is relativistic mass, and I don't think any distinction is
> required
> in the units ontology (though it would be in an ontology of physics).
> Relativistic mass is a very useful concept because it provides a simple
> definition of 'physical object' as an Object (primitive concept) that has
> some mass; that would include photons and any other fundamental particles
> that have relativistic mass. (01)
I think one should be careful not to make definitions TOO dependent on the
present state of physics. Wikipedia says: "The Standard Model of particle
physics assumed that neutrinos are massless, although adding massive
neutrinos to the basic framework is not difficult. Indeed, the
experimentally established phenomenon of neutrino oscillation requires
neutrinos to have nonzero masses." Since not long ago the standard model
was accepted, and neutrinos regarded as physical objects without rest
mass, physics may also in the future discover particles that they would
like to regard as both lacking rest mass and being physical. (02)
Ingvar J (03)
>
> Pat
>
> Patrick Cassidy
> MICRA, Inc.
> 908-561-3416,
> cell: 908-565-4053
> cassidy@xxxxxxxxx
>
>
>
>
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> (04)
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