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Thom Baguley
Report 18 years ago
Robert Low wrote:
[q1]> Thom Baguley <[email protected]> wrote:[/q1]
[q2]> >Having two contradictory definitions of the same concept must be logical inconsistent (which is[/q2]
[q2]> >not to say the argument is). The[/q2]
[q1]> That's not the same as having two different notions of mass (in particular, gravitational 'charge'[/q1]
[q1]> and inertial mass) which need not, in principle, have anything to do with each other. It was a[/q1]
[q1]> fundamental problem for a long time to explain the observed strict proportionality between[/q1]
[q1]> gravitational and inertial mass.[/q1]

That's not what I meant - though I explained badly.

[q2]> >argument breaks down unless the "size" of the the joined and unjoined objects is conceptually the[/q2]
[q2]> >same thing.[/q2]
[q1]> No. And, changing domains of discourse, it's not even true in modern physics that the mass of a[/q1]
[q1]> composite object is the sum of the masses of the component parts, if they interact strongly. The[/q1]
[q1]> mass of a deuteron is not the sum of the masses of a proton and a neutron. It is logically[/q1]
[q1]> possible that the inertial masses of the two could add while the gravitational masses have a small[/q1]
[q1]> binding energy deficit (or vice versa). Observationally, this does not happen. But it is not[/q1]
[q1]> inconsistent that it should.[/q1]

OK - it is likely true in the example too - mass is not the simple sum depending on the mechanism of
joining (e.g., the weight of the glue or string used). I meant something slightly different though.
The original verbal description says "small" and "large" object. The appeal to their different
speeds of falling when joined involves an essentialist notion of "size" as opposed to some function
of the original "sizes". They can't both be true unless two different meaning of "size" are used (in
which case the argument is underdetermined).

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