Ingvar, (01)
The important point for the UoM is that we agree that the details
of the physical theories are not relevant to the ontology: (02)
IJ> Nonetheless, I am of course of the opinion that this is not
> something that computer ontologists should worry about. (03)
In any case, I certainly admit that the definitions of the physical
units normally uses theoretical terminology of the time when the
definition was stated. But I would claim that those definitions
can be mapped to experimental methods that do not depend on the
theory. (04)
> The meter is defined as "the length of the PATH TRAVELLED BY LIGHT
> IN VACUUM during a time interval of 1/299 792 458 of a second"....
> If, somewhere in the future, physicists will come to the conclusion
> that this is not completely true, then the definition will in all
> probability be modified. (05)
I certainly agree. But note that the first sentence can be restated
in terms of the technology in use at the time the definition was made.
Whatever future discoveries change the assumption about the speed of
light, they would undoubtedly use technology and conditions far
beyond anything possible at the time the above definition was stated.
Therefore, they would not have any effect on the length of the meter
that was measurable at the time of that definition. (06)
> The ampere is defined as "that constant current which, if maintained
> in two straight parallel conductors of INFINITE LENGTH, of negligible
> circular cross-section, and placed 1 metre apart in vacuum, would
> produce between these conductors a force equal to 2 x 10-7 newton
> per metre of length". No one has ever made an experiment with
> "conductors of INFINITE LENGTH". (07)
I agree. But I would claim that the above definition is flawed
because it depends on the terms 'infinite' and 'negligible'. (08)
To be precise, the standards documents that include such definitions
should clarify limit terms such as 'infinite', 'negligible', 'vacuum',
and 'absolute zero'. They can be replaced by limiting statements: (09)
1. 'infinite length' means a length that is sufficiently long that
no further increase has a measurable effect. (010)
2. 'negligible' means sufficiently small that no further decrease
has a measurable effect. (011)
3. 'vacuum' means sufficiently rarified that no further decrease
has a measurable effect. (012)
In short, all such definitions should be modified to indicate
a procedure for showing how the unreachable limit term can be
approximated while still allowing for improvements in the ways
of determining what is measurable. (013)
John (014)
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