John Sowa wrote: (01)
> Chris, (02)
> In summary, (03)
> 3. The methods of measurement have improved enormously from
> the 19th to the 21st centuries, and the units such as meter,
> second, ampere, volt, etc., are specified with far greater
> precision, but they are independent of any changes in the
> physical theories. (The kilogram, by the way, hasn't
> changed in any way -- it's still defined by the same lump
> of metal stored in a vault in Paris.) (04)
No, the units are not independent of the state of physics. 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". The definition relies on the
theoretical presupposition that the speed of light in vacuum is constant.
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. Nonetheless, I am of course of the opinion that this is not
somethinng that computer ontologists should worry about. (05)
> Comment about point #3: The reason why the units of measure
> are independent of any theory is that they are defined in terms
> of repeatable physical experiments. The theories that interpret
> the results of those experiments have changed drastically over
> the past 150 years, but every new theory must be consistent
> with the brute facts observed in any repeatable experiment. (06)
No, this is not true without many qualifications that you are not
mentioning. The ampere is defined as "that constant current which, if
maintained in two straight parallell 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)
Ingvar J (08)
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