
Re: Metric Time (was Re: Why not 13 months? (Was La Systeme Metrique))
Richard Ottolini (stgprao@seismic.sugarland.unocal.COM)
11 Oct 1995 13:04:45 GMT
In article <DG9K8B.LCH@cwi.nl>, Dik T. Winter <dik@cwi.nl> wrote:
>In article <813358833snz@foxhouse.demon.co.uk> Fred@foxhouse.demon.co.uk writes:
> > The metre, however, is a contrived unit of length  an abstract
> > concept, which is DEFININED very, very precisely. You may 'know
> > the metre to a very high precision', but that knowledge is the
> > definition...
>
>You are wrong. The definition of the metre is exact (mumble mumble times
>the distance light travels in a vacuum mumble mumble in one second). As
>the speed of light is only known to a high precision the actual value of
>the metre is also only known to a high precision; but its definition is
>exact. (Of course the definition can change as it has done at least two
>times.) If the definition was only very precise the definition would
>contain the word "about" at least once.
Constants are redefined in terms of ones that can be more precisely measured.
Most 20th century physics points to the speed of light being a constant.
Time cycles can now be measured to about one part in 10^14 with a possibility
of 10^20. This good enough to measure interplanetary distances to centimeters.
The old meter was first a fraction of the earths circumference, then a
physical object reference. However, the length of that physical object could
in no be measured as precise as time cycles, besides the length varying with
minute changes in environment. Therefore the length can be measured to greater
precision if measured with respect to light.
