gjphw@ihuxm.UUCP (08/23/83)
Many comments have been made about the proposal to make the definition of
the meter dependent upon the speed of light. I thought that I might offer
some pretty random comments.
The old definition of a second was in terms of a small fraction of the year
1900. So, a very small fraction of the time required for the Earth to orbit
the Sun in the year 1900 used to be the definition of a second. The more
modern definition relies upon a certain number of ticks or activity of an
atomic clock. The difference between the astronomical second and the cesium
second was the reason for the several leap seconds that have been introduced
on WWV in recent years.
The old definition of a meter was the distance between two marks on a bar
kept at the Weights and Measures standards bureau in France. The present
definition relies upon a certain large number of wavelengths of a specific
laser (krypton, I think).
Using these standards for time and distance, the speed of light in a vacuum
can be expressed. But, you will notice, that the standards are somewhat arbi-
trary with the goals of being reproducible and portable. Distance, time, and
speed form an interdependent set of measures. The proposal for using the
speed of light as a standard from which distance can be derived is based upon
the available techniques for measuring time. In other words, time can be more
reliably measured than distance, so now time, and the speed of a well-known
entity, will form the basis for the distance standard.
Finally, the decay of atomic nuclei depends upon the excess energy con-
tained in the atomic nucleus and the so-called weak nuclear force. For the
nuclear decay mode called beta decay (an emission of an electron and a neu-
trino), the expression that provides the decay rate involves a ratio of con-
stants that includes the speed of light. The famous exponential decay law for
radioactivity arises as an approximation from the quantum mechanics of the
atomic nucleus. While I am no longer intimately involved with mainstream
research in physics, my popular level readings in science have made no mention
of anyone actively measuring a change in the decay rates for some common
radionuclides.
'Nough said.
Patrick Wyant
Bell Labs (Naperville, IL)
*!ihuxm!gjphw