Re: Gravitational constant.

Starblade Darksquall <[EMAIL PROTECTED]> wrote:

> [EMAIL PROTECTED] (John Devers) wrote in message
 news:<[EMAIL PROTECTED]>...
> > You guys might like the latest on using the Avogadro constant to
redifine mass.
> > 
> > 
> > 
> > Silicon joins race to redefine the kilogram
> > 
> > 
> > http://physicsweb.org/article/news/7/9/9
> 
> See? A kilogram ISN'T some stupid piece of mass located on some
> physical place on earth. It is a REAL thing.

What could be more real than a piece of platinum? I could hit you with
it, and you would feel the consequences as a nasty bump on the head.
It is the replacement (some     e digits on a piece of paper,
or some bits floating around in cyberspace)
which is unreal.

>From a fundamental point of view nothing much is going to change.
After all, the kilogram -is- the mass of a fixed number of platinum
atoms, stored in a vault at Sevres. What is going to change is not the
number, but our knowledge about it.
Redefining the kilogram is replacing one arbitrary standard by another.
This has many practical advantages (reproducibility, portability,
stability, etc), but no conceptual ones.

>From a metrology point of view what is happening is that the accuracy to
which Avogadro's number can be measured will be limited only by the
accuracy to which the kilogram can be reproduced. Claims of this have
been around for some time, but they are still false. There are
systematic, and as yet unexplained differences between results obtained
by different groups. The kilogram cannot be redefined untill these
problems have been resolved. (Or the errors systematised :-)

Best,

Jan