Saturday, May 17, 2008

Weighty Matters

One of the problems I have always had with the so-called "man made global warming" has to do with the accuracy of the instruments used to make the measurements. What good is knowing there is a tenth of a degree* rise in temperature over the last hundred years, if the instruments you took the measurements with a hundred years ago, were only accurate give or take a degree?

A similar dilemma faces scientists today:
GAITHERSBURG, MD. -- Forty feet underground, secured in a temperature- and humidity-controlled vault here, lies Kilogram No. 20.

It's an espresso-shot-sized, platinum-iridium cylinder that is the perfect embodiment of the kilogram -- almost perfect.
In the more than a century since No. 20 and dozens of other exact copies were crafted in France to serve as the world's standards of the kilogram, their masses have been mysteriously drifting apart.

The difference is on average about 50 micrograms -- about the weight of a grain of fine salt. But the ramifications have rippled through the world of precision physics, which uses the kilogram as the basis for a host of standard measures, including force of gravity, the ampere and Planck's constant -- the omnipresent figure of quantum mechanics.

In essence, no one really knows today what a kilogram is.
Just when you thought there weren't enough things in the world to worry about, is our kilogram gaining weight or is theirs losing it?

So, you have two samples, that should be identical, which differ by about the weight of a grain of salt. What to do?
Peter Becker, a physicist at Germany's National Metrology Institute, thinks he has a simpler solution: Count atoms. The idea is to define the kilogram as the number of atoms of a specific element.

Becker's hopes ride on two silvery croquet-ball-sized spheres of the purest silicon that cost $3.2 million to make. They are the roundest objects ever made -- within 30 nanometers of perfection, about the width of a few atoms, he said.
I'm surprised that Congress didn't come up with this solution! Spend $3.2 Million dollars to verify a measurement that used to be:
"...the mass of a liter of distilled water at the temperature of melting ice."
And now we get to the crux of the problem:
"The French government created the kilogram in 1795..."
Ah! That's what we get for trusting the French! Heh.

Cross Posted at Say Anything

*Correction: I meant to say "half a degree". I was thinking about reading tenths of a degree of an old mercury thermometer. I apologize for the error.

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