Kilogram Reference Losing Weight

doubleacr writes "Ran across a story on CNN that says the "118-year-old cylinder that is the international prototype for the metric mass, kept tightly under lock and key outside Paris, is mysteriously losing weight — if ever so slightly. Physicist Richard Davis of the International Bureau of Weights and Measures in Sevres, southwest of Paris, says the reference kilo appears to have lost 50 micrograms compared with the average of dozens of copies.""

Sublimation?

[Eustace Tilley]

Could it be a few atoms drifting off in the vapor? Well, why wouldn't the copies' atoms be drifting off as well?

Mass?

[forsetti]

High school physics was a while back for me now, but technically, isn't a kilogram a measure of mass? And therefore, if its weight is changing, isn't it actually possible that the mass has remained constant, but the force of gravity has slightly changed in that locality? Of course, other reference masses in the same locality could be used for comparison to determine gravitational fluctuations ... but how does one account for that?

Possible reason?

[robably]

Maybe it's because of where they weighed it - the strength of gravity is not the same all over the planet, and I'm guessing it can change in one place over time due to the movement of the Earth's outer core and give a different result.

The Faster We Go, The Rounder We Get

[Doc Ruby]

By Relativity, we must all be accelerating. How much more energy in the universe does 1:1E9 extra mass represent? Since that's probably more than in the equivalent 50ug, there's probably mass missing from all over the place.

Who's converting our extra mass to energy? This great criminal must be found before we all blueshift past the event horizon!

Or, this is just the greatest museum heist Paris has ever seen.

Re:The metre must be shrinking then...

[LiquidCoooled]

Actually, that might be possible.
Light speed is not constant in a gravitational field, if some of the other posters are correct and the kilogram has changed because of a localised gravitational shift, then its possible that the definition of a metre could also have changed..

Re:Mass?

[edwardpickman]

Technically if the table was higher the weight would be less. The mass is constant but weight is more of an interaction with the Earth's gravity. The higher you go the lower the gravity. The effect is enough to change time measurements on high mountains or high flying aircraft. I doubt there's any equipment sensitive enough to detect weight difference in an object that was moved several feet but there is a change. The shape of the earth is in flux so it's not impossible that that affected it. Gravity isn't even uniform over the surface so a measurement at a 100' above sea level in one location may not be the same at a 100' in another location. The ground would have changed height over a 100 years as well. More than likely it was either a measurement error or handling and gentle wiping of the object would be enough to cause the error. Far more likely than changes in gravity.

Re:The Kilogram is not losing weight

[Entropius]

You could specify the density of water at $PRESSURE and at its maximum density (somewhere around 4 C). The only problem with doing this for high-precision measurements is: what is water? Some fraction of the hydrogen will be deuterium, and that'll throw off the density. What fraction of the hydrogen should be deuterium for "standard water"?

Re:They should redefine a kilogram

[Falladir]

I'm pretty sure that the reason this hasn't been done is that G is not known precisely enough. It's an ironic state of affairs: of all the universal constants, G was the first to be identified (by which I mean that its significance was understood) and measured, and remains the least precisely known.

Re:Before making announcements of this nature...

[aeve]

How about: the other reference copies aren't quite so tightly guarded and occasionally pick up a fingerprint?

Re:Inertia

[Guppy06]

They're working on it. [wikipedia.org]

Re:The Kilogram is not losing weight

[FrangoAssado]

Not an issue, as the average rates of naturally occurring isotopes in the universe is already known (hence the non-integer masses in periodic tables).

Just a small nitpick: that's not the only reason for non-integer masses in periodic tables. When neutrons and protons come together in an atom nucleus, their mass change, and a corresponding amount of energy (E=m*c^2) is released or absorbed. For example, while the atomic mass of Carbon-12 is 12, the atomic mass of Hydrogen-1 (only one proton) is a little over 1.

In effect, that's how nuclear bombs work: when the nucleus of an atom of plutonium breaks up, the mass of the resulting pieces is less than the mass of the original nucleus; the difference is released as radiation and heat.

The funniest part

[aepervius]

Is that the pouind is defined as 1/2.2 Kg. In other word the two last country of earth resisting the introduction of SI, are using SI as reference.... It might be old news for many here, but I can't stop laughing at the irony.