Why is the kilogram standard mass changing?

[Naty1]

from the current Physicsworld newsletter:

The kilogram is currently defined by a lump of metal in Paris – but now researchers in the UK, France and Sweden have confirmed a key assumption of a new method of defining the standard based on fundamental constants. ...

The kilogram standard is made from platinum and iridium, and is housed at the International Bureau of Weights and Measures (BIPM) in Paris. Over the past 60 years, several comparisons of this kilogram with identical copies suggest that its mass is changing. As a result, scientists have been looking for a new way to define the kilogram using just fundamental constants.

?

 

[Naty1]

Much to my surprise, wikipedia has quite a bit on this subject!

Beyond the simple wear that check standards can experience, the mass of even the carefully stored national prototypes can drift relative to the IPK for a variety of reasons, some known and some unknown. Since the IPK and its replicas are stored in air (albeit under two or more nested bell jars), they gain mass through adsorption of atmospheric contamination onto their surfaces. Accordingly, they are cleaned in a process the BIPM developed between 1939 and 1946 known as “the BIPM cleaning method” that comprises lightly rubbing with a chamois soaked in equal parts ether and ethanol, followed by steam cleaning with bi-distilled water, and allowing the prototypes to settle for 7–10 days before verification.[Note 12] Cleaning the prototypes removes between 5 and 60 µg of contamination depending largely on the time elapsed since the last cleaning. Further, a second cleaning can remove up to 10 µg more. After cleaning—even when they are stored under their bell jars—the IPK and its replicas immediately begin gaining mass again. The BIPM even developed a model of this gain and concluded that it averaged 1.11 µg per month for the first 3 months after cleaning and then decreased to an average of about 1 µg per year thereafter.

But:

What has become clear after the third periodic verification performed between 1988 and 1992 is that masses of the entire worldwide ensemble of prototypes have been slowly but inexorably diverging from each other. It is also clear that the mass of the IPK lost perhaps 50 µg over the last century, and possibly significantly more, in comparison to its official copies.[12][14] The reason for this drift has eluded physicists who have dedicated their careers to the SI unit of mass. No plausible mechanism has been proposed to explain either a steady decrease in the mass of the IPK, or an increase in that of its replicas dispersed throughout the world.[

http://en.wikipedia.org/wiki/Kilogram#Stability_of_the_international_prototype_kilogram

 

[Maroc]

This can change so many things...

 

[Mordred]

I heard this one before, as well as several other articles related to various constants that were thought to be reliable showing slight changes over time. Wish I kept a link of those articles. One was the rate of atomic decay not being consistent ,slowing down faster in the past than now today by a small amount, the other was light speed being faster in the past than now today. Neither article has been able to understand why and therefore have not been able to prove it conclusively. Those articles I read around one year ago haven't seen anything since on either article. may or may not be related

 

[Mordred]

http://news.discovery.com/space/is-the-sun-emitting-a-mystery-particle.html
found one of em the atomic decay rate article.

here is the one for the fine structure constant that's still being debated

http://www.technologyreview.com/blog/arxiv/25673/

http://ldolphin.org/constc.shtml her is one of the articles on light slowing down over the past 250 years

 

[Drakkith]

The reason for the change is that it is a better idea to use something that is constant to the best of our measurements instead of something that is known to vary. The other measurements, such as the second and the meter are all based on constants that don't change according to our current understanding.