Kilogram Reference Losing Weight

Marc

Hunkered Down for the Duration with a Mask on...
Staff member
Admin
#1
A story on CNN says that 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.
 
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D

DsqrdDGD909

#2
I'd love to see the MU calculations on those.

Experts Urge Redefinition of the Kilogram


Shown above is the U.S. National Prototype Kilogram, which currently serves as the nation's primary standard for measuring mass. It was assigned to the United States in 1889 and is periodically recertified and traceable to the primary international standard, "The Kilogram," held at the Bureau International des Poids et Mesures near Paris.

© Robert Rathe

It’s time to replace the 115-year-old kilogram artifact as the world's official standard for mass, even though experiments generally thought necessary to achieve this goal have not yet reached their targeted level of precision. That's the conclusion of an upcoming Metrologia journal article* authored by five eminent scientists from the United States, United Kingdom and France that was discussed at a scientific meeting of the Royal Society of London on Feb. 14-15.

The authors of this Metrologia paper suggest replacing the kilogram artifact—a cylinder of platinum-iridium alloy about the size of a plum—with a definition based on one of two unchanging natural phenomena, either a quantity of light or the mass of a fixed number of atoms.

The five authors, including three from the U.S. National Institute of Standards and Technology (NIST), one from the University of Reading in the United Kingdom, and a former director of the Bureau International des Poids et Mesures (BIPM) near Paris, conclude that redefining the kilogram now in terms of an invariable property of nature rather than a material object could immediately have many benefits. For instance, it would improve the precision of certain electrical measurements 50-fold and would enable physicists to make more precise calculations in studying the fundamental quantum properties of atoms and other basic particles. The paper outlines how this could be accomplished without impairing the current international system of mass measurements.

For further information see www.nist.gov/public_affairs/newsfromnist_redef_kilogram.htm.

* I.M. Mills, P.J. Mohr, T.J. Quinn, B. Taylor, E. Williams, "Redefinition of the kilogram: A decision whose time has come," Metrologia, expected online publication, Feb. 2005.
 
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BradM

Staff member
Admin
#3
A story on CNN says that 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.
I wonder how they were able to take into account the changing of standard accuracy. Has it been losing weight, or variance in measurement?

Also, I wonder what kind of material it is made of; that may have something to do with it.
 
M

M Greenaway

#4
Interesting, is there any such thing as a natural constant, or does even the speed of light vary, albeit on a very minute level ?
 

Hershal

Metrologist-Auditor
Staff member
Super Moderator
#7
Actually, the kg is the ONLY one of the 7 base SI units represented by a physical artifact.....the other 6 are all represented by a natural quantity.....

The kg in a few years will join the other 6, and the debate right now is which method to use, or a combination of the two methods.....it is a rather heated debate.....

At that point, the kg, like the meter, will find that the physical representations are SECONDARY standards.

Hope this helps.
 

BradM

Staff member
Admin
#8
Actually, the kg is the ONLY one of the 7 base SI units represented by a physical artifact.....the other 6 are all represented by a natural quantity.....

The kg in a few years will join the other 6, and the debate right now is which method to use, or a combination of the two methods.....it is a rather heated debate.....

At that point, the kg, like the meter, will find that the physical representations are SECONDARY standards.

Hope this helps.
Do tell... I love such heated debates :tg:. Care to share some more juicy gossip?:notme:
 

Tim Folkerts

Super Moderator
#9
Interesting, is there any such thing as a natural constant, or does even the speed of light vary, albeit on a very minute level ?
There are certainly speculations about such changes, but I don't think there has ever been any hard evidence for such a thing. And it would be very hard to detect. All light currently goes the same speed (within any level of measurement we can make). What evidence would lead you to think that it once was going faster, but slowed down?That would be a pretty sophisticated theory & experiment to show a past change.

I wonder how they were able to take into account the changing of standard accuracy. Has it been losing weight, or variance in measurement?
It sounds like the weight loss is relative to the other secondary standards. And that is 50 micrograms out of 1000 g, or 1000.00000 +/- 0.00005, or 0.05 ppm. I don't know if they have a scale that can actually detect that change in absolute terms - it sounds like they only can detect the difference between this standard and the other standards.

Also, I wonder what kind of material it is made of; that may have something to do with it.
It is an alloy (Pt-Ir) that is supposed to be extremely inert to oxidation, and also fairly durable, so bits won't "rub off" when being handled.

Compared to the other fundamental metric quantities, this is an antiquated standard. If the metrology institute in France were destroyed, there would be no "official" kilogram. All of the other units can be recreated by labs around the world and no one place houses "the" standard. The kg is the only physical object still used as a fundamental definition.


Tim F
 

Stijloor

Staff member
Super Moderator
#10
Compared to the other fundamental metric quantities, this is an antiquated standard. If the metrology institute in France were destroyed, there would be no "official" kilogram. All of the other units can be recreated by labs around the world and no one place houses "the" standard. The kg is the only physical object still used as a fundamental definition.


Tim F
Hi Tim,

We better be nice to the French...imagine life without the "kilogram." :D:D

Stijloor.
 
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