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US Objects To the Kilogram
Velcroman1 writes "For 130 years, the kilogram has weighed precisely one kilogram. Hasn't it? The US government isn't so sure. The precise weight of the kilogram is based on a platinum-iridium cylinder manufactured 130 years ago; it's kept in a vault in France at the International Bureau of Weights and Measures. Forty of the units were manufactured at the time, to standardize the measure of weight. But due to material degradation and the effects of quantum physics, the weight of those blocks has changed over time. That's right, the kilogram no longer weighs 1 kilogram, according to the National Institute of Standards and Technology. And it's time to move to a different standard anyway. A proposed revision would remove the final connection to that physical bit of matter, said Ambler Thompson, a NIST scientist involved in the international effort. 'We get rid of the last artifact.'"
It clearly states this is an international effort, and the objection is not the the unit 'kilogram' but rather to using a decaying (however slowly) object as the reference mass.
Newton is a weight. The summary (and the Fox article) are incorrect, while the NIST article correctly refers to the reference mass.
MJC
and misses the point. The variability of the kilogram standard is a scientific and engineering concern, not a political one.
Wikipedia discusses the issue: http://en.wikipedia.org/wiki/Kilogram#Proposed_future_definitions
In a nutshell - in order to create 1 kilogram physical standard masses, you have to first know what a kilogram IS. The physical standards referred to in the article do not appear to have retained constant mass over time. You can't define a constant based on something that is variable, so the current masses are (as I understand it) acknowledged to be an inadequate basis for the definition of the unit. The problem arises when you try to pick something to define it with that is both stable (i.e. a fundamental property of the natural laws of the universe) and practical (can actually create one to use as a practical mass standard against which you can prepare working standards.)
From articles that have popped up about this over the years, my guess is they will have to pick something as a basis and then work on various practical techniques to get as close to that ideal as possible - the question is what specifically to pick. N Carbon atoms? N Si atoms? What are the pros and cons when trying to physically create something that represents those numbers? How stable will a standard created according to a chosen standard be over time? (I.e., how often to we have to make new master standards? It's an important question - obviously the existing masses were not chosen with the expectation that their mass would vary with time, so how do we know to trust a given solution?)
So it's not the US objecting to the kilogram as a unit, but rather concern over the methods used to DEFINE the unit. That's something quite rational, not specific to the USA, and of scientific interest. Editors, how about changing the title to "US to Propose New Method of Defining a Standard Kilogram" instead?
"I object to doing things that computers can do." -- Olin Shivers, lispers.org
Ain't no such thing, or else something as basic as an electronic weigh scale wouldn't work. To rephrase: solid metals are compressible enough to measure the effect (strain) due to very reasonable external loads -- you'd think that liquids would be, too. And yes, they are.
Bulk modulus of steel, commonly strain gaged in weigh scales: ~160 GPa
Bulk modulus of water: ~2.2 GPa.
Water is on the order of 100 times more compressible than steel. Yet steel's and similar metals' compressibility (modulus) is routinely used in measurement applications!
Now to give you an idea of how compressible metals are: a soft iron sphere with a single strain gage bonded to it will give you, IIRC, 1m depth resolution if you hook it up to reasonable digital strain meter. I did the math once on Yahoo Answers somewhere, don't have the link handy.
Don't believe all they tell you in grade school for a lot of it is bullshit.
A successful API design takes a mixture of software design and pedagogy.
The entire point of redefining the kilogram would be to allow any sufficiently-technical laboratory to make their own mass. Right now, there are forty artifacts that must be kept safe. If you do not have one of these artifacts, you in fact have no way to determine what your kilogram actually is. Hell, the artifacts probably do not even have the same mass as each other. So they are proposing to replace a few sets of metal with an instruction manual on how anyone with the right technology can make their own reference weight. That's a huge difference.
A NYC lawyer blogs. http://www.chuangblog.com/
http://en.wikipedia.org/wiki/Binding_energy#Mass_deficit
Essentially a sphere will be created of a specific isotope of silicon and a specific diameter. This sphere will have a known number of atoms. This is superior not only because of degradation of a physical standard, but also because it will be easier to create a standard from basic principles using appropriate lab equipment.
The US is quite late in it's objection as the problem has been known and accepted for many years. TIme and distance is essentially measured with light, and only the kilogram still has a physical representation.
It is probably a simple matter for the US to accept the new standard.
"She's a scientist and a lesbian. She's not going to let it slide." Orphan Black
The Avogadro project (the thing in your link) has been going on since 2007.
The NIST (the U.S. measurements standards body) provided an implementation of another possible solution to the problem in April of 2007.
To say that the U.S. is just now objecting is inaccurate.
To say that the U.S. is late in its objection ignores the fact that the U.S. has been working on the problem with international standards bodies for many years.
What (unsurprisingly) the Fox News article gets wrong is that the NIST is not submitting a formal objection.
The Consultative Committee for Units (one of the advisory groups for CIPM), of which the NIST is a member, has submitted a formal resolution to change the definition to the CIPM. The CIPM is about to submit that resolution to the CGPM, which is the international body that regulates these definitions.
Darth --
Nil Mortifi, Sine Lucre