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## Kilogram Gets Controversial; Why Not Split the Difference?520

gbrumfiel writes "As Slashdot has noted, the kilogram has a problem. The SI unit is officially defined as the weight of a 130-year-old platinum-iridium cylinder in France. But the physical object appears to be getting lighter. Scientists want to replace the cylinder with a new standard based on Planck's constant, but two experiments designed to facilitate the switch keep coming up with different results. Now one researcher is proposing a solution: just average the two diverging experiments and use that value as the official definition. Not everyone thinks that averaging the two amounts to sound research: 'Deciding to just average these two results would be perfectly proper mathematics, but it would not be science,' says Michael Hart, a physicist at the University of Manchester, UK."
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## Kilogram Gets Controversial; Why Not Split the Difference?

• #### Re:Bread not working? (Score:2, Insightful)

on Sunday January 30, 2011 @07:23PM (#35051646) Journal
Pounds are defined in terms of kilograms, so that's no help.
• #### Re:Impossible (Score:4, Insightful)

on Sunday January 30, 2011 @07:25PM (#35051678)

What I *still* don't get is why we moved away from the ORIGINAL definition of a gram which used to be the mass of 1 cubic centimeter of water. I've heard all the "because this type of measurement was more accurate", etc. explanations but it seems that now they have no idea how to get to where they were whereas(AFAIK) the mass of 1 cubic centimeter of water hasn't really varied. Anyone able to break this down into something that actually makes sense beyond the typical responses?

• #### Re:Can't the kilogram be derived from other SI uni (Score:5, Insightful)

on Sunday January 30, 2011 @08:30PM (#35052092)
A gram is not the mass of 1 cubic centimeter of water. It is 1/1000 of the weight of that lump of metal in france!

There are a ton of posts above arguing over that, and you can't use that to define mass because it is affected by pressure. Pressure has a mass component so it ultimately becomes circular.
• #### And there lies the rub... (Score:4, Insightful)

on Sunday January 30, 2011 @09:37PM (#35052528) Journal

It is a definition with a physical representation. Which is obviously showing changes over time.
And it really shouldn't as it is the physical representation that is being actively used by our society - not the definition.

The point of this article is that they are trying to create a new definition based on a process that would produce an identical physical representation EVERY time the process is run - and the results of which wouldn't change over time.
And failing.

Now, as every scale in the world is NOT calibrated to that prototype kilogram, but to a copy, of a copy, of a copy... Those errors accumulate.
Until one day measurements of some toxic substance/medicinal drug/anything requiring milligram measurement start being significantly lighter/heavier than they should be in the given sample.
Cause we're not talking homeopathy here.

• #### Re:Strange (Score:3, Insightful)

on Sunday January 30, 2011 @10:47PM (#35052894)

Averaging the results of two experimental measurements is not Science, whereas averaging the results of many hundreds of measurements to determine global temperature anomaly is.

Averaging the results of different experiments that consistently give different answers is not correct. Averaging multiple measurements of the same experiment is.

How about an analogy?
You have two rulers, which do not agree. If you measure something with both and then average the result, you get a wrong result - unless the two rulers happen to be out by the same amount in different directions. If one ruler is correct, you've just broken your result.

If you use one ruler then you can average the measurements you take with it, because it's a fair assumption that each measurement will be out by a random amount in a random direction. Then your average is as correct as your ruler.

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