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For decades, metrologists have strived to retire ‘Le Grand K’ — the platinum and iridium cylinder that for 126 years has defined the kilogram from a high-security vault outside Paris. Now it looks as if they at last have the data needed to replace the cylinder with a definition based on mathematical constants.
The breakthrough comes in time for the kilogram to be included in a broader redefinition of units — including the ampere, mole and kelvin — scheduled for 2018. And this week, the International Committee for Weights and Measures (CIPM) will meet in Paris to thrash out the next steps.
“It is an exciting time,” says David Newell, a physicist at the US National Institute of Standards and Technology (NIST) in Gaithersburg, Maryland. “It is the culmination of intense, prolonged efforts worldwide.”
[...] In 2011, the CIPM formally agreed to express the kilogram in terms of Planck’s constant, which relates a particle’s energy to its frequency, and, through E = mc2, to its mass. This means first setting the Planck value using experiments based on the current reference kilogram, and then using that value to define the kilogram. The CIPM’s committee on mass recommends that three independent measurements of Planck’s constant agree, and that two of them use different methods.
(Score: 5, Informative) by bob_super on Thursday October 15 2015, @10:16PM
The strength of the metric system is in the easy relationships between units. The metre is not less arbitrary than the foot, but It only takes a few seconds to approximate the weight of that tank of radioactive water being shaken by the earthquake (a daily occurrence, isn't it?)
As far as precision goes, scientists are looking for exact units, even if they are hard to reproduce, because tolerances do stack up, making good calibrations critical.
(Score: 1, Interesting) by Anonymous Coward on Thursday October 15 2015, @10:41PM
Agreed. I think the fundamental length should the the distance light travels in a nanosecond. That's very close to a foot, 0.98357... feet, and it makes the units closer to natural units (where the speed of light is 1).
(Score: 2) by bob_super on Thursday October 15 2015, @10:48PM
On a daily basis, my grandma would prefer to keep the density of milk at about 1. Makes measuring for cakes easier.
1dm3 = 1l = 1kg is nice, a cubic foot of water being about 27kg only helps if you really have a lot of guests.
(Score: 2, Interesting) by Francis on Thursday October 15 2015, @11:27PM
Why would she care about the density? We measure liquids by volume. Things like flour are generally best measured by weight just because they're easily compacted leading to uncertainties in the actual amount there.
And regardless of what system of measure you're using, the density of milk isn't going to be constant. It's going to depend upon the specifics of the milk. Whether you use whole milk or 0% fat milk is going to change the density of the milk, but in both cases the volume would be the same. That's generally why it's best to stick with the same brand and type of ingredients when possible as each brand may or may not act exactly the same way as the other options do. My mother restricts her purchases of flour to one or two varieties for that reason.
(Score: 3, Insightful) by fido_dogstoyevsky on Friday October 16 2015, @04:54AM
Why would she care about the density? We measure liquids by volume.
Not used a modern kitchen balance lately?
It's NOT a conspiracy... it's a plot.
(Score: 1) by Francis on Friday October 16 2015, @02:26PM
How is this insightful? It doesn't in any way shape or form address the question I asked.
For liquids, there's no reason not to use weight as a measure and at least one good reason not to. Weight varies a lot more than volume does globally. Needing to adjust the weights in addition to the other adjustments needed for cooking at various altitudes makes very little sense when it comes to liquid measures. Measuring flour by weight, does makes some sense as I've already acknowledged, but measuring liquids like that is stupid.
(Score: 0) by Anonymous Coward on Friday October 16 2015, @03:13PM
Well, if 1g is approximately equal to 1ml, you can use a scale to measure volume (after zeroing it with the container in place).
(Score: 0) by Anonymous Coward on Friday October 16 2015, @12:21PM
Whatever remains after removing all fat from the milk is not worthy of being called milk any more.
(Score: 3, Funny) by fido_dogstoyevsky on Friday October 16 2015, @04:59AM
I think the fundamental length should the the distance light travels in a nanosecond. That's very close to a foot, 0.98357... feet, and it makes the units closer to natural units ...
Only acceptable if the inch is also defined as 1 decifoot
... (where the speed of light is 1)
In a vacuum, but we'll ignore the spherical chickens as a first approximation.
It's NOT a conspiracy... it's a plot.
(Score: 2) by frojack on Thursday October 15 2015, @11:09PM
Looking for exact units?
The CIPM’s committee on mass recommends that three independent measurements of Planck’s constant agree, and that two of them use different methods.
All of these measurements can easily agree, when you set the precision required loose enough.
Also, in the past, where did they have to weigh these reference cylinders, or the things they were comparing to the cylinders? Altitude plays a part, no?
No, you are mistaken. I've always had this sig.
(Score: 3, Informative) by throwaway28 on Friday October 16 2015, @01:18AM
Altitude plays a part, no?
Balance scales are unaffected by local gravity. Spring scales and electronic scales are affected by local gravity. Some electronic kitchen scales say to recalibrate with a test mass if you change altitude. Looking for a reference to what NIST does, they /do/ measure local gravity when using their watt balance.
Gravity acceleration, g, is determined by a commercial gravimeter [15], which records the trajectory of a corner cube dropped in a vacuum. Figure 10 shows a graph for points from a typical measurement run. The continuous curve is from the tidal effects calculated from U.S. Geological Survey (USGS) software [16] for our location, and must be subtracted from the data to obtain the local average, 9.80101933 m/s2.
(Ok, that's so last year (1998) ( http://dx.doi.org/10.6028/jres.110.003 [doi.org] http://nvlpubs.nist.gov/nistpubs/jres/110/1/j110-1ste.pdf [nist.gov] ), but they probably still do something similar today.)
(Score: 2, Insightful) by Francis on Thursday October 15 2015, @11:11PM
That's not a strength. I continually hear people touting that as a strength, but it's not something that people do very much in the real world and it means that none of the units and sub-units are of convenient sizes. You convert between inches and feet or feet and yards and sometimes between feet and miles. But, each unit itself is something that's actually meaningful.
The foot isn't arbitrary, it's something that's easily related to a body part that nearly everybody has. Yes, people's feet do vary, but you learn what the length of your foot or hand is related to the measure and you have a convenient way of estimating short lengths. Same goes for the comparison between the inch and your fingers.
The meter though is completely arbitrary. It sort of makes sense a little bit on the planet Earth, but nowhere else in the universe does the unit makes sense other than on planets the size and shape of Earth.
(Score: 2) by bob_super on Friday October 16 2015, @12:10AM
The "foot" is longer than most people's feet, by about 50% in the case of average women.
The metre is about the height of a 3-year old, or of your bellybutton. What was your point?
> it's not something that people do very much in the real world
You do need to broaden your horizons. Do you know how to find Liberia and Burma on a map? Go anywhere else.
(Score: 1) by Francis on Friday October 16 2015, @01:40AM
I don't think you know what the word "arbitrary" means. There's nothing about the SI units that's empirical. They were arbitrarily defined and then over time they chose more and more reliable means of defining them so they wouldn't be constantly changing. But, the mass of an arbitrary lump of metal is completely arbitrary. As was the decision to base the meter off the distance from the equator to the North Pole.
Temperature is another one. Imperial measure uses Fahrenheit which hits 100F at about the temperature of the human body. Celsius which hits 0 at the freezing point of water at standard conditions up to 100 where water boils. There's absolutely no good reason for that. If we're going to be objective here, Kelvin would be the one to go with. At least Fahrenheit uses one point that approximates the temperature that people actually use for comparing temperatures. That is body temperature. We all compare temperatures with body temperature to determine whether or not we're comfortable and that's the only measure other than Kelvin that makes any sense.
As far as broadening my horizons, clearly somebody who spent years using SI units in college and then spent a year and a half using them in daily living is the one that needs to broaden his horizons; not the person who doesn't understand what the term "arbitrary" means.
FYI, neither China nor America are metric countries, you might want to actually do some research before making an ass of yourself. China isn't metric because they manufacture a lot of stuff for America, so things like clothes tend to be in imperial measure. America never did away with the imperial measures because we had a functioning system of measure that was enforced. Unlike most of the metric world that went along because they could no longer purchase things in their previous system of measure and couldn't produce enough of it on their own either.
(Score: 2) by bob_super on Friday October 16 2015, @06:05AM
I pointed out how a unit longer than my foot isn't more or less "meaningful" than the distance between the floor and your belly button. You see the meaning you want to see, others used to the other system see their basic unit equally as meaningful. It's arbitrary and it doesn't really matter.
You think the human body temperature is a good 100, many others think that 0-100 as a range for liquid water is pretty darn convenient. Again, it doesn't really matter, you get used to the arbitrary convention. -20 is too cold, and 120 or 45 is too darn hot...
What matters though, is that the metric system is internally consistent. It's 10 of this, or 10^n of that, as specified by the unit's name. Not 12x here, 16x there, 3x for that other, and whatever the F#$& a mile is in inches, or a ton in ounces.
The rest of the world is Metric, except for the UK pining to be different, and whatever needs to be exported to the US (and Liberia and Myanmar, but not for much longer). Sure there are way too many 7-eleven in Taiwan, but they sell metric-labelled products (even if, as a good unofficial colony, they used bloody 110V).
Clothes sizes for women are in an arbitrary ever-changing unit, which puts imperial to shame for resisting evolution. :o)
Men's clothes, in most of he countries I've been to, are in metric.
I've spent well over half of my life outside of the US. "In college" is cute: people keep telling me they've taken a "few years" of one of the languages I speak "back in college", and can't ever remember more than five words of it.
Oh, and Americans shouldn't be allowed to say E=mc2 unless they have memorized the constant that's missing to actually make it correct in imperial units.
(Score: -1, Troll) by Anonymous Coward on Friday October 16 2015, @02:37PM
In other words, you're too stupid to recognize your own ignorance and would rather post elitist bullshit to reinforce the group think rather than admit that somebody else has a point.
And, no, the rest of the world isn't metric. For example China is as metric as the US is, and really, not even as metric. They've got 3 systems of measures that they use, good luck buying clothes there without specifying sizes in inches.
Unlike you, I've used both systems long enough to actually understand how they work and the benefits of doing so. The fact that I've gone back to imperial measures says something about how much metric sucks. There's no reason why I couldn't be doing my cooking and such in metric measures. There are metric cookbooks out there and metric measurement tools out there. I don't generally use entire containers of things when cooking, so I wouldn't be using those.
The fact is, that metric just sucks for cooking and other things that people actually do, and no amount of whitewashing and hand waving is going to change that. The "benefits" that you're relying on are things that people just don't do with any regularity. And in exchange for the "benefits" you wind up with units that are inconvenient and ill-conceived of.
But yeah, feel free to keep drinking the kool-aid there. It's always nice the way you metric boosters can't bother to withhold the anti-Americanist jealousy that we have a working system of measures and aren't interested in converting to such a stupid set of measures.
(Score: 3, Touché) by bob_super on Friday October 16 2015, @05:02PM
> Unlike you, I've used both systems long enough to actually understand how they work and the benefits of doing so.
Somebody doesn't read the threads he/she replies to.
> The fact is, that metric just sucks for cooking and other things that people actually do, and no amount of whitewashing and hand waving is going to change that.
The best part of 7 billion people agree with your point of view, and are awaiting your donations before they starve. Most have spent the last 50+ years hanging on to traditional tins cups so that they can try to pass grandma's recipes onto their children, and praying that the metric police doesn't discover great-grandpa's school ruler behind the firewood stacks. Buildings have been capped off at three stories to avoid the risk of metric-based collapse, and all speed signs are just being ignored for everyone's safety.
You are correct, I'm an idiot.
(Score: 2) by Magic Oddball on Friday October 16 2015, @02:09AM
A few more good examples, though mostly horse-related:
(Score: 2) by tangomargarine on Friday October 16 2015, @02:37AM
What the heck is a "standard furrow"?
"Is that really true?" "I just spent the last hour telling you to think for yourself! Didn't you hear anything I said?"
(Score: 0) by Anonymous Coward on Friday October 16 2015, @06:41AM
About how far oxen can pull a plow before needing a rest.
(Score: 2) by bob_super on Friday October 16 2015, @05:50PM
European Oxen of African Oxen?
(Score: 2) by fido_dogstoyevsky on Friday October 16 2015, @05:14AM
I continually hear people touting that as a strength, but it's not something that people do very much in the real world...
Depends on where you live and what you are doing.
The foot isn't arbitrary
It's defined as 0.3048 metres exactly [wikipedia.org].
You convert between inches and feet or feet and yards and sometimes between feet and miles. But, each unit itself is something that's actually meaningful.
For some arbitrary meaning of meaningful... the width of my little finger is a more useful measure to me than the length of some arbitrary part of my thumb.
It's NOT a conspiracy... it's a plot.