Slashdot Mirror
Kilogram Conflict Resolved At Last (nature.com)
An anonymous reader writes: As the capabilities of science and engineering expand, they rely more on the precision of measurements. It's vitally important, then, to make sure the standard units underpinning those measurements don't change. This is a problem for the kilogram. For years, it has remained the only SI unit based on a physical object — a small cylinder of platinum and iridium. Scientists have been arguing about how to replace it for decades, but now it looks like their efforts are finally reaching fruition. They finally have all the data they need to define the kilogram with mathematical constants, which solves the problem of the variability of physical objects. "One method, pioneered by an international team known as the Avogadro Project, involves counting the atoms in two silicon-28 spheres that each weigh the same as the reference kilogram. This allows them to calculate a value for Avogadro's constant, which the researchers convert into a value for Planck's constant. Another method uses a device called a watt balance to produce a value for Planck's constant by weighing a test mass calibrated according to the reference kilogram against an eletromagnetic force." Further research has narrowed down the value of Planck's constant, and experimental data from standards bodies is finally matching up. "If they are proved right, in 2018, Le Grand K will join the meter as a museum piece."
I'm sorry.
Does this mean the US can now join the rest of the metric world, or are we still in the quagmire?
I thought the title read: "Klingon Conflict Resolved At Last"
Keep it rolling...
You're not going to win this one. From the nice Wikipedia article concerning the definition of a foot:
Since 1959, both units have been defined by international agreement as equivalent to 0.3048 meters exactly. In both systems, the foot comprises 12 inches and three feet compose a yard.
It's cylinders all the way down.
Faster! Faster! Faster would be better!
The metric zealots get mad at me for pointing out the points of weakness of the metric system. Here is one I forgot about. Their length unit is based on a physical cylinder of metal. Although it makes sense, since the original design spec apparently was "Make it a little longer than a yard, just to piss of those English bastards."
Perhaps your memory is failing you again..? A metre is defined as the distance light travels in 1/299792458 of a second. Originally, I believe in the 18th century, this was intended to be one ten-millionth of the distance from the pole to the equator. The former is obviously a better definition because Earth is not perfectly spherical.
In any case... Using the term 'metric zealot', apparently un-ironically, right out of the gate - doesn't do your credibility any favours (or it's a deliberate troll; in which case - well done).
If you're a genuine 'imperial zealot' then what, out of interest, is your best pro-imperial argument? I'm curious because as far as I can tell, imperial is shit. And I say that as someone who has had to deal with both systems.
I do not want your cheap brainburning drugs. They are useless for work. And I am a working man today.
Apparently more stable than a block of something which sheds some matter over time, yes.
So, your choices are: 1) measure according to a physical object which can change over time, or 2) measure according to a known set of physical properties which can be reproduced.
And there's nothing to say over time as the science gets better they don't tweak this.
But, in terms of defining in terms of a measure someone can reproduce, it's gotta be better than "1kg is this artifact we made".
I mean, this is what we have now:
So, it's gotta be more stable than an artifact.
Lost at C:>. Found at C.
Sixty octillion one hundred ninety-five septillion three hundred sixty-eight sextillion five hundred forty-one quintillion four hundred seventy-four quadrillion six hundred seventy-three trillion eight hundred twenty-two billion six hundred thirty-one million nine hundred forty-five thousand two hundred ninety-one, sixty octillion one hundred ninety-five septillion three hundred sixty-eight sextillion five hundred forty-one quintillion four hundred seventy-four quadrillion six hundred seventy-three trillion eight hundred twenty-two billion six hundred thirty-one million nine hundred forty-five thousand two hundred ninety-two... shit I lost count.
It goes back further than that. The Mendenhall Order switched the US from having physical reference artifacts for the yard and pound to basing them on the metre and kilogram way back in 1893. The US has been officially metric behind the scenes for 122 years.
When our name is on the back of your car, we're behind you all the way!
what, out of interest, is your best pro-imperial argument?
Personally a fan of Metric, but Imperial does have one major thing going for it - Easy divisibility by low prime numbers.
In the modern world, almost no one "does" math anymore. We use a computer or a calculator, and just get the answer. Shifting up or down by powers of ten makes for convenient readability, but otherwise doesn't matter in the least. Computers would actually work better if we switched to all binary, and wouldn't work any worse if we still used Imperial.
For most of human history, however, having units of measurement easily divisible into 2/3/4/5/6/8/9/10/12/etc parts meant that your average math-illiterate farmer or carpenter could still successfully figure out how to use a pair of oxen to spread four bushels of seed over a virgate (with a peck left over), or five cords of wood into 128 days of winter, and so on. No one cared about the weight of supper in terms of the speed of light in a vacuum, they cared about having enough to heat and eat through the winter.
The (to me dubious) advantage of dividing by low primes pales utterly when you need to quickly calculate how much water you need in your dam to last through winter, or any other quick conversion between dimensions involving volume, area or anything else which is not in discrete units - and since you don't measure oxen or days in meters or kilos I fail to even see how your examples apply.
Plus, plug SI into Metric and quickly, in your head, with only moving zeros calculate how much energy is required to heat some water, from that how long it will take given a specific wattage, or how much a given volume of water weighs (and if you can recall its density, thus how much something else weighs) and from that how much force it will exert on the surface it sits on, and how hard it will hit an object if it falls a certain distance, or pretty much any other physics calculation - with no constants involved for moving in SI (except for material conversion, such as density).
It's simply astonishing how difficult such calculations are in Imperial, and how simple they are in Metric and SI.
Through Paris.
The metre was officially defined as 1/10,000,000th the straight line distance between the North Pole and the Equator, through Paris, France.
It's why everything's in French (why the official term for "metric" is SI, or Systeme Internationale... French!).
Anyhow, the kilogram is the only unit of measure still based on a physical object, something they've been trying to change for decades now. The importance of this is if you can derive all the fundamental units of measure from physical constants, then it becomes a universal system of measurement.
And the reference kilogram has been losing weight, which means all of us have steadily started weighing more and more as time goes on.
so base 210 (7*5*3*2) would be an even better one
This is why the mile is 32*3*5*11 feet. OK, so the 11 is actually in there for different reasons than divisibility: there was a tradition of measuring any goods with 10-20% slop built in for spoilage. For land, a furlong (220 yards) gives you a 200 yard field with room to build a fence or road, and still have room to turn the oxen for the next furrow over. (An acre, BTW, is a rectangle a furlong by a surveyor's chain - a very handy unit for land measurement at the time.)
It's not entirely a coincidence that a furlong is very close to 200 meters. That was a strong influence in making the meter somewhat larger than the yard.
Socialism: a lie told by totalitarians and believed by fools.