Slashdot Mirror
Kilogram Gets Controversial; Why Not Split the Difference?
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."
The physical object cannot get lighter (less massive). By definition is 1kg no matter how much mass it has. The obvious conclusion is that the rest of the universe is getting heavier.
When our name is on the back of your car, we're behind you all the way!
A physicist, engineer and a statistician are out hunting. Suddenly, a deer appears 50 yards away.
The physicist does some basic ballistic calculations, assuming a vacuum, lifts his rifle to a specific angle, and shoots. The bullet lands 5 yards short.
The engineer adds a fudge factor for air resistance, lifts his rifle slightly higher, and shoots. The bullet lands 5 yards long.
The statistician yells "We got him!"
If Slashdot were chemistry it would look like this:Cadaverine
The differences are so minimal that I can hardly believe it matters. The only issue is if the difference between the new definition and previous measurements is statistically significant. If you can't show that that would be the case, then pick whatever number between the two measurements that is easiest to work with mathematically, perhaps one with the most zeros (in decimal, since the metric system is designed to work well with powers of 10).
Let them eat pounds!
Particles, stuff that matters.
The measure of length called a foot that we use for practical commerce was established in pretty much that way. See the story of the international foot as differed from the different foots which were already in widespread use.
...leaving traces. Over time, changes accumulate.
And when you are measuring something at 9 digits behind the point - a little can be a lot.
http://en.wikipedia.org/wiki/Kilogram#Stability_of_the_International_Prototype_Kilogram
Mit der Dummheit kämpfen Götter selbst vergebens
Why does it sound like that researcher was looking for a quick answer just so he could get to the pub?
It turns out that France imposed a Mass Tax in the last few years which means the cylinder has to cough it up for the good of the state.
On the plus (or more like the non-plus) side, the people of France are now looking fit & trim.
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Why don't they just take the weight of a gram and multiply it by 1024?
Sheesh, evil *and* a jerk. -- Jade
I floated this idea years ago to a few physicists and they hated it for reasons I can't fathom. The whole idea of basing a unit on a single, random object instead of something universal seemed silly to me.
Is a kilogram in terms of fractions of an elephant please?
In this case the background is that the standard for mass, unlike time or distance, cannot independently be constructed in the lab. This means that science and industry are susceptible to two issues. The first is degradation of a physical standard, in this case a hunk of metal in France. The second is that one is dependent on other to create proxies of the standard, and as a result have no true assurance of the accuracy of the standard. A suitable lab with suitable personal can masure time and distance without the need of a proxy manufactured by others, and no dependence on a fixed physical object.. There is a desire for the same to be true for mass.
Second, no one knows if the hunk of metal is shrinking, and if it is how much it is shrinking by. If the experts knew it was shrinking, then they could figure out how to at least partially correct it. The hunk of metal might not be charging at all, or it could be accreating matter. Without an independent standard, which does not apparently exists, as everything is based on the hunk of metal, all there is is guesswork.
The third is the idea that Planck's Constant is being used to create the standard. In fact Planck's constant is one two approaches. The other is to create a sphere from a silicon and use Avagadro's Constant to define the mass. The problem is that these two approaches do no lead to consistant results, with an error about an order of magnitude large than the expected error.
The issue with averaging is that while one does average within a result, and even results that are taken from similar procedures, it is unclear that averages in this case is suitable. It seems to me that the results point to an interesting area of research, and rather than just averaging, more work should be done understanding the inconsistency. If it is not random error, and not an artifact, then something really fascinating might be going on.
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The one that gets us more drugs!
How do they determine the mass of their 1Kg reference?
Is it simply by measuring the force it exerts when influenced by a gravitational force of 1G?
If so, how do they measure to ensure that 1G is still the same acceleration that it was when the standard was introduced?
Do they also allow for the fact that it is displacing a certain amount of air -- and therefore is subject to the forces of buoyancy that will tend to make it lighter, depending on air density, humidity, etc?
While the predominant factor is the mass of the earth, what about other factors such as the gravitational field of the moon (large enough to induce tides of several meters in magnitude) and other celestial bodies?
Trying to measure an absolute through the use of a another absolute is fine -- but how do you factor in the variables that also have an effect?
I'm sure they know what they're doing.
I'd have thought we'd have an experiment that comes up with say 0.3464kg and another that comes up with 0.0765kg, and they want to define the kilogram as 1/0.3464 * the result of the first one or 1/0.0765 * the result of the second one. But both of these would give exactly the same mass as the other.
Or if the measurements are inconsistent, they should just pick the one with the smallest variance within that experiment.
Clearly I'm missing something here.
A mathematican, an astrophysicist and a statistician were walking along a road in Scotland. They saw a black cow. The astrophysicist said, "All the cows in Scotland are black". The statistician said, "No, there is at least one black cow in Scotland". The mathematician said, "All we now know is, this side of that cow is black."
sed -e 's/Chuck Norris/Rajnikant/g' joke > fact
If the argument is that the average is "good enough" because the level of precision practically doesn't matter, then we can refer back to seventh-grade chemistry and the concept of significant figures. Your calculation is only as precise as the original measurement, and as long as it's good enough for what you're doing, all you have to do is drop everything that is in uncertainty. So cut off the precision of the kg measurements at the point where they diverge. Don't make shit up just to fulfill some desire to know more than we really do.
How about working out the number of grams from one mol of Oxygen(?) atoms? If they all have an atomic mass of ~16 you know they're about 16 grams. :o
Yeah...
A Local G effect. Pole vaulters be aware.
It must have been something you assimilated. . . .
First, define Avagadro's constant as exactly 6.02214179×10^23 + 4.
As one mole of C-12 is 12 grams, then one gram would be the mass of 50,184,514,916,666,666,666,667 atoms of C-12. Therefore, a kilogram would be the mass of exact 50,184,514,916,666,666,666,667,000 atoms of C-12.
Tell those physicists that from now on, Planck's constant is defined by the above definition of Avagadro's constant.
Problem solved. And lots of happy chemists.
1kg equals: 8.9876e+23 ergs
8.9876e+16 joules
6.6289e+16 foot-pounds
2.1481e+4 kilotons of TNT.
TNT? WTF?
I see many people making this statement, but it is false. Mathematics is based upon axioms which we assume to be true. We can then prove conclusively theorems derived from those axioms and be absolutely sure of the result. Science is based on observation of the real world and making hypotheses that match our observations. We can make hypotheses that match our observations but are not entirely correct. Math uses deductive reasoning. Science uses inductive reasoning. Science does use mathematical models for its hypotheses, but it is not math.
What a fool believes, he sees, no wise man has the power to reason away.
What's with all these science stories with country icons? First the "Atomic Disguise Makes Helium Look Like Hydrogen" is tagged as Canada, and now this is tagged as UK. Slashdot, make your story icons relate to the more relevant tags, like science.
I was about to type up a reply, but this suits you perfectly:
http://xkcd.com/687/
His math is perfect, his science is not.
My UID is prime... is yours?
So you are defining a somewhat universal (ok,at least, global) constant as something that should be there, but isnt?
The SI unit is officially defined as the weight of a 130-year-old platinum-iridium cylinder in France.
Where will we get a 130-year-old platinum-iridium cylinder next year? And the year after that? I wonder how they got hold of a 130-year-old platinum iridium cylinder 130 years ago?
There's a perfectly useful Atomic Mass Unit already defined: the dalton. http://en.wikipedia.org/wiki/Atomic_mass_unit
Why not define the kilogram in terms of a given number of Carbon 12 atoms?
Or if that is not stable enough, define it in terms of the electron rest mass. That's been stable for at least half the age of the universe.
Why don't they just count how many atoms are in it, and define the kilogram as the sum of the counts of each of the types of atoms making up the alloy?
Time is defined in a similar way, and don't tell me we don't have the technology, IBM has been shoving individual atoms around for decades now. They could do it again, and this time it would be for a cause more useful than making tiny IBM logos.
I'm not sure what the composition is, but I don't think there can be more than 6 * 10^24 atoms in it. Should be totally possible. If we are patient.
And don't lose count.
See that "Preview" button?
Here's an easy reference: Planck units.
Just define everything in terms of Planck units and nothing will ever change.
This is NOT dimensional analysis, sorry.
See:
http://en.wikipedia.org/wiki/Buckingham_%CF%80_theorem
...out hunting for ducks. The first one fires and misses a foot high. The second shoots and is a foot low. The third one yells "We got it!"
Has anyone explained the loss of mass? The metals involved should be stable. All I could think of would be impurities in the alloy. Trace amounts of a decaying isotope would cause the loss. If it isn't lost from handling it has to be a loss of energy or from a solid turning to a gas.
Someone earlier asked about that.
Standard Conditions: I assume you mean a known temperature and pressure.
How is pressure defined? Pressure = Force / Area.
How do we get force? Force = Mass X Acceleration.
How do we get mass? Oh wait, that is what we are asking for.
We can't use a unit to define itself.
The kg should nod be taken light-heartedly. Many other units depend on the kg. I say "keep sciencing" until a true solution emerges!
I hadn't the slightest objection to his spending his time planning massacres for the bourgeoisie... (P.G. Wodehouse)
Dude, the speed of light is 299,792,458 meters/second. I'd like to lose some weight, but I don't want to weigh 9.1035E-10kg.
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.
If we can['t] define a standard measure for mass why can't we create one for pressure? I don't see why it would be less reliable. Or they could just define mass as x molecules of Hydrogen.
null
I've always said this whole metric system has been a farce from the get go. First the unit of length is based on a fraction of the circumference of the earth, only measured WRONG, and now we get that the reference mass has been changing with time putting the amount of kippers in a kilogram in doubt.
I say we just scrap the whole thing and go to a more humanistic system based on things like the length of a man's stride etc. since obviously getting something accurate is just right out.
Metals which are pure elements?
Not Science you say? Well. I have a solution. Here's your science for a new official system of mass: The drachm is the base unit. One pound weight is 256 drachm. There are 12 once in a pound. The weight of a drachm is defined as 1/70400 my weight. All other units will be derived from that. Gravity is henceforth considered uniform everywhere on the surface of the Earth. You will not question this system, to do so is heresy.
Seems kind of silly to start with such a large mass as the base unit.
Why not just define a kilogram as the mass of 1000 moles of hydrogen?
Or... scientists have spent all this time measuring the mass of protons and blah blah blah... why not use that?
Mass bends space-time, right? So why not define it as a certain amount of curvature - say the mass needed to bend a light beam in vacuo by some measurable amount, divided by a chosen constant to give 1kg according to the theory.
Since "f = ma" and we can measure "f" and "a" easily enough.
Can't we define "m" based on that using a centrifuge or something?
Probably a stupid idea but was just wondering why not.
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.
Math is: When there's this room... with only one person in it... and then two people leave that room... now you have to wait until another person goes back in before it's actually empty.
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.
Mit der Dummheit kämpfen Götter selbst vergebens
Because that worked out so well for ATM.
as the article's image/icon ? kilogram has nothing to do with united states, unfortunately.
Read radical news here
Unfortunately, each time they do this they get slightly different results. The difference between the international standard and the average of the national standards is increasing.
Reminds me of the old quote: "A man with a watch knows what time it is. A man with two watches is never sure."
Is a kilogram in terms of fractions of an elephant please?
Isn't everything supposed to be quoted in units of Library Of Congresses?
The SI unit is officially defined as the weight of a 130-year-old platinum-iridium cylinder in France.
NO, it's not. It is defined as the mass of that cylinder. The weight is the force of attraction between Earth and the cylinder, it's not an intrinsic property of the body. I'd have hoped an article about mass would at least have that right.
OK...why not make it a multiple of the atomic weight of Hydrogen? or something?
Mathematically I was under the impression that one kilogram is what exactly one liter of water weighs.
Do not believe that the French developed the metric system for it is based on an ancient system of weights and measures based upon the time for Venus to move (transit) a particular distance across the sky. In those days a circle was divided into 366 degrees rather than 360 which matches the number of days in a year. The ancient clock system used then was more accurate than what we use today as well as the calender. Their system avoided the "leap year"
This technique developed thousands of years ago combines both the avoirdupois pound and the metric system and is based on what is referred to as a "Megalithic inch".
There is much substantiated already that ancient monuments such as Stonehenge were measured with an accuracy of 1/10000 of a millimetre.
For further information check Amazon for "Civilization One" by Christopher Knight and Alan Butler. A very interesting book, I am about half through this very enlightening book.
See what a pint, gallon, or bushel really is and how it was developed.
And in the end, the love you take is equal to the love you make
They should just post the problem on their Facebook wall or start a Wikipedia article on it and let the Net decide.
After watching a dozen hot topic scientific debates argued by the best and brightest in the world unfold into a never-ending stream of fraud and incompetence, the results from simple net polling couldn't possibly be any worse.
The French kilo appears to be getting lighter...or the copies might be getting heavier. Well if there's two other methods of weighing a substance, you don't they frigging use them, like duh. This article leaves a lot out and doesn't add up. And another thing: 175 parts per billion error is huge in some areas of science.
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I hate to troll but if it were possible that our solar system is a dual star with a brown dwarf, like Nibiru, as the star approaches would it change gravity and possibly make the weight lighter that originally weighed?
The only known potential infrared image I've seen suggesting it had the coordinates 5h 53m 27s, -6 10' 56". I've looked at more recent images in that portion of the sky and there is nothing. Was it there to begin with? Did it move as it should? Where is it if it exists?
Use a balance scale. Put masses on both sides. If it balances, the weights are the same on both sides. Since we think weight is directly tied to mass and gravity, and gravity doesn't vary that much in small areas, then the masses on both sides are the same and you have your own (non-canonical, but accurate) reference. It doesn't really matter if you did this in 0.5G, 1G or 10G, they'll still balance.
Two masses of the same material displace the same amount of air and thus you don't have to worry about the "air buoyancy" factor.
If you don't like all that, you could use a spring pendulum in a vacuum to compare the two. But I think that's just more hassle, due to what I said above about variances in gravity not mattering.
http://lkml.org/lkml/2005/8/20/95
"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."
Oh yeah? Ever heard of Quantum Physics?!?
Check and mate, sir.
I wonder if you graphed the change in mass if you would see the rate of change slowly increasing and that it would lead to the mass being 0 around the end of 2012?
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1kg refers to a unit of mass, not weight. In everyday conversation it could be fine, but not a slashdot article on physics
If the kg is getting lighter, then that explains increasing European obesity. The Yankees however, will need a different excuse.
How about deciding upon a fixed number for Mol? (ie. not basing it upon any other unit)
Then say that 1 Newton = X * Mol * <Atomic weight of some isotope of some element>.
Then the definition of a kg could happily change from the equator to a pole, as expected.
Would that be such a bad idea?
Why is the parent modded "Interesting"?? It is suppose to be INSIGHTFUL or INFORMATIVE.
Systematic errors in any measurements indicate you are doing it Wrong. If two different methods don't agree, then either the experiment is wrong (bad design) or the theory stating their equivalence is wrong (ie. it needs refinement at very least). There is no way around it and saying "average results" when such thing happens is the most unscientific thing one can do.
You're just describing the difference between mathematics and natural sciences.
A broad definition of "science", and one most people usually use, is: "a discipline that seeks to expand our knowledge of the world, in a systematic fashion" (hey, it's right there in the name). Mathematics is one such discipline (a "formal science").
Sure, people often use "science" to mean "natural science", but it's used in the general sense, too.
sic transit gloria mundi
Just come to me: How about deriving from light pressure? It may be doable...
Or they could just define mass as x molecules of Hydrogen.
That's precisely what they're trying to do here, except now you need to compute that exact number.
See all the shit we threw out into space? That came from us.
We have LESS MASS. Of course our kilogram is suddenly going to get lighter, even by the tiniest fraction of an amount, as we have LESS GRAVITY DUE TO LESS MASS.
Holy shit was that too hard to figure out, scientists?
Still waiting on Serviscope_minor to wake up to fucking reality and realize that Jessica Price isn't going to fuck him.
Or they could just define mass as x molecules of Hydrogen.
That's what this is about, only with carbon-12 rather than hydrogen. The problem is, we do not know the precise mass of atoms.
Determining the exact value of the Planck constant gives us the exact value of the Avogadro constant, which is the number of atoms in 12 grams of carbon-12.
upon the advice of my lawyer, i have no sig at this time
What I don't get is this. The 1kg reference mass is 130 years old. Unless the original kilogram was an arbitrary weight, whoever made it 130 years ago must have had some method of getting it to be exactly 1kg - so why don't they just use the same method used to make the original?
You're an idiot. The earth weighs about 5.9736×10^24 kg. One billionth of that would be about 6,000,000,000,000,000 kg. We haven't launched even remotely that much into space--it's over 10,000 times the weight of every living person.
If there's some sort of atmospheric leeching or similar effect I don't know about, you might actually have a point, but to say so confidently that launching stuff into space is the cause is just stupid.
What is lighter, a kilo lead or a kilo feathers?
The meter has a standardized definition based on the speed of light. 1 decimeter is 1/10 of a meter. 1 decimeter cubed is a liter. When the volume filling the liter is water at 4 degrees celsius (a scale based on water where it freezes at 0 and boils at 100), the water weighs 1 kilogram. So the meter is defined as a fraction of the speed of light, 1/10 of a meter cubed is a liter (volume), temperature is based on water, and mass is based on the mass of water for a defined volume. Done. I didn't think anyone was messing around with old platinum bars kept in a safe somewhere. The water has to be pure, thats the only trick (it should be a very poor conductor of electricity).
Are scientists dumber than I am? Mass is not a function of weight. If gravity changes, mass remains constant. That's why it still takes the same amount of force to stop a bus on the Moon as it does on Earth...
No, he could never have a point in a million years of launching whole chunks of the Earth into space. We're talking about mass not weight and the size of the Earth's gravitational field is utterly irrelevant.
Why don't they just count the number of Helium atoms it takes to achieve 1kg based on the standard prior to decay? That will give you a reproducible weight based on a static number.
...redefine the kilogram by just throwing out the prototypes and starting over from scratch?
can't we just define it in terms of libraries of congress?
I always understood that a litre of water was almost exactly 1kg, and was also 1dm^3
- Why not just switch the measurements of 1kg to 1dm^3 of water at 4C?
> As Slashdot has noted, the kilogram has a problem.
That is pure bullshit. It's not the kilo which has a problem, but each and every weight mesurement unit on planet Earth. The simple fact is there exists no other well-defined etalon or prototype object for mass but the platinum kilo-cylinder in Paris and therefore every other unit of weight, including the anglo-saxon pound, are officially defined in relation to the french kilo-cylinder, one lbs being declared as 0,452something kilograms!
He said "lighter". I was talking about having him possibly having a point about the object getting appreciably less heavy over time due to gravitational field strength changes caused by earth's mass decreasing. This is certainly tangential to the articles which as far as I remember only talked about mass changes, as you suggest.
I thought the kilo was based on the weight of 1 liter of H20. Since celcius is based on water wouldn't it make sense to base the kilo as well on water?
It's never wrong, and it was written by God. I'm sure there is some reference in there that can solve this all.
your experiment would generally give different results at different altitudes. and, if you want to measure the pressure to take that into account, than you're goint to need a unit of mass before.
new sig
Who cares?
When society was mostly innumerate, the maths for converting acres to square feet was never needed. Today, you only need to know that because it's used as a maths question in school. And scientists have to convert lots of things anyway (the density of water is not 1,000,000g/m^3) so is moot anyway.
So when you had an acre, you knew you could plough and seed it in one day with your Ox and you could do so efficiently. With a square field (the definition of hectare is square), you have many more turns to make, each turn wasting land you could work if you hadn't had to turn the plough at that point. Therefore you need more land to feed yourself and your family.
If you don't like the multitude of conversions, use the milli-acre (hell, why are we using hectares anyway? Why not sq m? Why do we use KILO gramme rather than gramme? See, we already jump through hoops with the metric system).
The only sensible reason for choosing metric over imperial is that there is less to change if we go that way than going TO Imperial.
Not everyone thinks that averaging the two amounts to sound research
Depends what the journalist means by "research". Averaging values is a perfectly valid experimental technique. It is definitely a very poor theoretical technique.
"Science flies us to the moon. Religion flies us into buildings." - Victor Stenger
Surely this is just another consequence of global warming! Just add it to the list http://www.numberwatch.co.uk/warmlist.htm
Synchronizing stop lights across the US = one less nuclear power plant
"If carbon-12 is expected to remain the standard, and the scientitific community therefore prefers an integer divisible by 12, then we suggest using [the cube of] 84,446,886. Then 1 gram would be the mass of exactly 18 [times the cube of] 14,074,481 carbon-12 atoms. Consequently, 1 amu would be exactly 1/(2 x 3^2 x 1,667^3 x 8,443^3) gram, and 1 mole of any entity would be exactly [the cube of] 84,446,886 of those entities."
http://www.americanscientist.org/issues/id.3743,y.0,no.,content.true,page.1,css.print/issue.aspx
What I cannot create, I do not understand
Not French.
Not everyone thinks that averaging the two amounts to sound research
Did anyone else read that as the "two amounts" (as in two values)? The sentence seemed unfinished after that. I would have chosen a different word, perhaps, "...two qualifies..."
No single raindrop believes it is to blame for the flood.
So simple! You're so clever!
Guys, the answer to this probably lies deep within Columbia.
Yes, Columbia.
I am certain that the cartels know how to measure a Kilo with precision. There is your new standard.. :)
Huh?
I suggest they use a platinum cylinder of about 1.15 inches in diameter and 1.35 inches high. Works for everyone else.
There is a quote that I can't be bothered to look up the originator that says
Of course, as we've seen elsewhere in the scientific community, we should be using a weighted average, so in fact, since there are so many more programming languages that use "0" as the starting index, the proper starting index should be 0.2774931....
--Joe
The kilogram doesn't measure weight, it measures mass
All I can say is that I'm glad that Metric system isn't arbitrary and open to interpretation or change like the Imperial system those stupid Americans use.
-Styopa
...to count all of those atoms with.
But seriously, something similar WAS suggested. It may even be adopted by the end of the year.
Mit der Dummheit kämpfen Götter selbst vergebens
You measure by comparing.
You can't compare hydrogen atoms to a packet of sugar in the market.
Or to some compound used in a making of a medicine, but which can be poisonous in higher concentrations.
Or anything else that simply needs accurate measurement in order for the reaction to work.
Mit der Dummheit kämpfen Götter selbst vergebens
An American company, back in the '80's, tried to introduce the measure, "one metric gallon," defined as consisting of four standard liters, as the name for the volume of its product - industrial-grade, liquid hand-soap - held by the company's standard containers. Possibly, this idea was inspired by the existence of the "metric tonne." IAC, it didn't work, for reasons of which I am unaware, and the company reverted to using "four liters."