Glorious silicon globes could hold key to elusive PERFECT kilogram

There's a piece of metal more than a century old just outside Paris causing men and women of science a lot of bother. It's considered so important to the world it's kept on land designated international territory, so that no single country can claim it, in a maximum security vault maintained by the International Bureau of …

[AndrueC]

Note to Americans and others using even older systems of measurement:

1 kilogramme is approximately 2.2 pounds. Well - depending which of the several 'pound's you happen to be using at the time.

[Chris Tierney]

Gravity probe.

Perhaps we should launch some sort of gravity probe with several high speed gyroscopes to determine & map the differences in Gravity between to places on earth.

We then should take these results and combine these with altitude & air pressure measurements to determine if the variance is due to these environmental factors.

[Anonymous Coward]

Re: Environmental factors

Sticking them in the same room was the first think I thought of, but they do look big, heavy and fragile.

[David Given]

Re: Gravity probe.

It's been done, many times, as it's pretty vital knowledge for doing anything weight related --- here's a link with some pictures in it and some decent pictures of the Earth geoid (as it's technically known):

http://planetearth.nerc.ac.uk/news/story.aspx?id=359

[Christian Berger]

One could put that data onto a clickable map

Oh wait, that's already been done:

http://www.ptb.de/cartoweb3/SISproject.php

[Scott Broukell]

FFS !

Oh! just get on with it, nothing in this universe is perfect, no matter how many bell jars are involved, it's all relative to the observer anyways. You just can't make two things identical, it's all approximation. Why do we insist on believing we are the custodians of perfection in the universe, cos we can chat about it over a latte!. The close proximity of an over-weight IPK botherer would have some bearing on relative mass wouldn't it ? The affect being lessened if a scrawny student of International Kilomass took it home for his/her homework project.

[Craig 2]

Re: FFS !

This comment just about sums up the apathy of the common man. What if everyone through the ages thought "what's the point in trying to improve?"

[Scott Broukell]

@Craig 2

Yes, improve by all means. Improve the approximation and your results will be finer still. But you will never be able to make two, three, four .... kilo blocks of alloy identical in every regard. So it just seems like a bit of an old waste of time when the differences are already comparable to a millionth of a gnats whisker and that's close enough for me, but thanks for asking.

[JDX]

Re: @Craig 2

It's not about having a perfect kilogram. It's about making sure measurements can be made consistently.

[Naughtyhorse]

Re: FFS !

from the above we can assume that

chris is a scientist

symon is an engineer

and scott is a programmer

[ian 22]

Re: FFS !

Reminds me of an old joke:

A scientist, an engineer, and a programmer were traveling together through Scotland when the programmer spies a flock of sheep, one of which is black. "There are black sheep in Scotland" he exclaims.

The engineer replies, "Well there is at least one black sheep in Scotland."

To which the scientist says "There is at least one sheep in Scotland that is black on at least one side."

[Stoneshop]

Re: FFS !

A balloonist is low over a golf course, having lost his way, and shouts to a guy below "Where am I?"

"You're in a balloon gondola, twenty feet over a golf course"

"So, you're a consultant, telling me something I already know, and not actually offering any useful information"

[Mike Scott]

[e-mail]

The mass of the standard kilogramme can't possibly be changing. Its mass was 1kg when it was made, and its mass is 1kg now, by definition. The number of atoms in it may be changing, resulting in the definition of 1kg changing over time.

[Anonymous Coward]

Re: [e-mail]

http://www.msnbc.msn.com/id/20744160/ns/technology_and_science-science/t/kilogram-prototype-mysteriously-loses-weight/#.UKt1lmea9hI

[TeeCee]

Re: [e-mail]

So we can deduce from that that the International Prototype Kilogram is male then?

If it were female, there would only have been a fuss if it had gained weight.

[perlcat]

Re: [e-mail]

Didn't the prototype also gain weight from mercury contamination? (The guy that polished it blew on it as he cleaned it over the years, and the mercury came from his dental fillings.)

[John Savard]

What Puzzles Me

If we know that the mass of the International Prototype Kilogram is changing, then we must have some way of telling that. Which means we already have a better way to define the kilogram, which we should be using while we're waiting.

[hplasm]

Re: What Puzzles Me

It's compared to a bag of sugar.

[Jerome Fryer]

Intercomparison is used

The method used to determine the IPK 'shrinkage' is intercomparison between the other master masses. Theoretically, several other masses could be experiencing an increase in mass, but the statistical likelihood points to the IPK slowly vanishing.

There are significant problems with the 'this here block of stuff is a kg' approach, however, and the point of the exercise of replacing a physical object (an artefact) with a repeatable process to determine a kg mass is to avoid those problems. Should you then desire to have a unit kg (to a theoretically arbitrary accuracy), regardless of where you happen to be, you can produce one through the magic of science -- or more than one.

(And also make the SI consistent with the idea that anyone should be able to produce the base units and thus derived units. So, if you should happen to misplace the IPK, the entire global economy isn't suddenly thrown into chaos because a base unit has vanished. And you probably think it is inconvenient when you misplace your keys...)

[davemcwish]

Chicanery explained (Dimensional Analysis)

For those that care:-

1 Joule = Energy expended applying a force of 1 Newton over 1 metre i.e. 1 N m

1 Newton = Force required to accelerate a mass of one kilogram at one meter per second squared. i.e. kg m s^-2

Therefore

1 J = kg m s^-2 m or kg m^2 s^-2

[JeffyPooh]

Re: Chicanery explained (Dimensional Analysis)

"Dimensional Analysis"

Well done sir. Along with 'Significant Figures', one of my favourites. Here's a ² (<- square) & √ (<- square root) for your future use. Cheers.

[Code Monkey]

So which is the prototype football pitch? FA rules allow pitches between between 100 yards (90m/~10 double-decker buses) and 130 yards (120m/~13 double-decker buses) long and between 50 yards (45m/~5 double-decker buses) and 100 yards (90m/~10 double-decker buses) wide.

And which is the protoype double-decker bus? (I'm guessing the Routemaster but open to suggestions from, say, Altlantean fans).

[Blofeld's Cat]

"And which is the protoype (sic) double-decker bus? "

That would presumably be "RM1" the first Routemaster prototype, currently housed at the London Transport Museum. I suspect "RM8" (the first production vehicle) would have to be ruled out as it has changed substantially over the years.

I do not know how "RM1" is cleaned, or how many bell jars it is kept under.

It's the anorak.

[TeeCee]

Ah yes. Bus enthusiasts, the pinnacle of anorakdom.

One I knew had his smugness quotient raised to stratospheric levels when playing the "Give Us A Break" trivia machine in the local boozer. He'd gone for the "Black Ball challenge" double or quits option on a jackpot win and the question that came up was "When was the last trolleybus run in London?".

Before the sodding answers came up he'd given us the exact date. Its route number. Its make and model. Where it was going from. Where it was going to. When it was due to depart. When it actually departed. When it was due to arrive. When it actually arrived. The name of the bloke driving it.

Yes, he could talk quite quickly under pressure.

For amusement value, when the answers came up he stood there completely foxed at the four years offered until one of us leant over and thumped the right one just in time, having deduced it from the date he'd previously given.

On the plus side, this meant free beer for the rest of the evening. Working against that was that said free beer came with everything we never really wanted to know about trolleybuses, trotted out in painstaking detail over the evening......

[Anonymous Coward]

I just had a Double Decker for lunch. Yum.

[Ed 13]

Leap Seconds

I'm all for keeping leap seconds, and doing so until a significant fraction of the population aren't living on this planet. No matter how you define time, most people prefer to synchronise their day by the rising and setting of the sun.

[The First Dave]

Re: Leap Seconds

And leap seconds is one of the main reasons why we still have the stupidity of "Daylight Savings Time" rather than just getting on with our lives according to actual needs. Which is why we have the stupidity of a twice-daily "rush hour" purely because of some arbitrary numbers on a clock.

[Tom 38]

Re: Leap Seconds

Leap seconds are one of the main reasons why we have DST? Run that one by me again Dave, since DST is solely about getting more daylight hours during the summer and harvest, prompted by a desire to reduce fuel costs on the country during war.

Leap seconds? Fuck all to do with it.

[Stratman]

Re: Leap Seconds

"DST is solely about getting more daylight hours during the summer"

So how do we do that?

[Tom 38]

Re: Leap Seconds

DST = we put the clock forwards by an hour in the summer. Did you really need that explaining?

In the summer in the UK, twilight starts at around 4am, daylight around 5 am. Normally, people are sleeping at that point. By putting the clocks forward, it will be light 'later' into the evening than otherwise, people will require less fuel and lighting, and you get a nice long day to get the harvest in, without getting up at 3 in the morning to do so.

[Gene Cash]

Re: Leap Seconds

You're STILL getting up at 3am in the morning, you retard. You've just fooled yourself that it's not by mucking about with the clocks. Mess with your own clock. Leave the rest of us out of it.

'After having Daylight Saving Time explained to him, a wise old Indian Chief said, "Only the government would believe you can cut a foot off one end of a blanket, sew it onto the other end, and end up with a longer blanket."'

[A J Stiles]

Re: Leap Seconds

Except you are getting up at 3:00 in the morning! You're just pretending it's 4:00.

[Tom 38]

Re: Leap Seconds

If we all say it is 4:00 AM, it is 4:00 AM. There is no universal time counter, time is a human invention of shared perception.

[Stoneshop]

Re: Leap Seconds

"DST is solely about getting more daylight hours during the summer"

So how do we do that?

Hot air, as emitted from any gathering of politicos, especially those bent on keeping DST. As you may well know, hot air rises, so after a while it will push against the underside of the cloud cover, tearing it up and letting sunlight through.

[Darryl]

Re: Leap Seconds

See? DST is the reason we have global warming... All those summer days with the sun heating things up for an extra hour, what do you expect?

(Just figured I'd get in on the crackpot theories too)

[A J Stiles]

Re: Leap Seconds

Um, no, we get more daylight hours during the summer anyway; but they are always roughly evenly spread before and after midday (12:00 in winter). So from March to October, in the Northern hemisphere, we pretend it's an hour later than it really is (so midday occurs around 13:00); all in order to keep business hours as being from 09:00 to 17:00 all year round, as opposed to the more sensible option of leaving the clocks alone and just working from 08:00 to 16:00 in the summer.

[TeeCee]

@The First Dave

Have a downvote.

Normally I wouldn't bother, but your pinning of the Boffin icon on that veritable cornucopia of cobblers swings it.

[Naughtyhorse]

Re: Leap Seconds

I call bollocks on that!

i sync my day by the ringing of my alarm!

in the winter i get up in the dark, in the summer a slumber through many hours of usable celestial illumination.

and on weekends i sleep in (isnt having no kids bliss sometimes - particularly around mid day on a sunday, or anytime at an ATM).

it would take thousands of leap seconds to change things _that_ noticably

[Dr Paul Taylor]

Abolish Leap Seconds

Greenwich mean time is so called because it's averaged over the year. There is a difference of up to a quarrter of an hour (called the equation of time) from the actual movement of the Sun.

We generally have hourly time zones, so there's another 30 mins difference, but for political reasons some countries are far from their time zones. Then there's Daylight Saving.

Leap Seconds are trivial in comparison. In the year 5000, we can make a political decision to move UK to what is now Central European Time and the rest of western Europe can move to the next time zone, etc.

[Christian Berger]

Re: Abolish Leap Seconds

"Leap Seconds are trivial in comparison. In the year 5000, we can make a political decision to move UK to what is now Central European Time and the rest of western Europe can move to the next time zone, etc."

Yeah, and move the whole world into chaos.

I'd say the more rational decision would be to abolish leap seconds for technical systems, and only have them for interfaces interacting with humans. If you look at the complexity of a time-zone database you can see that adding leap seconds to it wouldn't make much of a difference. Essentially that's the "GPS"-Approach. GPS doesn't know about leap seconds, it just counts seconds and weeks. Just leave the weeks and you are set.

[frank ly]

Definition of a metre

" .. one metre is equal to the distance travelled by light in vacuum in a 299,792,458th of a second."

The problem with this is that you need an accurate clock to measure the fraction of a second.

I thought that the 'latest' formal definition of a metre is a certain (large) number of wavelengths of a particular emission line from some named element isotope. Using this method, all you need to do is count them, not measure anything else. (Similarly, the second is defined as the time taken for a certain number of cycles of a caesium spectral emission line; only counting is involved with no reliance on other standards.)

The idea behind the definition of the kilogram as a particular number of a certain type of atom has the same principle, obviously.

Once you have the metre, kilogram and second defined in this way, every other SI unit can be derived from them, which is why it used to be called the MKS system (or mKs if you want to be picky).

[A J Stiles]

Re: Definition of a metre

No, that was the old definition of the metre you're thinking of.

We can now define a second more precisely than we used to, thanks to the invention of atomic clocks, so the metre is defined in terms of the second and the speed of light.

Avogadro's Number of carbon-12 atoms weigh exactly 0.012 kg. by definition, but the question is how accurately we can know Avogadro's number.

[frank ly]

Re: Definition of a metre

OK, so the 'caesium second' is so accurate and repeatable that it's good enough to be used to define the metre. Thank you for explaining that.

As for Avogadro's number, we can know that as accurately as we can define and measure the kilogram ...........aha.

It doesn't matter what Avogadro's number is, as long as it is accurately linked to the 'best' standard kilogram available at the moment. After that, we all agree on that value of Avogadro's number and we don't need a standard reference mass any more.

After that, everything can be linked back to a carefully constructed caesium clock and he ability to count.

[Tom 7]

Re: Definition of a metre

And with a bit of gravity the whole lot changes again!

[A J Stiles]

Re: Definition of a metre

Well, in theory, all we have to do is weigh out a quantity of something that matches the international prototype kilogram, count the molecules (without losing count) and re-weigh to make sure it still exactly matches the prototype.

That, however, could well be the very definition of "more easily said than done".

This whole business with Ampere balances versus molecule-counting has something of the history of determining longitude at sea about it.

The scientific establishment set great store by astronomical observation methods, which required precise observations and lengthy calculations; Harrison's method was to compare a watch (an especially accurate one, designed so as not to lose or gain time even while being shaken about on a sea voyage, and therefore always indicating the exact time on the Greenwich meridian) with a sundial showing the local time (which varies by 4 minutes for each degree of longitude).

[Matthew 3]

Re: Definition of a metre

Us Brits don't piss about with glass jars, steam cleaning and government minders. We just pinned our Imperial measurements to the North wall at Trafalgar Square (with a note that itthey were accurate at 62 degrees Fahrenheit). Joe Public could check out his ruler's accuracy for himself - without the government getting involved.

Yes, I know, it's Wikipedia. But they have a nice picture.

[JimmyPage]

Just to complicate things .... radioactive decay ?

Isn't there an experiment somewhere, where a mass becomes lighter over time, as it decays ?

[PC Paul]

Re: Just to complicate things .... radioactive decay ?

> Isn't there an experiment somewhere, where a mass becomes lighter over time, as it decays ?

Do you mean this one?

http://smp.uq.edu.au/content/pitch-drop-experiment

[Pet Peeve]

Huh?

The pitch drop experiment has absolutely nothing to do with radioactive decay.

In answer to the original question - Radioactive decay is not likely to be a factor - the two elements were chosen precisely because the only radioisotopes are very short lived so they're unlikely to be present. Fun fact though - platinum has one radioactive isotope with a half life measured in the tens of billions of years, so maybe, just maybe, an atom or two in the kilogram has decayed since the standard mass was cast.

At this level of precision of measurement, a few atoms knocked off by a stray dust particle are significant, hence the triple-bagged vacuum storage.

[Dr Paul Taylor]

Units of Planck's constant

Joules multiplied by seconds, not Joules per second. In terms of basic units, this is kg m^2/s.

In Heisenberg's Uncertainly Law, the uncertainty in Energy (Joules) multiplied by that in time (seconds) must be at least Planck's constant. Likewise, the uncertainty in momentum (kg m/s) multiplied by that in position (metres).

Given that the article is about units, this is a rather fundamental error, but otherwise it's a good article.

[diodesign]

Re: Units of Planck's constant

"Joules multiplied by seconds, not Joules per second"

Yes, I am kicking myself hard in the arse right now for not spotting that. I cannot express my rage at this moment :-(

The article's been fixed.

C.

[Moonshine]

It's a kg!

Can't they just agree that 1 Kg is exactly 1000 grams? A gram is too small to worry about, so problem solved! Now the boffins can concentrate on more pressing things like the time travel, x-ray glasses, invisibility and teleportation.

[FartingHippo]

Re: It's a kg!

kg not Kg; K is for Kelvin

[Psyx]

Re: It's a kg!

"A gram is too small to worry about"

Not a cocaine user, are you?

[Anonymous Coward 15]

Erm, something about silicon globes. Fnarr.

[Anonymous Coward]

It's those sexy_lips.png again ...

The difference between 6.626071 and 6.626068 is rather large, certainly not infinitesimal, and not "250 parts per billion", even if it's a wimpy little US "billion".

On the other hand, that woman's mouth is way too small ...

[Pet Peeve]

Re: It's those sexy_lips.png again ...

Do the math again. If you assume the correct number is the mean of the two, they are both off by pretty close to 250 parts per billion.

[imanidiot]

Talking about keeping it clean

If they are that worried about tiny mass differences they might start by putting the damn watt balance in a cleanroom environment. Even a class 10.000 (less than 10.000 free-floatingparticles of 5 micron or bigger per cubic meter,which is quite easy to achieve) would markedly reduce the number of stray fibers, dust and other crud accumilating in the works over time. (And no, just wearing latex gloves like in those piccies doesn't really help in that regard).

Also, How constant are they keeping the temperature and what temperature are they using? If one lab is constantly 23,4 degrees with a lot of equipment humming away, and the other is 21,2 degrees in a nice quiet isolated room, this could have an influence.

[Pet Peeve]

Re: Talking about keeping it clean

The experiment depends on balancing two known forces against an electrical field - dust should not be a factor. Plus, from the limited description of the apparatus, I think it's likely that the measuring parts are in vacuum anyway. Don't go looking for an easy answer from a popularization of the problem.

The issue is that the two experiments are attempting to measure the same thing with different apparatus, but if they have it all worked out properly, they should agree to within the threshhold desired (20 parts per billion).

Like the person wearing two watches not knowing what time it is, they don't know if one experiment is out of adjustment, or both are, or if their assumptions about what they're measuring is wrong.

This is a really fascinating subject. I get the idea of watt balances pretty well, what I would really like to know is how you precisely count a mole of atoms.

[James Haley 2]

Suggested fix ...

Have they made sure the fiber optic cables are seated correctly?

[MrAch]

Easy?????

This is a general statement, please criticize as I expect you to. But surely you could just say that a kilogram is a certain number of atoms of a certain substance (i.e. Water) at a specific temperature and pressure. Hell at a specific temperature and pressure, you could even say volume of a certain substance. I am aware that this is no doubt incorrect as i am sure this problem would have been solved many years ago had it been as simple as that. Thoughts????

[frank ly]

Re: Easy?????

The gramme was originally defined as the mass of a certain volume of water, yes, but this leads to the problem of how you construct a container with that volume. Easy, you say, use accurate rulers to construct and measurer it. Do you see the problem there? It's a lot better and easier to have a lump of stable metal as your defined standard.

As a side note, "a certain number of atoms of a certain substance (i.e. Water)" - water is not atoms, it is molecules. Even then, there are different types of water molecules that have different masses due to containing different isotopes of hydrogen and oxygen: not good for extreme accuracy.

[MrAch]

Re: Easy?????

Ok I see that.... how about atoms of Carbon-12... it's what the mole is based on???

[Yet Another Anonymous coward]

Re: Easy?????

That's the other approach - the Avagadro project.

Make sphere that's perfectly round to within a few nm and contains only silicon atoms with no impurities - then measure it's diameter (easy) and count the number of atoms in it (relatively easy)

[Anonymous Coward]

Using some British logic here...

A standard UK Teaspoon is 5ml, A standard UK Teaspoon of granulated sugar (not heaped) is around 4g. which means you can get 250 spoons of sugar out of a 1Kg bag. So using those numbers (very rough initial numbers and need need more precise measurements,) and the using the iconic British standard of Tea, White, one.

A Kilogram is equivalent to 250 cups of Tea!

[Anonymous Coward]

Use a bigger mass?

Presumably, keeping dirt off and stopping atoms leaving the surface is the main issue with the standard kg. So if it was scaled up, say, a million times in mass, the surface would be 10,000 times larger so the problem of keeping it sufficiently clean would be (relatively) 100 times easier.

[David Pollard]

Re: Use a bigger mass?

Is that why El Reg uses the double-decker bus as its standard?

[John Smith 19]

So what stuffed Quantas?

After all this leap second thing has been going on for a while.

I'd think it would be written into their SysAdmin SOP

[Mikey]

This is... I want to say hilarious, but I'm not so sure. It's funny though, and I've got a better appreciation for that goold old rough'n'ready Imperial measurement system. Sure, we need proper units for accurate measurements and all, but when all's said and done, the bloke on the street is happy with his 99p WH Smith ruler (cm and Inches) and set of kitchen weights (which still generally come in both metric and imperial, happily).

I quite like the irony in the definition of the meter though. What a rather odd number for the time interval, you'd expect it to be in multiples of 10 for SI, no? ;O)