# Boffins cook raw numbers, hope to bake PERFECT kilogram

A “recipe” to deliver the perfect kilogram as a mass standard that the world can trust is coming closer to completion as the physicists behind the project bake their raw numbers. International scientists met in late November and pushed forward a 21-page document that'll eventually instruct boffins responsible for managing …

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#### Not sure there is much point in a Quantum Kilogram

After all, if you know exactly how much it weighs you won't know where it is!

#### Re: Not sure there is much point in a Quantum Kilogram

You could store in a box with a cat

#### Re: Not sure there is much point in a Quantum Kilogram

Somebody please explain why this quantum kilo is required, after all the greengrocer won't be able to weigh ont a kilo of oranges unless that have a quantum mass balance.

Can the quantum kilo ever exist? I'd imagine that a blast of ionising radiation or even the odd neutrino would cause the quantum kilo to "knock one out" thereby changing the mass of the quantum kilo????

#### Re: Not sure there is much point in a Quantum Kilogram

Once we have a recipe we can bake a new one every week, and your greengrocer's scales would be calibrated using weights, that were themselves calibrated against whatever the freshest quantum one was at the time.

#### Re: Not sure there is much point in a Quantum Kilogram

After all, if you know exactly how much it weighs you won't know where it is!

If you want to know how much it weighs then you'd need to know where it is as weight (measured in Newtons) is dependent on the gravitational forces at a specific location where as the kilogram is a unit of mass.

To quote my physics teacher "Unit! Unit! You nit!"

#### Re: Not sure there is much point in a Quantum Kilogram

Once we've got the recipe down, we'll be able to knock out billions of them... so there'll be a reasonable chance of one popping up somewhere useful - like near some bananas that need to be weighed.

#### Re: Not sure there is much point in a Quantum Kilogram

If you are going to down vote a question like this please have the decency to explain why I'm wrong

#### Re: Not sure there is much point in a Quantum Kilogram

Errrr... I don't give a flying fuck about downvotes, what I was wondering was what use is a physical 1Kg mass/weight when the other SI units are not defined using a physical things.

I guess you don't know either madra.

#### Re: Not sure there is much point in a Quantum Kilogram

i nether know nor care

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#### Not an ordinairy article

But a very informative and interesting one (ok I deal with measurement albeit at a much simpler level).

Thanks.

#### 21-page document

21 pages? I can do it in 21 words

1 Kg is defined as the total mass of brain matter shared by DM readers at any given moment in time.

The advantage over the metal kilo is that the mass never changes it is just redistributed depending on the numer of readers, more readers means less brain matter per person. Could explain a lot.

I wonder how much the metal Kg will turn out to mass when measured against the new standard.

But since the metal Kg is de facto the "accurate one" at the moment, surely your question should be "...how inaccurate the new standard will be when compared to the existing standard"

...but isn't one kilo currently the mass of 1dm^3 H2O @ STP???

Presumably the new standard will match the old one on day 1, and the old standard will gradually drift.

>..but isn't one kilo currently the mass of 1dm^3 H2O @ STP???

Roughly, but that's not accurate enough (the water evaporates) or easy to make (different isotopes and impurities)

#### re: mass of 1dm^3 H2O @ STP

Almost.

The problem is that they are still too many variables:

Which STP? Standard Temperature and Pressure says 0°C (ice cube?), so you could use S(Ambient)TP, but how do you know each molecule is exactly @ 25°C? Same question is you used the NIST option (20°C).

Then how do you make sure you have pure H2O? In fact, how pure should it be? And how do you know you got it right?

Finally, how do you know you filled exactly 1 dm³? How can you tell that this container has one too many drop or one too few?

Using some universal constant (speed of light, planck's constants, number of transitions of a cesium atom, etc) is the best approach but determining which is hard.

#### Re: re: mass of 1dm^3 H2O @ STP

Sorry chaps, I wasn't meaning to imply that the litre of water is a good standard. It's obviously horribly crap. ...but isn't it the current standard? I thought it had replaced the "the same mass as the mass of a specific lump of platinum somewhere in France" definition, so, shouldn't the new standard be replacing (and compared to) the litre of water rather than the lump of metal?

#### hydrogen hydroxide as raw material

Anonymous Coward, no, a cubic decimetre of water &c. is not the current standard. However, it was the basis of the original standard of the gram, in the law of 18 germinal an III:

«Gramme, le poids absolu d'un volume d'eau pure égal au cube de la centième partie du mètre, et à la température de la glace fondante.»

On 4 messidor an VII, the original platinum prototype kilogram was presented, to match as closely as possible the mass of a cubic decimetre of pure water at 4 °C (then believed to be the temperature at which water is at its maximum density, presumably at the atmospheric pressure of Paris); unfortunately the prototype was slightly more massive than its intended target. Refinements of the prototype (such as the 19th century platinum/iridium copies) have been made to match the original prototype rather than to more closely match the original prototype’s goal, that particular cubic decimetre of water.

Thus, the new standard would be replacing the triply bell jarred platinum/iridium lump in the BIPM rather than, say, a cubic decimetre of Vienna Standard Mean Ocean Water.

So when will the Reg standardise and give us the quantum jub?

And will there be a dependency on left or right?

#### Which will weigh more?

A kilo of lead or a kilo of feathers?

I feel the need for a beer!

I always thought it would be funny to break into International Bureau of Weights and Measures, in the style of "sneakers" and swap "the kilogram" for the equivalent weights in pounds and ounces (and a bit of dust); that would show the French!

It would be funnier if the break in was in the style of the master criminal penguin from Wallace & Gromit and the kilogram was swapped for a pound of Wensleydale cheese.

#### Ha !

Too complicated - go back to Imperial

#### Re: Ha !

Imperial not complicated?

Where 1 pound of gold is lighter than 1 pound of coal and 1 ounce of gold is heavier than 1 ounce of coal?

(I hate people comparing gold and feathers and claiming they are the same)

Precious metals are normally weighed in Troy-weight and everything else in Avoirdupois. There are 480 grains to a troy ounce, 437½ grains to an avoirdupois ounce (gold is heavier) but only 12 ounces in a troy pound instead of 16 avoirdupois, so we have 5,760 grains against 7000 grains for the pound measurements. Both systems use the same grain, which is defined in terms of the kilo these days, so the imperial system is now based on the metric system anyway.

If you want to buy precious metals, make sure you know how heavy a pound is, or use kg.

#### Existential question

Is anything every truly constant ?

#### Re: Existential question

Welll Kaptain, that is the question, as a kg is constantly needed to be constant.

#### 1 Kg

= almost nine bags of cola cubes......

#### Star Trek approach?

Why not work this out backards?

Pick a sufficiently happy guesstimate number of Kilojoules liberated by a matter/antimatter reaction, then say 'we define x KJ will be liberated by 1Kg Matter reacting totally with 1Kg Antimatter'

Appropriately woolly and pins the numbers to maths assumptions rather than something tangible

:)

#### Chasing its tail (and no, not the aformentioned cat...)

Another approach is to count the number of atoms in a silicon sphere using the Avogadro constant.

An approach which intrigues me, given that the Avogadro number depends on the value (definition) of a kilogram.

#### Re: Chasing its tail (and no, not the aformentioned cat...)

Keep it simple - just smash two particles of cod in a large haddock colander and count the number of Higgs Bosun's produced!

I'm sure they'll redefine it such that it benefits people selling things in Kg, another finger to the consumer.

#### Some french and/or letters are required!

Among other things, the 'mise' will tell national measurements bodies how they should combine results from different projects to define the quantum kilogram to help ensure reliability. 'Mise en pratiques' accompany all SI units.

Mise en pratique means "The act of putting into practice". You cannot use the word mise alone because then it means a bet. As for the plural, you want to put the s ending on the other word!

Thus:

Among other things, the 'mise en pratique' will tell national measurements bodies how they should (and I think this is the SHALL from the RFCs) combine results from different projects to define the quantum kilogram to help ensure reliability. 'Mises en pratique' accompany all SI units.

#### bake?

Let's hope that they don't ask for bread and get handed a stone.

#### Ernst Mach

would have been proud at this emphasis on recipes - or mises en pratique> ! If you can't make it, you don't own it !...

Henri

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