Sunday 27 November 2022

Weighty Matter

Rijksmuseum etching, "Atlas carries the vault of heaven", printed by Jean Baptiste de Poilly after François Verdier's design, France, 1679-1728

Have you ever wanted to buy a Kibble Balance, Dear Reader? Trying to find one with Mr. Google invariably brings up pages of dog food suppliers, which is no help for it is indeed the tool that we are supposed to use for benchmarking the Kilogram from now on. So, what even is one? Behold:

A Kibble Balance in the wild.
You can build this baby with LEGO®!

And benchmarking the kilogram. What's that when it's at home? It seems that weighing devices like kitchen scales need to be calibrated because it's The Law and swindlers are always out to fleece you. Well, not really, but everything needs to be accurate these day and what it says on the box; else life is just guesswork.

Hence this Frankenstein's monster of electromagnetic [over-]engineering is all the rage these days and Governments are spending millions of pesos building their own in order to have the last word on the kg. Who knew? In typical fashion, scientific-types say tra labuild your own for it is no big deal, and point to a youtubes tutorial on building one with LEGO bricks. Can you imagine? 

If you have you been keeping up with the news, this story would be old hat but I had been caught unawares about the revolution in the realisation of our base units of measurement* owing to my on-off-sometimes news embargo. Luckily, four years ago Dear Brother sent me the article, "The kilogram is dead; long live the kilogram"

Trust me when I say that I'm more or less up to speed now & I have some Opinions about it all. Shaking up our scientific foundations like this is just the sort of Weighty Matter (hem hem) which occasionally leads to sleepless nights and self-medicating with doses of Animal/Vegetable/Mineral. Not owing to breathless excitement about it all, mind, rather hand-wringing consternation that we are in the embrace of scientific hubris.

Why, what, hubris?! For surely scientific progress in Metrology, the Science of Measuring Stuff, is meant to lead us out of a primitive wilderness where we once felt our way about our world with arbitrary benchmarks such as king's feet and grains of cereal**? Fudge-work and approximation begone!

The artefact formerly known as the Kilogram

To be sure, the French Revolution did usher in a brave new metric world and brought us Le Grand K, an elegant cylinder of platinum alloy that lives in a nest of bell jars in a vault in Saint-Cloud (patron saint of carbuncles and gout) in Paris, and which from 1795 was the physical prototype to represent the kilogram, newly defined as the mass of 1000 cubic centimetres of water at 4 degrees Celsius***. 

And you might think, like I, that this is very neat and tidy and praise be, &c. And isn't it marvellous that dozens of copies of the elegant platinum ur-kilogram have been made and distributed about the globe (Australia's national prototype lives at the National Measurement Institute in Sydney) and are the calibration benchmarks for measuring the mass of just about everything.

But the lofty ideal of these Revolutionaries that standardising measurements for all men, for all time didn't foresee the advent of, ahem, quantum mechanics. As science got more exciting, boffins wanted to decouple these olde ways of measuring the world with tangible artefacts like handy copies of Le Grand K into something rather more cerebral and release mankind from the tyranny of, you know, being the laughing stock of the universe for, say, weighing stuff with lumps of metal instead of physics. (Yes, boffins on the interwebs do say aliens would laugh at us.)

Lo!, our trusty metric system of measurement has now been completely overhauled, and the seven base units of the International System of Units (SI) have been redefined by natural physical constants and each other. The kilogram was the last base unit to be redefined and for several years now is defined in terms of the second and the metre, via h, the Planck constant. So it's all now about the speed of light and whatnot!

As you can see in the natty relationship schematic above****, it's an elegant and pretty system befitting the elegance of science. But, the kg lost its easy-to-visualise and -handle metric definition to an equation both confusing and beyond the scope of Your Correspondent to properly understand let alone put into sensible words - even interweb boffins scoff at one another's attempts to explain!

Luckily, it seems you can construct a kilogram equivalent with plain physics, and the various National Institutes of Measurement propose to use the aforementioned Kibble balance to make it so. And that, Dear Reader, is why anyone might want one. And will by necessity have to build one, since not even Mr. Bezos has one to sell you (it seems we've forgotten the for all men creed). *****

But ...

What about the Law of Unintended Consequences?

What if the end-of-days comes and the electricity is switched off forever and we're sitting about in the New Dark Ages? Even a LEGO Kibble balance will be useless, for it needs a couple of battery-run laser pointers and hooking up to some computer software, via, you know, a power point. Much less the handful of multi-million peso white elephant Kibble balances that have a whole viper's nest of power cords to plug in. 

And if we need to reinvent basic commerce again, measuring out food and materials on two-arm balance scales, a nugget of platinum is just the ticket to check a scale against swindlers. Mind we don't toss the precious platinum babies out with the bathwater in our haste to make measuring stuff elegant and futuristic and founded on the laws of physics, for we are as sure as onions going straight back to an arbitrary world of measuring said world with autocratic body parts and seeds and shells.

Stock up on the tools of the trade now &
You'll become a High Priest of Metrology!

This is all rather doom-and-gloom, I know, and along the way I've discovered interesting things: for inst., among the end-of-civilisation preppers, there are some stockpiling things like triple beam balances and spring-based scales, Pyrex measuring jugs and tape-measures and whatnot. Like the scribe who will be required for the functionally illiterate being churned out of our education systems, the home-metrologist with the locked vault of calipers and balances and measures will join the elite ranks of the mystery cults when the batteries in everyone's digital bathroom scales and whatnot go kaput.

And even if this over-wrought future does not come to pass, (the mind does go to strange places when insomnia takes a grip), at the very minimum science as a school subject will become even more baffling to kids and there'll be even less able teachers coming through the ranks. If we all thought we once knew what a kilogram meant in principle, that's now gone out the window. Science has become hard again.

Not to mention that the egalitarian principles about weights and measures have been theoretically taken back from the everyman into the hands of the elite (read countries with the $$ and institutions to make this stuff mysterious again).

I did express these concerns in email communications with a Guv'ment metrologist at Australia's NMI, and asked for specifics about the destiny of our copy of Big K, and a whole suite of other pertinent questions, alongside philosophical questions relating to the obvious folly of relying on the need for the electricity to be switched on to define the kilogram. 

The boffin assigned to my impertinence was stubbornly mute on the salient points and made general noises about science being exciting and hard work and much $$ and waiting with interest while "international partners" get on with it and at least 10 years &c. &c. 

Reading between the lines, this country's Guv'ment is sitting on its hands and hoping to buy cheap versions off-the-shelf one day (with some custom finishes, obv, for that's how we roll in this land) and if the world goes to hell-in-a-handbasket in the meantime, we'll be sitting pretty with our copy of Le Grand K and crowing about foresight.

But I think the last word should go to Mr. Marcus P. Foster, a now-retired researcher at the CSIRO who some years ago published a paper on the future of the SI: "It is easy to conceive of a shiny new logical, consistent, unambiguous quantity and unit system. Admittedly, introducing such a creation would be expensive and difficult, and it would likely become the Esperanto of unit systems, admired but ignored." Phew! So much for a weighty matter. I've been losing sleep over nothing then.

* Viz. the second, metre, kilogram, ampere, kelvin, mole and candela.

** And still used today in such diverse and obscure things like measuring shoe sizes and humidity and gold fineness and archer's arrows!

*** The metre being defined as one ten-millionth of the distance from the North Pole to the Equator along the Paris meridian (and a whole other story).

**** Yes, yes, the mole is sitting on its Pat Malone in this schema but it is defined by the Avogadro constant and see how nicely it closes the heptagon.

***** So don't forget to add LEGO to the Xmas wish list!

Image credits: 1: Rijksmuseum; 2: NIST; 3-5: via Google


  1. I had always believed the 'kilo' to be the weight of a litre of WINE, not water; because water was never sold, and wine was! The metre we all know to be the length of a Roman soldier's pace (very accurate), and a foot to be the length of an average person's foot (even more accurate). All this making the Kibble Balance totally unnecessary.

    1. Bravo, dear Cro, for braving the workings of the fraught Pipistrello, and you can see straight through the Emperor's new clothes, too! Much $$ frittered away for what? I'd not heard the water into wine theory such as yours before now. Makes a seat-of-pants kind of sense.

  2. Splendid post well written and good reading.
    In my dyslexia I read "and brought us Le Grand K" as "and brought Ursula K. Le Guin" which is very good. (this is Urspo)

    1. Thank you, dear Urpso! Any mention of Earthsea around these pages is always welcome. Even when it's an eyes-mind sleight of hand trickster kind :)

  3. It's but laziness that is cutting this comment short, Signora Pipistrello: Excellent!


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