What is a kilogram?
The technical definition of a kilogram is not consistent with how it’s treated by scientists.
Until May 20, 2019, scientists will tell you that a kilogram was anything that weighed the same as International Prototype Kilogram, IPK, a platinum alloy kept in a safe in France.
But is that what a kilogram really is? Suppose it were otherwise, would the world be any different? I don’t mean to ponder whether it takes, say, fewer atoms of Platinum to measure one kilogram; rather to ask whether by some historical accident if we had used a different sized IPK then would the world be any different? While this is an untestable counterfactual, I think everyone will agree that the exact weight of a kilogram doesn’t actually matter so long as we all agree on what that weight must be. (I think this is so because the definition of the kilogram has changed many times in the past and yet, here we all are.) It’s easy to imagine a different universe where everything’s the same as ours except their kilograms are heavier than ours. (Maybe they just took a bigger platinum alloy for their IPK.) So, while the me from this universe and me from that universe would weigh the same, his BMI would be on the right side of 25¹.
Why does the IPK definition hold only until May, 2019?
Because last week, on Nov 16, 2018, they decided to redefine “four of the seven base units of the SI: the kilogram, ampere, kelvin and mole; and all units derived from them, such as the volt, ohm and joule”. ‘They’, in this case are the International Bureau of Weights and Measures (BIPM). It was decided at the General Conference on Weights and Measures in Versailles, France.²
Why did they decide to change it?
Because, in “1988–1992, when [the IPK] participated in a formal verification of all kilogram prototypes belonging to the 51 Meter Convention member states” it found the IPK was lighter than many of its clones. The article continues that this “alarming show of instability is driving global efforts to redefine the kilogram”³.
When you think about it, this is a rather curious reaction. For, if the kilogram were, by definition, whatever the IPK weighed, then the scientists wouldn’t have reacted with alarm but set out to adjust the weight of the clones and perhaps looked for ways to keep the clones from changing. That they did this reflects, certainly to me, that the kilogram isn’t what it’s defined as but as something independent of this definition. If I go to the grocery store and the vegetables are more expensive today than they were last week, I don’t get into a discussion on value-theory with the store clerk. Instead, I take it that (say) if bananas cost $1 last week but $10 this week, that’s what they cost.
In his posthumously published book, Philosophical Investigations (1953), the philosopher Ludwig Wittgenstein observed that,
There is one thing of which one can state neither that it is 1 metre long, nor that it is not 1 metre long, and that is the standard metre in Paris. — But this is, of course, not to ascribe any remarkable property to it, but only to mark its peculiar role in… measuring with a metre-rule. (pg 29ᵉ)
At that time even the meter was defined by a stick in France (of what length, I cannot tell you, because I do not wish to be haunted by Wittgenstein’s ghost). In 1983 they redefined the meter to be a factor of the speed of light.
A real example that’s more in line with Wittgenstein’s thinking is economics. If I wished to measure, say, what it would cost me to drive my car from point A to point B, I cannot do it because the fuel prices keep fluctuating so. In a stable economy I could perhaps give an estimate with a ± but just as the BIPM scientists wouldn’t accept such an answer I don’t see why I ought to. Furthermore, what happens if I’m in hyperinflation Zimbabwe? (Google it, it’s at once alarming and hilarious.)
This reminds me of the bitcoin joke:
A boy asked his Bitcoin-investing dad for $10.00 worth of Bitcoin currency.
Dad: $9.67? What do you need $10.32 for?⁴
My favorite example in these lines is from Joseph Heller’s 1961 masterpiece, Catch-22. The book is set during WWII and revolves around some American troops stationed on the island of Pianosa, just off the coast of Italy. The military’s top brass plan to send the airforce to bomb the town of Bologna and for various reasons the bombing keeps getting delayed (some detailed below). In the excerpts below, pay special attention to “the bomb line”:
When it did stop raining in Pianosa, it rained in Bologna. When it stopped raining in Bologna, it began again in Pianosa…. All through the day, they looked at the bomb line on the big, wobbling easel map of Italy. The bomb line was a scarlet band of narrow satin ribbon that delineated the forward most position of the Allied ground forces in every sector of the Italian mainland.… [T]hey began to hate the bomb line itself. For hours they stared relentlessly at the scarlet ribbon on the map and hated it because it would not move up high enough to encompass the city. When night fell, they congregated in the darkness with flashlights, continuing their macabre vigil at the bomb line in brooding entreaty as though hoping to move the ribbon up by the collective weight of their sullen prayers.
‘I really can’t believe it,’ Clevinger exclaimed to Yossarian… ‘It’s a complete reversion to primitive superstition. They’re confusing cause and effect. It makes as much sense as knocking on wood or crossing your fingers. They really believe that we wouldn’t have to fly that mission tomorrow if someone would only tiptoe up to the map in the middle of the night and move the bomb line over Bologna. Can you imagine?’ … In the middle of the night Yossarian knocked on wood, crossed his fingers, and tiptoed out of his tent to move the bomb line up over Bologna.
Sure enough, once the bomb line was moved, the news percolated up the chain of command and the mission to bomb Bologna was once again canceled.
Footnotes
¹ Yes, I know BMI isn’t a great measure.
² Nov 16, 2018, National Physical Laboratory, http://www.npl.co.uk/news/international-system-of-units-overhauled-in-historic-vote.
³ “The Kilogram Isn’t What It Used to Be — It’s Lighter”, by Dava Sobel, published March 2009 http://discovermagazine.com/2009/mar/08-kilogram-isnt-what-it-used-to-be-its-lighter.
⁴ I don’t remember where I originally read it but Google gave me the above version on Reddit which I’ve copied verbatim. Reddit link: https://www.reddit.com/r/Jokes/comments/7ieoji/a_boy_asked_his_bitcoininvesting_dad/.
