From the 20th of May 2019, the way the kilogram is measured and standardised is going to change. The difference is so tiny that it won’t change the way you do anything. But it’s a huge deal because it will affect every scientific and technological industry and enterprise. So, why all the fuss and effort?
In the Beginning: Establishing Standards
Hundreds of years ago, we had no uniform way to measure anything. Think about what that must have been like. If you ventured into another village, it would almost be like trying to speak another language. As humans moved around trying to connect with each other and share knowledge, this was clearly not going to do.
The obvious solution was to standardise measurements. In the late 1700s, the metric system was established to do just that. The International System of Units had 7 basic measurements, with the idea being to make them “for all times, for all people” according to Stephan Schlamminger, head of the National Institute of Standards and Technology in the United States.
The 7 measurements are the meter, the second, the mole, the ampere, the Kelvin, the candela and, of course, the kilogram. They made our functional, physical world possible. Without them, trains wouldn’t run on time and we literally wouldn’t even know it if they were.
Up until now, the reference for the kilogram has been Big K, or Le Grande K, a piece of iridium and platinum that is kept in a temperature-controlled vault in the International Bureau of Weights and Measures, located in Sèvres, France.
Big K Isn’t Constant Enough
The thing about physical reference points is that they change and degrade, depending on where they are in the world, and what elements they are exposed to. Apparently, this is always true, even when something is in a vault, with temperature control, and nestled under 3 glass bell jars.
Over time, all the measurements in the International System of Units have been replaced with constants that have been determined by physicists. A lot of us are only learning about this now, but the kilogram is actually the last to go.
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Replacing the actual weight with a constant figure that is the same everywhere makes sense anyway, but it has become imperative. Big K has only been removed and measured a few times, but its mass has lessened by 50 micrograms.
That’s the size of a grain of salt, which is tiny in our day-to-day lives but could have a massive impact in industry and research settings. Besides this, if the constant reference point is not, well, constant, we’re not really going to know what we’re doing.
The 2011 Resolution
In 2011, the General Conference on Weights and Measures passed a resolution to redefine the kelvin, the ampere, the mole and the kilogram. Now, at last, it is the kilogram’s turn. For the past 7 years an international team of scientists, including Schlamminger and many other noted thinkers, has been working on this new definition. The fundamental factor that it will now be based on is known as Planck’s Constant.
What is Planck’s Constant?
This constant was discovered by a physicist called Max Planck and, essentially, put the Quantum into Quantum Physics. Planck determined that the photons of all atoms vibrate at a certain frequency, or whole-number multiples of that frequency. He named that frequency h, and this is what has become known as Planck’s Constant.
Applying this to the current Big K problem, the Kibble Balance is used. This is like a measuring scale, but instead of knowing how much one side weighs and then comparing it with another until they balance, the multiple of Planck’s Constant can be determined. The amount of atoms that is present in a 1-kilogram silicon sphere has also been determined, and through calculations can be converted to Planck’s Constant.
By triangulating these two methods, the project’s researchers have been able to refine kilogram measurement to within a certainty of 1 part in 100,000,000. This is about the quarter of the weight of an eyelash. On 16 November 2018, the General Conference on Weights and Measures met in Versailles, and representatives from more than 60 countries voted that this was good enough.
The smooth co-operation and adoption of this new system is heartening, and shows that people can co-operate to make daily life work better for us all. Perhaps some of our current politicians should take a leaf out of the scientific community’s book!