The way we measure things will radically change in 2019. Today in Versailles, representatives of the 60 member states of the Bureau International des Poids et Mesures have voted unanimously for the adoption of a revised system of units. Now, all seven fundamental base units will no longer be defined by comparing them to a physical object but by the fundamental laws of the universe. The change will come into effect on May 20, 2019.
The International System of Units, or SI, is historically based on seven quantities from which all the others are defined. SI units include the meter, the second, and the kilogram, which most people are familiar with. Quite well known are the kelvin, the official unit of temperature, and the ampere, which is used in measuring electrical current. Then there are the two more unusual ones: the mole, which is the amount of substance of a system, and the candela, which is the unit for luminous intensity.
The vote will have the kilogram, the kelvin, the ampere, and the mole finally defined by physical constants, and the meter, the second, and the candela will have their definition only slightly edited based on the bigger changes. The seven constants will from now on be defined as single numbers with no uncertainty. The numbers we have are exact values and they won’t change ever again.
“The importance of changing the four units is about the foundation of measurement. Because these standards are used in so many places, we take a very conservative attitude towards changing anything about the way they are defined,” Dr Michael de Podesta, a metrology expert from the National Physical Laboratory, told IFLScience.
“We are trying to put in new foundations which are indistinguishable in size, so there should be no change in the way 'the building' is supported. They are made of new materials so they’ll never crumble or crack."
How will it affect us? "People won’t notice," he added. "If people notice, we’ve screwed up!”
However, this is not a simple revolution in metrology. It’s an epochal shift. Since the dawn of civilization, humanity has tried to standardize measurements. After all, measurement is a quantitative comparison of one thing against another. You can make a universal stick or pick the length of your king’s foot. Base your temperature on boiling water or freezing brine. There are lots of ways to create scales. But as long as you use a physical object, your measurements will have fundamental limitations. The kilogram is the perfect example.