In 1960, important events took place, for example, seventeen African countries became independent, John F. Kennedy was elected as the president of the USA, and Fidel Castro held 4.5-hour marathon speech in the United Nations.
A less known event in 1960 was the redefinition of meter. It started a series of events which will be completed next year. Meter had been introduced already in 1799 and it was based on the length of one particular metal bar which is stored in Paris, France. The definition of meter was further defined a few times but in 1960 it was replaced with a definition based on the wavelength of krypton spectral lamp.
In 1983 the speed of light in a vacuum was declared as a physical constant. It has since formed the basis for the definition of meter. An exact constant offers the best possible definition for meter now and also in the future.
Next year is going to be big for measurement science. The International System of Units (SI) is going to be revamped and all units will be based on physical constants. SI units have always been based on the most exact methods available at the time. The new system will be published in the 26th meeting of the CGPM in Versailles and adopted on May 20th 2019 which is the annual World Metrology Day.
In addition to meter, SI units are kilogram, second, ampere, kelvin, mole, and candela. The new definitions of these units and their usage guidelines are already available for download.
For example kilogram will get a new definition next fall. At first, kilogram was defined as a cubic decimeter of water. At the end of the nineteenth century, a platinum-iridium prototype of kilogram was created and stored also in Paris. Kilogram has been the final obstacle for renewing the SI system. Over a hundred years old prototype has been the best way to define kilogram until these days.
In 2011 started a development work based on two methods, which enable adopting the new definition. These methods are based on watt, or Kibble, balance and the number of atoms in a silicon sphere. These new methods are linked together with Planck’s constant.
Defining SI units might feel quite distant for a layman. However, the more you think of it, the more important it starts to seem. The exact nature of units is in the core of science and you have to be able to trust them in calculations and applications built on top of those calculations. Well-functioning definitions also enable global collaboration. This is essential in modern industry, where products are assembled of components from all over the world.
There are dozens of application areas for measurement science. Trade and industrial production are the most traditional ones. The amount of measurement data grows at an accelerating speed also on other domains and exact methods enable better functioning applications. In some areas such as healthcare, energy, and aviation even the smallest measurement errors can lead to catastrophic consequences. New areas enter the field of measurement science all the time. At the moment such are for example environmental technologies and manufacturing.
As the national metrology institute, VTT has a special role in Finland regarding measurement science and SI units. It is VTT’s responsibility to maintain, develop, and control the SI system in Finland. And being a research institute, VTT naturally carries out several measurement science projects together with domestic and international partners.
The prototypes of meter and kilogram are these days secondary. You don’t have to base your calculations on them anymore. In 2018, as the new SI units will be introduced, measurement science will again jump to a next level.
Vice President, MIKES Metrology
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