Thursday, June 20, 2019
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The world is being re-measured

HDid you already weigh yourself this morning, look at the thermometer, or perhaps even read the electricity meter? And have you noticed no change? However, from this Monday (May 20, 2019) new rules apply as to how the world will be measured. From now on, the more than one hundred member countries of the Meter Convention unanimously voted in Versailles on November 16, 2018, receiving from the seven basic physical units of the International System of Units (SI) – seconds, meters, kilograms, amps, Kelvin, Mol and Candela – even the last one a new foundation, and indeed the most stable thing that physics has to offer: natural constants. These quantities are – as far as we know today – immutable for all eternity. Ideal prerequisite for calibrating the coordinate system with which we measure time, space, mass, temperature or electricity. Another good news: In everyday life you will notice nothing of this new regulation.

Manfred Lindinger

The reason for the completed remediation of the SI system is due to deficiencies in previous definitions of kilogram, kelvin, ampere and mole, the unit of chemical mass. These variables were in contrast to meter and second until yesterday on idealized, but impractical measurement requirements, unstable material properties or artificially created artifacts set. These historically grown conventions had long since ceased to meet the precision requirements of the present, and certainly not of modern metrology, which can count atoms and weigh molecules.

The Urkilogramm loses in mass

The kilogram required the greatest need for action. Because the unit of the mass was the only one of the SI basic sizes, which was still set on a reference object – a cylinder made of a platinum-iridium alloy. All the weights of the world, including those of the store around the corner, related to this Urkilogramm, which is kept since 1889 in a vault in Sèvres near Paris. A scare the guards of the Urkilogramms when they found that their gem has become easier over time against some of its duplicates, by 50 micrograms. Because of its "volatility" was the metrologists the Paris Urkilogramm therefore long a thorn in the eye. To make matters worse, central physical quantities such as energy, pressure or force and thus the amperes, which are linked to the fragile original kilogram, were therefore not reliable enough.

Rescue by the immutable

So it was high time for a general overhaul of the SI system, which was officially introduced in 1960 and whose regulations are committed to almost all countries of the world. Exceptions: the United States, Liberia and Burma. In recent years, thanks to sophisticated experiments, it has been possible to determine many natural constants very precisely. Out of seven of these Immutable, the values ​​are now so well known that they can be used to set the base units of kilograms, amps, kelvin, and moles. And if the natural constants are determined more accurately, then the units will also benefit accordingly.

. (TagsToTranslate) primary kilogram (t) Candela

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