We measure things all the time ̵
Attempts have been made to define the units of measurement over the years. But today, International Metrology Day sees the complete revision of these standards in play.
You will not notice anything – you will not be heavier or lighter than yesterday – because the transition has been made to be seamless.
Only the definitions of the seven base units of the SI (Système International d & # 39; Unites or the international unit system) are now completely different from yesterday.
How we used to measure  People have always been able to count, but as we evolved, we quickly moved to measuring lengths, weights, and time.
The Egyptian pharaohs caused the pyramids to be built based on the length of the royal forearm, known as the Royal Cubit. This was held and proclaimed by engineering clergymen who maintained the standard of death pain.
But the cub was not a fixed unit over time – it was about half a meter, plus or minus a few tens of millimeters by today's measure.
The first proposal for a universal set of decimal measures was made by John Wilkins, in 1668, then Secretary of the Royal Society in London.
The progress of doing something practical came with the French Revolution. It was the French who defined the first standards of length and mass with two platinum standards representing the meter and the kilometer on June 22, 1799, in the Archives de la République in Paris.
Scientists supported the idea, the German mathematician Carl Friedrich Gauss was particularly keen. Representatives of 17 nations came together to set up the international unit system by signing the Convention on the Metric Convention on May 20, 1875.
France, whose street circle had threatened violence in the Franco-Prussian war and was not the scientific power it once was, a beaten chateau in the forest of Saint-Cloud offered as an international home for the new system.
The Pavilion de Breteuil still houses the Bureau International de Poids et Mesures (BIPM), where the international prototype of the Kilogram (hereinafter Big K) in two safes and three glass bristles.
Big K is a polished block of platinum iridium used to define the kilogram, against which all kilogram weights are ultimately measured. (The original is only weighed three times against a number of almost identical copies.)
The British, who had been prominent in the discussions and had given the source of the platinum iridium, refused to sign the treaty until 1884.  Even then, the new system was only used by scientists where everyday life was measured in traditional imperial units such as pounds and ounces, feet and inches.
The United States signed the treaty during the day, but it never actually implemented it and hung on its own version of the British Imperial System, which it still uses most today.
The US may have destroyed this decision in 1999 when Mars Climate Orbiter (MCO) went away in action. The report in the incident strangely called an "accident" (which cost $ 193.1 million in 1999) and said: "[…] The reason for the loss of MCO spacecraft was the lack of metric units coding a ground software file , "Small Forces" used in runway models. "
Essentially, the spacecraft was lost in the Mars atmosphere, as it went down lane than planned.
The new SI definitions
So why change today? The main problems with the previous definitions were, for the kilogram, that they were not stable and for the electric power supply, the amplifier could not be realized.
And from weighing against official copies, we believe that Big K lost mass mass.
All units are now defined in a common way by what BIPM calls the "explicit constant" wording.
The idea is that we take a universal constant – for example, the speed of light in a vacuum – and from now on we store its numerical value to our best-measured value without uncertainty.
The reality is fixed, the number is fixed, and therefore the units are now defined.
We should therefore find seven constants and make sure that all measurements are consistent in measurement uncertainty and then start counting down to today. (All technical details are available here.)
Australia had a hand in designing the red macroscopic object on the ground, a silicon sphere used to measure the Avogadro constant, the number of units in a fixed amount of substance. This now defines the SI unit, mole, which is widely used in chemistry.
From standard to artifact
What about the Big K standard source? Today, it becomes an object of great historical importance that can be weighed and its mass will have measurement uncertainty.
From today, the kilogram is defined by the Planck constant, something that does not change from quantum physics.
However, the challenge is to explain these new definitions for humans – especially non-scientists – so they understand. It is easy to compare a kilogram to a metal block.
Technically, a kilogram (kg) is now defined: "[…] by taking the fixed numerical value of the Planck constant h to 6.626 070 15 × 10 -34 when expressed in the unit Js, which is equal to kg m 2 s where the meter and the second are defined in terms of c and Δν Cs ]. "
Try to explain it to anyone!
Kilomet is redefined – explains a physicist
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The way we define kilograms, meters and seconds changes today (2019, May 20)
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