# May 20, 2019 is the day the world begins to use new definitions of kilograms.

On May 20, 2019, the scientific community around the world will begin to use the new definition of 4 units of measurement including kilograms, meters, seconds and amps (the other 3 units are Kelvin Mole And that candle will be officially announced in 2026 )

This decision was the outcome of the 26th meeting of the General Conference on Weights and Measures on November 16, 2018, in Versailles, France. When all 60 member countries unanimously decided to define 7 standard measurement units based on various constants in nature including velocity, light, constant, Boltzmann, electron charge, Planck constant, etc., with no change And there are no errors like the speed of light is equal to 294,792,458 meters / second. As defined earlier, there are standard wood meters. And mass standard kg In fact, these things were never standardized. Because the length of the meter AND the weight of the mass is not equal every time there is a measurement

From the past, ancient peoples wanted to communicate with one another about size, volume, area, time, temperature, distance, etc. They had to measure and compare the values ​​obtained. And he discovered that trade between foreigners and foreign languages ​​became very difficult and agreed upon. As each nation uses different units of measure, for example, the Romans use units of weight as pounds (1,728 carats). Traders who sail in the Mediterranean Sea use 1,000 grains of wheat or barley as the standard unit of weight. The Romans used the measure of distance as a uncia, giving the length of the king equal to 12 uncia. The English used the finger as a unit of measurement of length. When specifying the width of a man's thumb (1 inch is about 2.5 cm) In the year 790, the French Emperor Charlemagne determined that the length of the king on his feet were standard feet (32.5 cm).

Later, the English people defined the standard length as 1 yard, the length of the cycle (waist), which with the passage of time, the length of this waist is not stable. Until the beginning of the 12th century, Henry 1 therefore established a new pattern for 1 yard in length, giving a distance from the tip of the nostrils (nose) to the end of the Angkut (thumb). Provide convenience for people who want to use it at all Because when one wants to have a good standard measure, it should be disturbed by the heart all the time.

Therefore, in 1445, King Henry 1 ordered the designers to create a model of standard yards. A straight long bar made of silver But there was another unstable value Because if money used has other elements mixed The expansion or contraction of standard yard bars will be different. When the temperature changes

This is to show that everything that is created by man can not be used by default

For standard weight, there are also problems with the setting. The ancient Egyptians had two weight standards, one of which was the standard weight of the pharaoh. And the second type is the standard weight of the villagers Pharaoh will collect the villagers' land tax in the form of agricultural products according to Pharaoh's standard. But when the king wants to buy products from the villagers He will mainly use the pattern of the farmers. Because the pharaoh's standards are more valuable than the farmers So when switching products The property in the treasury will be added each time.

In ancient Greece, mass was defined as a talent, which is the mass of water used to fill the Greek water amphora, that is, the standard mass is about 28 kilograms. But we know that each pitcher containing water does not have the same volume So confusion And then cheating occurs frequently

For the temple area, it is equally chaotic, for example, in the Roman state, the area was designated as 1 ager (this term means rice fields). And converted into acre later) is the area where 2 cows can be plowed for 1 day because all cows are unequal and the plowing area gives the plow a comfort that is not the same. The 1 acre area, therefore, has a value that depends on the cow and the condition of the rice field.

The year 1789, which was the year in France, caused a great revolution, with the fall of the French Academy Lord Louis, 16. In seeing the chaos of the country in all respects, there is no standard. This can be used as a device Even in France, people in different regions use different units of measurement, such as the 1 place of people in the north, with about 3 miles in length, but for the people of southern France. This same unit is a distance of 6 kilometers.

The revolutionary committee, therefore, established a committee for scientific reform. With two world-famous scientists and mathematicians Antoine Laurent de Lavoisier and Joseph-Louis Lagrange as president and deputy chairman of the reform This committee agreed that To facilitate the use and calculation The default unit should use the base number 10 using the prefix deci = 10.-1centi = 10-2, milli = 10-3micro = 10-6nano = 10-9peak = 10-12 E femto = 10-15 Or deca = 101, kilo = 103mega = 106giga = 109tera = 1012 E peta = 1015 Etc.

Then 1 microgram, therefore, = 10-6 G. and the committee determined that the length of 1 meter is = 1 / 10,000,000 from the pole distance until the latitude mapped via Paris to the equator. And to get a standard distance of 1 meter is concrete The committee gave two astronomers named Jean-Baptiste-Joseph Delambre and Pierre-François Andre Mechaim and an assistant named François Arago to create a new future of a standard length of 1 meter.

The research team spent 8 years traveling to measure distance as specified. And simulated 1 meter long. The standard is a bar made of platinum metal to the whole world to refer to And brought this standard meter to the emperor Napoleon Bonarparte, who made him very happy Because thinking that from now on the whole world will accept what French scientists do Because at that time the French Empire was very powerful So acceptance is likely to be very likely.

But the truth can not be found Because other national scientists are of the opinion that the measurement is very flawed The main thing is that the world does not have smooth skin like orange. The values ​​obtained from the measurement are approximate.

Until 1960, satellite images showed that The distance from the north pole to the equator is not equal to 10,000 kilometers, but is 10,002 kilometers.

Scientists have to find a new standard length of 1 meter. In 1983, the Organization for Standardization determined that the length of 1 meter is the distance that light travels in a vacuum in a time of 1 / 299,792,458 seconds.-8 This second is a story that today's physicists can do comfortably. (We currently have the optical clock that can measure the most accurate time. It is a mistake to walk no more than 1 second in 14,000 million years)

In terms of the definition of a standard mass, 1 kg was also reformed from the original in 1889, in which the standard mass of 1 kg was a cylindrical bar made of platinum metal mixed with iridium and collected in a vacuum glass lid. In the storage room at Sevres, outside Paris, although the dough is well protected. Do not let the dust fall. And the standard mass was simulated by 6 masses. The new mass measurements for all six simulations gave different results for all 6 masses , which means that the mass of the prototype should also be changed. This is because the atoms that are on the surface of the mass With movement in and out Therefore, the standard mass is unstable.

Another fear of the French scientists is whether the standard mass is stolen Or the standard mass storage facility has been bombarded The world will be free of the standard mass immediately. As an event that occurred in 1834 in the British mass standard of 1 pound That was stored in the Palace of Westminster was destroyed Because the museum that collected mass was burned

Therefore, scientists have to try to define the definition of a new standard mass of 1 kg using the principle that they do not have to trust or invoke any invention. But use natural constants instead, such as the Planck constants that are set to 6.62607015 x 10-34 Kilogram 2 meters / second, because h is a quantity related to quantum energy and the unit of h consists of kilograms, meters and seconds, so if able to accurately measure h, distance of the meter and seconds of time will know immediately the value of the mass kg

In 1975, Bryan Kibble and the faculty proposed a method to find the standard kilogram. Using techniques related to NMR (nuclear magnetic resonance) research using Watt scales (Watt balance), which are nowadays called Kibble balance, which depend on the power to resist mechanics. Keep the system in balance

Kibble's scales consist of coils hanging from the scales. What is in the magnetic field with flux density equal to B when electricity is released in the coil Will cause gravity When in equilibrium

mg = BI kW (1)
In this equation, m is the mass of the coil, g is the acceleration due to the Earth's gravity and kW It is a constant that depends on the nature and shape of the coil

When the energy is turned off And then moving the coil to the magnetic field at a velocity of v will cause the electric force This can be obtained from equation

E = Bv kW(2)

From equation (1) and (2) if k is eliminatedW Will stay
EI = mgv (3)

Here mgv is power of mechanics

He is the power

Which these values ​​can be accurately measured, as E, is measured by the Josephson constant, whereas I is measured by the quantum resistance of the hall.

Then, representing the resistance Hall = h / e2
E of the current constant of Josephson = 2e / h

Then mgv = 4 / hr

So if we measure h, gev, we can measure m

In the whole picture, this is a measure of mass. Using electrical technology

When this was the case, any laboratory in the world with the Kibble scales used physicists there to measure mass without the need to travel to compare with the default values ​​in Paris.

Another way scientists use to find 1 kilogram of mass is to create a sphere made of pure 28-silicon atoms and count the number of atoms in that sphere.

The new setting of this default drive will not affect the convenience of many residents. But for scientists This is the agenda to set new standards important for the Le Grand K that the world has been using for 100 years and that should be reduced to a second priority. From May 20 onwards