In 1872, by decision of the International Commission on Standards of the Metric System, the mass of the prototype kilogram, stored in the National Archives of France, was adopted as a unit of mass. This prototype is a platinum cylindrical weight with a height and diameter of 39 mm. Prototypes of the kilogram for practical use were made from a platinum-iridium alloy. A platinum-iridium weight, closest to the mass of the Archive’s platinum kilogram, was adopted as the international prototype of the kilogram. It should be noted that the mass of the international prototype kilogram is somewhat different from the mass of a cubic decimeter of water. As a result, the volume of 1 liter of water and 1 cubic decimeter are not equal to each other (1 liter = 1.000028 dm 3). In 1964, the XII General Conference on Weights and Measures decided to equate 1 l to 1 dm 3.
The international prototype of the kilogram was approved at the First General Conference on Meters and Weights in 1889 as a prototype of a unit of mass, although at that time there was no clear distinction between the concepts of mass and weight and therefore the mass standard was often called the weight standard.
By decision of the First Conference on Weights and Measures, platinum-iridium kilogram prototypes No. 12 and No. 26 were transferred to Russia from 42 kilogram prototypes produced. The kilogram prototype No. 12 was approved in 1899 as an optional state standard of mass (the pound had to be periodically compared with the kilogram) , and prototype No. 26 be used as a secondary standard.
The standard includes:
a copy of the international prototype of the kilogram (No. 12), which is a platinum-iridium weight in the form of a straight cylinder with rounded ribs with a diameter and height of 39 mm. The prototype of the kilogram is stored at VNIIM. D. M. Mendeleev (St. Petersburg) on a quartz stand under two glass covers in a steel safe. The standard is stored while maintaining the air temperature within (20 ± 3) ° C and relative humidity 65%. In order to preserve the standard, two secondary standards are compared with it every 10 years. They are used to further convey the size of a kilogram. When compared with the international standard kilogram, the domestic platinum-iridium weight was assigned a value of 1.0000000877 kg;
equal-arm prism scales 1 kg. No. 1 with remote control (in order to eliminate the operator’s influence on the ambient temperature), manufactured by Ruprecht, and equal-arm modern prism scales for 1 kg No. 2, manufactured at VNIIM. D.M. Mendeleev. Scales No. 1 and No. 2 serve to transfer the size of a unit of mass from prototype No. 12 to secondary standards.
Error in reproducing a kilogram, expressed by the standard deviation of the measurement result 2. 10 -9. The amazing durability of the standard unit of mass in the form of a platinum-iridium weight is not due to the fact that at one time the least vulnerable way to reproduce the kilogram was found. Not at all. Already several decades ago, the requirements for the accuracy of mass measurements exceeded the possibilities of their implementation using existing mass unit standards. Research into mass reproduction using the known fundamental physical mass constants of various atomic particles (proton, electron, neutron, etc.) has been ongoing for a long time. However, the real error in reproducing large masses (for example, a kilogram), tied, in particular, to the rest mass of the neutron, is so far significantly greater than the error in reproducing a kilogram using a platinum-iridium weight. The rest mass of a single particle - a neuron - is 1.6949286 (10)x10 -27 kg and is determined with a standard deviation of 0.59. 10 -6.
More than 100 years have passed since the prototypes of the kilogram were created. Over the past period, national standards were periodically compared with the international standard. In Japan, special scales have been created using a laser beam to record the “swing” of a rocker arm with a reference and tare weights. The results are processed using a computer. At the same time, the error in reproducing a kilogram was increased to approximately 10 -10 (according to standard deviation). One set of similar scales is available in the Metrological Service of the Armed Forces of the Russian Federation.
What is a kilogram? Children's question! This is the mass of a liter of water. To get it at home, all you need is a water tap and a liter jar. But the “real and full-bodied” standard kilo has recently been rapidly losing weight.
Alas, the world standard kilogram, as is clear from the New York Times, has fallen victim to a mysterious and long-lasting illness. Let's take a look at the history.
In the 18th century, a kilogram was defined as the mass of a cubic decimeter of water at the temperature of its highest density (4 o C). As it turned out, such a definition is not entirely constructive: you need a very accurate cubic decimeter, completely clean water and an absolutely correct thermometer.
For additional information about the sick person, please refer to the Book of Fates - TSB.
“The kilogram, a unit of mass, is one of the seven base units of the International System of Units (SI). It is equal to the mass of the international prototype stored at the International Bureau of Weights and Measures. The prototype in 1799 was made in the form of a cylindrical weight made of platinum.
The mass of the prototype kilogram turned out to be approximately 0.028 grams more than the mass of one cubic decimeter of water.
The most important kilogram today is just a piece of iron (photo bipm.org).
In 1889, the existing definition of the kilogram was adopted and a weight with the sign K (“K” is a Gothic capital), made of a platinum-iridium alloy (10% Ir) and shaped like a cylinder with a diameter and height of 39 mm, was approved as an international prototype.”
It turns out that the platinum-iridium kilogram, created by an English jeweler, is the only basic SI unit that has valiantly preserved its definition since the century before last. And itself stored in the form of a material artifact.
The meter, for example, initially correlated with the length of the earth's circumference, is now equated to the distance traveled by light in one 299,792,458th of a second. And the second itself is the time during which a cesium atom makes 9192631770 vibrations.
Not only are these units defined with appropriate quantum precision, but they can also be adequately reproduced anywhere in the world. Cloning a kilogram is much more difficult, in addition, it requires a complex bureaucratic procedure.
Apparently, for a long time this unique position of the kilogram suited everyone, since there were not sufficient incentives to create its scrupulous formula.
But the changeable kilogram drags with it the Watt and other related units of measurement into drifting swimming.
And there is no doubt about the variability of the kilogram, despite all the precautions: the standard is stored under three sealed glass covers in the safe of a guarded castle in the vicinity of Paris, and the keys to the safe are held only by three especially close bureaucrats from the International Bureau of Weights and Measures (Bureau International des Weights and Measures). Poids et Mesures - BIPM).
Kilogram and 6 of his henchmen are kept in a permanently locked safe (photo bipm.org).
Along with the main kilogram, there are 6 successors in the safe, and in total during his reign, more than 80 copies were made in his image and likeness.
For the examination of the elderly kilogram, which occurs once a year, it is ceremonially removed from its storage. And every time a microscopic weight loss is detected.
The kilogram is wasting away. This is clearly demonstrated by comparisons with other inhabitants of the safe. The nature of the disease is mysterious, but all the symptoms are obvious: in a hundred years, a kilogram loses about 0.00000003 of its precious mass.
But even losing weight by just 50 micrograms (less than the weight of a grain of salt) can seriously distort the results of complex scientific calculations. There is no doubt about the need to replace the unique kilogram with an abstract kilogram.
An international team of researchers from Germany, Australia, Italy and Japan, under the auspices of the German standards laboratory, wants to redefine the kilogram as the mass of a certain number of atoms. A perfectly round one-kilogram ball of pure crystalline silicon is made in the laboratory.
If you know exactly which atoms make up the crystal and at what distance they are from each other, then by measuring the size of the ball, you can calculate the number of silicon atoms that make it up. This number will be the definition of a kilogram.
To produce the ball, it was necessary to obtain a very highly purified silicon isotope. Russia provided assistance in this endeavor - at the old Soviet nuclear weapons factories there are centrifuges used to produce highly enriched uranium.
Perhaps this silicon ball will become the new kilogram. But only in the form of the number of its constituent atoms (photo nytimes.com).
The resulting ball had to be measured for “roundness”. The crystal was meticulously measured at half a million points. Conclusion: the ball is the most round creation of human hands. If the ball were enlarged to the size of the Earth, Everest would be only four meters high.
An intriguing feature of the ball: it is completely impossible to determine by eye whether it is at rest or rotating. Only if a speck of dust falls on the surface will there be something for the eye to catch on.
Although the number of silicon atoms that make up the unique object has not yet been calculated, the technique is already drawing criticism from another camp, which has brought together scientists from the USA, England, France and Switzerland.
In their opinion, with today's technology it is impossible to accurately count the number of atoms, so a kilogram is easier and more reliable to calculate using electrical voltage. Measuring energy, they say, is simpler than counting atoms. It may be simpler, but not in words.
The work uses a complex mechanism called the Watt balance. The technique is based on the equivalence of mechanical and electrical power.
An electromagnetic field should be created, a reference kilogram should be placed in it, and the parameters of the experiment should be measured. Since the gravitational field is constant and determined by the location of the three-story installation, the values of mechanical and electrical quantities can be related through the reference kilogram.
True, it is also necessary to take into account tidal influences, and other manifestations of the external environment can be excluded by placing the installation in a deep vacuum.
Silicon sphere created at Australia's National Measurement Laboratory (NML).
By measuring the values of length, time, electric current and resistance (and all of them can be calculated on the basis of fundamental and invariant quantum phenomena), it is possible to digitize the basic unit - the kilogram - in a quantum way. The mass of the electron has already been determined in a similar way.
It is too early to talk about the accuracy of the sophisticated and roundabout method of calculating a kilogram; scientists are preoccupied with eliminating voltage fluctuations in electrical circuits. However, they are confident that victory will be theirs, and not the designers of silicon balls.
According to the New York Times, the BIMP mass section - the body that ultimately determines the fate of the kilogram - is leaning towards the latter approach, but making a final choice is still very difficult. But they want to choose between these two, although there are other options.
For example, like everything in our world of buying and selling, the notorious kilogram can have an exact price expression.
To calculate it, you need to find out the number of atoms in a kilogram of pure gold. According to today's estimates, this number should be about 25 digits, but nothing more definite can be said about it.
Mass standard
This is a kilogram weight made of a platinum-iridium alloy, of a certain shape, stored under a double cap, and so on. Several such weights were made, they are taken to Paris once every few years and so on, see above the discussion about what the accuracy of the standard is. The natural question is why not take a natural standard - the atom. Here is someone who, according to all modern views, is doing well with the constancy of mass. The answer is simple - because the atom is small, and counting Avogadro's number of atoms is a pain in the ass. The degree of ten is so large that even a fullerene made from uranium would not save the matter. But I want to switch to a natural pseudo-atomic standard. Therefore, work is underway to create a mass standard based on the meter standard and atomic properties (that is, in the end it is still an atomic standard). Namely, it is assumed that it will be a ball of precisely known size made of monoisotopic silicon. Ball - to avoid uncertainty associated with the true geometry of the fins, silicon - since purification technologies have been developed for it. Silicon has three stable isotopes, which makes it difficult to obtain exact copies of the standard, but methods for removing impurities have been developed for silicon, and isotope-pure silicon, as they say, is of interest for semiconductor technology and the technology for its production exists.
From the book Ritz's Ballistic Theory and the Picture of the Universe author Semikov Sergey Alexandrovich§ 1.15 Relativistic effect of mass change Kaufman's experiments are equally well explained either by assuming absolute motion with varying mass or by considering mass as constant and motions as relative. They are also quite
From the book Notes of a Builder author Komarovsky Alexander Nikolaevich§ 1.16 Annihilation and equivalence of mass and energy The body of things is indestructible until it collides with a force that their combination is capable of destroying. So, we see that things do not turn into nothing, but everything decomposes back into basic bodies... ....In a word, not
From the book Very General Metrology author Ashkinazi Leonid Alexandrovich§ 1.17 The nature of mass and gravity Zöllner's explanation, accepted by Lorentz, is, as is known, that the force of attraction of two electric charges of opposite sign is slightly greater than the force of repulsion of two charges of the same sign and the same absolute value.
From the author's book§ 3.13 Nuclear reactions and mass defect All changes in nature that occur are of such a state that as much of something is taken away from one body, so much is added to another. So, if a little matter is lost somewhere, it will multiply in another place... This universal natural
From the author's bookAppendix No. 3 TECHNOLOGY FOR PRODUCTION OF PRODUCTS FROM PAPER PULP To prepare 1 kg of paper pulp (mastic) take (in g): Ground chalk - 450 OB grade casein glue - 200 Natural drying oil - 100 Rosin - 20 Paper dust (knop) - 200 Aluminum alum - 15 Glycer in
From the author's bookStandard of length At first, standards were natural, for example, the standard of length was, perhaps, the belt of King Charles so-and-so. Then the king became a little corroded and the economy went crazy. Therefore, we took the length of a pendulum with a certain period (thus linking the length standard to the standard
From the author's bookStandard of time Nature is full of periodic processes, so there were no problems with the natural standard of time, although I personally would not take the rotation of the Earth, but the periodic occurrence of the desire to devour. Because whether the Earth rotates or not, we see only during the day, but eat
From the author's bookThe standard of quantity of a substance is the mole, which in general duplicates the standard of mass, but is retained as a concept for the convenience of mainly chemical calculations. There is no separate mole standard. By definition, this is the amount of substance that contains so much
From the author's bookTemperature standard In physics there are several different “temperatures”, high metrology knows one - thermodynamic temperature. This is the one that is uniquely related to energy through the Boltzmann constant (which is why physicists often measure temperature in units of energy
From the author's bookCurrent standard Historically, the standards of electrical quantities were first current (through the galvanic process and the weight of the deposit) and resistance (through the resistance of a mercury cylinder), voltage was determined by Ohm's law, and transmitted by a particularly stable galvanic cell
From the author's bookStandard of luminous intensity Light is electromagnetic radiation in the range of direct human perception. Therefore, in technology and, accordingly, metrology, more attention is paid to it. As is known, there are four light units - luminous flux, luminous intensity, luminosity and
There is no such thing as too much precision. That is why a system of international measurements has been created and exists throughout the world, expressed in the standards of all measurements known to man. And only the kilogram standard stands out in the line of units of measurement. After all, he is the only one who has a physical, actually existing prototype. How much the international standard kilogram weighs and in which country is stored, we will answer in this article.
Why are standards needed?
Does a kilogram of, for example, oranges weigh the same in Africa and in Russia? The answer is yes, almost. And all thanks to the international system for determining the standards of the standard kilogram, meter, second and other physical parameters. Measurement standards are necessary for humanity to ensure economic activity (trade) and construction (unity of drawings), industrial (unity of alloys) and cultural (unity of time intervals) and many other areas of activity. And if your iPhone breaks in the near future, it is very likely that this happened due to changes in the weight of the most important mass standard.
History of standards
Each civilization had its own standards and standards, which replaced each other over the centuries. In Ancient Egypt, the mass of objects was measured in kantars or kikkars. In Ancient Greece these were talents and drachmas. And in Russia, the mass of goods was measured in pounds or spools. At the same time, people of different economic and political systems seemed to agree that the unit of measurement of mass, length or other parameter would be comparable to a single contractual unit. Interestingly, even a pood in ancient times could differ by a third among traders from different countries.
Physics and standards
Agreements, often verbal and conditional, worked until a person took up science and engineering seriously. With the understanding of the laws of physics and chemistry, the development of industry, the creation of the steam boiler and the development of international trade, the need for more precise uniform standards arose. The preparatory work was long and painstaking. Physicists, mathematicians, and chemists all over the world worked to find a universal standard. And first of all, the international standard of the kilogram, because it is from this that other physical parameters are based (Ampere, Volt, Watt).
Metric Convention
A significant event took place on the outskirts of Paris in 1875. Then, for the first time, 17 countries (including Russia) signed the metric convention. This is an international treaty that ensures uniformity of standards. Today, 55 countries have joined it as full members and 41 countries as associate members. At the same time, the International Bureau of Weights and Measures and the International Committee of Weights and Measures were created, whose main task was to monitor the unity of standardization throughout the world.
Standards of the first metric convention
The standard of the meter was a ruler made of an alloy of platinum and iridium (9 to 1) with a length of one forty-millionth of the Paris meridian. A kilogram standard made from the same alloy corresponded to the mass of one liter (cubic decimeter) of water at a temperature of 4 degrees Celsius (highest density) at standard pressure above sea level. The standard second became 1/86400 of the duration of an average solar day. All 17 countries participating in the convention received a copy of the standard.
Place Z
The prototypes and the original standard are today stored in the Chamber of Weights and Measures in Sèvres near Paris. It is in the outskirts of Paris that the place where the standard kilogram, meter, candela (light intensity), ampere (current intensity), kelvin (temperature) and mole (as a unit of matter, there is no physical standard) is stored. The system of weights and measures that is based on these six standards is called the International System of Units (SI). But the history of standards did not end there; it was just beginning.
SI
The system of standards that we use - SI (SI), from the French Systeme International d'Unites - includes seven basic quantities. These are meter (length), kilogram (mass), ampere (current), candela (luminous intensity), kelvin (temperature), mole (amount of substance). All other physical quantities are obtained by various mathematical calculations using basic quantities. For example, the unit of force is kg x m/s 2. All countries in the world except the USA, Nigeria and Myanmar use the SI system for measurements, which means comparing an unknown quantity with a standard. And a standard is the equivalent of a physical value that everyone agrees is absolutely accurate.
How much is the standard kilo?
It would seem something simpler - the standard of 1 kilogram is the weight of 1 liter of water. But in reality this is not entirely true. What to take as a standard kilogram from about 80 prototypes is a rather complicated question. But by chance, the optimal alloy composition was chosen, which lasted for more than 100 years. The standard kilogram of mass is made of an alloy of platinum (90%) and iridium (10%), and is a cylinder whose diameter is equal to its height and is 39.17 millimeters. Its exact copies were also made, amounting to 80 pieces. Copies of the kilogram standard are located in the countries participating in the convention. The main standard is stored in the outskirts of Paris and covered in three sealed capsules. Wherever the kilogram standard is located, reconciliation with the most important international standard is carried out every ten years.
The most important standard
The International Standard of the Kilogram was cast in 1889 and is kept in Sèvres, France, in a safe at the International Bureau of Weights and Measures, covered with three sealed glass covers. Only three high-ranking representatives of the bureau have the keys to this safe. Along with the main standard, the safe also contains six of its duplicates or successors. Every year, the main thing that is accepted as the standard kilogram is solemnly removed for examination. And every year he becomes thinner and thinner. The reason for this weight loss is the detachment of atoms when extracting the sample.
Russian version
A copy of the standard is also available in Russia. It is stored at the All-Russian Research Institute of Metrology. Mendeleev in St. Petersburg. These are two platinum-iridium prototypes - No. 12 and No. 26. They are on a quartz stand, covered with two glass covers and locked in a metal safe. The air temperature inside the capsules is 20 °C, humidity 65%. The domestic prototype weighs 1.000000087 kilograms.
The standard kilogram is losing weight
Standard comparisons showed that the accuracy of national standards is about 2 micrograms. All of them are stored under similar conditions, and calculations show that the standard kilogram loses 3 x 10 −8 weight over a hundred years. But by definition, the mass of the international standard corresponds to 1 kilogram, and any changes in the real mass of the standard lead to a change in the very value of the kilogram. In 2007, it turned out that a kilogram cylinder began to weigh 50 micrograms less. And his weight loss continues.
New technologies and a new standard of weight measurement
To eliminate errors, a search is underway for a new structure of the kilogram standard. There are developments to determine a certain amount of silicon-28 isotopes as a standard. There is a project “Electronic kilogram”. The National Institute of Standards and Technology (2005, USA) designed a device based on what is necessary to create an electromagnetic field capable of lifting 1 kg of mass. The accuracy of such a measurement is 99.999995%. There are developments in determining mass in relation to the rest mass of the neutron. All these developments and technologies will allow us to move away from being tied to a physical mass standard, to achieve higher accuracy and the ability to carry out reconciliation anywhere in the world.
Other promising projects
And while the world's scientific luminaries are determining which way to solve the problem is more reliable, the most promising is considered to be a project in which the mass will not change over time. Such a standard would be a cubic body made of atoms of the carbon-12 isotope with a height of 8.11 centimeters. There would be 2250 x 281489633 carbon-12 atoms in such a cube. Researchers from the US National Institute of Standards and Technology propose to determine the kilogram standard using Planck's constant and the formula E=mc^2.
Modern metric system
Modern standards are not at all what they were before. The meter, originally related to the circumference of the planet, today corresponds to the distance that a ray of light travels in one 299,792,458th of a second. But a second is the time during which 9192631770 vibrations of a cesium atom pass. The advantages of quantum precision in this case are obvious, because they can be reproduced anywhere on the planet. As a result, the only standard that exists physically remains the kilogram standard.
How much does the standard cost?
Having existed for more than 100 years, the standard is already worth a lot as a unique and artifact item. But in general, to determine the price equivalent, it is necessary to calculate the number of atoms in a kilogram of pure gold. The number will come from about 25 digits, and this does not take into account the ideological value of this artifact. But it is too early to talk about selling the kilogram standard, because the only remaining physical standard of the international system of units has not yet been disposed of.
In all time zones on the planet, time is determined relative to UTC (for example, UTC+4:00). What is noteworthy is that the abbreviation has no decoding at all; it was adopted in 1970 by the International Telecommunication Union. Two options were proposed: the English CUT (Coordinated Universal Time) and the French TUC (Temps Universel Coordonné). We chose a medium neutral abbreviation.
At sea, the "knot" measurement is used. To measure the ship's speed, they used a special log with knots at the same distance, which they threw overboard and counted the number of knots over a certain period of time. Modern devices are much more advanced than a rope with knots, but the name remains.
The word scrupulousness, the meaning of which is extreme precision and accuracy, came into languages from the name of the ancient Greek standard of weight - scruple. It was equal to 1.14 grams and was used when weighing silver coins.
The names of monetary units also often originate in the names of measures of weight. Thus, sterling in Britain was the name given to coins made of silver; such coins weighed a pound. In Ancient Rus', “silver hryvnias” or “gold hryvnias” were in use, which meant a certain number of coins expressed in weight equivalent.
The strange measurement of car horsepower has a very real origin. The inventor of the steam engine decided to demonstrate the advantage of his invention over traction transport in this way. He calculated how much a horse could lift per minute and designated this amount as one horsepower.
Probably, many readers remember the television advertisement of one mobile operator, in which the famous slogan “How much is it in grams?” appeared. “Precision is never superfluous,” one of the heroes summed up his question roller. In fact, he was cunning - it is impossible to accurately weigh, say, 200 grams of something. And it’s not just that existing weighing methods are bad - it’s just that people don’t have a reliable standard for a kilogram, and therefore a gram.
The need to develop standards, based on which it is possible to determine the values of mass, time, length and temperature (and after the advent of physics, the intensity of light, the intensity of current and a unit of matter) arose among humanity a long time ago. This need is quite understandable - in order to build roads and houses, travel and trade, constant units were needed, using which two builders or traders could understand what was drawn in each other’s drawings and what quantities of goods were being discussed.
Each civilization had its own units of measurement: for example, in Ancient Egypt, mass was measured in kantars and kikkars, in Ancient Greece - in talents and drachmas, and in Rus' - in poods and zolotniks. As scientists like to say, when creating each of these units, people seem to agreed, that from now on the mass, length or temperature of something will be compared to one unit of mass, length or temperature, respectively. The number of those who directly participated in these agreements was very small - the poods of two traders from different parts of the country could easily differ by a third.
How would an agreement worked great until people began to seriously engage in science and master engineering. It turned out that approximate values are not enough to describe the laws of nature or create a steam boiler, especially if people from different countries take part in the work. Realizing this fact, scientists from all over the world began to develop uniform, accurate standards, or standards, for basic units of measurement. On May 20, 1875, an agreement was signed in France to establish these units - the Metric Convention. All countries that signed this document committed to using specially created standards as standards. To provide signatory states with the most accurate standards, the International Chamber of Weights and Measures (or International Bureau of Weights and Measures) was created. The tasks of this organization include regular comparison of national standards with each other and supervision of work to create more accurate measurement methods.
In Russia, the introduction of the metric system is associated with the name of Dmitry Ivanovich Mendeleev, who created the Main Chamber of Weights and Measures in 1893 and generally did a lot for the development of metrology. He explained his interest in precise measurements as follows: “Science begins as soon as they begin to measure. Exact science is unthinkable without measure.” Thanks to the efforts of Mendeleev, from January 1, 1900, in Russia, along with national ones, metric measures were allowed to be used.
After the signing of the Metric Convention, experts began developing common standards for the meter and kilogram (these units of measurement existed before 1875, but there were no standards that were recognized throughout the world). The standard meter was established after the famous expedition to measure the length of the arc of the Paris meridian and was a ruler made of an alloy of platinum and iridium in a ratio of 9 to 1, the length of which was equal to one forty millionth of the meridian. Based on the location where it was stored, it began to be called “archive meter” or “archive meter.” The kilogram standard was cast from the same alloy, and its mass corresponded to the mass of one cubic decimeter (liter) of pure water at a temperature of 4 degrees Celsius (when water is at its maximum density) and standard atmospheric pressure at sea level. In 1889, during the first General Conference on Weights and Measures, a system of measures was adopted based on the newly produced standards of the meter and kilogram, as well as the standard of the second. The standard for a second began to be considered 1/86400 of the duration of an average solar day (later the standard was tied to the tropical year - a second was equated to 1/31556925.9747 of its part). Countries that recognized the new system of measures received copies of these standards, and the prototypes were sent to the Chamber of Weights and Measures for storage.
After some time, the standards of candela (light intensity), ampere (current intensity) and kelvin (temperature) were added to these three standards. In 1960, the Eleventh General Conference on Weights and Measures adopted a system of weights and measures based on the use of these six units and the mole (a unit of quantity of a substance - there is no standard for it) - the new system was called the International System of Units, or SI. It would seem that this was where the history of standards should have ended, but in reality, it was just beginning.
Everything that can go wrong...
As measurement technology improved, it became clear that all the standards stored in Paris were not ideal. Gradually, scientists came to the conclusion that it was worth taking not man-made objects as the standards for basic units, but much more advanced examples already created by nature. Thus, the standard second was taken to be a time interval equal to 9192631770 periods of radiation corresponding to the transition between two hyperfine levels of the ground (quantum) state of the cesium-133 atom at rest at 0 kelvin in the absence of disturbance by external fields, and the standard meter was the distance that light travels in a vacuum in a period of time equal to 1/299792458 of a second. Unlike the old ones, the new standards are atomic or quantum, that is, the most “basic” laws of nature “work” in them.
Gradually, six of the seven basic SI units received reproduction methods that did not require a unique standard stored somewhere in one place. Theoretically, any scientist who wants to know exactly (very accurately), for example, how long a second lasts, can take a milligram or two of the cesium-133 isotope and count when 919,263,1770 periods of radiation occur (by the way, their own atomic time standards are established, for example, at all GPS satellites). Only a kilogram of “in girls” remains - its standard is still collecting dust in a deep basement near Paris.
The word “gathering dust” in the previous paragraph is not a stylistic decoration at all - dust is in fact gradually accumulating on the kilogram standard, despite all countermeasures. It is impossible to take out a platinum-iridium cylinder and wipe it - firstly, when removing it, dust will again settle on it, and secondly, wiping or even fanning with a brush will inevitably lead to several molecules “bouncing off”. In other words, no matter what is done or not done to the standard, its mass changes over time. For a long time it was believed that these changes were insignificant, but a check carried out several years ago showed that recently the standard had “lost weight” by 50 micrograms, and this is already an impressive loss.
Mole, silicon and gold
A possible way out of this sad situation (over the next billion years the standard will become one third lighter) was proposed in 2007 by two American scientists from the Georgia Institute of Technology. Instead of a changeable cylinder, they proposed to consider a cube of carbon, which would contain a strictly defined number of atoms, as the standard of mass. Since the mass of each individual atom is constant, the mass of their aggregate will also not change. The researchers calculated that a cube weighing exactly one kilogram would consist of 2250 x 28148963 3 atoms (50184513538686668007780750 atoms), and its edge would be 8.11 centimeters. Over the course of three years, scientists clarified some details and presented their thoughts in an article, a preprint of which can be found on the website arXiv.org.
American physicists were concerned with the problem of the kilogram standard and chose carbon as the “reference” element for a reason - before that they were working on refining Avogadro’s number, one of the fundamental constants that determines how many atoms are contained in one mole of any substance. Although this number is one of the most important in chemistry, its exact meaning does not exist (among other questions, scientists, for example, decided whether it was even or not). Avogadro's number is chosen so that the mass of a mole in grams is equal to the mass of a molecule (atom) in atomic mass units. A carbon atom has a mass of 12 atomic mass units, which means the mass of a mole of carbon must be 12 grams. By refining Avogadro's number and taking it equal to 84446886 3 (602214098282748740154456), the researchers were able to calculate the required number of carbon atoms in the standard.
It is possible that the new work will be considered at the next General Conference on Weights and Measures, which will be held in 2011. However, scientists from Georgia have competitors. For example, the Washington National Institute of Standards and Technology is very actively working on the concept of the electronic kilogram. Briefly, the essence of the method they propose is as follows: the standard is determined through the current strength, which is necessary to create a magnetic field capable of balancing a load of one kilogram. This method is very good because it allows you to achieve high accuracy (it is based on the use of another fundamental constant - Planck's constant), but the experiment itself is extremely complex.
Another version of the new standard is a silicon sphere, the parameters of which are calculated in such a way that it will contain a strictly defined number of atoms (this calculation can be carried out, since scientists know the distance between individual atoms, and the process of producing pure silicon is very well established). Such a sphere was even created, but difficulties immediately arose with it, reminiscent of the difficulties of the current standard - over time, the sphere loses some of its atoms and, in addition, a film of silicon oxide forms on it.
The third approach to creating a standard assumes that it will be produced every time de novo. To obtain a mass standard, it is necessary to accumulate bismuth and gold ions until their total charge reaches a certain value. This method has already been recognized as unsatisfactory: it takes too much time and the results are poorly reproducible. In general, with a high probability, all the described methods for obtaining a new kilogram standard, except for the method based on the use of Avogadro’s number, will remain only in the memory of historians of science, since, unlike the others, the kilogram standard in the form of a cube from the carbon-12 isotope is based on direct using one of the fundamental atomic concepts.
It is unclear whether the carbon standard will become generally accepted or whether scientists will come up with a new, more convenient way. But there is no doubt that the cylinder stored in Paris, which faithfully served people for 120 years, will soon retire.
