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Since 1889, human civilization has depended on one magical rock. Known as Le Grand K, it sits under the protective glass in St Cloud, France. The magic rock of mankind is actually a piece of metal alloy that has 90% platinum and 10% iridium. His magic does not come from a supernatural power, but because human scientists have stated that it was exactly one kilogram in mass. Today, an international committee representing more than 60 nations has stated that Le Grand K is no longer magical.

The kilogram is part of a system of weights and measures known as the International System of Units (SI), commonly known as the metric system. The metric system is used all over the world to determine the distance of a road (meters), the duration of a working day (seconds) and the mass of raw materials (kilogram). While Americans are proud of using their own system to use our own system of miles and pounds, these units are also defined in terms of the metric system. A mile, for example, is defined as *exactly* 1,609,344 meters. Our lives depend on these standard units of measurement.

Throughout most of the history, units of measurement were determined by royal decree or local regulations. This meant that even the same unit could have different values according to the region. In France, the foot or *pied du roi *It had about 0.325 meters in length, while the English foot was about 0.305 meters. Since most shops were local, these differences were not a problem, but as trade became more global, an international standard was necessary.

Thus, in the 1800s, an effort began to create a system based not on the whim of a king, but on the physical world. The subway was defined in the circumference of the Earth, so that the circumference of the Earth was exactly 40 million meters. A second was established stating that the duration of an average day was exactly 86,400 seconds (24 hours). The kilogram was defined as the mass of 1 liter of water, which is a bucket of water 10 inches from the side. This meant that the kilogram depended not only on a physical material (water), it also depended on the length of a meter. If the length of an accountant changed, that would be the mass of one kilogram.

This system was not without their problems. In the early 1800s, the circumference of the Earth was not known with great precision. In addition, the Earth is not a perfect sphere, so the length of a meter will depend on the circumference it has used. Thus, in 1867, using the best measurements of the Earth at the time, they made two marks in an alloy bar of platinum-iridium. When it cooled to the melting temperature of the ice, the two brands were declared *exactly* one meter away. In other words, the accountant was defined by the "magic stick."

Time was measured by the apparent movement of the stars. As the Earth rotates, the stars rise and settle in the night sky and astronomers can measure their movement with great precision. Astronomers have become so precise that they could measure small changes in Earth rotation. The rotation of the Earth is diminishing gradually, and that meant that the duration of a second was getting longer. Thus, in the 1960s, the General Conference on Weights and Measures** **redefined the second using very accurate atomic clocks. These atomic clocks are based on an element known as Cesio. Like all elements, Cesio emits light at specific frequencies. The light emits from an atom when an electron moves from a quantum state of greater energy to an inferior one and under the true conditions they are always the same. A particular emission of cesium 133 is known as a hyperfin floor state, and is used to regulate an atomic clock as a swing of a pendulum regulates a grandfather's clock. & Nbsp; In 1967 the frequency of light emitted by this hyperfinian transition was defined to be & nbsp; 9.192.631.770 Hz. When measuring the frequency, you know the duration of a second.

For the first time, a unit of human measurement was based on a cosmic physical standard. No longer had to be on Earth to determine the duration of a second. No matter where you are in the universe, you can create an atomic clock and know exactly how long it lasts for a second.

In 1983, the General Conference on Weights and Measures eliminated the magic cane of the metric system when defining the meter based on the speed of light. The speed of light in the void is always the same, so the conference declared the speed of light *exactly* 299.792.458 meters per second. From anywhere in the universe, you can measure the light that travels in a second, and you know the exact length of a meter.

Over time, more measures were defined to a universal standard, but the kilogram was still defined by magical rock. And it was becoming a serious problem. Since Le Grand K was always exactly one kilogram, if you shaved a bit of material, it would still be a kilogram. It would weigh less, but then it would be a kilogram. For several reasons, Le Grand K dims the dough a little. Compared to the official copies of kilograms, it seems that it has increased slightly in mass. Thus, there was a great impulse to define the kilogram of the way we define meters and seconds.

The obvious option would be to define the kilogram in terms of the universal gravity constant G, but the gravity is a weak force. We could only measure G within 1 part in 10,000, which is not sufficiently precise to define a new kilogram. Instead, scientists tried to use a different physical constant known as the Planck constant.

The Planck constant is fundamental for quantum mechanics. He is famous for giving quantum theory to its blurred uncertainty properties, but also relates to the energy and impulse of quantum objects. As Einstein discovered, energy is related to mass, so the mass and the Planck constant are related. One of the ways in which Planck's constant can be measured is through a scale known as the Kibble equilibrium. Measure the current that an electromagnet needs to maintain a certain mass. By measuring the current required to keep one kilogram, you can determine the Planck constant. But the Planck constant is defined to have a specific value, then the kilogram is defined in terms of the Planck constant. To make it work, the balance of Kibble should have been more accurate than the standard kilogram variations. They had decades to reach that accuracy, but we finally got in the last two years.

What brings us to today. Today the General Conference on Weights and Measures has declared that from March 20, 2019 the Planck constant will be exactly h = 6.62607015 and times; 10^{-34} & nbsp; **J ⋅ s**. On that day, the magic rock humanities will no longer be. On that day, our measure of the universe will truly be based on the universe itself.

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Since 1889, human civilization has depended on a magical rock. Known as Le Grand K, it sits under the protective glass in St Cloud, France. The magic rock of mankind is actually a piece of metal alloy that has 90% platinum and 10% iridium. His magic does not come from a supernatural power, but because human scientists have stated that it was exactly one kilogram in mass. Today, an international committee representing more than 60 nations has stated that Le Grand K is no longer magical.

The kilogram is part of a system of weights and measures known as Système international d '(SI), commonly known as the metric system. The metric system is used all over the world to determine the distance of a road (meters), the duration of a working day (seconds) and the mass of raw materials (kilogram). While Americans are proud of using their own system to use our own system of miles and pounds, these units are also defined in terms of the metric system. A mile, for example, is defined as *exactly* 1,609,344 meters. Our lives depend on these standard units of measurement.

Throughout most of the history, units of measurement were determined by royal decree or local regulations. This meant that even the same unit could have different values according to the region. In France, the foot or *pied du roi *It had about 0.325 meters in length, while the English foot was about 0.305 meters. Since most shops were local, these differences were not a problem, but as trade became more global, an international standard was necessary.

Thus, in the 1800s, an effort began to create a system based not on the whim of a king, but on the physical world. The subway was defined in the circumference of the Earth, so that the circumference of the Earth was exactly 40 million meters. A second was established stating that the duration of an average day was exactly 86,400 seconds (24 hours). The kilogram was defined as the mass of 1 liter of water, which is a bucket of water 10 inches from the side. This meant that the kilogram depended not only on a physical material (water), it also depended on the length of a meter. If the length of an accountant changed, that would be the mass of one kilogram.

This system was not without their problems. In the early 1800s, the circumference of the Earth was not known with great precision. In addition, the Earth is not a perfect sphere, so the length of a meter will depend on the circumference it has used. Thus, in 1867, using the best measurements of the Earth at the time, they made two marks in an alloy bar of platinum-iridium. When it cooled to the melting temperature of the ice, the two brands were declared *exactly* one meter away. In other words, the meter was defined by a "magical stick".

Time was measured by the apparent movement of the stars. As the Earth rotates, the stars rise and settle in the night sky and astronomers can measure their movement with great precision. Astronomers have become so precise that they could measure small changes in Earth rotation. The rotation of the Earth is diminishing gradually, and that meant that the duration of a second was getting longer. Thus, in the 1960s, the General Conference on Weights and Measures** **redefined the second using very accurate atomic clocks. These atomic clocks are based on an element known as Cesio. Like all elements, Cesio emits light at specific frequencies. The light emits from an atom when an electron moves from a quantum state of greater energy to an inferior one and under the true conditions they are always the same. A particular emission of cesium 133 is known as the state of hyperfinite soil, and is used to regulate an atomic clock as a swing of a pendulum regulates a grandfather's clock. In 1967, the frequency of light emitted by this hyperfin transition to 9.192,631,770 Hz was defined. When measuring the frequency, you know the duration of a second.

For the first time, a unit of human measurement was based on a cosmic physical standard. No longer had to be on Earth to determine the duration of a second. No matter where you are in the universe, you can create an atomic clock and know exactly how long it lasts for a second.

In 1983, the General Conference on Weights and Measures eliminated the magic cane of the metric system when defining the meter based on the speed of light. The speed of light in the void is always the same, so the conference declared the speed of light *exactly* 299.792.458 meters per second. From anywhere in the universe, you can measure the light that travels in a second, and you know the exact length of a meter.

Over time, more measures were defined to a universal standard, but the kilogram was still defined by magical rock. And it was becoming a serious problem. Since Le Grand K was always exactly one kilogram, if you shaved a bit of material, it would still be a kilogram. It would weigh less, but then it would be a kilogram. For several reasons, Le Grand K dims the dough a little. Compared to the official copies of kilograms, it seems that it has increased slightly in mass. Thus, there was a great impulse to define the kilogram of the way we define meters and seconds.

The obvious option would be to define the kilogram in terms of the universal gravity constant G, but the gravity is a weak force. We could only measure G within 1 part in 10,000, which is not sufficiently precise to define a new kilogram. Instead, scientists tried to use a different physical constant known as the Planck constant.

The Planck constant is fundamental for quantum mechanics. He is famous for giving quantum theory to its blurred uncertainty properties, but also relates to the energy and impulse of quantum objects. As Einstein discovered, energy is related to mass, so the mass and the Planck constant are related. One of the ways in which Planck's constant can be measured is through a scale known as the Kibble equilibrium. Measure the current that an electromagnet needs to maintain a certain mass. By measuring the current required to keep one kilogram, you can determine the Planck constant. But the Planck constant is defined to have a specific value, then the kilogram is defined in terms of the Planck constant. To make it work, the balance of Kibble should have been more accurate than the standard kilogram variations. They had decades to reach that accuracy, but we finally got in the last two years.

What brings us to today. Today the General Conference on Weights and Measures has declared that from March 20, 2019 the Planck constant will be exactly h = 6.62607015 × 10^{-34} **J ⋅ s**. On that day, the magic rock humanities will no longer be. On that day, our measure of the universe will truly be based on the universe itself.