Sealed in a vault under the former palace of a former tribal dynasty among forest forests west of Paris, sits an apple-size object that determines the weight of the world.
The ark in the background of scientific and political reversals after the French Revolution, a small small platinum-iridium alloy cylinder has laid greatly for nearly 130 years, because it is a world reference for what is exactly a kilogram.
The international prototype of the kilogram, or "Le Grand K", as they do not know it, is one of the brightest relics of science, an analog against which all other weights and totems of the metric system are compared that followed the era of freedom, equality and fraternity.
It is so respected, in fact, that it only behaves four times, and the room located in the de Breteuil Pavilion can only be opened when there are three key holders – which for security reasons must be of different nationalities – turn the lock at the same time.
Still, it will be out of business soon.
Hundreds of scientists from around the world this week will gather in the fortune of the Versailles Palace at the 26th General Conference on Weights and Measures.
There, in the act that seeks to fulfill the promise of the founder of the metric system "For All Ages, For All People", it will replace the Grand K with a universal formula that defines a kilogram using the quantum laws of Nature.
"Kilogram is the latest measurement unit based on a physical object," said Thomas Grenon, director of the French National Laboratory for Metrology and Testing.
"The problem is that he had a life, he could change. That's not enough, given the level of precision we need today."
What's in a second?
With the adoption of the metric system, scientists at the end of the XIX century are required to codify a structure that has expressed the distance, time, electrical processes and mass in similar, portable measurement units.
They defined one meter as one ten million quadrants of the Earth – naturally through Paris.
"Now we look back and say that the process that went through is pretty good, today would not do so quite differently," said Martin Milton, director of BIPM, an international guardian of our measurement systems.
The meter was used to define the mass: no matter how much a decimeter thickness (10 cm to 10 cm to 10 cm) is heavier than water, it would be called a kilogram below.
But science continued from the day of the revolution.
The meter now defines how far the light travels in a vacuum in a few seconds.
The other was expressed in relation to the rotation of the Earth. But since the 1960s, it was officially the time when a cesium-133 atom was needed, which could drop 9,192,631,770 times – not less revolution.
Instead of referring to the mass of a single-core physical object, the kilogram will be defined in the future in terms of the Planck constant – the ratio of quantum energy whose frequency can carry at the same frequency, or 6.626 to 10-34 joules per second.
Energy is inherently related to the mass, as Einstein showed by his equation E = mc2.
Planck's constant, in combination with two quantum phenomena that allow the generation of electricity, can be used to calculate the mass based on the equivalent mechanical force required to replace it.
"If you press the mass, the power you need depends on that mass and you can fully base that power on the electricity that our quantum constants provide," Milton told AFP.
Proponents of this approach say they will be at least a million times more stable than physical artifacts and will have a number of practical applications in the future.
"For many applications, one kilogram is a very large mass," said Milton.
Progress in pharmaceutical and chemical production means that drug ingredients are increasingly measured in micrograms, and become more precise.
"One kilogram is good for potatoes, where you do not need precision, but this is not the right weight for many applications in demanding science and industry. The new system is infinitely scalable."
& # 39; Countries that come together & # 39;
Scientists will also use the Versailles Summit to change the way of defining ampers (electrical currents), kelvin (temperature), and brittle (atom), all of which are expressed through the universal laws of Nature.
Milton said that the decision was a way to ensure that the world would always agree on exactly what is one kilogram – that is, a sugar bag, a liter of water, or a precise quantum relationship.
"We are in a world where people are concerned about stopping and focusing on multilateralism, but here, in metrology science, the states really come together to agree," he said.
As for Le Grand K, he may have survived his usefulness as a perfect pound, but his contribution to science is far from over.
"He'll stay here in the backyard in the conditions that he has since 1889," Milton said.
"It's actually a long-term experiment, because we will evaluate it in the coming decades to see how it responds to the conditions. It's still a matter of interest in science."
Four base units measure in a metric system that needs to be changed