Absolute cold. What the hell is this?

This post is an adaptation in english of my post "Le Froid absolu" that I published last month. I would like to share this article with the English-speaking community.

The conquest of the cold is extraordinary and has led us to the frontiers of ultra-cold. For centuries no one really knew what cold was and especially how to tame it...
However, over the last 100 years, the cold has never stopped revolutionizing the way we work !
Imagine our life without freezers and refrigerators, buildings without air-conditioning, hospitals without liquid oxygen... Cold technology also allows us to explore the cosmos and our brain...
It could even change the way we think and act !
Over the last 4 centuries scientists have descended further and further down the cold scale to enrich our knowledge and with the ultimate goal of reaching the "Absolute Zero".

Definition of ABSOLU ZERO :

The absolute zero is the lowest temperature that exists. According to an international agreement, its value is: -273.15°C (Celsius) or -459.67°F (Fahrenheit).
As the speed of light that cannot be achieved with a physical system, the thermodynamic temperature of a physical system cannot reach absolute zero.
Due to the quantum mechanics and inequalities of Heinsenberg, there is a residual motion state which is the minimum residual energy state for a physical system.

What's the cold ?

For centuries, the extreme cold has always appeared as an evil force, associated with death and darkness. Is it a substance? A process? Or a particular state of matter ?
In the 17th century England went through a small ice age and the effect of the cold was strongly felt.
University of Cambridge scientist Simon Shaffer tells us "of a world with extreme cold where people were lit up by fire and cold all the time, they felt the cold as a presence that influenced their lives. A dominant idea inherited from Greek philosophers and Aristotle, said that "2 elements in the world, hot and cold, functioned symmetrically and could be combined or separated".
Man felt he was at the mercy of this divine power that inspired fascination and fear.

A little history :

The first alchemist who tried to manipulate the cold is called "Cornelius Drebble" (1572 - 1633, is a Dutch physicist and mechanic).
In 1620, he invited the King and his court attended a novel experiment: he claimed to be able to produce cold and cool a Westminster room ! He already knew that mixing salt with ice would lower the temperature, but that was not enough, he had created a machine with a fan. It was the first air-conditioning system in history. He put a lot of jars filled with ice and salt on shelves and placed them behind the fan. This created cold drafts and the air dropped to about 10 degrees.
The King was seized by the cold, bewildered by this phenomenon which he probably associated with the hand of God or with demonic forces !

In 1702, Guillaume Amontons (French physicist) tried to reach absolute zero, he discovers that the pressure of a gas put in a given volume increases by about 1/3 of a third when it goes from a "cold" temperature to that of boiling water.
He therefore believes that a sufficient drop in temperature will cause the absence of pressure.

At the moment, there was no universal temperature scale. The idea was that when the air heats up the substances tend to expand and take up more space, and that as they cool down they retract.
There is one essential instrument missing to advance in this discovery of extreme cold: the thermometer !
And it was not until the 17th century that glass blowers in Florence, Italy began to manufacture calibrated thermometers. It is now possible to measure in degrees the cold and hot temperatures...
Instead of mercury, alcohol is used, the thermometers are long : more than one meter and spiral. The problem is that there is still no universal temperature scale.
The Swedish astronomer Anders Celcius designed the simplest temperature scale in 1742, divided it into 100 parts and it remains the most widely used one today.

What is the absolute limit of cold ?

The more air cooled, the lower the pressure. But what happens if we keep cooling it down? The answer is about -273.15°C (Celsius) or -459.67°F (Fahrenheit).

500 nanokelvins! This is the temperature difference between absolute zero and the temperature difference that a team of physicists at the Massachusetts Institute of Technology (MIT) managed to obtain with potassium sodium molecules.
These molecules behaved in a way that we could see at room temperature.
These are molecules: sodium potassium in the form of gas. The MIT team tried to create ultra-cold molecules with sodium and potassium atoms.
This mixture of atoms is subjected to a magnetic field to obtain a bond. This bond is weak and the molecule vibrates a little on its axis, but this is enough to create an entity.
This is the first time that researchers have succeeded in creating a molecule at such a low temperature.

The states of matter

According to Daniel Kleppner (physician), matter can have several states, atoms carried at high temperatures form gases. If one cools the gas it becomes liquid, if one cools the liquid it becomes solid, but if one cools atoms at very low temperatures, they undergo curious transformations: a kind of identity crisis !
The quantum mechanical properties of atoms become important, each atom starts to have wave properties.
He says it's hard to know why, but that's what's going on. At very low temperatures these bundles of atoms become longer and longer, then they overlap. They have lost their identity and are everywhere at once! They form a single quantum system...
There is nothing else similar in physics or human experience.

No one has yet reached the ABSOLU ZERO.
The temperature of the sun is about 5000 K, at 1000 K the metals melt, at 300 K it's the temperature of an ordinary room, the air liquefies at 100 K, hydrogen at 20 K, and helium at 4 K. The temperature of the sun is about 5000 K, at 1000 K the metals melt, at 300 K it's the temperature of an ordinary room, the air liquefies at 100 K, hydrogen at 20 K, and helium at 4 K.
The descent does not stop there: with ultra-cold refrigerators we go down to 0.0001 K, with laser cooling we are at 0.0000001 K, and finally with magnetic cooling we reach 0.0000000001 K.
This is the lowest temperature ever reached in a laboratory in Helsinki: 100 pico-kelvin.

Will we ever go down to the absolute Zero? To achieve this would take a time of the age of the universe and a device the size of the universe...

References :

Chaîne TV Arte
https://fr.wikipedia.org
https://www.futura-sciences.com/sciences

#For those who would like to know more, here are some links about the subject:#

https://www.youtube.com/watch?v=TNUDBdv3jWI
https://www.sciencedaily.com/terms/absolute_zero.htm
https://www.nature.com/news/quantum-gas-goes-below-absolute-zero-1.12146
https://sciencealert.com/after-a-century-of-debate-cooling-to-absolute-zero-has-been-declared-mathematically-impossible

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