What is the lowest temperature you can imagine? The lowest temperature ever recorded on Earth in Antarctica is -89.2℃. It can drop below -200℃ in some parts of the Moon.

But an international team of scientists has reached an even lower temperature, the lowest temperature ever measured in the universe.

Researchers from Rice University in the United States and Kyoto University in Japan obtained a temperature in the lab. It’s 3 billion times colder than interstellar space.

Scientists have used lasers to cool atoms to a temperature of one billionth of a degree above -273.15℃, which is absolute zero on the Kelvin scale. This is the temperature at which all motion of the atoms completely ceases.

The experiment is not just a great achievement at the laboratory level. Moreover «opens the door to the development of new materials with unimaginable properties», pointed BBC World Francisco José Torcal-Milla is a professor in the Department of Applied Physics at the University of Zaragoza.

At temperatures near absolute zero, for example, helium becomes superfluid, “a state characterized by a complete absence of viscosity. This means that it can pass through walls and any material, porous or not, and climb the walls of containers containing it,” added the Spanish expert.

One of the authors of the experiment and the study that described it is Mexican atomic physicist Eduardo Ibarra García Padilla, who is now a postdoctoral fellow at the University of California Davis after completing his doctorate at Rice University.

Ibarra explained BBC World It is phases of matter that can only be reached at the lowest temperatures.

And accessing these temperatures and these phases will allow us to better understand problems in physics such as the following. “superconductivity in copper oxides, which will have important technological applications».

How was the experiment done?

Researchers in the United States and Japan have reduced the temperature of atoms of ytterbium, a rare earth element, a chemical element with the symbol Yb on the periodic table, to extremes.

To achieve this they use «Cooling techniques with lasers and evaporative cooling»Ibarra explained.

“Evaporative cooling It’s like drinking a very hot soup. What man does is to blow into the soup; by doing this it removes the hottest particles and in this way cools the soup”, the Mexican physicist noted.

“The experiments do the same thing: it plays with the light trap in which the atoms are kept and removes the hottest atoms and therefore cools the system.”

What are these light traps?

Torcal-Milla, who wrote a popular article about the experiment, told BBC Mundo the procedure was surrounded by cutting-edge technology.

“It starts by sublimating the ytterbium atoms (converting directly from solid to gas without going through a liquid state). This procedure is usually performed by shining a high-power laser onto a solid block of ytterbium causing a small amount of it to evaporate.’

Once the diluted gas is obtained, it is kept in a chamber where an extreme vacuum is created and The atoms are held in optical traps that look like a kind of lasso made of light.

“Then they are hit with laser beams from different directions. When the laser’s photons interact with the mixing gas atoms, they slow them down, lowering their average velocity and, as a result, their temperature.

Where was the experiment done?

The laboratory, which reached record temperatures, is located at Kyoto University. The group led by Yoshiro Takahashi and Shintaro Taie worked there.

“We provide the theoretical and numerical part of the work that allows us to infer the temperatures at which the experiments were performed,” Ibarra said.

One of the best known sites for low temperature tests, Cold Atom Laboratory, CAL, on the International Space Station.

The CAL has the advantage of zero gravity, although Ibarra points out that zero gravity is not necessary in the work done on this occasion.

Torcal Milla believes it would be interesting to perform these experiments aboard the International Space Station, “because although the gravitational interaction that individual atoms undergo due to Earth’s gravitational interactions is very small, it becomes more important the smaller the rest of the interactions.” ».

How does the behavior of matter change?

“There are two types of particles in nature, bosons (like the photons of a laser) and fermions (like electrons in a solid), which behave differently at very low temperatures,” Ibarra said.

The scientists used an isotope of ytterbium called 173Yb, which is a fermion.

At temperatures as low as those reached in the experiment, matter behaves in an extraordinary way.

Torcal-Milla explained that in the case of bosons, they all fall into a minimum energy state, called the ground state, where they become indistinguishable. Bose-Einstein condensation.

On the other hand, if these are fermions (the fundamental particles that make up matter), they become what is known as Fermi gas or liquid, which can go up and even through walls.

The best-known examples of strange behavior at low temperatures are: superconductivity and superfluidity. Superconductivity occurs when a substance can conduct electricity without resistance.

On the other hand, hyperviscosity consists of the total viscosity loss of a substance. This state of matter can be achieved with a Fermi fluid at extremely low temperatures very close to absolute zero.

At these temperatures, almost everything freezes, except for some isotopes of helium, which become superfluid. In this case, the liquid can climb the walls of the container containing it.

What applications might such experiments have in the future?

pointed out by Ibarra BBC World As it reaches lower temperatures, different exotic phases of matter will emerge. They can have completely different magnetic or transport properties from other materials.

For example, in the case of a future superconductivity of copper oxides, one possible application, according to the Mexican expert, is as follows: Use superconductors to levitate trains.

“An example is maglev trains. However, I think they will probably be useful for other applications as it implies having a lossless electric current».

According to Torcal-Milla, “any experiment that improves knowledge is important, no matter how small the progress. If we told our grandparents that with a small device in my pocket, I could access all the information I need and even talk and even instantly see someone who is in opposite poles, they would treat us like crazy or charlatan».

“Some discoveries have to wait to be implemented, and maybe that’s the case, but there’s no doubt they will reveal new physics. We can’t even predict.” Spanish expert added BBC World.

“Who knows if the study of these systems will reveal us to the definitive theory that unifies all the fundamental forces, or to new physics that reveal the properties of matter at still unknown microscopic levels?”