We usually say that cold is the absence of heat, but then, what happens when we “take” all the heat out of an object? It is not an easy question to answer since we can only approximate this situation The current record is in 38 trillionths one degree above zero and was achieved in a laboratory in Germany.
What is temperature after all?
For years scientists have tried in various ways to get closer to the limit of -273.15 degrees Celsius, zero degrees Kelvin, absolute zero. Temperature is, despite the fact that we perceive it in a very different way, it is actually a measure of movement.
Heat is generated by movement a kind of vibration of molecules and atoms. Cold is therefore the absence not only of heat but of movement. Zero temperature is the total stillness of the molecules.
Reaching that point of absolute zero is, according to our present knowledge of physics, as impossible as reaching the speed of light. However, we have managed to get quite close, up to 38 billionths of a degree (38 picokelvins).
Throw the experiment out the window.
Reaching 38 picokelvins was no easy task. The team wanted to analyze the Bose-Einstein Condensate (BEC), a state of matter that only appears under exceptionally cold conditions. To achieve this, the team of researchers used gas from rubidium atoms (about 100,000 atoms in total). He introduced this gas into a vacuum chamber and lowered its temperature to two billionths of a degree.
At the time this was a record (the previous one was at 36 millionths of a degree), but was not enough for the team. The European Space Agency and the University of Bremen have a tower for experiments in microgravity, from which the experiment could be launched. And they do it like that.
In 120 meters of free fall, the researchers quickly turned the magnetic field on and off, minimizing the motion of the gas atoms and allowing the BEC to float within the chamber. The details of the experiment were published in the form of article in the magazine Physical Review Letters.
The Bose-Einstein Condensate.
The BEC is the so-called fifth state of matter (the other four being the three “classical” solid, liquid and gas, and plasma). The characteristic that makes this state of matter interesting is that in it the atoms pass into behave as a single entity. This makes it possible for physicists to study the quantum properties of matter.
This state of matter was achieved for the first time in the United States in 1995, also starting from rubidium. Shortly after, also in the United States, another team managed to create it from sodium. In 2001, the three researchers who spearheaded these experiments received the Nobel Prize in Physics.
The strange physics in the extremes.
Black holes are extremely dense regions of our Universe where the laws of physics do not seem to behave as they do in other places. However, extreme density is not the only condition that can make the laws of physics choke on us. Extreme temperature is another case.
Specifically the extreme absence of temperature. For example, a 2017 study published in the magazine Nature Physics He foresaw that, at extreme cold, light can behave like a liquid. Another study from the same yearthis one published in Nature Communicationsexplained that helium in a superfluid state could move without experiencing any friction.
The coldest place in the Universe (that we know of).
The experiment achieved 38 picokelvins for just a couple of seconds, but microgravity conditions can be exploited to prolong this period, perhaps as much as 17 seconds. The International Space Station was a pioneer in this regard, but it is possible that the next record be marked on another similar ship, Tiangong, the Chinese space station.
In any case, one wonders about the universality of these records. As far as we know, these temperatures are much lower than those that are achieved in the Universe naturally. The coldest known region in the Universe It is the Boomerang Nebula, located about 5,000 light years from us, in the environment of the Centaurus constellation. The average temperature of this area is approximately one degree K or -272º C.
Image | THIS
