Looking for absolute zero

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In the attempt to get as close to 0ºK as possible, the last milestone belongs to a group of scientists from Germany and France who managed to reach 38 picokelvin from the limit.

When it comes to low temperatures, science shows that there is a limit. It is the so-called absolute zero. Thermodynamics shows that, in round numbers, absolute zero is at -273.15ºC. In order to avoid negative temperatures, instead of degrees Celsius degrees Kelvin (K) are used. On this scale, absolute zero is 0ºK. Thus, 0.001ºK means that we are one thousandth of a degree from absolute zero. In an attempt to get as close to 0 ° K as possible, the latest milestone is a publication from August 2021. A group of scientists from Germany and France managed to reach 38 picokelvin from absolute zero. This temperature is 0.000000000038ºK, a record. It is the experiment that any experimental scientist would like to do. Unfortunately, it is impossible in Spain due to the criteria used to finance science. Let’s see what that low temperature means and the importance that this scientific achievement can have.

Temperature, on a microscopic scale, is associated with the movement of particles, atoms, and molecules. For example, in a gas, as the temperature drops, its atoms slow down. At absolute zero there would be total rest. Therefore, one way to measure temperature is to measure the velocities of atoms. The aforementioned experiment was carried out at the University of Bremen which has a 110 meter tower under microgravity conditions. A tower where the effect of gravity is greatly reduced. The experiment is excessively complex and its explanation needs to use concepts whose meaning is complex. Despite this, an attempt is made, above all, to emphasize the importance of this achievement, which affects what is beginning to be called the new physics. The first step consisted of placing about 100,000 rubidium atoms in a vacuum chamber and holding them together by means of a magnetic field. Then, using well-known techniques, they cooled down to two billionth of a degree from absolute zero. Thus, they managed to create what is called a Bose-Einstein condensate. This condensate is theoretically explained from the quantum properties of atoms and, the experimental demonstration of its existence, was awarded the 1998 Nobel Prize.

In a very qualitative way it can be said that the 100,000 atoms in the condensate begin to behave like a large atom. As a consequence, quantum effects become visible on a macroscopic scale. This condensate was placed on top of the tower and dropped. During the fall, in order to slow down the gas expansion, they applied and suppressed the magnetic field several times. Thus they came to reduce the speed of the atoms to the value compatible with the 38 picokelvin of temperature. This temperature record was held for 2 seconds. But, the simulations of the experiment indicate that in conditions of total weightlessness, for example in the space station, it could hold up to 17 seconds. This experiment brings innovations in matter wave optics and paves the way for the incorporation of gravitation into quantum mechanics. An aspiring Nobel Prize winner.

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Looking for absolute zero