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It is estimated that around 68% of the universe is made up of dark energy and that another 27% corresponds to dark matter. That means that the nature of most of the mass of the cosmos remains a mystery. Clearing these unknowns requires progress in the development of physics models and improving the precision of the instruments with which some of the fundamental phenomena are observed.
That is why NASA scientists have tested their Cold Atoms Laboratory (CAL) aboard the International Space Station (ISS), with which they have managed to generate the fifth state of matter , called Bose-Einstein condensate. The details of the experiment are described this Thursday in the journal Nature .
The Bose-Einstein condensate is halfway between the microscopic world, where the rules of quantum mechanics rule, and the macroscopic world, where those of classical physics apply. This state of matter is formed when a gas of bosons (in this case, rubidium atoms) is cooled to bring it close to 0º Kelvin (-273ºC, or absolute zero), the lowest possible temperature.
"This state is only obtained at the lowest temperatures and at the highest densities," explains Jim Kohel, one of the co-authors of the paper. "So the set of atoms, which can be seen with a camera, behaves like an individual particle. It could be described as atoms acting collectively, like a wave ."
Experiments of this kind provide scientists with a unique opportunity to study fundamental properties of quantum mechanics. The problem is that, on Earth, any precision analysis of this state of matter is hampered by the planet's own gravitational pull .
To overcome this limitation, the NASA Jet Propulsion Laboratory (JPL) team decided to ship their instruments on the ISS. "The goal is to provide humanity with one of the most sensitive instruments ever built," explains Robert Shortwell, project manager.
Freefall
Because in the station's microgravity (which is in a perpetual free fall state) the laboratory is able to generate a Bose-Einstein condensate, confine it in a shallow atom trap, and observe it for much longer periods than on land before. to scatter.
According to the authors, the advantages provided by these conditions will also allow the creation of much colder condensates than have been achieved so far, since the expansion of atoms outside their container causes lower temperatures, in which quantum effects Exotics are becoming more prominent .
"One of the things that allows us to cool atoms beyond the point at which Bose-Einstein condensation occurs is that we can weaken the trap," explains Robert Thompson, one of the project's researchers. "That allows the atomic cloud to expand and, as it expands, it cools. It's kind of like what happens when you use an aerosol can , because by spraying the gas inside it expands, cooling the can " At the moment, a temperature of one ten millionth of a degree above absolute zero has been achieved, making it the coldest object known in space (the record was set by MIT on Earth).
Possible applications range from the search for dark energy and gravitational waves to space navigation or prospecting for underground minerals of planetary bodies, in addition to verifications in the Theory of General Relativity.
"But one of the most important implications is that maybe we have a new paradigm for how physics is done ," says Thompson. "So far our understanding of the inner workings of nature has come from particle accelerators and astronomical observatories, but in the future I think precision measurements with cold atoms are going to play an increasingly important role."
A century of research
In 1924 the young Indian physicist Satyendranath Bose wrote a letter to Albert Einstein. "Dear Sir, I have dared to send you the attached article. I am eager to know what you think of it." The article in question, which had already been rejected by a scientific journal, maintained that any object emits a certain light and that this luminosity depends on its temperature. It also described certain rules for determining whether two photons should be considered identical or different. Einstein immediately understood its importance , personally translated it into German, and recommended its publication to the Zeitschrift für Physik magazine .
One of the implications was that, below a certain temperature, these types of particles, which will be called bosons in memory of the Indian scientist , tend to adopt the same microscopic state: the Bose-Einstein condensate. This fifth state of matter passed from theory to reality 70 years later, when Carl Wieman and Eric Cornell managed to generate it in the laboratory of the University of Colorado at Boulder, a milestone that earned them the Nobel Prize in Physics in 2001.
Cooling down the clouds of atoms at such low temperatures requires suspending them using magnets or lasers, but once they are turned off for observations, the condensates fall and dissipate. "We want to study the atoms and observe them for longer periods of time," says Thompson, "and that is only possible in microgravity."
To be able to board the ISS, its creators have had to adapt the instruments to the station's strict requirements for mass, volume and power consumption, while achieving a design robust enough to function for years without need for maintenance.
"Typically, experiments with Bose-Einstein condensate involve enough equipment to fill a room and require almost constant monitoring by scientists," Shotwell says. "While CAL is about the size of a small fridge and can be remotely operated from Earth."
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