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Understanding the origin of the Universe is the pursuit of many researchers, who rely on the most powerful telescopes such as James Webb to probe the boundaries of the Universe. But the solution may lie in the laboratory. Recently, a fluid of ultracold atoms showed quantum dynamics similar to what is believed to have existed moments after the Big Bang, starting a new era of laboratory exploration of the early Universe.
The idea that the early Universe went through a phase of rapid inflation was originally proposed to solve some of the outstanding puzzles of the Big Bang. But scientists soon realized that this theory of inflation could also explain the origin of the cosmic structure of the Universe. Like all events that occurred in the early universe, the inflationary phase has long been inaccessible to direct experience, but that does not necessarily prevent the exploration of the physics involved.
Recently, a group of physicists led by Célia Viermann from Heidelberg University (Germany) created a small expanding “universe” with a “quantum field simulator” made of ultra-cold potassium atoms. The study was published in the journal NATURE.
Simulating the post-Big Bang with quantum fluids
It should be noted that the dynamics of quantum fields in a curved universe gives rise to various interesting phenomena. Among them is the production of particles in the expanding universe. Célia Viermann, the lead author, explains: This process is likely responsible for seeding the large-scale structure of the Universe, which, in turn, causes changes in the temperature of the cosmic microwave background and grows in the distribution of galaxies and galaxy clusters that we see today. “.
In this study, the researchers simulated this process in an ultracold quantum gas. Specifically, they cooled more than 20,000 potassium atoms in a vacuum, using lasers to slow them down and lower their temperature to about 60 nanokelvin, or 60 billionths of a kelvin above absolute. which is zero. At this temperature, the atoms therefore form a cloud about the width of a human hair and, instead of freezing, form a quantum phase of fluid matter called a Bose-Einstein condensate (BEC).
Remember that the fluids we know in everyday life do not flow without resistance. Large pumps and turbines are needed to move the water, and the honey slowly drips from the spoon. This is due to the internal friction of the fluid, where the motive energy is finally converted into heat. This can be very different from a quantum fluid – closely related to the Bose-Einstein condensation phenomenon.
The Bose-Einstein condensate is a special quantum state of atomic gas that can be reached at very cold temperatures. A cloud of individual atoms in this state behaves collectively as a fluid. This quantum fluid is able to flow without resistance – it is extremely fluid. According to Professor Oberthaler, in the past decades Bose-Einstein atomic condensates have been created from different types of atoms such as sodium and rubidium, but more recently also from more “exotic” atoms, such as erbium and dysprosium.
In this experiment, the atoms placed in this phase can be controlled by illuminating them – using a small projector, the researchers precisely define the density of atoms, their arrangement in space and the forces they exert on each other.
By changing these properties, the team made the atoms obey an equation called the space-time metric, which in a large real universe determines how much it bends, how how fast light travels and how it “bends” near large objects. with New ScientistOberthaler says this is the first experiment to use cold atoms to simulate a curved, expanding universe.
Understanding the expansion of the Universe
In an article by Vice, the authors explain more precisely that by transmitting sound waves through the condensate – an analog of light in the Universe – they were able to examine physics similar to that which arose in the early universe. The sound waves from the experiment act as light waves in the real universe, because their path through the condensate is influenced by different configurations, similar to curved spacetime.
The researchers discovered that the atoms move in exactly the kind of ripple pattern one would expect when particle pairs appear – a phenomenon called ‘particle pair production’.
Liebster, co-author, says: ” It is possible that in the past our universe had different types of spatial curvature, and that is what we can adapt to our system. We have control over these types of parameters “. He added: ” The way a sound wave travels through a system is a very effective way to find the shortest path between two points, because a sound wave always takes the shortest path. Sound waves are like light waves in real cosmology. They have the same properties, and so we use them to explore our space-time “.
So through these simulations, the team was able to examine the dynamics behind them, which Liebster called “a dream of cosmology.” Overall, the experiment matched theoretical predictions for various curvatures of time and space, confirming this simulator approach, although it did not prove or disprove any particular model of the early universe. at the time.
In the article of New Scientist, Alessio Celi of the Autonomous University of Barcelona in Spain, says that the new experiment is a very precise playground for pairing quantum effects and gravity. Physicists aren’t sure how the two come together in our universe, but experiments with ultracold atoms may allow them to test some hypotheses. These results may inspire new targets for observations of the cosmos.