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Understanding the origin of the Universe is the quest of many researchers, relying on super-powerful telescopes like James Webb to probe the confines of the Universe. But the solution may lie in the laboratory. Recently, a fluid of ultracold atoms exhibited quantum dynamics similar to those thought to have existed moments after the Big Bang, ushering in a new era of laboratory exploration of the early Universe.
The idea that the early Universe underwent 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 very 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 preclude exploration of the physics involved.
Recently, a team of physicists led by Célia Viermann from Heidelberg University (Germany) created a tiny expanding “universe” with a “quantum field simulator” made of ultra-cold potassium atoms. The study is published in the journal Nature.
Simulating the post-Big Bang with quantum fluids
It should be known that the dynamics of quantum fields in a curved universe give rise to various intriguing phenomena. Among them is the production of particles in an 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 the temperature fluctuations in the cosmic microwave background and grows in the distribution of galaxies and galaxy clusters that we observe today “.
In this study, the researchers simulated this process in an ultracold quantum gas. Concretely, they cooled more than 20,000 potassium atoms in a vacuum, using lasers to slow them down and lower their temperature to around 60 nanokelvins, or 60 billionths of a kelvin above absolute zero. At this temperature, the atoms therefore form a cloud 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 fluids as we know them in everyday life do not flow without resistance. Large pumps and turbines are needed to move the water, and the honey slowly drips from a spoon. This is caused by the internal friction of the fluid, through which the motive energy is ultimately converted into heat. This can be radically different in a quantum fluid — closely related to the Bose-Einstein condensation phenomenon.
A Bose-Einstein condensate is a special quantum state of an atomic gas that is reached at very cold temperatures. A cloud of individual atoms in this state behaves collectively as a single fluid. This quantum fluid is able to flow without resistance — it is superfluid. According to Professor Oberthaler, over the past decades Bose-Einstein atomic condensates have been created from very different types of atoms such as sodium and rubidium, but more recently also from more “exotic” atoms. like erbium and dysprosium.
In this experiment, the atoms put in this phase can be controlled by illuminating them – using a tiny projector, the researchers precisely defined the density of the atoms, their arrangement in space and the forces they exert on each other.
By modifying these properties, the team made the atoms follow an equation called the space-time metric, which in a large-scale real universe determines how much it bends, how fast light travels and how it is “bent” near massive objects. For New ScientistOberthaler says it was the first experiment that used 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 passing sound waves through the condensate — an analogue of light in the Universe — they were able to examine physics that would be similar to that which appeared in the early universe. The sound waves from the experiment acted as light waves in the real universe, as their path through the condensate was influenced by different configurations, similar to curved spacetime.
The researchers then discovered that the atoms move in exactly the kind of ripple pattern that one would expect if particle pairs appeared — a phenomenon called ‘particle pair production’.
Liebster, co-author, says: “ It could be that in the past our universe had different kinds of spatial curvature, and that’s what we can tune into our system. We have control over these kinds of parameters “. He adds : ” The way the sound wave travels through the system is a very effective way to check what is the shortest path between two points, because the sound wave always takes the shortest path. Sound waves are like light waves in real cosmology. They have the same properties, and that’s why we use them to probe our space-time “.
So through these simulations, the team was able to examine the dynamics behind them, what Liebster called “a dream in cosmology.” Overall, the experiment matched theoretical predictions for different curvatures in time and space, validating this simulator approach, although it did not confirm or disprove any particular model of the early universe at the time. actual hour.
In the article of New Scientist, Alessio Celi of the Autonomous University of Barcelona in Spain, says the new experiment is a very precise playground for pairing quantum effects and gravity. Physicists aren’t quite sure how the two combine in our universe, but experiments with ultracold atoms may allow them to test some hypotheses. These results could inspire new targets for observations in the cosmos.