Artist’s interpretation of the Big Bang. Image:
Flash movie via Getty Images
The first moments after the birth of the universe are shrouded in mystery, in part because we can’t go back far enough in time to observe what happened in this ancient era. Scientists believe that the universe must have undergone a huge expansion right after the Big Bang, but it is not at all clear how this phase of rapid inflation took place.
Now a team of physicists has created a sort of tiny expanding universe with a ‘quantum field simulator’ made of ultracold atoms, reports a study published on Wednesday in Nature. The experiment was able to simulate different versions of curved spacetime that fit models of the universe as spherical or hyperbolic in its geometry, for example. These adjustable space-time curvatures influence how particles are produced, among many other factors.
The purpose of the experiment was to explore dynamics that might be similar to the early universe in different scenarios in a lab, with the ability to pause the entire system and analyze it more closely, which that you can’t do with the real universe.
The success of the experiment suggests that similar simulators “offer the possibility of entering unexplored regimes” in quantum physics, which is the study of matter and energy at the tiny scales of atoms, said the team in the study. While no experiment can produce conditions directly comparable to conditions in the early universe, the new research probes mechanisms that may be somewhat analogous to physics governing spacetime and particle production in the instants that followed the Big Bang.
“We’re certainly not the first experiment to do some sort of expansion or to show this particle production,” Nikolas Liebster, an experimental physicist at the University of Heidelberg in Germany and co-author of the study, said during the interview. a call with Motherboard. “But we’re the first to put it in this specific context of how these different kinds of inflationary stories — like an accelerating universe, a decelerating universe, or an ever-expanding universe — can change the particles that you produce.”
“The general role of these analog cosmology and analog gravity experiments is to be able to see, if I have a system that is analogous to some kind of cosmological model – whether it’s a hydrodynamic model, or a quantum model, or all of these kinds of things – what experiments can I do to learn more about what could have happened in the cosmological framework of the history of our universe?” Liebster noted. “And how can experiments push the theory further far to deepen our understanding of how we got to where we are now?”
Liebster and his colleagues explored these questions by cooling about 20,000 potassium-39 atoms to temperatures just above absolute zero (about -400°F). In this freezing environment, atoms form what is called a Bose-Einstein condensate, which is a state of matter that can be used to simulate the kinds of exotic physical phenomena that occur around black holes or in the primitive universe.
The condensate in this experiment was a superfluid, that is, a fluid that exhibits no viscosity, which had the shape of a two-dimensional pancake. The configuration could be adjusted to simulate different theories of cosmic inflation as well as different types of spacetime curvature, such as flat, spherical, and hyperbolic patterns.
By passing sound waves through the condensate – an analog of light that shines through the universe – Liebster and his colleague were able to examine the strange physics of each model, which may be similar to those that appeared in the universe. primitive. 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.
“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,” Liebster explained. “We have control over those kinds of parameters.”
“The way the sound wave travels through your system is a very effective way to check what is the shortest path between two points, because the sound wave will always take the shortest path,” he said. for follow-up. “Sound waves are like light waves in real cosmology. They have the same properties and that is why we use them to probe our space-time.
This way, the team was able to simulate patterns of cosmic inflation that could be stopped 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.
“Our work is primarily a comparative analysis of how our simulator works,” Liebster said. “There are a lot of very interesting theoretical questions you can ask about different kinds of space-time curvature and space curvature, and what the effects are,” although he added that “there are a number of hurdles to overcome before you can do a live one.” one-to-one comparisons” to the real universe.
“It’s just an approximation in the end,” Liebster continued. “I would be safe to say that there are very specific concrete results for cosmology. But we know that for these specific assumptions for this model system, it fits very well with the theory, and now we can ask questions that go beyond what current theory can answer.
To that end, the researchers sketched out a host of fundamental questions in quantum physics that could be explored with future versions of the simulator. Experts from many fields of physics will be needed to unravel the answers to these long-standing questions about this strange universe we find ourselves in, but at least the roadmap is becoming clearer.
“I don’t necessarily think we’re close to discovering the secrets of the Big Bang,” Liebster concluded. “But even this collaboration between theory and experiments – and asking what questions can we answer that you can’t, and what questions can you answer that we can’t – is very motivating,”
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