A miniature universe shows particles may emerge out of empty space

A first-of-its-kind experiment using ultracold potassium atoms to simulate the universe suggests that in a curved, expanding universe, pairs of particles emerge from empty space.

An experiment with cold atoms indicates that particles emerge from empty space. Alamy Stock Photo / vitacop

A miniature, expanding universe made of extremely cold potassium atoms has been created. It could be used to help us understand cosmic phenomena that are extremely difficult to detect directly, such as pairs of particles created as the universe expands.

Markus Oberthaler of Heidelberg University in Germany and his colleagues used lasers to slow down and lower the temperature of over 20,000 potassium atoms in a vacuum to about 60 nanokelvin, or 60 billionths of a degree kelvin above absolute zero.

At this temperature, the atoms formed a cloud the width of a human hair and, rather than freezing, transformed into a quantum, fluid-like phase of matter known as a Bose-Einstein condensate. Atoms in this phase can be controlled by shining light on them - the researchers precisely set the density, arrangement in space, and forces exerted on each other using a tiny projector.

By changing these properties, the team forced the atoms to obey an equation known as a space-time metric, which determines how curved the universe is, how fast light travels, and how much light must bend near very massive objects in an actual, full-scale universe. Oberthaler claims that this is the first experiment to use cold atoms to simulate a curved and expanding universe.

When the researchers used their projector to make atoms move in the shape of an expanding universe, the atoms moved in the exact ripple pattern that would be expected if pairs of particles were forming - a phenomenon known as particle pair production. According to the researchers, this suggests that particle pairs can be produced in an expanding universe like ours.

According to Alessio Celi of the Autonomous University of Barcelona in Spain, the new experiment is a very precise playground for combining quantum effects and gravity. Physicists aren't sure how the two interact in our universe, but experiments with ultracold atoms may allow them to test some hypotheses, and they may inspire new targets for observations in our much larger and more complex cosmos, he says.

Future experiments with the same system, according to Stefan Floerchinger of the University of Jena in Germany, could lead to a better understanding of the quantum properties of our universe.

Journal citation: Nature, DOI: 10.1038/s41586-022-05313-9


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