Ultra-Cold Atoms Recreate The Expanding Universe In Tabletop Experiment

Eerie similarities unite vastly different scientific ideas in sometimes utterly surprising ways. One of these similarities may have allowed scientists to recreate the expanding universe - on a countertop.

Researchers accomplished their feat using Bose-Einstein condensates, which are collections of certain atoms held to the near coldest-possible temperatures. Bose-Einstein condensates let scientists see teeny quantum mechanical effects on a much larger scale, and have been used to do lots and lots of wild physics. These scientists hope they can use its quirks to model the behaviour of the far grander cosmos.

"It's hard to test theories of cosmology," study author Gretchen Campbell, from the University of Maryland's Joint Quantum Institute, told Gizmodo. "Maybe we can actually find a way to study some cosmological models on the laboratory scale."

Everything is an analogy in this system. The vacuum of the universe is represented by around 10,000 sodium atoms confined to a ring shape by light beams, held at just above absolute zero, the lowest temperature. The universe's speed of light is represented as the speed of sound through the atoms. The universe's particles are represented as phonons, the smallest possible units of vibrational energy (sound) travelling through the atoms, according to the paper published yesterday in Physical Review X.

It might sound completely different, but it appears the two systems - the early expanding universe and the super-cold atoms - are governed by some very similar maths. That means that if you observe how the atoms change over time, you may be able to predict how the universe evolved early in its life. Two things governed by the same equations should change in the same ways.

The researchers quickly increased the size of the ring faster than the speed of sound, similar to how the universe briefly expanded faster than the speed of light during the inflation just after the Big Bang. The condensate demonstrated a few behaviours similar to the way energy might have behaved in the inflating universe. That includes phonons stretching as the condensate expanded, called "redshifting," and energy of the expansion turning into vibrational disturbances reminiscent of the particles supposedly created as inflation ended.

Again - this is just a first attempt at drawing the comparison, so it can't replace actually looking to space. But scientists have long used analogies in Bose-Einstein condensates to explain weird things in the universe. Recently, one scientist recreated Stephen Hawking's most famous theory of evaporating black holes using a Bose-Einstein condensate. Campbell hopes to better understand the effects they're seeing and to better design these experiments to study these and other strange things that may have happened in our expanding universe.

And others are watching, too. "I find the results quite exciting, since they establish a novel connection between cosmologists, and condensed-matter and atomic physicists," said Misha Lemeshko, an assistant professor at the Institute of Science and Technology Austria, who was not involved in this study. "Trying to explain the early universe in terms of dynamics of phonons and vortices in a Bose-Einstein condensate provides us, the 'terrestrial' physicists, with a nice intuitive picture."

So, while it's not quite the same as actually looking out into the universe, modelling the vast cosmos using an experiment in a lab can be an enlightening substitute.

[PRX]

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