Expanding Universe Recreated In The Lab Thanks To Humming Atoms

E. Edwards/JQI

Scientists studying a peculiar state of matter have discovered that it behaves similarly to the accelerated expansion of the early universe, which could allow astronomers to test new models in laboratory settings.  

The study, published in Physical Review X, looked at a Bose-Einstein condensate (BEC), a state of matter where a dilute gas of particles is cooled to almost absolute zero. The team was looking at the expansion of such a state by expanding a cloud of atoms in a donut shape. This expansion was so fast that it left all the gas vibrating, in what the scientists call humming.

So how does this humming connect to the astronomy? The universe is believed to have experienced a similar period of rapid expansion in the first instants after the Big Bang. This time, known as cosmic inflation, is still poorly understood but, using a BEC it might be possible to clear some doubts.

"From the atomic physics perspective, the experiment is beautifully described by existing theory, but even more striking is how that theory connects with cosmology," said lead author Stephen Eckel, from the National Institute of Standards and Technology, in a statement.

"Maybe this will one day inform future models of cosmology. Or vice versa. Maybe there will be a model of cosmology that's difficult to solve but that you could simulate using a cold atomic gas."

BECs are systems where quantum phenomena become apparent and since the particles in a BEC have very little free energy (as they are so cold) it is possible to use them for simulating some complex and sometimes extreme physical scenarios. BECs have been successfully used to simulate black holes.

The team planned two experiments. In the first, they looked at how waves propagate in an expanding medium. They put a sound wave in the original BEC and studied how it changed as the condensate expanded. The sound wave ended up stretched and dispersing, and the dampening effect looked like the cosmological parameter known as Hubble friction, which plays a role in cosmic inflation. The team also let the gas expand without any sound waves, and they still saw vibrations in the gas mimicking what’s found in cosmological theories.

While intriguing, this is not a direct comparison between the whole universe and the BEC. An important point of disagreement is the energy transfer. In cosmic inflation, some of the leftover energy ends up transforming into matter and light, but nothing similar was seen in the BEC. Quantum effects become dominant there creating vortices, making the ring rotate, and changing the properties of the atoms.

The team hopes to better understand these energy transfers and continue looking for cosmological analogies in BECs.

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