- Scientists created Bose-Einstein condensate and configured it into a quick-expanding ring.
- This ring of ultracold atom exhibits features that resemble characteristics of an expanding universe.
- One can use it as a laboratory test bed for cosmic phenomena.
We all know that the universe is expanding at the rate of about 67 kilometers per second. Now scientists have created an interesting cosmic analog that explains the physics of the universe after the big bang.
Since it’s very hard to study the aspects of the universe experimentally, researchers at the University of Maryland used a bunch of cold atoms to emulate physical systems like black holes, superconductors or supersolids.
They created a Bose-Einstein condensate — a state of matter in which atoms are cooled to temperatures near absolute zero — and structured it into a small, quickly expanding ring. This ring exhibits some features that resemble characteristics of an expanding universe. One can use it as a laboratory test bed for cosmic phenomena.
This is not the first time researchers have created Bose-Einstein condensates to evaluate the unknown things in the universe. In 2014, a team at the University of Cambridge used it to simulate a black hole.
How Did They Create This Ring?
Image credit: E. Edwards/JQI
To make Bose-Einstein condensate, researchers cooled hundreds of thousands of atoms of sodium-23 to temperatures very close to absolute zero (0 Kelvin). They trapped the condensate in a ring-like structure, using laser beams.
Then they expanded the diameter of the ring by 4 times — from 23 micrometers to about 90 micrometers — over a period of 15 milliseconds. This caused the condensate to grow at supersonic speed.
They collected data (like condensate density, frequency and amplitude of phonons propagating in condensate) and analyzed the behavior of the ring during and after the expansion.
What Are Those Similar Features?
Scientists found 3 features that were very similar to those anticipated for a universe expanding at significant rate.
1. Increase in wavelength of condensate’s phonons resembles the universe’s redshift effect.
As the size of the ring expanded, the sound waves propagating through the Bose-Einstein condensate increased in wavelength. This is analogous to the cosmic redshift effect – light shifted to the red end of the spectrum (longer wavelength) as the universe expanded.
2. Damping effect similar to Hubble friction.
The sound waves in the condensate is shown to have a damping effect, which relates to what is known as Hubble friction – the decline in density of particles in the universe’s early stage.
Density of Bose-Einstein condensate reduces as it expands | S. Eckel et al., Phys. Rev. X
Reference: Physical Review X | doi:10.1103/PhysRevX.8.021021
3. Energy transfer process relates to preheating phase of early universe.
The expansion of condensate triggered an energy transfer process, which transformed the sound waves from one type to another. More specifically, it converted the radial excitation modes into localized vortices, heating the Bose-Einstein condensate.
In physical cosmology, this is called inflation where preheating occurs at the end of rapid expansion phase (or before universe settles into a normal expansion rate). This happens when inflatons convert into other particles.
In addition to these possibilities, other interesting cosmological phenomena could be realized with enlarging condensates. The effects related to vacuum scaling could be observed by enhancing imaging method that captures initial thermal and quantum fluctuations.
In particular, cosmological particle production could be observed. A ring with higher radial confinement will suppress transverse excitations, unveiling the things arising from the recombination of disconnected regions.