Accurate Determination of Hubble Attenuation and Amplification in Expanding and Contracting Cold-Atom Universes

Understand

In the expanding universe, relativistic scalar fields are thought to be attenuated by "Hubble friction", which results from the dilation of the underlying spacetime metric.

• By contrast, in a contracting universe this pseudo-friction would lead to amplification.
• Here, we experimentally measure with five-fold better accuracy, both Hubble attenuation and amplification in expanding and contracting toroidally-shaped Bose-Einstein condensates, in which phonons are analogous to cosmological scalar fields.
• We find that the observed attenuation or amplification depends on the temporal phase of the phonon field, which is only possible for non-adiabatic dynamics.