  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. The measured strength of the
Hubble friction disagrees with recent theory [J. M. Gomez Llorente and J.
Plata, {\it Phys. Rev. A} {\bf 100} 043613 (2019) and S. Eckel and T. Jacobson,
{\it SciPost Phys.} {\bf 10} 64 (2021)]; because our experiment probes physics
outside the scope of this theory -- with large excitations in rings of
intermediate thickness -- this indicates the presence of new physics.

Quantum Physics;Quantum Gases