  We identify a signature of quantum gravitational effects that survives from
the early universe to the current era: Fluctuations of quantum fields as seen
by comoving observers are significantly influenced by the history of the early
universe. In particular we show how the existence (or not) of a quantum bounce
leaves a trace in the background quantum noise that is not damped and would be
non-negligible even nowadays. Furthermore, we estimate an upper bound for the
typical energy and length scales where quantum effects are relevant. We discuss
how this signature might be observed and therefore used to build falsifiability
tests of quantum gravity theories.
