  Experimentally distinguishing different primordial universe paradigms that
lead to the Big Bang model is an outstanding challenge in modern cosmology and
astrophysics. We show that a generic type of signals that exist in primordial
universe models can be used for such purpose. These signals are induced by tiny
oscillations of massive fields and manifest as features in primordial density
perturbations. They are capable of recording the time-dependence of the scale
factor of the primordial universe, and therefore provide direct evidence for
specific paradigm.
