  Current theoretical investigations seem to indicate the possibility of
observing signatures of short distance physics in the Cosmic Microwave
Background spectrum. We try to gain a deeper understanding on why all
information about this regime is lost in the case of Black Hole radiation but
not necessarily so in a cosmological setting by using the moving mirror as a
toy model for both backgrounds. The different responses of the Hawking and
Cosmic Microwave Background spectra to short distance physics are derived in
the appropriate limit when the moving mirror mimics a Black Hole background or
an expanding universe. The different sensitivities to new physics, displayed by
both backgrounds, are clarified through an averaging prescription that accounts
for the intrinsic uncertainty in their quantum fluctuations. We then proceed to
interpret the physical significance of our findings for time-dependent
backgrounds in the light of nonlocal string theory.
