  The effect of the scalar spectral index on inflationary super-Hubble waves is
to amplify/damp large wavelengths according to whether the spectrum is red
($n_{s}<1$) or blue ($n_{s}>1$). As a consequence, the large-scale temperature
correlation function will unavoidably change sign at some angle if our spectrum
is red, while it will always be positive if it is blue. We show that this
inflationary filtering property also affects our estimates of the size of the
homogeneous patch of the universe through the Grishchuk-Zel'dovich effect.
Using the recent quadrupole measurement of ESA's Planck mission, we find that
the homogeneous patch of universe is at least 87 times bigger than our visible
universe if we accept Planck's best fit value $n_{s}=0.9624$. An independent
estimation of the size of the universe could be used to independently constrain
$n_{s}$, thus narrowing the space of inflationary models.
