  Inflation drives quantum fluctuations beyond the Hubble horizon, freezing
them out before the small-scale modes re-enter during the radiation dominated
epoch, and subsequently decay, while large-scale modes re-enter later during
the matter dominated epoch and grow. This distinction shapes the matter power
spectrum and provides observational evidence in support of the standard model.
In this paper, we demonstrate that another mechanism, based on the fluctuation
growth in the R_h=ct universe, itself an FLRW cosmology with the added
constraint of zero active mass (i.e., rho+3p=0), also accounts very well for
the observed matter power spectrum, so this feature is not unique to LambdaCDM.
In R_h=ct, the shape of the matter power spectrum is set by the interplay
between the more rapid decay of the gravitational potential for the smaller
mode wavelengths and the longer dynamical timescale for the larger wavelengths.
This combination produces a characteristic peak that grows in both amplitude
and mode number as a function of time. Today, that peak lies at k approx 0.02
Mpc^-1, in agreement with the Ly-alpha and Planck data. But there is no need of
an inflationary expansion, and a complicated epoch dependence as one finds in
LambdaCDM.
