The R_h = ct Universe
  The backbone of standard cosmology is the Friedmann-Robertson-Walker solution
to Einstein's equations of general relativity (GR). In recent years,
observations have largely confirmed many of the properties of this model, which
is based on a partitioning of the universe's energy density into three primary
constituents: matter, radiation, and a hypothesized dark energy which, in
LambdaCDM, is assumed to be a cosmological constant Lambda. Yet with this
progress, several unpalatable coincidences (perhaps even inconsistencies) have
emerged along with the successful confirmation of expected features. One of
these is the observed equality of our gravitational horizon R_h(t_0) with the
distance ct_0 light has traveled since the big bang, in terms of the current
age t_0 of the universe. This equality is very peculiar because it need not
have occurred at all and, if it did, should only have happened once (right now)
in the context of LambdaCDM. In this paper, we propose an explanation for why
this equality may actually be required by GR, through the application of
Birkhoff's theorem and the Weyl postulate, at least in the case of a flat
spacetime. If this proposal is correct, R_h(t) should be equal to ct for all
cosmic time t, not just its present value t_0. Therefore models such as
LambdaCDM would be incomplete because they ascribe the cosmic expansion to
variable conditions not consistent with this relativistic constraint. We show
that this may be the reason why the observed galaxy correlation function is not
consistent with the predictions of the standard model. We suggest that an
R_h=ct universe is easily distinguishable from all other models at large
redshift (i.e., in the early universe), where the latter all predict a rapid
deceleration.
