The isotropic and homogeneous FLRW cosmological model, although
certainly incomplete, has been so successful in describing the
observable Universe that it is commonly referred to as the
``standard model''. Furthermore, and to its credit, the model is
relatively simple so that it allows for calculations and
predictions to be made of the very early Universe, including
primordial nucleosynthesis at
seconds after the Big Bang, and even particle interactions
approaching the Planck scale at
seconds. At present, observational support for the standard
model includes:
the expansion of the Universe
as verified by the redshifts in galaxy spectra and quantified
by measurements of the Hubble constant,
the deceleration parameter
observed in distant galaxy spectra (although uncertainties
about galactic evolution, intrinsic luminosities, and standard
candles prevent even a crude estimate),
the large scale isotropy and homogeneity of the Universe
based on temperature anisotropy measurements of the microwave
background radiation and peculiar velocity fields of galaxies
(although the light distribution from bright galaxies seems
more tenuous),
the age of the Universe
which yields roughly consistent estimates between the
look-back time to the Big Bang in the FLRW model and observed
data such as the oldest stars, radioactive elements, and
cooling of white dwarf stars,
the cosmic microwave background radiation
suggests that the Universe began from a hot Big Bang and the
data is consistent with a black body at temperature 2.75
K,
the abundance of light elements
such as
H,
He,
He and
Li, as predicted from the FLRW model, are consistent with
observations and provides a bound on the baryon density and
baryon-to-photon ratio,
the present mass density, as determined from measurements of luminous matter and
galactic rotation curves, can be accounted for by the FLRW
model with a single density parameter to specify the metric
topology,
the distribution of galaxies and larger scale structures
can be reproduced by numerical simulations in the context of
inhomogeneous perturbations of the FLRW models.
Because of these successes, most work in the field of physical
cosmology has utilized the standard model as the background
spacetime in which the large scale structure evolves, with the
ambition to further constrain the cosmological parameters and
structure formation scenarios through numerical simulations. The
reader is referred to [40] for a more in-depth review of the standard model.