Truly data-driven cosmology has been made possible within the last 2-3 decades by observational advances on three major fronts:

We discuss each of these on separate pages. It is important to realize that each set of observations provides a different window on the evolution of the universe. This is in part because each observational set provides a view of the universe at a different look-back time, quantified by the redshift of the radiation reaching us. This is illustrated in an approximate way (not to scale) in the figure below. The CMB radiation we observe in microwaves provides a snapshot of the 'infant universe', whereas observations of supernovae, galaxies and quasars show us conditions in a more evolved universe. The ΛCDM model ties these different pieces of information together in a cohesive picture. If the standard model cannot explain data from all redshift ranges within the observational uncertainties, then there is either the exciting possibility for new physics, or alternatively, the possibility that the observational errors are not well understood.

Contributed by the NASA / LAMBDA Archive Team.

A service of the HEASARC and of the Astrophysics Science Division at NASA/GSFC
Goddard Space Flight Center, National Aeronautics and Space Administration
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