The 21-cm cosmology

Neutral hydrogen (HI) has persisted for much of cosmic history, making it
the best tracer to probe the Universe. Observation of the redshifted 21-cm
signal due to the hyperfine transition of HI is a promising method to
study its three-dimensional distribution in the Universe. The first
billion years of cosmic history of the Universe mark the formation of the
first stars and galaxies. After years of theoretical predictions, a
considerable international effort is now producing the first tentative
results, e.g. EDGES, SARAS, GMRT, LOFAR, MWA, HERA, etc. The coming theory
and observations will reveal the mysterious era of cosmic dawn and
reionization, including the properties of the first stars and galaxies,
and possibly more exotic discoveries. There are also plans to probe the
pre-stellar "dark ages" with telescopes on the moon. I will give a summary
and update on current studies of 21-cm Cosmology and the Epoch of
Reionization (EoR).