Probing the Universe through Neutral Hydrogen Distribution

As is well known, hydrogen is the most abundant element in the
Universe. Hydrogen in the low density intergalactic medium is
photoionized by radiation from galaxies and other sources, while they
remain in neutral form in very high density regions because of
shielding. The evolution of neutral  hydrogen through cosmic times
passes through a number of interesting phases, namely, the dark ages,
reionization and post-reionization epoch. Understanding each of these
phases holds clue about the cosmology and galaxy formation in our
Universe. In the talk, we will review our understanding of the
physical processes related to cosmological distribution of neutral
hydrogen and then present some recent results on these issues. We will
also discuss prospects for using neutral hydrogen as strong probe of
cosmology using future observational probes.