"THE CENSUS OF MATTER IN THE NEARBY UNIVERSE: THE INTERGALACTIC
POPULATION"
Measurements of the cosmic microwave background and the
abundances of light
elements (e.g., deuterium), both in good accord with
theoretical predictions,
provide strong support for the big-bang cosmological
theory. These
observations also constrain the amount of ordinary (baryonic)
matter which
should exist in the universe, and this has raised a puzzle:
the predicted
amount of baryonic matter substantially exceeds the quantity
found by
inventories of readily-observed baryons in the nearby
universe. Is this a
symptom of a problem with the big-bang model, or is there
a hidden population
of baryons which have eluded the matter census?
Theoretical arguments and
observational evidence that there is a substantial reservoir
of baryons in
the intergalactic medium will be reviewed. I will
argue that this
intergalactic population may solve the missing baryon
problem. Finally,
future observations that are needed to confirm current
evidence will be
briefly discussed.