Metals in the Intergalactic Medium

The absorption lines seen in the spectra of quasars trace gas over a very large range of overdensities, from galaxies to voids and probably account for most of the baryons at high redshift. Once thought to be a chemically pristine remnant of the Big Bang, the Lyman alpha forest has now been shown to contain significant quantities of metals. We summarise the results of the latest searches for weak C IV lines in low density regions of the intergalactic medium together with recent theoretical work aimed at understanding the origin of such widespread metal pollution and what it can tell us about the first generations of stars.