Cosmology from the structure of the $Ly \alpha$ forest

A convincing physical picture for the Lyman-alpha forest has emerged from simulations and related semi-analytic studies of structure formation models. Observations can be be used in the context of this picture to study cosmology using the structure of the forest. With the availability of well motivated predictions, not only has it become possible to test models directly, but the physical processes involved appear to be simple enough that we can attempt to reconstruct aspects of the underlying cosmology from observations. We briefly summarise the method of Croft et al (1997) (astro-ph/9708018) for recovering the primordial mass power spectrum from Lyman-alpha forest data, emphasising the physical reasons that the derived P(k) is independent of unknown "bias factors". We present an illustrative application of the method to four quasar "spectra" reconstructed from published line lists