The Lyman-alpha Forest: a Cosmic Gold Mine

In recent years, a remarkably simple physical picture of the Lyman-alpha forest has emerged, which allows detailed predictions to be made and turns the forest into a powerful probe of cosmology. We point out ways in which such a picture can be tested observationally, and explore three areas in which the Lyman-alpha forest can yield valuable constraints: the reionization history, the primordial mass power spectrum and the cosmological constant or its variants. The possibility of combining with other high redshift observations, such as the Lyman-break galaxy surveys, to provide consistency checks and complementary information is also discussed.