Cosmologists work to answer some of the oldest questions of humanity:
How did the Universe begin? What is it made of? What rules does it follow?
Observations of the large-scale structure of the Universe address these
questions in several ways:
Measurements of the scale dependence of density fluctuations tell us about
the initial conditions for structure formation, set in the very early Universe.
Measurements of the expansion and growth of structure with time tell us about
the matter content and gravitational laws.
I will mostly discuss one large-scale structure probe:
the Lyman-alpha forest (LyaF) - the absorption in high redshift quasar spectra
by neutral hydrogen in the intergalactic medium.
The LyaF provides a good probe of the density field at z~3 on scales down
to ~100 kpc.
When combined with the CMB on larger scales, the LyaF observed in thousands of
quasar spectra from the Sloan Digital Sky Survey currently provides the best
constraints on the power spectrum of initial density perturbations, neutrino
masses that affect structure formation, and warm dark matter. These
constraints should improve significantly in the near future. I will also
discuss the possibility of probing dark energy by using a future large survey
to detect baryonic acoustic oscillations in the LyaF.