Cosmology: from theory to data, from data to theory
  Cosmology has come a long way from being based on a small number of
observations to being a data-driven precision science. We discuss the questions
"What is observable?", "What in the Universe is knowable?" and "What are the
fundamental limits to cosmological knowledge?". We then describe the
methodology for investigation: theoretical hypotheses are used to model,
predict and anticipate results; data is used to infer theory. We illustrate
with concrete examples of principled analysis approaches from the study of
cosmic microwave background anisotropies and surveys of large-scale structure,
culminating in a summary of the highest precision probe to date of the physical
origin of cosmic structures: the Planck 2013 constraints on primordial
non-Gaussianity.
