  Our knowledge of the Universe remains discovery-led: in the absence of
adequate physics-based theory, interpretation of new results requires a
scientific methodology. Commonly, scientific progress in astrophysics is
motivated by the empirical success of the "Copernican Principle", that the
simplest and most objective analysis of observation leads to progress. A
complementary approach tests the prediction of models against observation. In
practise, astrophysics has few real theories, and has little control over what
we can observe. Compromise is unavoidable. Advances in understanding complex
non-linear situations, such as galaxy formation, require that models attempt to
isolate key physical properties, rather than trying to reproduce complexity. A
specific example is discussed, where substantial progress in fundamental
physics could be made with an ambitious approach to modelling: simulating the
spectrum of perturbations on small scales.
