The Gaiasphere and the limits of knowledge
  At the heart of a successful theory of galaxy formation must be a detailed physical understanding of the dissipational processes which form spiral galaxies. To what extent can we unravel the events that produced the Galaxy as we see it today? Could some of the residual inhomogeneities from prehistory have escaped the dissipative process at an early stage? To make a comprehensive inventory of surviving inhomogeneities would require a vast catalog of stellar properties that is presently out of reach. The Gaia space astrometry mission, set to launch at the end of the decade, will acquire detailed phase space coordinates for about one billion stars, within a sphere of diameter 20 kpc -- the Gaiasphere. Here we look forward to a time when all stars within the Gaiasphere have complete chemical abundance measurements (including alpha, s and r process elements). Even with such a vast increase in information, there may exist fundamental -- but unproven -- limits to unravelling the observed complexity. 
J. Bland-Hawthorn (AAO)