  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.
