  We consider maximal globally hyperbolic flat (2+1) spacetimes with compact
space S of genus g>1. For any spacetime M of this type, the length of time that
the events have been in existence is M defines a global time, called the
cosmological time CT of M, which reveals deep intrinsic properties of
spacetime. In particular, the past/future asymptotic states of the cosmological
time recover and decouple the linear and the translational parts of the
ISO(2,1)-valued holonomy of the flat spacetime. The initial singularity can be
interpreted as an isometric action of the fundamental group of S on a suitable
real tree. The initial singularity faithfully manifests itself as a lack of
smoothness of the embedding of the CT level surfaces into the spacetime M. The
cosmological time determines a real analytic curve in the Teichmuller space of
Riemann surfaces of genus g, which connects an interior point (associated to
the linear part of the holonomy) with a point on Thurston's natural boundary
(associated to the initial singularity).
