Hidden past of dark energy cosmological models

In this Letter we analyse the possibility of having homogeneous isotropic cosmological models with observers reaching t = infinity in finite proper time. It is shown that just observationally-suggested dark energy models with w epsilon (-5/3, -1) show this feature and that they are endowed with an exotic curvature singularity. Furthermore, it is shown that non-accelerated observers in these models may experience a duration of the universe as short as desired by increasing their linear momentum. A subdivision of phantom models in two families according to this behavior is suggested. (c) 2007 Elsevier B.V. All rights reserved.