  One way to explain the present acceleration of the Universe is Einstein's
cosmological constant. It is quite likely, in view of some recent studies, that
a time-dependent equation of state had caused the Universe to evolve from an
earlier phantom-energy model. In that case traversable wormholes could have
formed spontaneously. It is shown in this paper that such wormholes would
eventually have become black holes. This would provide a possible explanation
for the huge number of black holes discovered, while any evidence for the
existence of wormholes is entirely lacking, even though wormholes are just as
good, in terms of being a prediction of general relativity, as black holes.
