In cosmology it has become usual to introduce new entities as dark matter and
dark energy in order to explain otherwise unexplained observational facts.
Here, we propose a different approach treating spacetime as a continuum endowed
with properties similar to the ones of ordinary material continua, such as
internal viscosity and strain distributions originated by defects in the
texture. A Lagrangian modeled on the one valid for simple dissipative phenomena
in fluids is built and used for empty spacetime. The internal "viscosity" is
shown to correspond to a four-vector field. The vector field is shown to be
connected with the displacement vector field induced by a point defect in a
four-dimensional continuum. Using the known symmetry of the universe, assuming
the vector field to be divergenceless and solving the corresponding
Euler-Lagrange equation, we directly obtain inflation and a phase of
accelerated expansion of spacetime. The only parameter in the theory is the
"strength" of the defect. We show that it is possible to fix it in such a way
to also quantitatively reproduce the acceleration of the universe. We have
finally verified that the addition of ordinary matter does not change the
general behaviour of the model.Comment: 13 pages, 7 figures Typos; section V on Newtonian limit adde