Regular Article - Theoretical Physics
Aspects of the cosmological “coincidence problem”
Departamento de Física, Universidade Federal do Espírito Santo (UFES), Av. Fernando Ferrari, 514 Campus de Goiabeiras, Vitória, Espírito Santo, CEP 29075-910, Brazil
* e-mail: firstname.lastname@example.org
Accepted: 28 October 2014
Published online: 22 November 2014
The observational fact that the present values of the densities of dark energy and dark matter are of the same order of magnitude, , seems to indicate that we are currently living in a very special period of the cosmic history. Within the standard model, a density ratio of the order of one just at the present epoch can be seen as coincidental since it requires very special initial conditions in the early Universe. The corresponding “why now” question constitutes the cosmological “coincidence problem”. According to the standard model the equality took place “recently” at a redshift . The meaning of “recently” is, however, parameter dependent. In terms of the cosmic time the situation looks different. We discuss several aspects of the “coincidence problem”, also in its relation to the cosmological constant problem, to issues of structure formation and to cosmic age considerations.
© SIF and Springer-Verlag Berlin Heidelberg, 2014