Analysis of big bounce in Einstein--Cartan cosmology

Understand

We analyze the dynamics of a homogeneous and isotropic universe in the Einstein--Cartan theory of gravity.

• The spin of fermions produces spacetime torsion that prevents gravitational singularities and replaces the big bang with a nonsingular big bounce.
• We show that a closed universe exists only when a particular function of its scale factor and temperature is higher than some threshold value, whereas an open and a flat universes do not have such a restriction.
• We also show that a bounce of the scale factor is double: as the temperature increases and then decreases, the scale factor decreases, increases, decreases, and then increases.