Bouncing Universe from Nothing

Understand

We find a class of solutions for a homogeneous and isotropic universe in which the initially expanding universe stops expanding, experiences contraction, and then expands again (the "bounce"), in the framework of Einstein gravity with a real scalar field without violating the null energy condition nor encountering any singularities.

• Two essential ingredients for the bouncing universe are the positive spatial curvature and the scalar potential which becomes flatter at large field values.
• Depending on the initial condition, either the positive curvature or the negative potential stops the cosmic expansion and begins the contraction phase.
• The flat potential plays a crucial role in triggering the bounce.