Is classical flat Kasner spacetime flat in quantum gravity?

Understand

Quantum nature of classical flat Kasner spacetime is studied using effective spacetime description in loop quantum cosmology.

• We find that even though the spacetime curvature vanishes at the classical level, non-trivial quantum gravitational effects can arise.
• For the standard loop quantization of Bianchi-I spacetime, which uniquely yields universal bounds on expansion and shear scalars and results in a generic resolution of strong singularities, we find that a flat Kasner metric is not a physical solution of the effective spacetime description, except in a limit.
• The lack of a flat Kasner metric at the quantum level results from a novel feature of the loop quantum Bianchi-I spacetime: quantum geometry induces non-vanishing spacetime curvature components, making it not Ricci flat even when no matter is present.