  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. The
non-curvature singularity of the classical flat Kasner spacetime is avoided,
and the effective spacetime transits from a flat Kasner spacetime in asymptotic
future, to a Minkowski spacetime in asymptotic past. Interestingly, for an
alternate loop quantization which does not share some of the fine features of
the standard quantization, flat Kasner spacetime with expected classical
features exists. In this case, even with non-trivial quantum geometric effects,
the spacetime curvature vanishes. These examples show that the character of
even a flat classical vacuum spacetime can alter in a fundamental way in
quantum gravity and is sensitive to the quantization procedure.

General Relativity and Quantum Cosmology