Solution
= Solution
The positive-curvature term identifies $R$ as the curvature radius of the spatial three-sphere when the dimensionless scale factor is $a=1$; the physical curvature radius is $Ra(t)$.
= Solution
The positive-curvature term identifies $R$ as the curvature radius of the spatial three-sphere when the dimensionless scale factor is $a=1$; the physical curvature radius is $Ra(t)$.