  Physical decomposition of the non-Abelian gauge field has recently solved the
two-decade-lasting problem of a meaningful gluon spin. Here we extend this
approach to gravity and attack the century-lasting problem of a meaningful
gravitational energy. The metric is unambiguously separated into a pure
geometric term which contributes null curvature tensor, and a physical term
which represents the true gravitational effect and always vanishes in a flat
space-time. By this decomposition the conventional pseudo-tensors of the
gravitational stress-energy are easily rescued to produce definite physical
result. Our decomposition applies to any symmetric tensor, and has interesting
relation to the transverse-traceless (TT) decomposition discussed by Arnowitt,
Deser and Misner, and by York.
