Baumgarte–Shapiro–Shibata–Nakamura formulation (BSSN formulation)

The Baumgarte–Shapiro–Shibata–Nakamura formulation rewrites the Einstein evolution equations using a conformal spatial metric, conformal traceless extrinsic curvature, the trace $K$, and conformal connection functions.

In vacuum geodesic slicing, discarding nonnegative shear leaves ${\partial }_{t}K=K^2/3$. Positive initial $K_0$ therefore gives $K=K_0/[1-K_0(t-t_0)/3]$ and blows up at $t=t_0+3/K_0$.