= Conjugate point to a spacelike surface
= Conjugate points to a spacelike surface
{synonym}
A <conjugate point to a spacelike surface> occurs where normal <geodesics> develop a focal degeneracy: the transverse <Jacobi field> map from initial points on the surface ceases to be invertible. Collapse of the transverse area makes the <null expansion> diverge. Beyond a first such point, the normal <null geodesic> cannot continue as a generator of the <achronal boundary> of the surface's future.
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