The absence of this quantity in the Wheeler-Dewitt equations necessitated approaches that generate this quantity, such as the emergent definition of this quantity in the Page-Wootters formalism. A foliation produces a series of surfaces indexed by this quantity in the ADM formalism. The integral of “ds over (-5[1])c” (15[1])along a worldline defines one (-5[1])form of this quantity. (15[1]-5[2])The “problem” of this (-5[2])quantity tries to reconcile its dynamical treatment (-5[1])in general (*) relativity with its treatment as an absolute background parameter (10[1])in quantum mechanics. Intervals that are negative, (10[1])and thus fall inside (10[1])the light (-5[1])cone, are described as “like” (10[1])this quantity. (-5[2])This quantity (-5[1])changes (10[1])more (10[1])slowly for a sibling (10[1])traveling in a (10[3])rocket (10[5])in (-5[1])the (10[1])twin (10[1])paradox. (10[4])For 10 points, (10[1])relativity (10[2])unifies space with (10[2])what quantity? (10[2])■END■ (10[4])