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 c” (15[1])along a worldline defines (15[1])one form of this quantity. (15[2]-5[4])The “problem” of this quantity tries to reconcile its dynamical treatment (-5[1])in general (-5[1])(*) relativity with its (10[1])treatment as an absolute background parameter (10[1])in quantum mechanics. Intervals that are negative, (10[2])and thus fall inside (10[1])the light (-5[1])cone, (-5[1])are described as “like” (10[2])this (10[1])quantity. (10[2]-5[2])This quantity (-5[1])changes (10[1])more slowly for a sibling traveling in a (10[1])rocket (10[6])in (10[1])the (10[1])twin (10[2])paradox. (10[5])For 10 points, relativity (10[1])unifies space with what quantity? (10[4])■END■ (10[4])