In canonical general relativity, Hamiltonian closure is the standard procedure for recovering an internal time variable from Einstein’s theory, which contains no background time. The mathematical reduction that produces this clock variable yields two branches with opposite signs. Conventional treatments keep one and discard the other as an algebraic artifact. The algebraic reduction process, known as deparameterization, involves a quadratic constraint whose solution yields the familiar branch pair σ = 1. Because the underlying theory is general relativity, the branch structure should inherit geometric content; yet that content has largely gone unexamined. We show that, both spatially and mathematically, σ represents a genuine three-dimensional canonical structure undergoing three distinct involutions, producing the geometrically opposite configurations corresponding to σ = +1 and σ = −1.
Austin Stewart (Thu,) studied this question.