The topology of a closed loop universe-antiuniverse pair embedded in a multiverse.*

Based on the CPT theorem and two hypothetical principles: (1) Spacetime has no boundaries, and (2) Physics has no infinities, a closed loop topology follows naturally. The universe is closed, almost (but not perfectly) flat, with zero total energy. Consequences are that time at the level of fundamental particles, as in the CPT theorem, is a closed loop, and is different from the time of complex systems (entropic and psychological time). At the big bang a universe anti-universe pair was created; both are closed 3-spaces connected only at the big bang, which was not a singularity, and in the far future after protons (and all complex structures) have decayed. Fermion number is conserved; fermion world-lines have no ends, as in Feynman's interpretation of oppositely directed electron and positron world-lines, and time at that level is a closed loop. Black holes cannot evaporate to nothing. The universe and anti-universe have identical physics (particle masses and forces), together with a vast number of disconnected universes, a version of the multiverse idea explaining how the physics in our Universe can allow life.