  We review a new traversable-wormhole solution of the gravitational field
equation of general relativity without exotic matter. Instead of having exotic
matter to keep the wormhole throat open, the solution relies on a 3-dimensional
"spacetime defect," which is characterized by a locally vanishing metric
determinant. We also discuss the corresponding multiple-vacuum-defect-wormhole
solution and possible experimental signatures from a "gas" of vacuum-defect
wormholes. Multiple vacuum-defect wormholes appear to allow for backward time
travel.
