 Reissner-Nordstrom spacetime

The four-dimensional charged spherically symmetric electrovacuum solution has radial function $f=1-2M/r+Q^2/r^2$. For $0<|Q|<M$, its outer and inner horizon radii are $r_{\pm }=M\pm \sqrt{M^2-Q^2}$. A complete two-ended spatial bridge has a maximal Cauchy development ending at smoothly extendible inner Cauchy horizons in the exact solution.