Non-traversability of the Schwarzschild bridge
= Non-traversability of the Schwarzschild bridge
In <Kruskal–Szekeres coordinates>, every future-directed radial causal curve has nondecreasing $U$ and $V$. The right exterior has $U<0,V>0$, while the left has $U>0,V<0$. No future-directed causal curve can travel between the exteriors because it would have to decrease one null coordinate. The spatial bridge on a time-symmetric slice is therefore not a traversable passage.