Nigel

I think that Thorne's book came out in 1994. I've seen a more recent (2010) book by another student of JA Wheeler that focuses on wormholes: The Physics of Stargates -- Parallel Universes, Time Travel and the Enigma of Wormhole Physics by Enrico Rodrigo.

It appears that this question was already asked over at PhysicsForums.com. Here's the posted answer that seems most credible to me, because it cites references: BEGIN POST "What happens if an advanced civilization is able to construct a wormhole with one end on its own planet and the other end of the wormhole below the event horizon of a black hole?Will they be able to see what is happening below the event horizon of the black hole?" Actually, the answer to the latter question appears to be "yes". I found two sources that confirm this. Both are written by physicists. 1) "Wormhole as a device for studying a black hole's interior", by V. Frolov and I. Novikov, Physical Review D volume 48, page 1607 (1993) Here's the abstract: "It is shown that by using a traversable wormhole one can get information from a black hole's interior. The change of a black hole's geometry in the presence of a wormhole falling into it is analyzed. The causal structure and the properties of the event horizon of a Schwarzschild spacetime with a wormhole are considered. Information and energy extraction from the interior of a black hole by using a wormhole is discussed." 2) The Physics of Stargates: Parallel Universes, Time Travel and the Enigma of Wormhole Physics, by Enrico Rodrigo, Eridanus Press (New York) 2010 On page 33, in a question/answer section: "Could I use a wormhole to escape from the inside of a black hole? Yes. Classically, there appears be to nothing to prevent the existence of a wormhole that connects the inside of a black hole with the region exterior to its event horizon. However, to an observer within the horizon, the outward direction points to the past, i.e. backward in time. So escaping a black hole via a wormhole is only possible, if time travel by wormhole is possible." END POST I recently purchased the second reference and can confirm that it's accurately quoted.

It turns out that you are correct. There is a relationship between the separation of wormhole mouths and the maximum paradox-free time jump. To avoid paradoxes, the exit mouth cannot be in the "past light cone" of the entrance mouth. In other words, if you want the paradox-free time jump to be T years, the spatial separation between exit mouth and the entrance mouth must be greater than the distance that light can travel in T years. However, according to the book I'm getting this from, that sort of time travel would not be considered "true" time travel. The reason is that there exist observers (moving at a particular velocity) for which your backward paradox-free time jump appears to be a forward time jump. The only sort of time jumps for which there are no such observers are the paradox-generating jumps into your own past-light cone. Source: The Physics of Stargates -- Parallel Universes, Time Travel and the Enigma of Wormhole Physics, by Enrico Rodrigo (Eridanus Press, New York 2010) p. 284