Vacuum energy destruction of wormhole

[nomadreid]

In Kip Thorne's popularization "Einstein's Outrageous Legacy", the author explains why a wormhole which has been arranged to connect two points in spacetime so that they are spatially close to one another but not the same time would find vacuum energy entering the "future" mouth, exiting out the "past" mouth, and then traveling through normal space towards the "future" mouth, and after the time period separating the two mouths, re-entering the "future" mouth, and so forth in a snowballing attempt, eventually having too much positive energy in the wormhole, which then would collapse. However, it seems to me that the only restriction on the distance/time differences is that light must have time enough to travel from one mouth to the other in normal spacetime. I see no need for the mouths to be nearer to each other. Is this correct?

 

[JesseM]

I haven't read "Einstein's Outrageous Legacy", but if he just says "spatially close to one another but not the same time" that is a fairly ambiguous description. I believe you're right that this sort of feedback loop is only postulated to happen when the wormholes are moved in such a way that the point where you enter one mouth crosses over into the future light cone of the point where you exit the other mouth (considering only light thtat travels through 'normal' spacetime and not through the wormhole itself). So if this idea is right, you could arrange wormholes such that entering one mouth would allow you to exit the other mouth 100 years in the past as long as the wormholes were over 100 light-years apart (relative to some quasi-inertial frame, assuming spacetime is close to flat everywhere except the immediate vicinity of each mouth), but as soon as you tried to move wormholes with a 100-year time difference to a distance of 100 light years or closer they would be destroyed.

 

[nomadreid]

Thanks. With appropriate tinkering, this would seem to take care of the paradoxes of time travel which a stable wormhole might create: you couldn't get back to your starting point fast enough to murder your grandfather.