[codethief]

Since it's part of the introductory chapter, my interpretation had been that the portion I quoted was supposed to be a general, well-known "law" implied by quantum theory, i.e. not a result specific to the situation at hand. Hence my question where that supposed law is coming from.

But it seems they were indeed merely announcing a result specific to the wormhole they constructed since on p. 6 the authors say:

> In deriving (2.12) we assumed that the distance d between the two black holes is smaller than l, d << l. Even when we do not make that assumption we find that the time through the wormhole is always longer than through the outside, πl > d.