In the end of Xenocide,
They discover a "place" called Outside that doesn't have the usual rules of physics. In particular, there is no "there" there.
So how can they communicate with each other?
Note: I have an answer to this which I will post.
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It was explained in Xenocide that Jane was the key to holding the pattern together. In the Enderverse the universe is made of philotes--- people, air, photons, everything --- and aiuas, a special kind of philote that binds the philotes that make up a living thing. It was up to Jane with her vast memory and inhuman level of concentration to maintain the interrelationship of all those philotes long enough for Ela's new virus to be created and tested.
Ender imagined himself breaking into a trillion constituent parts, scattering through chaos. Personal survival depended not only on Jane holding the pattern of the ship, but also on him being able to hold the pattern of his mind and body. Only he had no idea whether his mind was really strong enough to maintain that pattern, once he was where the laws of nature were not in force.
Each person's aiua maintained their bodies. Jane was responsible for binding the philotes that had no binding aiuas plus the aiuas themselves. So it was Jane who made sure the air philotes did what they were supposed to do.