Dopple Gangers in Science Fiction

In some stories, there is a rift between universes through which one can communicate or even travel to meet one's dopleganger. In another class of stories, the transport of our function ccidentally exiles the passengers to a phantom zone where they are imperceptible to everyone in the ordinary world,. So they have the distressing experience of yelling and gesticulating in vain to their shipmates, who are oblivious and walk right through them. Such a story may end with the exiles discovering that they can, after all, have some effect on the ordinary world. They then may begin new lives as separate people, or they may merge with their originals. The latter option violates the principle