“I have other sheep that do not belong to this fold. I must bring them also, and they will listen to my voice. So there will be one flock, one shepherd” (John 10:16).

The Other Life is but the latest work of fiction (though the author says not science fiction) to explore the idea of parallel universes. In the book, written by Ellen Meister, a woman is married and pregnant in one reality, while she is single in another. She goes back and forth between the two through a portal in her basement, if I recall correctly from the discussion on NPR.

Alternate worlds and parallel realities have been a mainstay in sci-fi for quite a while. “Star Trek” used the device from the classic series through “DS9” to “Enterprise.” “Stargate SG-1” had a “quantum mirror” through which one moved between alternate worlds, an infinite number of them. And, my current favorite, “Fringe,” makes parallel worlds the central focus of the plot. So, in the show, in our world, 9/11 took out the Twin Towers, which still stand in the alternate version. John Kennedy and Martin Luther King, Jr. did not die by assassination in the other world. Indeed, one denomination of currency in the alternate reality is nicknamed a “Jr.” since it has MLK’s face on it.

Ridiculous? Not really. Brian Greene, the renowned physicist, has written seriously about such parallel worlds, an idea that actually began to be talked about as early as 1957. He says that every decision we make creates a new universe. Every decision that is possible is realized, each in its own reality. Each possibility allowed by quantum mechanics does in fact happen.

What, then, if there were a world in which there was no rebellion against God? Or suppose that Joseph had not been thrown in the pit by his brothers or Moses had not been rescued from the Nile? Consider what the world would have been like if the Greeks, not the Romans, had ruled at the time of Christ. What if Jesus did not die by execution, but lived to a ripe, old age and kept teaching? And on and on.

Every decision we make is important, from which route we take to work to how we will respond to a critic to whether we take a risk and meet someone we have admired from afar. That may be frightening in some respects, to realize how much our choices matter. But in another way, it’s heartening to know that when we make a terrible mistake, there may in fact be another version of ourselves who chose rightly. And the ripples that stone of decision made did not set up a tsunami of negative consequences, but instead started justice rolling down like waters.

© 2011 Tom Cheatham

For a conversation with Brian Greene, listen in at http://www.guardian.co.uk/science/blog/audio/2011/mar/21/science-weekly-podcast-brian-greene-tim-jackson.