Do parallel universes exist? We might live in a multiverse.

Parallel universes are no longer just a feature of a good sci-fi story. There are now some scientific theories that support the idea of parallel universes beyond our own. However, the multiverse theory remains one of the most controversial theories in science.

Our universe is unimaginably big. Hundreds of billions, if not trillions, of galaxies (opens in new tab) spin through space, each containing billions or trillions of stars (opens in new tab). Some researchers studying models of the universe speculate that the universe's diameter could be 7 billion light-years (opens in new tab) across. Others think it could be infinite.

But is it all that's out there? Science fiction loves the idea of a parallel universe, and the thought that we might be living just one of an infinite number of possible lives. Multiverses aren't reserved for "Star Trek," "Spiderman" and "Doctor Who," though. Real scientific theory explores, and in some cases supports, the case for universes outside, parallel to, or distant from but mirroring our own.