Einstein postulated that space may not be linear. Current physicists state that in theory it may be possible to open what is called a "worm hole" to travel across one of these folds. Some also think that entering a black hole would result in being pulled in so fast that you (an object rather) would shoot out the other side in a different universe. They also state that with string theory, mathematics predicts that there are several parallel universes. If you want more, look up string theory and worm hole with a search engine.