Well after a teeny bit of research, the idea of some, is in response to a well-known paradox involving going back in time. Say you were to go back in time, and killed your grandmother when she was a baby, what would happen? Since your grandmother is dead, 1 of your parents wouldn't be alive, neither would you, so your grandmother wouldn't be killed, so you would exist, so she wouldn't be alive, etc. An idea is that, when you go back in time and change an event, you automatically create a parallel universe. Someone, I believe Einstein, used this theory to theorize the beginning of the universe.