Some like the idea of "worm holes," which may be shortcuts through space-time. This and other ideas are wonderfully interesting, but we don't know at this point whether they are possible for real objects. Still, the ideas are based on good, solid science. In all time travel theories allowed by real science, there is no way a traveller can go back in time to before the time machine was built. Toast and Red discuss time travel movies and books! With a guest appearance from Chimps!