Said he went back in time and entered our universe from a slightly different, alternate universe. John Titor claimed that the way time travel works is that you go back in time, but to a slightly different universe. Infinite versions of yourself, all in different universes, do the same. Of course in still more infinite universes you never enter the time machine at all, but that's besides the point. Titor said that you can't go back in time and alter your present universe - that's impossible. But you can go back in time to retrieve something from a slightly different universe that's close enough - information or an object. Titor may have been one of the first master class Internet trolls.
Time Traveller John Titor