I take the following view of the past: Â Anything that happens stays happened. Â Once an event has passed, it cannot be altered, even if time travel is something that eventually comes to be. Â If one was to try and go back in time and (for example) assassinate Hitler, one would be unable to because it is an even that has already taken place. Â I like multiple universes as a fictional idea (particularly Heinlein’s fictons idea, where any book you read is actually telling a story about real people in some other dimension) but I think the real world is more solid than that. Â This leads me to the following conclusion: