but it was fun trying to figure it out. We had a motto in our class, "Phsyics is Phun":)

Of course in order for time travel to work, we need to have the ability to move in space as well as time. This is because the universe is moving and where the Earth was say 100 years ago, could be empty or or have something else there. The TARDIS took care of this with its massive computer model of the universe. Too bad it is just SciFi, but you can see they thought about it a lot when creating the show.