The trouble with the relativity bit of physics is you start trying to figure out Sci-Fi physics.
First attempt: There's nothing special about the inside of the Tardis, just that the outside appears stationary and the door that lets you go back and forth between two wildly distinct frames. The inside of the Tardis is moving at about 0.99995 the speed of light with respect to us.
Second look: Wait a second, that would mean that the inside of the Tardis is moving in all three dimensions with respect to the Earth! Okay, there's something special about its inside, too.
Hence the name Time And Relative Dimension In Space.
First attempt: There's nothing special about the inside of the Tardis, just that the outside appears stationary and the door that lets you go back and forth between two wildly distinct frames. The inside of the Tardis is moving at about 0.99995 the speed of light with respect to us.
Second look: Wait a second, that would mean that the inside of the Tardis is moving in all three dimensions with respect to the Earth! Okay, there's something special about its inside, too.
Hence the name Time And Relative Dimension In Space.