Re: the Back to the Future / Earth moves problem. The UK television series Red Dwarf did a joke based on something similar (just tried to find the clip on Youtube, but no luck, so quoting from memory) Anyway, in the show they're a long way from earth in deep space. They find a time-travel drive. Wow lets go back to 1955 (whatever the year was), they activate the drive and *flash* still sitting in deep space.
The android/mechanoid on the show, the ecyclopedia of knowledge, confirms that yes they are in 1955, in deep space. The time drive just changes the year, not the location. You need a teleport drive for that to work.
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Pics unrelated, these things are awesome.