Okay so I have been pondering a little bit. In Dr.Who, they opened the rift between the two worlds, you all know the story, Rose in "Petes world" and the Dr still in the one he has always been in. If it is an alternate dimension in "Petes world" and everything is the same, there is still a vast galaxy and there are the same aliens. But what if in that world the time war went different, resulting in a truce between Time Lord and Dalek. Then the Time Lords would have enough time to create more inventions. They create a Tardis capable of traveling through the worlds freely. The Doctor of "Petes world" finds Rose by some off chance, she opens up to him, he takes her across the dimension to The Doctor. Boom, new seasons of Dr.Who with The Doctor, Rose, and a new Doctor who can world jump.
I haven't finished Tennents run so I don't know what happens.