A plea to the Doctor Who fans on my list.

[adoxerella]

I need an explaination why travel between dimensions is impossible in the Whoverse. Feel free to explain this as someone well versed in Whoverse cannon would do so, and feel free to assume that your audience has a the kind of passing knowledge of space/time travel one gets from excessive viewing of science fiction (like, say, *cough*Star Trek*cough*)

Thanks a bunch. Seriously.