Re: TNG: Dark Mirror by Diane Duane Review Thread (Spoilers!)
^Parallel timelines actually occupy the exact same physical location as one another. They aren't physically separate realities, but alternate quantum states of a single universe.
And to use another example: DC Comics. The multiverse, and Hypertime (or whatever the hell they're calling it now) are two different things. Each of the separate universes in DC can have its own set of alternate timelines.
This is what I meant when I pointed out earlier the difference between a timeline and a universe.
"If the world was perfect, it wouldn't be." - Yogi Berra