For "The Road Not Taken," PM brings in Michio Kaku, physicist and author of Physics of the Impossible, to discuss Alternate Reality theory. According to Kaku:
There are numerous theories in physic that pertain to the existence of parallel universes—and Fringe is combining two of these theories. The first, called the "Many Worlds Theory," is widely accepted by theoretical physicists. "The universe splits every time a decision is made," Kaku explains. "One tiny quantum event could separate us from another reality." In "M-theory," on the other hand, our universe is an expanding membrane, sort of like a bubble—and there could be other bubbles out there. "These other universes, these bubbles, most of them are probably dead universes, so we don't have to worry about them,"PM: Fringe Season Finale Flirts With Theoretical Physics
You can read other "Fringebusters" posts here.