 Brian also believes that they may have also caused a butterfly effect, as shown with the additional changes to their timeline.Despite Brian's objections about leaving his idea of a "perfect" world (in which there are flying cars that run on vegetable oil and Gore has killed Osama bin Laden by strangling him with his bare hands), Peter wants to go back to the past so he can undo his mistake.This seems to be a challenge because Death can only be summoned if someone dies, and Brian believes Al Gore's universal health care and zero-tolerance gun control laws have led to people living much longer.