Well, this theory comes from these 3 videos from the Lost Panel at Comic Con. Here goes... Season 6 opens, and the shock is... you're gonna see a scene you've seen before. You wonder why an old flashback, then you see something that is drastically different. This will be a "flash-sideways". You're gonna see old scenes from previous flashbacks making you think yo're watching an repeat of an old scene, yet you'll see subtle differences, and eventually you'll see large differences by the time you get up to Sept 22nd, 2004 (like Oceanic 815 not crashing). You'll also see scenes where if you listen closely, you'll realise them as the whispers you've been hearing for the last 5 seasons. "The whispers are bleed-through of different versions of the same events in parallel worlds (hence they seem to comment on what is happening): The island is a nexus where all these worlds meet." When Juliet detonates the Jughead nuke at the Swan site, the explosion near the pocket of energy causes a splinter reality to form parallel to our own. The Losties hear alternate events as whispers, except for a few individuals who can actually see individuals from the other side (Jack sees Christian, Hurley sees Charlie, etc). This is what Charlie meant when he told Hurley "I'm dead and I am also here", because technically, it IS true: Charlie is dead in our universe but alive in the tangent one. This is also what Jacob means when he tells Hurley "what if you're not crazy" in reference to hearing whispers/ seeing ghosts. I'd bet anything that on the other side, is an Island destroyed from a nuclear blast. Basically at the point of the explosion you have a Schroeder's Cat development, where one reality has a nuclear explosion and in the other (our own) the nuke is unexploded. Points where the worlds bleed into each other are a) the mysterious food drop from season 2 b) the four toed statue What might be cool is if Matthew Abbadon (a miracle happened to me) and Iiana (in bandages from nuclear radiation) are from the other side, Fringe style. But even with this splinter reality, the universe's funny way of "course correcting" will start to take place and the realities will start merging, which is why most of the strange things people have been experiences were stuff from the other side, another life. Now I can't yet tie this in with the Smoke Monster, Esau and the fact that some people like Micheal couldn't die until the island was done with them. I figure that the way Jack, Kate, Sawyer, Sayid, Juliet etc survive the explosion is that their minds "jump" across to the other reality at that very instant, ala Desmond's mind jumping in The Constant and Flashes before your Eyes (well, except on a much grander scale). Maybe Desmond's mind jumping helps them merge the realities into once and for all by mid season, so they can finally face the Smoke Monster threat. I'm working on it, maybe someone could take a crack at it.
