At the end of season 5, we see Juliet bloodied up and laying in the bottom of a big hole. She's got a rock in her hand and she's doing something so absurd it would be comical if we weren't watching LOST -- she's beating on the nuclear core of a hydrogen bomb, trying to get it to blow up in her face.
Suddenly, it seems to work -- FLASH! BOOM! There's a blinding white light, followed by an inverted version of the LOST ending logo.
Nine months later, season 6 begins, and we again see Juliet beat on Jughead until there's a big FLASH, but what comes next only baffles and confuses us. Instead of changing the timeline and erasing all of their experiences on the island, they find themselves in the year 2007. They're still on the island and nothing has changed. Absolutely nothing. There's not even any nuclear fallout. As I've said in other threads, the detonation of a hydrogen bomb would obliterate every living thing and render the island uninhabitable for at least a good hundred years, but it didn't.
Some people have offered up an explanation for this by simply saying that the bomb actually DID work, which in the FST everybody survives the plane ride to Los Angeles and we see, through a beautifully rendered CGI animation, what appears to be the remains of the island underwater. A simple solution, yes? FST shows what everyone's life would have been like if they hadn't gone to the island, which for the most part is a lot happier.
But it's wrong.
When have the writers ever just HANDED us any answers? They're going to start off the season with something THAT obvious, and we're going to buy that deception hook, line and sinker? I thought after five and a half seasons of this, we'd be better at it. The writers are experts at making something SEEM like one thing, then suddenly showing us it was something else the whole time. The carefully trained (or at least very skeptical) eye, however, can see through these illusions.
Let's say for a minute (for the sake of argument) that Jughead DID explode. All right. So that tour we get Jacob's Spectacular Underwater Kingdom is a result of the island sinking due to that explosion, right? Great. Now tell me how it's possible. During that tour we see the following:
-The jungle, complete with foliage
-The sonar fence
-The foot of Tawaret
If a hydrogen bomb had gone off on an area the size of the island, it would have obliterated EVERYTHING. Even if the island had sank because of it, the explosion would have first stripped the land of all plant life and man-made structures. That jungle we saw would have been mostly cinders and would not have been teaming with green leaves. The barracks were wooden frame houses and would have been incinerated instantly. That wouldn't have been anything more than some scorch marks on the bedrock. The sonar fences would have been destroyed. They were advanced technology, but they weren't so great that they could stand up to a nuclear blast. As for the remains of the statue, the actual full statue was knocked over and destroyed by a wooden slave ship and some big waves. Are you telling me that a hydrogen bomb wouldn't finish the job?
So what happened?
Jughead did not detonate, that much is crystal clear. However, a clue to what DID happen is heard almost immediately in this little exchange between Hurley and Jin:
HURLEY: What just happened?
JIN: I found a flashlight.
HURLEY: Dude, who cares? The sky just went from day to night! What happened?
JIN: I think we moved through time.
HURLEY: How do you know that?
JIN: White flash. Headache. Can't hear. Happened to me before.
Here Jin attributes the white flash, lack of hearing, and pounding head NOT to the detonation of a hydrogen bomb as we all did, but to a time flash.
So here it is:
What if they experienced one last time jump as Juliet was trying to detonate the bomb? Daniel Faraday DID say that sometimes the jumps could be years apart. What if there was one more skip left? I really have no theories as to WHY time would be skipping here or what would have caused it, but it would explain a couple of things: why the island isn't a barren and radioactive wasteland, and why the Losties are still there.
I hear someone out there arguing about the FST. "If Jughead never exploded," you may be saying, "then why did we see everyone back on flight 815? And why did Juliet say it worked?" Let me address the second part of that first. Juliet didn't actually SAY "It worked". She actually said "It didn't work; we're still on the island" while talking to Sawyer in the wreckage of the hatch. She died before she could relay her "really important" message. Later, after she was buried, Sawyer asked Miles to talk to her, but Miles said "she's gone", which prompted Sawyer to throw him down onto the grave and hold him there. Miles was lying to appease someone who was so upset he was damn near crazy. Whatever he said that Juliet told him, it was clearly a lie.
Now to address the first part of that question: " Why did we see everyone back on flight 815?" This is the part where I defend one of my favorite theories. I've stated before (on other websites anyway) that, due to certain oddities and due to ABC's insistence that the FST is "not an alternate time line", the FST is actually the Losties AFTER the events that are happening on the island now.
MIB will either escape or be defeated and the island will sink. Whatever causes the sinking of the island removes the crash of flight 815 from the timeline entirely and returns them at the end of the series to a flight that safely lands in Los Angeles. Their memories are wiped so that they might FEEL like they know each other, but they don't remember anything.
Want evidence? Jack has a strange mark on his neck when he goes into the airplane bathroom. Where did he get it? Perhaps from the bombs detonating on the beach, or perhaps in one of the remaining episodes he gets shot in the neck. When he gets put back on the plane, the mark is still there but he doesn't understand where it came from. Also note his look of perplexity when the episode starts. He has this "Where am I?" look on his face, as if he was somewhere else just seconds before but can't remember.
One last bit of evidence I'll leave you is this: Christian's coffin was put on the plane in Sydney but somehow VANISHED in mid-flight. The airline has no idea where it is. Maybe it stayed on the island. When everything else was reset, maybe Christian's body remained behind for some reason. Maybe Jack makes that decision because he feels the island has BECOME his father's final resting place. That, and he also has no idea where the body is on the island.