Okay I have a very complex theory that hurts my head when I think about it, but I'm going to share it with you. Before I say my theory about what happened when Juliet detonated the bomb, I am going to list some other theories and say why they are impossible.
THE BOMB DESTROYED THE POCKET OF ENERGY AND FLIGHT 815 NEVER CRASHES: This is what Jack thought would happen but it is impossible. If Oceanic 815 never crashes and they never come to the island, then how could they go back in time to destroy the energy and stop themselves from crashing?! I don't think Jack thought this through...
THE BOMB DIDN'T DESTROY THE ENERGY AND THEY CRASH ANYWAY: Come on, it's a HYDROGEN BOMB! I don't think there's a chance that it didn't destroy the pocket of electromagnetic energy.
THE BOMB CAUSED THE INCIDENT: This is a good theory but wasn't the incident a leak of electromagnetic energy caused by drilling into the pocket. Nobody ever mentioned a hydrogen bomb.
MY THEORY: Okay, this is extremely complicated. I think... when jughead exploded it DID destroy the energy and something else crashes the plane onto the island. On the island everything happens almost exactly the same except for things that have to do with the pocket, for example, because the swan station was never built to bottle up the energy, Kelvin and Radzinsky are killed in the purge, and when Desmond washes up on the island after the storm maybe the others find him, or he lives alone on the island like Danielle Rousseau. Anyway, The freighter comes the island so Ben has to move the island which causes the time flashes and the survivors end up in Dharma-times. Only, this time it wasn't the electromagnetism that brought down the plane so they don't drop the bomb and destroy the energy. Instead they try to stop whatever brought the plane down in this timeline but don't destroy the energy and that starts the whole thing all over again but this time it WAS the electromagnetism that brought down the plane in 2004. So there are two different timelines that link together to create a massive loop. Let's say the monster brings down the plane in the second timeline. In the first timeline the electromagnetism brings down the plane so they destroy that in the past but not the monster. In the second timeline the monster brings down the plane so they somehow (lol) destroy it in the past but they don't destroy the electromagnetism.
Um, do you have any questions?