After talking with a friend of mine, we both are convinced that the sideways world is not long for this world.
In the first scene of the sideways world, we see the plane flying over a fully submerged island.
We are meant to assume that this is due to Juliet setting off the bomb.
I believe that the island is not underwater due to the H-Bomb. I believe that the island is underwater because Juliet set the bomb off, the plane never crashed, and thus no Canidates to stop Smokey and his evil plan. A plan that involves sinking the island to the bottom of the sea.
So smokey sinks the island and waits for his escape craft. He waits for the plane to fly over the sunken island, but wait..smokey needs a dead body to take the form of. Perhaps a dead body that is on the plane. Christian Shepard. A body that is missing once the plane lands.
Smokey sneaks off the plane in the form of Christian, and begins to reak havok on the world. The losties will soon remember the island life, and realize that the plane must crash for them to save the world. They will somehow (the music box?) relay a message to island reality Juliet to tell her not to set the bomb off. This will be successful, the bomb will not go off, and this is where the island reality of this season starts. Kate in a tree and Juliet under the hatch. So, when Juliet says it worked, she didn't mean the plan to blow up the bomb, she will mean the plan to not blow up the bomb.
Just a thought, but sounds like it could be right. Any thoughts?!