THE INCIDENT vs. Schoredinger´s cat
My previous theory gave support for closed timelike curves (CTC) by assuming that the origin of it is a rotating black hole. Whatever, it fails in justify the existence of two universes.
In a CTC the usuall causality-effect relationship is not valid; an effect can preceed its cause.
The event which caused the existence of the universe U1 happened when Juliet hit the H-Bomb with a rock. Like in the Schroedinger's cat experiment, the cat is both alive and death. Both wavefunctions are valid, until one opens the box and reduce the wavefunction to one condition. In this experiment, the "poison" to kill the cat was triggered by the decay of radioactive isotope.
The dual possibility for the isotope: to decay or not, give raised to two universes: one where the cat is death and other where the decay didn´t happened and the cat is still alive.
When Juliet hit the bomb, both situations could be true: one where the bomb went off and other where the bomb did not explode. Each situation represents different quantum states and lead to two distinct universes.
That´s why the episode was named The Incident.
In my opinion, was the explosion of the H-Bomb the true responsible for the leaking of exotic matter and, finally, the crash of Oceanic Flight.
So, finally, the reason for the LOST people to go to the Island: to allow the creation of the Universe U1, where the plane crashed. The existence of that universe was based on the triggering of the H-Bomb. Without that, that universe would never exist.
And I don´t think they will haver leave the Island. They are going always be simultaneously in two universes: LOST within the closed timeline curve (the Island) AND Lost (figurative way) in the real world (our universe). The version of them who went to the Island are faded to be LOST on that CTC forever.