Ok, just a thought that I have wondered about, when we see the island flash through time, should we assume that the whole world is flashing also or just the island. The reason I am asking this is b/c when Sawyer and Juliet are sitting on the submarine dock debating to join DI or to leave one of them says that it 74 there is nothing to go back to. But how do they know that? I have probably forgotten but I don't recall this question being addressed on the show.
I know that Daniel left the island by means of the submarine and came back but how do we know he was still in the 70's during that time? I mean that submarine could be like Marty's DeLorian.