Bomb explodes --> Losties go from 1977 to 2007 --> Losties push reset button --> Plane flies by in 2004, nobody remembers anything.
They thought the bomb was the reset button, but what it did was send them back to their time. Maybe the reset button is something else, like, I don't know really, maybe killing Smokie. It's just a theory, one I really don't want to happen. We've seen flashbacks we believed were the present, flashforwards we believed were flashbacks, now we may be seeing flashsideways that are in reality flashforwards of a still unexisting past. lol That doesn't make sense at all. They would have to travel in the past, again, because the island has to sink, or do something that affects the past.
So, yeah, alternate realities, hoping they merge soon.