Here is a fairly quick and simple one. I’ve been trying to keep up on theories around here, but so many coming up lately that this may or may not have been mentioned, if so, I apologize. I think I know why the island has been sunk in this alternate timeline, it’s because the bomb didn’t cancel out the magnetic force while digging at the Swan site, because our Losties were never there. They never time traveled in this parallel timeline and they never detonate the bomb to save the island.
In the timeline that we’ve been watching, the losties travel to the past to make sure the jughead is buried, which is later used to offset the overpowering magnetic flux density that Radzinsky tapped in to while building the Swan. In the other parallel universe, all of the digging causes the island to pretty much implode and sink to the bottom of the ocean, but the losties aren’t around to offset that energy with the jughead. There are other events that occur in this parallel timeline even further back that have a butterfly effect that result in all of the changes between the two.
There we have it folks, two separate, but self consistent timelines that do not intersect or have an effect on one another. I think that Juliet’s message of “it worked” is because in her death, she flashed or saw the alternate timeline and we may see a future where she meet Sawyer again. I think that is how she knows that it worked, because in another life, they get to meet up, go dutch on some coffee, and eventually fall in love again.