How Lost Might End
Between seasons two and three there was an ARG called The Lost Experience. ARGs tend to be produced by outside teams, but this had a couple show writers and featured a great deal of input from the show runners (Carlton Cuse and Damon Lindelof, aka Darlton). Key parts of the Lost Experience are considered canon by Darlton.
One of those key parts is something called The Valenzetti Equation. Let me quote the Lostpedia:
Its creation was the result of efforts made following the Cuban Missile Crisis by the United States and the Soviet Union to find a solution to the hostility and danger of imminent global disaster created by the Cold War. The equation was secretly commissioned through the UN Security Council and is used to predict the time of human extinction.
…The Valenzetti Equation “predicts the exact number of years and months until humanity extinguishes itself.” … The numbers, 4, 8, 15, 16, 23 and 42, are … the numerical values to the core environmental and human factors of the Valenzetti Equation.
These are of course the famous Lost numbers, the ones that Hurley won the lottery with, that are inscribed on the hatch, that appear in pretty much every license plate, etc. etc. If you’ve been watching the sixth season, you’ll know that the numbers have reappeared on the show in a big way. The numbers correspond to the main protagonists including Jack, Hurley, Sawyer, Sayid, etc. They are potential “candidates”, and magical island steward Jacob has been subtly manipulating them in order to get them to show up on the island.
In the scenes we’ve seen of this (mostly in the season five finale), we see Jacob visiting our heroes at different times in their lives, including when they are children. Jacob, like Richard Alpert, appears to be ageless, and able to travel off-island with relative ease. While his appearances don’t necessarily mean he can time travel, he has to be able to see the future at the very least. As the show has already established that time travel is one of the magic powers enabled by the island’s “unique properties”, we could presume that Jacob, the head honcho of the island, can McFly around at will.
Take that far enough, and Jacob would be able to travel forward in time to see when the world ends.
One of the big themes of the show is that of free will vs. predestination. It is a duality, of course, that intersects nicely with issues surrounding time travel. If Jacob knows that the world will end at a set time and believes in free will, he will attempt to change events. Clearly he is doing so by manipulating these key players.
In opposition to Free Will Jacob, we have Mr. Predestination, the Man in Black aka the Smoke Monster aka Fake Locke. He was revealed in the finale of season five, when he and Jacob have the following conversation:
MIB: Still trying to prove me wrong, aren’t you.
Jacob: You are wrong.
MIB: Am I? They come, they fight, they destroy, they corrupt. It always ends the same.
Jacob: It only ends once. Anything that happens before that is just progress.
It’s what you might call cryptic, but it certainly implies that there is an ending, a bad ending, that both of these men are aware of. The Man in Black is resigned to this bad ending and its correlative judgment of mankind as inherently negative, whereas Jacob is hopeful, committed to a good solution.
In brief, then: the world is going to end, and Jacob and his rival know how and when. Jacob is devoted to changing this course of events by bringing people to the island and guiding them, and the Man in Black is opposed to this.