Ok so after last night I notice something and it gave me an idea. In the Season 5 finale, they showed a bunch of scenes of Jacob intervening in the candidates' lives, and in every scene he touched them with his hand in some way. Also in Season 5 Ben was saved by Richard (on Jacob's team) in the temple, presumably by clear water because Dogen and Lennon commented how the water was dirty when they brought Sayid in there and he is on Locke/Man in Black's team. Lately Locke/the Man in Black has been shown offering his hand to numerous people (Kate, Ben, Sun, maybe more) but none of them have accepted his touch yet.
The basic gist of this theory is that once Jacob touches you, you become one of his candidates up until the point when you are either touched or claimed by the Man in Black, die, or are drowned in the dirty water in the temple and after that point you are officially off Jacob's list of candidates. This lea! ds me to believe the Sideways Timeline is the timeline that would happen when the Man in Black was the one who touched all the candidates. When Jacob touches the candidates, they all come to the island because that is Jacob's home and where he wants to stay. The Man in Black wants to go home, so in the reality that he touches the candidates, the plane lands safely and none of them ever come to the island. However I think Jacob/Widmore know of MIB's plan and are planning against it. Jack is going to be Jacob's heir, and last night we saw him offer his hand to Sun in the same way MIB offered it to her, but this time she took it. I think maybe if Jack is the one who touches all the candidates, and the 6 of them leave together, it can create a third reality where all of them actually do get what MIB is promising them but most likely cannot deliver. Jin/Sun/Ji-Yeon would be together, Sayid would be with Nadia, Desmond and Penny, Jack would get closure with his father, Kate would! re-unite Aaron and Claire, Locke can walk again AND be happy ! with Helen, etc. I don't necessarily know where Desmond fits in, but I think the reason Widmore's people were asking Jin about the electromagnestism is because they want to find the Orchid and possibly have Desmond turn the Donkey wheel to move the island and create the third reality. Desmond may be the only one who can actually create the perfect reality and this is why Daniel called him "miraculously special."