Bioshock Infinite

You can supposedly "hear" the songbird at 0:14

There is only one ending, the player is given the illusion of choice and though the choices differ but the result is always the same. Well, for the player anyways...

If you listened to all of the Letuce recordings it's quite clear that Rosalind does not give one fuck whether or not Elizabeth is the harbinger of doom even though both her and Robert are largely responsible for her fate. Robert however does not feel the same way, as indicated in the "What's Done is Done" recording.

"Our contraption shows us the girl is the flame that shall ignite the world. My brother says we must undo what we have done. But time is more an ocean than a river. Why try to bring in a tide that will only again go out?"

"What's Done is Done" or is it? With the above in mind I think it's a good assumption that the Letuce twins experiment are basically trying to see whether or not they can change Elizabeth's fate because being at fault for the destruction of the world doesn't quite sit well with Robert.

And so, in order to do this, they use Booker DeWitt to kill Comstock, who are essentially the same person. Comstock kidnapped his own daughter from a different universe and the twins go back to Booker DeWitt and offer him a chance at redemption and unknown to him at the time, a chance to get back his daughter by bringing her back to New York. They use many, many different Booker's from many many different multiverses in order to try and accomplish this task, the dead man in the lighthouse is just one of those Booker DeWitt's who happened to fail at his task. You can actually see how many times they've gone through the Columbia scenario by counting the amount of tallies on the chalkboard when the coin toss is done at the beginning of the game.

Eventually they accomplish this task by mixing different universes in with each other and pinpointing the time at which Booker DeWitt became Comstock and killing him, thereby removing the existence of the universes that branched from that point and the sad tale of Elizabeth's fate from coming to fruition. However, one has to remember that the Letuce twins are no longer the Letuce twins, they no longer exist as brother and sister, the events that led them together never took place and they do not exist across multiple universes (they do, but not in the same form) as they were never "killed". So I think there may be more behind the reasoning for their experiment or as to what it truly is, what would drive someone to give up what they had?

At the end of the credits there is an extra scene, Booker goes into the babies room and finds a crib there, which I will just assume has Anna in it, it might not, the whole Schrodinger's Cat business. Right then, under my assumption one would assume that it wouldn't have ended, because Booker will just sell Anna again right? Wrong.

Remember this?

“The mind of the subject will desperately struggle to create memories where none exist…” – R. Lutece, Barriers to Trans-Dimensional Travel, 1989

Because of the events that happened in the other universes Booker still has "memories" of the events that took place, though the events could not possibly have happened, it is clear that it will make him think twice about selling his daughter based on the way he's calling her name as he goes into the crib room.

Rapture, and really all the events of the original BioShock are direct, alternate parallels of everything that happens in BioShock Infinite, right down to the characters themselves.

“There’s always a man, a city, and a lighthouse.” – Anna DeWitt / Elizabeth Comstock

This is further reinforced by the fact that only Andrew is able to operate Bathyspheres and in Infinite you end up being able to do so as well, which means they must be the same person. The little girls likely represent a fractured version of Anna / Elizabeth.

Thoughts are a bit jumbled, I need sleep but that's what I can make sense of the plot.

She's allowed to open tears because she's an anomaly. She exists in two universes simultaneously since her pinky got severed in DeWitt's world while existing also in combstock's world. At least that's what Lutece speculates in one of the Voxophones. If you want to find the voxophone I believe it's before you meet Elizabeth for the first time.

Having not played the original Bioshock, it will be my first time exploring Rapture