What is the meaning behind this scene in the game? I'm certain that there's more meaning to it than just what we see.
Edit: I was going to spoiler tag this in case people didn't finish the game.. anyway rewording the entire thing.
There are two main theories about the meaning of the ending. One focuses on what occurs at the ending using words and what actually happens. The second is more about the wording of the song itself.
The song itself is called Cara Mia Addio.
The lyrics translated in English.
Dear beautiful, my beautiful darling!
My child, oh Chell! [pun: "oh heavens!"]
For I hold her in esteem...
For I hold her in esteem.
Farewell to my dear!
My dear girl,
why do you not walk away?
Yes, away from Science,
My dear, my dear girl?
Ah, my beautiful!
Ah, my dear!
Ah, my dear!
Ah, my child!
Oh dear, my dear...
These are the theories found at the wikia http://half-life.wikia.com/wiki/Turret_Opera :
The first one is thought to be that she had died in the elevator. This theory is because the song being sung is like she is being sent to Heaven. In Greek/Roman Mythology when someone dies they arrive at a field with their closest companion. The field in Greek is known as Elysium.
When Chell arrives to see the turret quartet in the elevator, they begin singing. Then after arriving at a wheatfield, Chell is accompanied by the Companion Cube, her only friend. Chell is believed (in this theory) to have died in the elevator with the 4 turrets."
The second main theory is that Chell is actually the offspring of both Cave Johnson and Caroline. This theory is due to the fact that the song as translated earlier hints at this. The meaning of the words could be interpreted this way because a Mother would call their daughter darling and dear.
This song could also be used to prove the theory that Chell is daughter of Cave Johnson and Caroline. If you think that GLaDOS was singing the lyrics in English there are words like "Darling" and "Dear", words a mother would use to call her daughter.
Another potential nod to the fact that Chell could be the daughter was mentioned in an IGN Article Portal 2 Ending in 2011.
First off, we should assume that Caroline is the biological mother of Chell, as evident by the turret song and several of GlaDOS' lines towards the end. Not to mention that Chell literally means 'daughter.' (http://www.biblical-baby-names.com/meaning-of-chell.html)
Now these theories are fun but Valve has never confirmed that these theories are in fact true. The only thing that we know is that Valve hints at the fact that Chell is actually alive in the DLC Peer Review as well as in the Co-Op Campaign.
There is no official corroboration from Valve, or any evidence of this being the case. In addition, since the protagonist will often die while players go through the game (prior to reattempting the stage they died in), the occurrence of Chell's death is very familiar to most, if not all, players, and a similar experience is notably absent from the final elevator scene, casting doubt on any such interpretations. Furthermore, GLaDOS seems to refer to Chell during the Peer Review DLC, fearing that an old prototype of her chassis has been taken over by a "mystery woman" and that "she" has returned (believing that "she" is behind many of the malfunctions that occur throughout the game, unaware that the source of the malfunctions is a bird) where "she" could be Chell, or Caroline if it's wrong.
The Turret Opera appears at the end of Portal 2
The words are (in bad Italian)
Beautiful dear, my darling beauty!
My child, oh heavens (Chell)!
That she respects!
That she respects!
Oh my dear, farewell!
My dear child... Why don't you walk far away?
Yes, far away from Science!
My dear, dear baby...Ah, my beloved!
Ah, my dear! Ah, my dear! Ah, my little girl!
So dear to me...
Several theories exist about the meaning of these words, namely that Chell died in the elevator at the end (which makes little sense given how regularly you die in the game) or that the song somehow suggests that Chell is the offspring of Cave Johnson and Caroline.
Neither of these theories (or any others) have been confirmed by Valve.
Just a curious side-note, the great big leopard-spotted turret king in the back was referenced waayyy in the beginning of the game, in the animated infographic relating to an animal king take-over. This in itself could imply that a whole developed society of turrets, independent of GLaDOS' control, had been witness to Chell's adventures, maybe even rooting for her as a champion who opposes, and wins out over, their former master.
The fact that all Aperture turrets are self-aware is made clear throughout the game, and the only indication of the time period in which Portal 2 plays out is given in the opening, when Chell's wake-up timer announces 999,999- days (roughly 2,700 years) since her last wake-up call, ample time for a society to form. Between the secrecy of the location of the Enrichment Center, and the Combine invasion of Earth (and subsequent oppression of all things science-related), GLaDOS and all the other robotics in the facility could have been there for a very long time, forgotten and unhindered between Portals 1 and 2.
Not as deeply philosophical a theory as the 'death in an elevator' or 'daughter of Caroline' theories, but worth throwing out there I think ;)
Um, My theory is that they are singing a song that means, to them, good bye. I think that maybe Chell was born raised at Apature. Maybe those same turrets raised her since she was a baby.