For the TV show:
Britten and Harper were involved when they were younger.
Britten is dead.Rather like the ending to Ashes to Ashes and the flashsideways from LOST, both worlds are part of some sort of afterlife or purgatory. Either both the wife and son are really alive, or neither of them are. Of course, if the creators did do this, they'd likely be seen as ripping off Lost (especially since "everyone's dead and in purgatory" was a ludicrously common WMG for that show), so they might want to avoid that possibility. Unless they count on viewers expecting them to avoid it for that reason...
Britten is in a coma.The entire series is a string of Adventures In Coma Land. The last scene will be him waking up to find both his wife and son are alive.
Neither reality is real.His wife and son both died, and he created both realities as a way to cope.
A third world will be addedA world where neither are alive and maybe even one where both are.
One of the worlds is actually realFrom previous guesses we seem to be expecting a Take a Third Option, so to trick us Genre Savvy folks, one world is real and the other is a coping mechanism.
Britten doesn't wake as soon as he goes to sleepHe gets a full night's sleep and slides right before he's supposed to wake up.
Both worlds are realThere are two Brittens in two timelines, and they somehow share consciousness.
The split worlds didn't start with the deathIt started before the car accident, and in fact caused the car accident
Britten is a cortexiphan kid.The accident triggered his abilities. Britten's consciousness really is slipping back and forth between realities, inhabiting Britten's body in both, as opposed to him being physically transported.
Eventually Britten will start changing worlds at times other than when he falls asleep.How awkward would that be?
Whoever's pulling Britten's strings is aware of the dual realities.Either that, or it's a side-effect of whatever's really going on behind the scenes.
Everyone's in on it.There's only one reality, but literally everyone we see is involved in a conspiracy to make Britten think there're two. Whenever he falls asleep, everyone scrambles to assume their new places and roles.
More than one person is also jumping between realities and they're using that to get ahead (insider information, for instance). Britten was targeted because they needed a patsy.That would certainly fit with the end of episode two. I like it.
The son lived.Assuming only one reality is real, evidence for the son living (Green reality) goes here.
The wife lived.If we have a list for one side, we may as well work on evidence of the other.
Both universes are real, a la Fringe.There are two parallel universes, and therefore two of each character. One of the wives died and one of the sons died. The two Brittens' consciousnesses were fused in the accident, which leads to the bouncing back and forth.
If neither world seen up until this point is real, the real world will be filmed in brown and gray tones.Because Real Is Brown.
Eventually, Britten will have to choose which reality is real.I'm feeling sorry for him already.
Britten will end up taking a third option in regards to the realities.]] He will take a third option and either 1) force both realities to merge resulting in a 'best' reality or 2) end up rewinding back in time to before the car accident and the accident will be averted (or happen but where no one dies). Alternatively, this will be something that occurs slowly over time - for example, one day, he wakes up and Captain Harper (in both realities) is replaced by his more senior partner who was put in after the car accident with his junior partner assigned to him in both realities to keep an eye on him.
Each reality is slightly offset in time from each other thanks to his jumping.In "Guilty", Hannah notes that he was tossing and turning in his sleep during which in the other reality, Rex is kidnapped. He wakes up because he forces himself to sleep in order to get information. This would suggest that each reality cycles one after another (in effect) rather than occurring more or less in unison.
Each reality is more closely tied to him than Brittan realisesFollowing from the previous WMG, Hannah notes Brittan's sleeping body reacting to the stress in the other reality when he's asleep. So when he's awake in one reality, his body is sleeping in the other. This would account for at least the physical complications of lack of sleep since each reality's body is actually getting rest. And we see him take sleeping pills to force a transition which might suggest that he's developed insomnia (eliminating what might happen if he were to take a nap). However, by proxy, this may mean that very stressful situations might be hazardous to both bodies or even cause him to flip back and forth uncontrollably.
His jumping is causing problems due to greater and greater differences building up.He might have been doing this before the accident but not realized it. The mystery group might be trying to fix things to prevent him from making the two realities diverge too much. Regardless, his interference will begin to cause issues (whether simply due to diverging details or actually metaphysical harm) with which he will have to deal with.
Both Hannah and Rex are deadThe two realities Britten occupies were originally one. In that reality, this mysterious organization arranged his family's death for some reason. But something went wrong and the single reality split in to two: Red, where his wife is alive and Green where his son is. Both are equally real and will eventually merge back together.
There will be an episode that follows Rex where his Dad is deadIt will probably be in the second season, possibly the season premier.
Both realities are real but he will have to choose oneBritten switching realities is damaging them.
Britten isn't switching realitiesThe Brittens of both realities were connected during the accident.
The series will end with Britten 'awaking' just before the car accident.In one reality, he's suggested as drinking and in the other, he simply doesn't remember. So it may be that he was asleep and in another reality but hadn't realized it. So at series end, he wakes up back just before the accident and, knowing what happens, does enough to save the life of Hannah and Rex though the crash still happens. However, he will die as a result... but he will then wake up in a different reality where he survives the accident with Hannah and Rex. So... Esoteric Happy Ending since it's a happy ending just not for anyone not in that reality.
Both the Wife and Son Survived in both realitiesIn the Green world after finding out about the conspiracy to kill her husband the wife went into hiding and in the red reality the group that caused it captured the son.
Westfield Distribution was a front for some kind of secret virtual reality programBritten discovered it, but the makers of the program didn't want it to be exposed, so they captured him and trapped him inside it, then created the dual realities as a way to keep his mind occupied and prevent him from investigating. There never was an accident and both his wife and son are alive in the true reality. (The versions he sees are just simulations.) The guy at the taco place was one of many human plants used to effectively simulate reality, but he went rogue for some reason and tried to tip off Britten.
The Gemini Killer can also switch between the two realities the same as BrittenThe stuff he said to Britten at the end of the episode seemed to hint at it. It won't really be much of a suprise since most sci-fi/fantasy (however you choose to describe the switching) premise based shows inevatably seem to end up revealing There Is Another.
If Britten goes to Oregon, he will meet up with Nick Burkhardt.Britten will use his skills to help Nick with a case involving a creature that only exists in one universe.
Britten goes on to move to Japan and become the fourth Akibaranger.He could put all his delusion power to good use.
The world of Harry Potter is the real reality.All of this is a hallucination caused by a potion or a spell on Lucius Malfoy.