By skyforbes Firstly, Director Matt Osterman has been asked about the ending and he has said "I’d be giving it all away if I put it together for the audience, but the clues are all there if they want to find an answer! The actual ending to me is when Theo and Emily hold hands."
So he is saying two things here:
1. There is a definitive ending if you want to use the clues to find an answer.
2. This movie is about Theo and Emily's relationship.
So if we go on the assumption that there are clues to an actual ending, let's dive deeper into what those clues are.
Right from "take off" there is a systems problem that the crew needs to fix and realize that this experiment is probably going to be a series of "Walter-created" problems to test them.
Walter says to Emily "remember our deal". Theo overhears this and later confronts Emily about it. He calls her out for hiding something because he says she always pulls her earlobe when she hides something from him. She admits that she had a deal with Walter to break up with Theo right before the 400-days experiment or else they would not be allowed to go. But is she hiding more than just that? Theo catches Emily trying to communicate with Walter when no one else is around and she seems genuinely startled that Theo caught her doing this.
Oddly, we notice that Emily the doctor injects the 3 men with something every day but she takes pills instead. She claims that it is to prevent the spread of viruses which is nonsense so there has to be another motive here. Possibly a drug that causes hallucinogenic effects? Because very soon into the experiment all the men (and not Emily) start experiencing hallucinations. Dvorak sees a message flash on a computer screen: "She is poisoning you." Since Emily is the only female, either someone on the outside wants Dvorak to know Emily is maliciously injecting them (being helpful and moral) or they are revealing that information only to feed the psychosis and conflict in Dvorak. I like the latter.
One big clue is revealed when the whole "ship" shakes and Dvorak says: "Are we moving?" He detects that the whole bunker that they are in is being moved to a new location. But why?
When they first go outside they test the dust and they find a substance this is only typically on the moon indicating that there may be an apocalypse involving the moon. Dvorak quickly dismisses this by saying "they know that we would test this".
When the crew decides to eventually leave the bunker they conveniently walk in the direction to find the house of the scrounger. This also indicates that at least one person in the crew knew where to go. It was not a lucky accident that they found that house. There they find the clue that leads them to the town. The ground that they walk on is always flat. When you're outside, only man-made surfaces are flat. So where was their bunker moved to?
The town looks exactly like what it is: a cheap TV set. At town, they are greeted by an overly friendly man named Zell who plays his role well of convincing them that an apocalypse has occurred and that this town was somehow spared and that they are just trying to survive. Dvorak notices that these are the same people that were reporters at the beginning of the movie and "Miss February" is there also convincing him that this proves that all of this is staged. But the biggest clue of the movie is revealed when Theo notices the earpiece in Zell's ear and calls him out by saying "Is Walter telling you what to say right now?" And an even bigger clue is Zell's reaction to the call out. A normal person might try to explain the earpiece but Zell didn't. Instead he overreacted, got angry, jumped out of his chair and distracted/gaslighted Theo which is exactly how someone getting caught for scamming would react (executed perfectly by actor Tom Cavanagh).
After Miss February starts to flirt with Dvorak, he disappears with her, never to be seen again in the movie without further explanation. Soon after, Bug disappears as he begins to lean more towards the "fake" theory rather than there was an apocalypse. And he also disappears without explanation. If you believe the apocalypse theory they were killed by the townsfolk but there was zero indication of that. It seems more likely to me that they were removed early from the experiment because they were getting too close to the truth.
So now it is time to address the 3 biggest reasons why there may have been an actual apocalypse based solely on what Theo experiences.
1. Theo is stabbed. If the situation they were in is just a simulation/experiment how could stabbing Theo be a planned part of it? Well Theo wasn't actually stabbed, he ran around the corner into the lady's knife. And she genuinely looked shocked, backed away and said "I am so sorry." In other words, that was never part of the plan. It was a legitimate accident.
2. Emily dies. Again, that can't be part of the plan. Or can it? Remember if Emily is in on it, all she would have to do is hold her breath long enough for Theo to see that she was not breathing. At no time did he actually check for a pulse.
3. The violent knife fight between Theo and Zell. Again, if this was an experiment only, fighting with knives is not a good idea. Interestingly, when Zell realizes that he is in a stand-off situation because both he and Theo have a knife, he is quick to put his knife down and offers Theo to do the same. But it is Theo who reengages the fight and Zell is clearly a better fighter than Theo and gets on top of him forcing a knife down towards Theo's chest. Just when it appears that Zell's knife will penetrate Theo's chest he has a very strange reaction. He gets a confused look on his face, slowly gets up without saying anything, and sits against the wall. We see Emily with a bloody knife in her hand and then Zell falls to the side revealing a bloody smear on the wall and Theo determines that Emily saved him by stabbing Zell in the back. But we never see Emily stab Zell and if someone stabbed a huge knife in your back, would you not suddenly scream in pain or even a wince on your face? Again, the "Emily is in on it" theory is holding up.
Emily and Theo hold hands after the "experiment is over" announcement indicating that their relationship is repaired, making this all worth it.
And of course lastly, the bright white light that shines down right on time when the experiment ends and the upper hatch is open revealing that there was no apocalypse, just an elaborate hoax to "ruse the Routh". See what I did there? lol
I saw online that someone has a side theory that suggests that this whole thing was Theo's hallucination and it a was strange way of repairing his relationship with Emily but I think that's reading too much into it and I'm going to claim Occam's Razor here.
TLDR: It was all a social experiment, the "outside" house and town were fake with actors, Emily the doctor was in on it, and there was never any apocalypse.
So what are your thoughts? Did I get it right or are you also angry at me for wasting your time like the movie did?