FAQAdd to FAQ (Coming Soon)
There are a number of interpretations for this question:
1. Everytime there's a cut to black, we watch another universe and the events taking place thereof before the start of the Coherence. That would explain why it happens several times in the first act of the movie. Note how Beth acknoledges the small flower vase twice.
2. The screen goes black everytime there's a point of bifurcation in the story, therefore the movie only lets the audience see a an increasely narrower number of possible universes as the story unfolds. Note how it happens at 1:06:42, just before the big fight starts, for instance.
3. The probability of jumping from one given universe to another is actually a lot higher and it happens even when the characters are inside the house. Note how after the cut to black after 1:06:42, Mike is completely sure of the number in his photo (he says it's 3, but nobody had a 3 in the Prime Universe) and he has not left the house in a while.
4. It may be just an stylistic decision by the filmmakers. Edit (Coming Soon)
Beth has some particular beliefs. It's no unusual for people that open-minded to take recreative drugs. At the start of the movie, she offers to her guests the content of a vial that has, among other ingredients, Ketamine. As Wikipedia states, it "is a medication used mainly for starting and maintaining anesthesia. Other uses include sedation in intensive care, as a pain killer, as treatment of bronchospasm, as a treatment for complex regional pain syndrome and as an antidepressant. It induces a trance-like state while providing pain relief, sedation, and memory loss. Heart function, breathing, and airway reflexes generally remain functional. Common side effects include psychological reactions as the medication wears off. These reactions may include agitation, confusion, or psychosis... Ketamine's use as a recreational drug has been implicated in a number of annual deaths... Ketamine may increase the effects of other sedatives, including, but not limited to: alcohols, benzodiazepines, opioids, and barbiturates." (https://en.wikipedia.org/wiki/Ketamine, emphasis added).
As the film unfolds, we only know for sure that in the Prime Universe, Lee took it in order to take some sleep and Beth took it with a glass of wine in order to battle with the stress the whole situation has lead her to. Although the exact amount of ketamine inside the vial is never explicitly given, as Beth says it's only a little, they both show symptoms of its consumption. However, it's possible that contrary to what she repeats several times, she could have put some of it in the food served in the dinner. While this does not explain the entire movie's confusing story, it could explain several facts, such as the way Mike falls taking more and more wine and the way Laurie flirts to Kevin caring so little of being caught. An artistic liberty could have been taken with this drug as justification to Beth's nasal bleeding near the end. Even possible hallucinations and confussion are prevalent in the oneiric atmosphere of the film, therefore, is open to interpretation if they all took the drug or not. Edit (Coming Soon)
"Schrödinger's cat is a thought experiment, sometimes described as a paradox, devised by Austrian physicist Erwin Schrödinger in 1935. It illustrates what he saw as the problem of the Copenhagen interpretation of quantum mechanics applied to everyday objects. The scenario presents a cat that may be simultaneously both alive and dead, a state known as a quantum superposition, as a result of being linked to a random subatomic event that may or may not occur. The thought experiment is also often featured in theoretical discussions of the interpretations of quantum mechanics. Schrödinger coined the term Verschränkung (entanglement) in the course of developing the thought experiment." (https://en.wikipedia.org/wiki/Schr%C3%B6dinger's_cat)
Inside the context of the film, Hugh's brother takes cue from this thought experiment to explain, more or less, the many worlds theory, which states there's an infinite versions of the universe conforming the multiverse. If we think of the characters as the cat inside the box, the Coherence what happens when the cat gets out of the box alive and ends up observing and interviening inside several parallel boxes and finding copies of itself living in some of them, and dead in others, all happening at the same time. Edit (Coming Soon)
"Coherence" is a mystery film in the same spirit "The Twilight Zone" episodes used to have. Eight old friends get together for a nice dinner party the night a comet flies by the Earth at an uncommonly short distance. While they eat dinner, strange phenomena start to happen.
It's not meant as a hard science fiction story but as drama with a supernatural, pseudo-scientific framing to enhance the characters motivations and actions. In its core beyond the initial premise, the film explores the idea that everybody has secrets and things can (and does) happen in any possible way given that infinite universes co-exist at the same time. Edit (Coming Soon)
Hugh's brother wrote about a theory, stating "that two states continue to exist separate and decoherent from each other, each creating a new branch of reality based on the two outcomes. Quantum decoherence ensures that the different outcomes have no interaction with each other." Interpreting this in the context of the film, it means that a normal reality is a way events happen in an unique way and such reality never comes in contact with any other. However, the comet somehow nulifies the so-called "quantum decoherence" in the house, thus creating a situation that allows the different outcomes from the common event of the dinner to ACTUALLY have interaction with each and any other at random. This situation is called presumibly called "coherence" by Hugh's brother, hence the movie's title. Edit (Coming Soon)
While the comet is passing by the Earth, everytime somebody leaves the house and iluminated areas surrounding it, including the cars close by, he or she enters a zone between the universes, granting access to one among a limitless number of parallel universes that are extremely close in situations and events to the universe where the person who left the home comes from, given the common root event of the eight friends coming to the house to have dinner. There's no way a person can choose which universe he or she is going to end up. In other words, whoever leaves the house area never comes back to the house that was left in the first place. Edit (Coming Soon)
Once the characters understand that the other house in sight in front of theirs is a parallel universe, they start to look after discrepancies between their reality and the other to identify who comes from which universe. The problem is that if there is such a thing as a multiverse, there's an infinite number of universes, some very similar one to another, others are very different. Even with the narrow chain of events from every single instance of universes of the eight friends eating dinner that night together, infinite instances are still possible. Taking as anchor the reality where Em only leaves the house when the others began to be violent (for convenience called "Prime Universe" onward), we can understand this:
- THE GLOWSTICKS: In the Prime Universe, they used exclusively the blue glowsticks, thus everybody with a green or red flare has a 100% chance of coming from another universe... although statistically speaking, there's a chance of 33.33333...% that somebody with a blue stick comes from another universe besides the Prime Universe. Note how in a certain point of the story, a version of Hugh and Amir have two glowsticks each, red and blue, therefore they have crossed paths with at least one other universe before coming inside the Prime Universe.
- THE BOX AND ITS CONTENTS: The box, having each photo coded with random numbers taken from the Yatzhee dices written down with random colors, and a random, small object, is the most extreme way the movie gives the audience to understand the infinite universes "out there". While every single universe has the very same empty box, the chance of finding another box with similar content is a lot higher given the characters' situation of isolation and similar ways of responding to the whole situation. The most unrepeatable item is Amir's photo because it has to be (A) coded with the same number between 1 and 6, (B) written in the same color, (C) taken in the same precise moment and (D) at the very same place. As the movie itself states, the odds of finding exactly the same box's contents, combined with each having exaclty the same color of the glowsticks are 1 against 5'038.848, not counting factor C and factor D in Amir's photo, nor the narrower chain of events itself that lead to the creation of the box. That's why at some point, the people inside the Prime Universe make their own version of the box, created at random in order to make as different as possible from the first one, as well as any other that could ever exist, in order to identify everyone beyond the glowsticks. The box having red-coded photos (including Amir's impromptu taken one and coded with a red six) and a ping-pong paddle was retrieved from an universe where the people inside that precise house had already experienced some contact with another universe beforehand. This box was taken to the Prime Universe by a extremely close version of both Amir and Hugh who left their respective universe with the same intention the original Amir and Hugh had, which was calling via a hardwired phone but failed. This hints that the event's closeness matter when crossing between universes but still the possibilities are endless inside such an even narrower chain of events.
- THE HANDWRITTEN NOTE: At least three confirmed instances of the note appear. The first is being written by Hugh with the intention of leaving it in the "neighbor's house" before they realize about the Coherence. The second is put in the Prime Universe's house by some other version of Hugh and Amir with the exact same intention. The third is put in the Prime Universe's house but yet another version of Hugh and Amir with the ver same intention. As anyone could guess, the odds of that very small.
- THE BOOK OF HUGH'S BROTHER: It's present in every single universe. However, not in every one of them the people inside the house are aware of it existence. That's why in the Prime Universe the try to take it before the "other" universe takes it and thus preventing hostile actions from there. As it's obvious, that's useless since every time they reach Hugh's car in another universe, there's still an infinite other universes where such universe's party are at hand of taking the book themselves.
- THE SMALL FLOWER VASE: It's shown only twice. Each time it's shown we are looking at a different universe. See "Why does the film have sudden cuts to black?".
- BETH'S VIAL: Present in every single universe, it has no meaning to identify anyone's identity, nor the universe somebody is standing in. In that sense, is just a red herring for the audience of the film, but it plays out as an atrezzo for the overal story, given what Beth does and does not with it. See "What's up with Beth's Vial?".
- HUGH'S BANDAGE: When Beth is taking care of his injury, Hugh doesn't care which bandage she puts on his eyebrow. At some point, when he returns after leaving the house again, it's noticeable for everybody that he's got on the opposite option he receive earlier, therefore it's completely sure he is a Hugh who comes from a universe exactly like the Prime Universe except for that small detail. The odds are very, very dim but that's the case, given that he's aware of everything else just the way it happened.
- EM'S RING: Em takes her own copy of the ring by taking it from her car. However, the Kevin she hugs afterwards is not the one from the Prime Universe. That's why they retreat from each other and later, when she shows it to the Kevin inside the Prime Universe, he reacts in a different, more quiet way. When Em decides to search for a universe where he others didn't resolt to violence, she attacks that universe's version of herself in order to take her place, but she loses her own ring. Noting that somehow that universe's Em also have her ring, she takes it... but that universe's Kevin eventually finds it.
- THE BROKEN SMARTPHONES: The broken smartphones are the most weird items in the film. In the Prime Universe, the smartphones' glasses suddenly break and they do not work while the Coherence is taking place. Why do they break up is never explained nor hinted beyond assuming the comet itself caused it. Not all electronic devices are rendered useless, as somebody takes Amir's photo with a digital camera and somehow prints it on paper. However, in the last scene, Kevin's smartphone is not broken at all, and he actually answers a call from that universe's Em calling from her own smartphone, having survived Prime Universe's Em attack. It could be argued that it's just one extremely unlikely random event from the Prime Universe (and any given other universes as a matter of fact) that simply never happened in another different set of other universes and Em ended up in one of them. In the end, it seems that in that precise universe, the Coherence ended and simply nobody left the house whatsoever and/or never notice it at all but until they realize now there's two Ems.
Edit (Coming Soon)