I have an idea about an alien that conquers the world by assuming human form and releasing a film that drives whoever watches it insane. The masses that see it go on to destroy civilization in a constant fit of anxiety and terror. It would be the audio visual equivalent of the fear toxin in Batman Begins.
Scientifically, how could a film do that to any human?
It is a trope of science fiction that there are so-called "basilisks" that will neurologically impair anyone who views them. These things are visual patterns/shapes/whatever that human brains (or perhaps any brain) cannot process without being harmed in some way (think about bricking an electronic device). Common examples are the movie Bird Box, an episode of Star Trek The Next Generation (used against the Borg), and about 3000 articles on the SCP collaborative fiction website.
For a basilisk to be viable, one would have to know how a human mind processes information (whether this is the whole brain, or just the visual cortex, I couldn't say) to some very profound level, and to debug it like you would any other software. You might identify some inputs that crash this software, and given that human brains don't have a reset button (that we're aware of), it would likely stay in this locked-up state forever after (especially if it crashes the visual cortex, so that no one can feed therapeutic inputs to it that revert the brain to a non/less-crashed state). The sorts of experiments that would be necessary to conduct this research would be, by necessity, absolutely unethical. It might even require being able to simulate human minds (something we don't currently have enough processing power to do, let alone several other missing technologies).
For the purposes of your story, these might be still images, or might be video. They might or might not have an audio component. They could work in such a way that some are immune, or none are. The details would be entirely up to you.
Does it matter?
Sometimes things don't need a full explanation. We never learn why Phil is forced to relive the same day over and over in Groundhog Day. We don't get to hear or read Monty Python's "Funniest Joke in the World". (How could we? It would kill us too!) If the means by which the movie drives the viewer insane is not important to the plot of the story, why not just leave it out?
Explaining things like this creates the risk of creating a "voodoo shark": the explanation is less believable than the thing it attempts to explain. And, in fact, the Groundhog Day script did originally have an explanation for why Phil was forced to relive the same day over and over again—a sort of voodoo curse, as it happens—and it was cut because it was just silly. The writers tried a few different explanations, but none of them worked better than no explanation at all, so that's what they went with.
It's not the movie itself, it's rather the movie and what they spray in the room where the movie is projected.
Psychedelic drugs are known for
Put the two together, with a movie which creates the right "set", and most of your audience might turn psychotic.
Sentience Off-Switch.
In the distant past some apes were artificially given sentience by a race of advanced aliens.* These apes became modern humans. When these aliens performed the uplift they added a failsafe that the sentience could be deactivated by issuing a certain visual pattern.
The pattern only works when observed in its entirety at the correct speed and frequency. If any of the variables are off it looks like white noise. The movie contains the pattern.
When someone views the movie they revert to feral ape behaviour. Wild apes are mostly nonviolent in their natural home on the Savannah. But the modern world contains hundreds of people and noises and flashing lights that get the ape all riled up. Then all nearby humans are recognized as interlopers on their territory and attacked.
*Please do not ask me how these aliens themselves acquired sentience. It is a mystery.
Meme.
A movie that produces doubt and suspicion about the underpinnings of civilization (examples: rule of law, democratic ideals, civil society) with slick, plausible and easy to digest ideas that augment tropes and concepts already circulating in the populace.
The old tropes and concepts which the movie augments have themselves persisted because these concepts can manifest ambient anxiety and fear in the susceptible population. Augmented ideas level up and become memes, reproducing themselves and gaining power and audience. More people watch the movie to find out what it is all about and become hosts to these ideas. The memes mutate and evolve, with more powerful and transmissible ideas gaining dominance.
Skillful political operators take advantage of the large and growing population infected with these memes. They stoke the fear and anxiety that feed the memes, which become stronger. The operators use the infected population to gain political power.
Led by these operators, the population infected by the memes destroy their own civilizations from the inside out. Civilization is replaced with a different type of society of a form driven by the memes and anxieties / fears they nurture. This destruction is in some cases gradual, over years and in some cases paroxysmic.
It takes persistence to kill civilization. Civilization is big and durable. It will take more than one shot.
Drives them insane - this is part of the OP. Are infected people insane? They do not think so. They do not froth at the mouth and eat their pets. But they will vigorously defend the reality of the memes they are infected with. They will defend them against evidence and common sense. The memes are a shared delusion - fixed false immutable beliefs. Delusions are a hallmark of mental illness.
Just a fun fictional scenario for a work of fiction!
What you describe is partially possible; you can get a small portion of humanity to get aggressive and murderous with the right push. Case in point: Pizzagate. It's just a stupid fabrication about a polictician using a chain of restaurants to sell babies to satanists. This could have ended there, but Youtube and other social media had thousands of people making videos describing it. And then this happened:
Members of the alt-right, conservative journalists, and others who had urged Clinton's prosecution over the emails, spread the conspiracy theory on social media outlets such as 4chan, 8chan, and Twitter. In response, a man from North Carolina traveled to Comet Ping Pong to investigate the conspiracy and fired a rifle inside the restaurant to break the lock on a door to a storage room during his search. The restaurant owner and staff also received death threats from conspiracy theorists.
You may think that was an isolated case, but a few years later the same kind of stuff led not just a guy but a whole mob to storm the US capitol.
Right now about half of the american population votes and stands for the party that endorses policticians such as Marjorie Taylor Greene, who speaks publicly for the execution of house representatives for the mere crime of being against the former government's projects. She also pushes further conspiracy material in her social networks. She is actually one of the main spreaders of the whole Pizzagate thing, as well as being associated with Qanon.
Now imagine a world in which that woman is a chief of state - does 't have to be the US, could be any other country - with extensive support of the media and masses. Any government-backed movie telling you that some portion of the population should be eliminates for the greater good will lead to people to go killing each other.
Photosensitive seizures
Primitive lifeforms sometimes end up causing seizures with primitive forms of what the Majestic Zeta Reticulans can accomplish with properly crafted long form videos.
The simple versions? cause seizures... flashing lights of the wrong form. Like a baby babbling causing headaches.
Long form versions can reprogram the conscious - way past what hypnosis can do. Simpletons and their hypnosis. Primitives not knowing how to properly use the flashing lights to reprogram the soul.
Time to show those baby apes what a real advanced society can do.
The aliens have abducted countless humans and experimented extensively on their brains. From this, they were able to create the perfect combination of words, music, visuals, etc. to put a human being into a hypnotic trance state. From there, they are able to subtly implant false memories or suggestions in them that can nudge at least a few of them into becoming psychotic serial killers.
We take for granted our safety in modern civilization. In truth, it would only take a tiny handful of concerted mass murderers to bring civilization to its knees. You don't need to make EVERYBODY insane from the movie directly. Even if only 1 in 100 people who watch it decide to grab a gun, walk into a public place, and start shooting people indiscriminately with no regard for their own lives (for example), it would easily cause widespread panic and anxiety. Civilization is fragile and the resulting panic, looting, and paranoia (any of us could be brainwashed! It could be you, it could be me, it could be your own mother or child...) could easily break society.
Insanity. n. mental illness of such a severe nature that a person cannot distinguish fantasy from reality, cannot conduct her/his affairs due to psychosis, or is subject to uncontrollable impulsive behavior.
By this criteria, any successful advertisement causes insanity.
Ditto any propaganda or indoctrination which "takes".
So imagine a 45 minute movie that gives any person, no matter ability skill or how 'sound of mind', simple instructions to create an all-powerful device that will certainly cause the death of everyone.
For instance, by knowing somehow a system of quantum mechanics that is beyond (or within) our understanding, the aliens say 'put a cup of x with a cup of y, add a dash of z, and you can make a black hole that will destroy the world'.
Now that everyone on the planet is armed by this simple knowledge, everyone now knows that at any time the world will end. This is now an extreme form of PTSD. Everyone knows that there is always one lunatic somewhere in the world, who could build the device and cause the planet now to collapse, killing you and everyone you love.
It now makes logical sense for your own survival, or even your duty, to go mad and destroy as much as you can, in the vain small chance that you can do so before some lunatic creates the doomsday device.
(Oh no... I have just created a basilisk :( May need to delete this answer to not give anyone crazy any ideas...)
Ok - I have undeleted my delete because I realised that if I haven't thought of this basilisk, someone else would eventually. So the only defence is to know about it... and prevent any person from making a movie like this.
I'm already going insane just thinking about this. We need worldwide laws on this now.
For something like this, I think it is best to stay away from too detailed a scientific explanation, or at least anything that refers in too much detail to how it works.
We all understand that our psyches are influenced by what we see and hear. You don't need science to imagine that there could be some sights and sounds that are just too much to bear.
You could make analogies with computer malware, and you could also have your characters speculate. Obviously they can't research it directly.
This is not a totally new idea. The Neal Stephenson novel Snow Crash is based on something that's similar in principle, and the Dennett/Hofstadter compilation The Mind's I reprints a story where a mere concept makes people comatose. These references aren't meant to discourage you but really more to give you examples.
The movie is laced throughout with a language of the aliens race.
Just like we have many languages on Earth, so do they on their planet. One of those languages is a weapon on their world.
Another language makes machines move, another language provides energy, another language allows them to travel from one place to another, etc. This is a large part of their technology, controlling the world around them with language, written and spoken.
Their "Dark Language" is used to kill one another with during times of war, and in humans it creates the insanity you're looking for.
The movie has these images cleverly inserted throughout, and the soundtrack has it in there too. Its like subliminal stuff but more profound.
How does it all actually work? Scientifically, I don't see how. So handwave. Its alien.
P.S. The Alien should really download the movie throughout TV, social media and streaming services too.
This reminds me a little of Halloween 3: Season of the Witch
The film presents the alien civilization's advanced understanding of human mental processes and of their resulting behaviors and social interactions.
The video offers detailed, accurate and verifiable proofs that these mental processes are deeply flawed and through their sheer existence, will inevitably lead to collective decisions bringing about our civilization's destruction.
The destruction itself can be through war, climate change or resource depletion - it doesn't really matter, as long as it's brought about eventually by choices and actions born of some inescapable flaws of the human mind.
The movie is long enough to contain very convincing explanations at various levels of complexity, ranging from abstract and formal to dumbed-down and easy to understand, even for children. Seeing it might trigger existential dread and fits of anxiety and terror, but that's just icing on the cake of proving that we all are already insane and self-destructive, but we didn't yet know it.
This isn't quite what you're looking for, but if you're happy to settle for 'causes mass instability and drives many people insane', consider revealing some terrible truth about the world.
The example that came to mind was an event in Scott Alexander's Unsong, where the Devil releases a video tape which he forced a deceased National Geographic presenter to film, depicting the horrors that await people when they die and gloating that even knowing about them won't be enough for people to avoid sinning. You can read the whole chapter here, but a few relevant extracts:
The Broadcast had destroyed the original United States, driven a lot of people insane, even made a couple commit suicide despite that maybe being literally the worst possible response to its contents. I like to think of myself as a dabbler in forbidden mysteries, but the Broadcast just had the wrong ratio of enticing-to-horrifying.
[There follows quite a lot of description of the contents of the video, which you can read for yourself if you want]
Thamiel [Satan] thrust his bident at the camera, and as the tip pierced the lens there was some final vision of ultimate horror – something I will never be able to describe and which really was no worse than any of the rest but which seemed more ontologically fundamental – and then the screen went black.
“So,” said Ana. “That’s the Broadcast. What did you think?”
I vomited all over the couch.
Shepard tones are a certain pattern of sounds that trick the ear into believing that the pitch or rhythm is infinitely increasing or decreasing. Extended exposure is known to cause panic and anxiety attacks in people.
SOURCE: DON'T CLICK IF YOU ARE PRONE TO ANXIETY ATTACKS
If Shepard tones are paired with things that you want to become the subject of someone's anxiety, then you can classically condition them to go into a state of panic whenever the see the paired stimulus. So if your movie pairs Shepard tones with scenes of social gathers, cooperative behaviors etc. and only stops them during times of violence or isolation, you can train a person's mind to have anxiety attacks around positive social behaviors and to seek out antisocial behaviors to alleviate the anxiety.
While it is possible that this is a malicious attempt by aliens to harm humans, it could also be explained as an innocent misunderstanding depending on your plot needs. The human mind breaks up sound into chunks of frequencies called octaves which make this illusion and subsequent mental distress possible, but the alien minds may not chunk/process sounds the same way that humans do; so, while a human film director may never intentionally make a film that pairs Shepard tones with positive interactions, the aliens might find these patterns soothing and use them the same way that humans like a soft flute or violin melody to emphasize the positive experience of a scene.
Theoretically, it's impossible. But what's this forum for, eh?
When you say "insane", I will assume you mean psychosis, a symptom which causes difficulty to discern what is real. There are many different disorders which can manifest psychosis, but for a large part they only manifest in people with specific genetics or that have been involved in substance abuse(weed or hallucinogens). There are a few left though, including extreme depression and PTSD. Assuming Marvin from the hitch hikers guide is unavailable, the best chance is PTSD.
PTSD is a very complicated disorder, but at it's most basic level you can think of it as someone being trapped in a moment. (This is clinically inaccurate. It's far more complicated than that.) It can manifest gradually, but the example everyone will recognize is shell shock. In battle when something extremely violent or surprising happens people will just stop reacting, freeze and lose perspective of what is going on. If not treated immediately (there is a simple protocol for this.) that person will probably suffer from PTSD for the rest of their life, possibly reacting violently to psychosis reminding him of the incident.
If you could somehow shock the entire audience in some very unexpected way, possibly also lacing the movie with subliminal messaging to build the person's tension, you could then just let them sit until the end of the movie. The rest of the film doesn't really matter. Of course, the results wouldn't be a theater of violently insane, but more a bunch of nightmare screaming individuals who's disorder can be triggered by certain sites and sounds.
The movie changes itself to fit the viewer, and even presents itself differently to multiple people who are viewing it at the same time.
The movie would show the viewer themselves acting out the thing the alien wants them to do, and it does so in a way that convinces the viewer that this is their future and that it is inevitable.
I imagine any premise that proved to the viewer a boolean-logic impossibility, objectively, would cause a lot of people to flip. That is, self-contradicting circular logic, showing that something must be true because it's false and vice versa. Anything that would knock down fundamental axioms of logic.
The major advantage would be that people would immediately, as it sank in, lose their trust of the people, and world, around them. It wouldn't matter if they were delusional or not, because the world would become a delusion to them in itself.
Maybe the alien is from a species that already jumped that shark and is one of the survivors, putting it to good personal use conquering planets. Perhaps planet-conquering is just an odd nervous habit to help it cope with its own insanity. Who knows.
Propaganda
This is arguably already happening in the world. Your hypothetical alien creates a film arguing that COVID originated from a Chinese lab as a weapon of war, that the virus was actually released by the Chinese government to damage all other economies, etc. Some people will be ready to believe this kind of theory, and once they watch the film, they'll even happily watch sequels and/or venerate your alien as their prophet. Then this group of people start launching pre-emptive attacks on China "in a constant fit of anxiety and terror", and your alien achieves their goal.
Carduus wrote a more in-depth explanation of how this kind of technique works in a question on the Politics.SE, if you are interested.
(Warning: TvTropes links abound.)
You basically want a brown note. This is a sufficiently common trope that it may be better to not explain it, because trying too hard risks either losing your audience with an implausible (or disturbing or distasteful) explanation, or being worse than what your audience comes up with on their one (note). Instead, just let willing suspension of disbelief do the work. You don't need to explain how it works, and depending on your end goal, doing so may be counterproductive, at least with respect to your audience's enjoyment.
(I want to say something about eldritch entities, black speech and so forth, maybe even point you at Call of Cthulu, but it sounds like you aren't looking to write classic horror. Other answers have already suggested more "science fiction" slants on this approach.)
