Jtdylktuy

"Some kind of exotic particle? Or perhaps a form of gravity that we haven't encountered yet?"

I'd go way more realistic: make it a virus, (maybe developed by some weird apocaliptic cult), and there you go.

Wikipedia states that

Aphasia is an inability to comprehend or formulate language because of damage to specific brain regions

Which is perfectly achievable for a fungus or virus.
Making it "handmade" would explain how it could spread so far/quick.

The few/one normal people could have a natural immunity or could be one of "the chosen few" from the original cult, that had some sort of cure genetically implanted.

One of the more common symptoms of certain kinds of stroke or TIEs (Transient Ischemic Episodes) is aphasia - for you, this is perfect - you should have a prion disease which selectively targets that brain region, and causes a ton of small bleeders... in specific, the area your prion disease should attack is called Wernicke’s area.

Damage to the Wernicke's area of the temporal lobe may result in a fluent aphasia that is called Wernicke's aphasia; individuals with Wernicke’s aphasia may speak in long sentences that have no meaning, add unnecessary words, and even create new “words.” Individuals with Wernicke’s aphasia usually have great difficulty understanding speech and are therefore often unaware of their mistakes. These individuals usually have no body weakness because their brain injury is not near the parts of the brain that control movement.

Rather than some disease or mental condition, what if the aphasia was brought about by the collapse of technology?

Imagine that most or all the planet has progressed to the point that everyone communicates by way of a sort of technological telepathy. They have brain augmentations that detect when they are trying to convey a message or expression to someone else. The brain signals are then interpreted and processed into a universal digital language which is then transmitted wirelessly to the recipient(s) augmentation, where it is parsed and fed into the brain in a way that the person(s) are able to comprehend the message. Perhaps the augment even simulates aural signals making it so the recipient actually "hears" the message.

This kind of population would gradually lose the need for verbal and perhaps even written communication since everyone can just "think" at each other. Over time, while some vestiges of individual languages might linger as part of people's long-term memory, the very concept of language itself would fade into a sort of communication singularity.

Then suddenly, this technology stops working. Maybe it's an apocalyptic scenario, maybe some hacker or terrorist cell caused the servers supporting the augments to fail. Whatever the reason, people can no longer use their thoughts to communicate directly and must revert back to verbal communication. The problem is they have been largely mute for decades, so their vocal muscles have atrophied and their understanding of their natural language has been stunted as well as distorted by their reliance on the augment's universal translator. People might remember various words and phrases, but everyone would be speaking as though they were first or second year language students at best.

Also, because people had been relying on the augment's automatic translation capabilities, even people who originally spoke the same language might find it difficult to understand each other due to differences in dialect, slang, or other such linguistic differences. Perhaps the reliance on the augment has even lead to the language portions of the brain developing a distinct "dialect" for each individual person due to the augment interpreting their brain signals slightly differently, leading to a situation where even if someone who once knew a language tried to speak it to someone else who also used to speak the same language, it would still come out as mostly incomprehensible.

And, of course, the only person or people who are still able to flawlessly read and speak are those who rebelled against the augment all along, electing to instead use their natural voice. Those with augments could still understand them due to a legacy feature when the augment was still a luxury rather than a technological staple, but they were rarely interacted with and treated with mistrust since no one "knew what they were thinking". But now that the augments are offline, those who shunned them from the start are the only ones who are able to meaningfully communicate.

They're under the goddamn ground!

I also favor the realistic approach, and I like the idea of a bacteria, but @Hobbamok points out the problem of transmission, which has to be handwaved one way or another. Every developed society while have a WHO or CDC equivalent fighting back against the spread, and we can't have that.

Fortunately, there's a way of giving people diseases that doesn't require them to catch them from someone else: have it come out of the goddamn ground. On Earth, we're running into this problem with diseases like anthrax, which can lie dormant for decades only to awaken at an inconvenient moment and start killing people and animals by the hundreds.

On your planet, there's a similar life form that dwells in the soil. Maybe a sporelike bacterium, maybe a fungus, or maybe (for cool factor) a cyclical brooding insect like cicadas. We have limited understanding what causes spores to leave dormancy, so you don't even necessarily need to explain the trigger. One way or another, this organism comes to life all across your planet, ready to take the next stage in its life cycle. The aphasia you're looking is just an unfortunate side effect the humans happen to intersect.

Possible methods:

1. If the emergence is bacterial or fungal, it manifests as an infection: everyone on the planet will have breathed in endless lungfulls of the stuff before the first symptoms start showing up, too late for quarantine, vaccination, or cure. By the time people need to collaborate on a cure, it's too late: they can't even talk to each other.


2. If the emergence is insectoid, you get to have even more fun: take a cue from harmful algal blooms. Decades or centuries of hibernation have provided the insects with plenty of nutrients, and their carapaces have built up an external shell heavy in cyanotoxins, which, among other things, when inhaled, can cause brain damage that can include effects as unusual as aphasia. Imagine, all over the world, swarms of insects exploding out of the earth, blotting out the sky, tiny flakes of their shells raining down in a fine glittering dust from above. Once again, people will figure out you shouldn't breathe the stuff much too late to save themselves from the effect.

The most beautiful part is that even if some fraction of people don't experience aphasia, if no one else understands what they're saying, they might as well be: if a person with aphasia and a person without are locked in a room together, from inside, there's not really a way to tell who's who, after all. Both think the other one is taking gibberish while they are speaking sense.

From a story perspective, this could also let your character run into one or two people who, like them, was spared: the world is aphasiac to them, but they understand each other perfectly.

Wernicke's and Broca's areas of the brain are the ones you're looking for.

Damage caused to Wernicke's area results in receptive, fluent aphasia. This means that the person with aphasia will be able to fluently connect words, but the phrases will lack meaning. This is unlike non-fluent aphasia, in which the person will use meaningful words, but in a non-fluent, telegraphic manner.

Damage to Broca's area is commonly associated with telegraphic speech made up of content vocabulary. For example, a person with Broca's aphasia may say something like, "Drive, store. Mom." meaning to say, "My mom drove me to the store today." Therefore, the content of the information is correct, but the grammar and fluidity of the sentence is missing.

So your language processing goes basically like this:

1. Your brain thinks of something it wants to say




2. Wernicke's area concentrates your thoughts into words and passes them to Broca's area




3. Broca's area adds grammar and fluency to your sentence




4. You say your fully processed sentence out loud

Both of those areas process text information in a similar way to speech processing. So if you fully lose either one of those regions, you can still process information from your surroundings and think normally, but you fully lose your ability to comprehend or output language; written, spoken, or otherwise.

If you lose either of those areas partially, the effects differ a bit. With damage to Wernicke's, your sentences sound normal but they don't have any meaningful content, since Wernicke's area cannot fully process what thoughts you want to convey with language. With damage to Broca's, your brain cannot encode the thoughts picked up by Wernicke's to fluent language, so you can burst out single words at best (which do have meaning). The effect works both ways, so it is similar when tried to comprehend received sentences.

Now, if you want to go with gibberish, the obvious solution is to do some damage to Wernicke's region of the brain. This way people will still talk and write, but it will make no sense. Telepathic communication might still be possible, since the actual thought process is not really impaired.

Now, how can you do 'alotta damage' to this specific region of the brain? Easy answers are CRISPR gone wrong, virus, fungus, amoeba, whatnot. But if your story is set into the near future, one nice way would be cybernetic implants. Brain implants are not too far in the future.

Imagine a world where everyone has a cybernetic implant planted into Wernicke's area to store memories digitally. This is at least pseudo-reasonable, since Wernicke's area essentially concentrates thoughts. Now, in a world with everyone having electronics in their head, a catastrophic solar storm could have huge concequenses. The implant is fried and everyone gets their Wernicke's area irrepairably damaged.

What few people might have remained without implants would have no use for their language, since nobody can understand them. Children would be born having their Wernicke's intact, but teaching language to children when you can't understand it yourself would be problematic.

In any case, your protagonist could be someone who did not have an implant, and who therefore survived the catastrophe.

Do not explain.

"You have a sense for the black things, Sparrowhawk," said the
Doorkeeper. "You ever did. Say what you think is wrong."

"I do not
know. There is a weakening of power. There is a want of resolution.
There is a dimming of the sun. I feel, my lords- I feel as if we who
sit here talking, were all wounded mortally, and while we talk and
talk our blood runs softly from our veins..."
The Farthest Shore, Ursula LeGuin

Things can fade and disappear. A person who can do a thing easily then struggles, and then cannot do. Some are frustrated at their loss, and some lose the memory of what was and so are not frustrated. Sometimes there is no explanation. If your story explores what happens with loss, and how what remains can change and develop in the absence of what was, leave the loss unexplained. Instead describe what happens after the loss. Naming a thing makes it smaller; categorizes it - controls it. Leave the central event of your story unnamed and let your readers learn its nature through your characters and their struggles.

This is the idea behind the recent Bird Box movie, in which there are things in the world which, if seen, drive whomever sees them insane. The nature of these things is not explained. This makes the movie more visceral and terrifying.

use crispr/cas9 in a gene drive, eg you can give lung cancer to mice by infecting them with a virus that has been altered by crispr. Not too much of a stretch to use crispr to destroy Wernicke's area, or do more subtle things... This can be done in a garage lab. Cheerful thought!

Robots/Nanites do not like language

Some fed up grammar nazi releases robots/nanites that attack people vocalizing or writing things in language.

As for the person whose language is not affected, you could say they were somehow able to hide from the nanites.

This also explains who the person can create telepathy. They would invent a sign language, and teach it to people. Sign language is essentially a form of telepathy, if you define telepathy as the ability to send messages between minds through empty space. For whatever reason, the nanites aren't programmed to attack sign language users, so everything goes back to normal except people use the new form of communication.