u/Temporary_Rule_9486

Here are some of mine:

• A virus wipes out most of humanity’s gut bacteria. Everyone survives the infection, but nearly all existing food becomes indigestible. Crops still grow, supermarkets stay stocked, yet mass starvation spreads across the planet because people can no longer extract nutrients from what they eat. A desperate new Space Race begins: nations and corporations race to recover the feces left behind by the Apollo missions, hoping dormant bacteria preserved in lunar waste can restore the human microbiome.
• Time travel exists, but there’s a catch: you can choose where you depart from, never where you arrive. Every traveler returns to the exact instant they left, but the destination point in the future is effectively random. Since time stretches infinitely forward, every jump ends leads to the heat death of the universe. The technology becomes useful only for harvesting exotic matter from the end of time. Then one mining expedition discovers something impossible waiting in the darkness of the far future.
• Neural interfaces become universal in the 22nd century. Then an AI-borne cognitive virus tears through the network, infecting minds through memory itself. To contain it, governments divide civilization into “mnemonic zones.” Crossing from one territory to another quarantines most of your memories; inside each zone, you can only fully recall experiences tied to that specific region. Information smuggling becomes the most valuable criminal trade on Earth, johnny mnemonic style.
• In the world of Roadside Picnic, researchers begin identifying “lesser zones”: subtle regions suspected of alien visitation beyond the known Zones. These places contain no obvious anomalies or artifacts. Their effects are statistical, almost invisible: light distortions in probability, behavior, fertility, weather, or mental illness detectable only across large populations over decades. Some zones appear to drift geographically over time, changing shape according to cycles nobody understands. Others may exist deep beneath the oceans.
• A pelagic planet is divided between two incompatible biospheres. Millions of years ago, a meteorite seeded alien microorganisms into the deepest trenches of the ocean. Their biochemistry is fundamentally incompatible with native life. Where the two ecosystems meet, organisms cannot consume one another; they simply rot together into a vast, semi-organic membrane suspended across the mesopelagic depths. Within this boundary layer, bizarre chiral scavengers evolve: creatures capable of digesting biomass from both worlds.
• Long before event on Antarctica, the organism known as “The Thing” consumed an entire planet far from Earth. Every ecosystem, every species, every ocean was assimilated into a single planetary superorganism. But total biological unity proved unstable. Ecological collapse followed. As the world died, the Thing buried itself deep beneath the crust and entered dormancy. Billions of years later, a human expedition investigates an anomalous dead world orbiting a cold star. Beneath miles of fossilized chitin and dried tissue lies a colossal subterranean anatomy (something like the Flesh pit national park). Deep inside, explorers recover some living cells, and it's the same story all over again.
• Faster-than-light travel allows humanity to colonize nearby stars. Then a frontier colony fifty light-years from Earth suddenly goes silent. Probes vanish investigating the blackout. Stealth warships disappear next. Eventually, a scientist maps the final known positions of every lost vessel and realizes the disappearances form part of a perfect sphere expanding through space at light speed. The center of the sphere lies seven billion light-years away, and its edge is moving towards Earth.
• A detective investigates a string of murders identical to those committed by a serial killer he nearly captured a decade earlier. The killer disappeared during a catastrophic teleportation accident caused by a religious terrorist attack that destroyed part of the transit network. Forty thousand travelers vanished mid-transfer and never rematerialized on the other end, including the murderer. Now the killings have resumed along the oldest and least reliable teleportation routes. The perpetrators are always ordinary people with no history of violence. Each murder occurs within twenty-four hours of a teleportation jump. Afterward, the killer calmly returns to another transit gate, after this second jump they remember nothing of the last day.

This is for a story with detectives pursuing a criminal that uses teleportes. Imagine some profesor giving a monologue to one of the detectives, explaining how this tech works, and it goes like this: "The problem with having something is that you cannot have it surrounded by nothing. Even if you come up with a tiny bit of space out of nowhere, it begets another piece that goes up and down, to the sides, as well as behind and up front. Same goes for time: any moment requires another one in the future as well as in the past. You cannot create the tiniest fraction of spacetime without it requiring infinte more to maintain causality. Space creates more space and time creates more time. When you heard people talking about the big bang, they inevitable make the question: well, then what was before? Most cinic of men would answer than that is like saying what's north of the north pole, unaware of how unsatisfactory this answer is. There's another answer: That big bang did not only created the future of the universe, but it created its past as well. In fact the future is being created right now, as causality expands everywhere at the speed of light, in the same way, but in opposite direction, the past is also being created. There's no beyond these limits of causality, the other aspects of the universe are either contained within spacetime, or are perceived to exist in its outermost "membrane". The impossible surface which is not a surface, cause it's pushing out and further at the speed of causality, the speed of light. Being an edge that is unreacheable means it's not at edge at all, at least as far as inner events are concerned. This membrane is thick with all the particles that, traveling at the speed of light, where caught on its boundary at the very moment of the big bang. So it shines forever with the fire of creation, although, as space expand, and the membrane grows in size, this light is constantly being dissolved into an ever increasing canvas. And it will come the time when the painting, once blazing with light, will turn pitch black. Meanwhile in a opposite arrow of time, the past before the big bang is been created as well, events being put into place to meet the criteria of all that will come to pass in consequence. But there's no infinite universe. Not yet. It grows in time and distance, it grows faster than anything contained within can surpass. But it's still growing. There's much that must happen and it still not here. And there's much that should've happened and still is not there."