Up the population by a couple of billions, that's how! Despite Earth's current population growth slowing down and estimated to peter out around between the 9th to the 13th billion barring outside influence as third-world developing countries go through the four stages of demographic transition, the concept of 'of course there will be more people in the future, duh!' is one that seems self-evident to many readers, and thus it is an easy way to get across how far into the future you are, with populations only growing bigger as you get further and further into the future. These populations will often be so mind-bogglingly huge that they are unfathomable to our current worldview.
How such a large population came to be or is sustained, is rarely addressed, though there's sometimes an in-show justification (often involving colonizing other planets and simply needing more people to populate them so a modern society could function). It's popular in space operas with their sprawling space filling empires.
This trope can easily collide with Science Marches On and Society Marches On, since figures which match this trope in older fiction can these days be not just plausible, but reality. Make Room! Make Room! has seven billion people on Earthnote , while Isaac Asimov's short story "The Winnowing" has humanity starving at sixnote .
Often overlaps with Overpopulation Crisis when the enormous population size begins to cause problems, but settings can have massive populations without suffering negative consequences as well.
- In The Fifth Element, the President of Earth mentions "some 100 billion of my fellow citizens", although these might not all be on Earth.
- Star Wars: Plays with the usual connotations of the trope in that the Star Wars setting as a whole takes place "A long time ago in a galaxy far, far away." Yet this is easy to mistake for taking place in the future with sci-fi tech and City Planets. One such is Coruscant, the capital of the Galactic Republic and later the Galactic Empire, has a population topping a trillion all by itself according to a reference book published prior to The Force Awakens's release. The entire galaxy has a million inhabited planets, according to some sources, so the galactic population could be a quadrillion.
- Soylent Green (and the Harry Harrison novel that inspired it, Make Room! Make Room!) have a 21st-century New York City populated by 35-40 million people (actual 2017 population estimate: 8.6 million). If that growth is representative of the rest of the planet, that means around 35 billion people live on Earth.
- The Millennial Project: Colonizing The Galaxy in Eight Easy Steps considers the intellectual consequences of living in a society where there are "5 billion billion people". While there would be many problems, such a society could invest vast intellectual resources solving those problems.
- Isaac Asimov
- In Foundation, there are 25 million inhabited planets in the galaxy, and while the total population is said to be quadrillions of people, no exact numbers given. While this means the setting as a whole qualifies, the average inhabited planet doesn't: even if we take "quadrillions" of people to mean "100 quadrillions", this gives each planet a population of 4 billion.
- The planet Trantor is the capital of the Galactic Empire. In Foundation and Empire, the population of administrators alone on the planet is said to be 400 billion. In later stories, Asimov realized how impossible that was and lowered the figure to a more reasonable (?) 40 billion. He also said that its population was fed by the combined output of 20 farm planets.
- "The Last Question" mentions "a trillion, trillion, trillion" people, spread all over the universe.
- The short story "2430 A.D." is about shutting down the last remnants of the last zoo, so that Earth can finally have its perfect, stable society... no animals, no plants except for edible plankton, and as many humans as the planet can support - fifteen trillion.
- Aeon 14: The colony ship GSS Intrepid around which the story revolves has a population/crew of millions all on its own, and individual space stations with populations in the hundreds of billions are described: a 9th millennium 1600-kilometer space station with 150 billion residents is seen as only mildly impressive by protagonist Tanis Richards, who is from 42nd century Earth when the Sol system had probably tens of trillions of people and had stripped Uranus and Neptune of their atmospheres and mined or combined almost every rock in the system for living space and resources.
- Robert Silverberg's novel The World Inside is set on Earth in the year 2381, when the population of the planet has reached 75 billion people. Population growth has skyrocketed due to a quasi-religious belief in human reproduction as the highest possible good. Most of the action occurs in a massive three-kilometer high city-tower called Urban Monad (Urbmon) 116. Most of humanity lives in these mammoth thousand-floor skyscrapers arranged in "constellations", where the shadow of one building does not fall upon another. The population is supported by the conversion of all of the Earth's habitable land area not taken up by Urbmons to agriculture.
- Discussed in Stand on Zanzibar (written in 1968, set in 2010). With the world population reaching seven billionnote , society is definitely beginning to feel the stress of the huge population, but, as pointed out in the comment that gave the book its name, you could still fit them all, standing shoulder to shoulder, on the island of Zanzibar.
- In The Starchild Trilogy by Frederik Pohl and Jack Williamson, the population of Earth has reached the thirteen billion mark.
- Kris Longknife: The sequel series starting with Emissary reveals that the Iteeche Empire's core worlds are insanely overpopulated and has been for centuries, to the point where the Imperial planet's sea level has dropped by an amount visible from orbit due to. The Imperial Planet alone has roughly 150 billion inhabitants, which means living space is at a premium and, when combined with Iteeche Honor Before Reason attitudes, means life is not nearly as valued as it is by humans, at least by the noble classes: they behead people for minor offenses, their current civil war is destroying fleets hundreds and thousands of ships strong on both sides, and as we learn in Admiral, if the rebels gain space superiority over the Imperial Planet, they'll nerve gas the whole thing from orbit and resettle it with their own civilians to try to erase any trace of the preceding dynasty (this has happened at least four times in the past).
- Several of the short stories collected in "Welcome to the Monkey House" by Kurt Vonnegut (including the titular story) involve a future where the population of Earth has reached over 17 billion and suicide is actively encouraged by the government.
- Warhammer 40,000: Hive cities often reach the tens of billions in population, the vast majority of which are impoverished scavengers feeding on the refuse of the upper atmospheric spires where the nobility lives. The Imperium of Man even outright states in regards to its Forever War with the rest of the galaxy: "We count the lives of planets, not men." - implying the Imperium has grown so vast the population changes so rapidly that when you finished counting, you'd have to restart again - and a callous disregard for the individual humans they send into the meatgrinder.
- EV Nova: All the Auroran capital worlds have populations in the high tens of billions (Heraan approaches 90 billion residents) stuck in large Arcologies due to industrial pollution making the surface uninhabitable.
- In StarCraft, Earth's population is around 23 billion by 2301.
- In Galactic Civilizations a planet's population is limited only by the number and quality of farms can be built on it. Earth has a potential population of 50 billion. Colony Ships and troop transports transfer population in units of a million, and the basic ships can carry 500 of those units.
- Played with in Orion's Arm. The population of "baseline" (not substantially genetically modified) humans falls from 15 billion to 2 billion between 2400 and 2900 A.D., and are considered an Endangered Species in the very far future (c. 10,000 - 20,000 A.D.). However, in that same far future, our genetically modified descendants number in the hundreds of thousands of billions.