Imagine a city full of people that are immortal; they can't die by aging and normal weapons can't hurt or kill them. So the government needs to find ways to overcome its overpopulation issues.
After a protest of their previous attempts to handle the situation by execution, they were executed by weapons with special material that basically counters their immortality, by the government of the nation or city.
What is a sensible way to handle this issue?
"Thank you, sir," said the hostess. "Your city thanks you; your country thanks you; your planet thanks you. But the deepest thanks of all is from all of the future generations."
There are two measures of population control:
The federal buraeu of Termination has set up an assisted suicide line, allowing every person to voluntarily end their life in a painless manner. They also track all other deaths, resulting in a quite well known number of population.
But now let's assume people learned from the murder incident described in the short story. Instead of driving people mad and go to kill to make space, they prevent the tragedy in the first place. The federal bureau of Beginning is the administration considering birth licensesing. Without such a license it is impossible to get the needed fertility treatments to counteract the contraceptives that are administered with every and all food that can be bought.
Reduced Fertility
These people are already half-like the Elves from bog standard Fantasy. Barring misadventure they are immortal. Here is a picture.
Fig A. Heavily Pregnant Elf.
So why is Middle Earth not chock full of leaf-munching Elves who eat every last shred of vegetation until it becomes a barren desert?
It is because they reproduce slowly. Their gestation lasts 22 months. Longer than man gestation, but in the grand scheme of a thousand year life not too bad right? Wrong. That's 22 Elf-months. Elf months are longer than man months.
On top of that the Elves take hundreds of years to become sexually mature. They have low sex drive, and this is compounded by the hundreds of years of child-rearing it entails.
The solution to your problem is to double down on the Elfiness. Instead of releasing a pathogen that makes everyone mortal, the government releases one that screws with people's ability to reproduce.
Making them into slow reproducing Elves is one thing. But it is biologically implausible. And it is not reversible, which is a problem if there is a sudden war and we need to replenish the population. They could make a pathogen with an on/off switch. But that is even less plausible.
Perhaps an easier solution is to make everyone sterile, so they can only have children through government-sanctioned Genetic Engineering Clinics. Then the government can control the population growth directly by not giving permission.
Every time the city expands or makes a new colony, they issue a wave of birth licenses. Otherwise it a lottery for the one or two licenses each year to keep the population stable.
Spread out
https://www.masslive.com/news/erry-2018/10/298f230f208827/these-are-the-51-oldest-towns.html
A time tested method to deal with surplus population is emigration. That works for many species. You have one city full of immortals. Clearly they need more space to house their numbers.
Attached a map of Plymouth colony. You will see new towns were founded every generation. People live in between the towns too - a lot of them. These are farmers. The towns are sited to provide a central place for people who make a living in the country to congregate.
If other cities are out there and not suffering the same issues, send people there. If there are not many cities, send your people out into the land as pioneers to found new cities.
If the land outside your single city is so inhospitable your people cannot survive there, where is the food for this overpopulated city coming from? High tech? Or maybe they don't have to eat?
How about controlling the immortal population with some sort of birth control? I believe that there are many scientific methods of birth control, and in so far as your story might be a fantasy there could be magical methods of birth control.
The lowest technology method of birth control is to capture all the immortals and transport the males and the females to different places where they will be guarded.
Maybe they will be put on separate islands & the waters around the island will patroled. Immortals trying to sail away will be captured and tortured until they promise never to try to escape again.
Or maybe two separate regions on land for the two genders could be surrounded by walls and guards.
The immortal might be free to do whatever they want in their restricted areas so long as they don't try to escape, or they might be locked up in prison cells.
IF guards come in routine contact with the immortals, presumably men would guard male immortals and women would guard female immortals, to avoid producing any half immortal offspring.
I note that immortals don't have any need to reproduce to perpetuate the group. So persumably immortals would hav evolved or been created without any strong urges to reproduce. Thus they will find being unable to reproduce less stressful than most humans would.
I also note that for thousands of years males were prevented from being able to reproduce by castration.
So there are low tech ways to prevent immortals from reproducing, as well as more advanced medical or magical methods.
Some immortals just want to die. We can let them suicide with special weapons.
Some immortals are assholes, making the life of other immortals harder. We can execute them. For example, in our society, many people support execution of rapists.
I don't see why this is "inhumane". In most human socities, most people supported capital punishment for some crimes.
Finally, we should severily restrict the birth rate. Just like in our society you need a license to drive an airplane, in this society you need a license to become a parent.
1000 years is ages. Three days after your 1000th birthday, you get executed.
For many, the last 20 years are spent contemplating death, leading to religious and/or philosophical awakenings. A few try hedonism or to complete bucket lists.
Couples born within 50 years of one another that have been married for at least 200 years get to go out together at 1000 +/- x years, effectively transferring a few years allowance to the older partner.
Your population may not die from aging or weapons but they will most probably die from hunger when the farms around the city are not enough to support the whole population. Probably this is what your government tries to solve in the first place, but the public will be much more helpful once dead, skeleton like bodies fill up the streets.
If your people can not die from hunger as well, and do not feel hungry, congrats, you dont have an overpopulation problem.
If they do feel hunger, but can’t die from it, follow the next solution.
Purge is a film series where the government allows killing for one night to combat overpopulation. Your society might be very elegant to organize one, but once hunger and lack of houses kicks in, they will participate. Hunger is a big gamechanger in human behaviour. So, your government just organizes a purge night,gives special weapons to the public and get out of the way. They don’t have to do the job themselves. Lack of quality of life will do it.
And then there is one other option.
This is a bit different then just expanding. You should expand to places that are already occupied. Brainwash your public to go to war and create a never ending war, 1984 style, so that you can mobilise/conscript whenever necessary. You might suffer from success a couple times if your enemy uses conventional weapons, which expands your territory anyway, but at one point they will be equipped with the special weapons and the government will just be the victim of this never ending war.
Ask for volunteers to die. What can you do for your country?
Many of them are probably bored out of their minds for living for so long. Some of them probably want to die already.
If that's not enough, provide incentives. How? You can't pay them money; that's not something that they can take with them after they die. But maybe you can incentivize them with some pleasurable, one-of-a-kind experience that they've never had before. Maybe that experience is not normally available for any number of reasons. Even though people are immortal, that doesn't mean necessarily mean that they can't suffer permanent effects from a rare or illegal drug that could leave someone insane or debilitated1. Maybe it's so pleasurable and addictive that any immortals taking them would never want to stop, which would be so detrimental to society that the government needs to keep it tightly controlled, made available only as a "last meal".
Heck, you don't even to create a logical explanation for what that one-of-a-kind experience is. Keep it a secret, and people will volunteer anyway, at which point the government can execute them with fewer complaints.
1 For that matter, being immortal doesn't necessarily mean that they can't become sick with incurable, chronic conditions and be in constant pain.
This race isn't immortal, just really hard to die. Because of this they have long come to the conclusion that they will die eventually and instead of trying avoiding it, they march to their deaths once they decide it is worth the risk. This race is full of glory seekers who would rather die doing what they love or fighting for what they believe in than by the many accidental deaths that could happen like drowning or starvation (everything is likely if you're going to repeat it forever), which in turn make them die earlier.
Maybe mental health keep deteriorating with time, and I am not talking abou memory or sanity. Happiness is such a fragile and fleeting thing, one day you are the luckiest man in the world, the next day the love of your life elope with her secret lover and take your child with her, your best friend turn on you for reasons "you know very well" and on top of everything you hear a not very comforting comment about the whole affair from your neighbors. When life just keep going forever, is easy to get tired of it. Even if they don't straight up kill themselves over it, they may just stop bothering with life after a certain age, or even snap and go full psycho. And when it happens, the government can dispose of then in a humane way (literally putting then out of their misery).
I think they have a similar justification for why vampires don't have friends in World of Darkness ttrpg, petty grudges keep adding up and become spite.
Simply put, it is illegal to have a child without the government permission. Couples must apply to get the permission, until then and for those who don't want kids anyway, there are options ranging from normal contraceptives to induced infertility.
In dnd, elves have a magical version of this. Instead of a government, there's a set amount of elven soul and the elf deity recycle the soul of the dead to use in the future new borns. If there's been happening too much births, its probably because something bad is going to happen (if they didn't need extra numbers, the deity wouldn't expend the emergency stock). That's also why they don't go extinct for lower fertility rate after tragedies, if there's extra souls lying around, the birth rate increase to compensate.
The curse of the immortals is that over a long enough time, no matter how they try, eventually each one must eventually speak some word so benighted that it cannot be pardoned, or perhaps even post a complete sentence that, if not caught by content filters at the time of utterance, will surely be understood to be intolerably profane or insensitive in a decade or a few centuries.
When that time comes, these people must be excluded from the economic life of the city, never to be hired or welcomed to a public event. Without money, they must eventually lose all right to real estate. The police take them to the Pauper's Shelter, where they are hammered into a metal tube and dropped into a deep, deep borehole in the ground, never again to trouble civilized people with their inexpiable sin. Space above ground remains abundant.
I would think very carefully indeed before you criticize this system, so essential for the orderly function of society.
What is a sensible way to handle this issue?
Culture. You are currently assuming that an immortal race will essentially have cultural norms, mores, and desires precisely equivalent to their mortal neighbors.
If this immortality appears suddenly in a specific population (whether by a genetic mutation, a god's blessing/curse, etc.) then, okay, it is likely that those "first generation" immortals will be very similar to their mortal neighbors... But! It would only take a "generation" or two before culture is bound to diverge as more and more immortal children are born from immortal parents.
Think of it this way: would any immortal mothers tell their immortal children "Don't play with that, you'll poke an eye out!" if mothers and the children themselves know that they are literally impervious to swords and arrows? (Presumably no; though gripes of "I just bought you that shirt, and it already has holes!" are likely to continue.)
Similarly, ideas of "I'd better have a dozen kids so that at least one or two will survive to take care of me in my old age." will fade out quickly. Firstly, because the near-perfect survival rate makes that level of redundancy unnecessary; and secondly, but perhaps more importantly, because having immortality with no apparent age-of-enfeeblement completely eliminates the need for elder-care altogether. Your immortal city is likely to see birth rates plummet just as happens when countries nowadays become rich and developed.
Lastly, how is "overpopulation" even defined for your immortals' city? The typical biological definition involves a population outpacing the carrying capacity of the location leading to die-offs. If natural "die-off" is completely impossible for your immortals, then the carrying capacity is effectively unlimited. In which case, "overpopulation" for your city is more of an artificial "NIMBY" problem than a technical one - and in which case economic and political power are likely what will determine what is acceptable and what "solutions" are possible. It seems odd that emigration isn't the simplest most obvious solution, though.
1. Biological Immortality, not Magical Immortal Basically your species just doesn’t age once members hit their prime and/or are very difficult to kill, therefore they live forever . But, they can be killed, or be starved to death
2. Reduced fertility, Sex Separation, Sexuality First is simple: No matter how much they copulate,chances of impregnation are very low.
Or, their culture is very sex positive and safe & protected sex is the norm
Or, Most of the population is homosexual/ gay-leaning bisexual and heterosexuals are the queer and proud (You could also heterophobia as a flaw in society,”eww, breeders” or something). Or just make them asexual and machine-like logical beings ,similar to vulcans in Star Trek.
3. Go Big and Wide
You have a setting where world is quite big compared to our earth, and flora & fauna is quite a lot more dangerous. In this setting, you could have them separated and scattered across planet in very small groups, and rampant danger makes it quite difficult to establish large settlements like cities. So, it’s just small villages in places hidden or guarded by natural barriers like mountains, hills and stuff.
The mortal population of your world can decide to store the immortals in the smallest box they could find (likely a coffin shaped box), and make a stack of those.
The immortal can't use energy, since energy transformation only go one way (from high quality to low quality, 2nd law of thermodynamic). This means that if they used/required feeding, they would die (thus, they won't be immortal).
So, in the end, they can stay here forever.
Without them being able to escape their box, they can't reproduce (again, energy here would be a problem, since you can't create matter out of nowhere), so the overpopulation problem soon becomes (only) a storage problem.
Even if you have plenty of immortals in your world, it's always a lot less than the planet's available volume, so you should be able to store them in underground caverns, like we do for used radioactive material.
That could be a punishment in law for immortals that are reproducing.
What is a sensible way to handle this issue?
The government decides to heavily promote a self-destructive culture by giving attention to bad things (mostrly caused by the government itself), also advertising all kind of unhealthy behaviour and stuff, and polluting food, water and air. After a while, the population internalizes the culture and keeps it up running without any help from the government.
This is not going to kill them, but it will make them less fertile and also less willing to have a child in the first place. Also because most of them are reduced to be broke af so that they basically live only to work.
The result being that the population will grow much slower. Slower enough that by the time overpopulation becomes a real threat, they are technologically capable of colonizing another planet.
