It is said that in the future, scientists will achieve immortality and soon every human on earth would be immortal.
When I say immortal, I mean not dying by any means, not from aging, diseases, murder, nothing.
But without anyone dying, won't there be a burst in population growth? How would we deal with this issue?
Population control is the only way to sustain a immortal human race on one planet without triggering a system collapse. What might have happend during in the bronze age. Of-course people still die from accidents. So depending on your society who gets to give birth will be determined according to different standards. A evolution of our current capitalist society is a possible system Aka only the rich can afford children. A computer auction could be called whenever a old person dies by accident/murder for the right to give birth in daily or yearly intervals. Just remember that any immortal capitalism society needs major safe guards against wealth gaps. Basically like Norway but with more robots and even a bigger universal welfare system. And possible restrictions like only 1 child per 100 years per person if they can afford it.
In the very unlikely case that truly nobody dies ever. Sterilization of everyone on earth is the only way to survive. Probably the medicine one needed to take to become immortal would include a cocktail to ensure no births at all. In a advanced medical society where people have no need to fear the government it would be very unlikely any births would occur after the last mortal human dies or accepts the treatment. Of-course not all medicine is perfect but after say a 1000 years of total immortality I doubt there would be people being born. Maybe a lab somewhere is trying to get a person pregnant but it might simply make the mother mortal again. And with the immortally serum a possible state secret any child born would simply die off after a 100 or so years.
I assume of-course there is no convenient way to travel between solar systems so space is limited. And even a possible ringworld around the sun would have a upper limited to how many people could live there. Simply because of the amount materials there exist in our solar system.
Well, as I see it, you mean humans can't be killed by ANYTHING, right? Not natural causes, not unnatural causes. They are indestructible. This situation has a few consequences.
First, no matter how dense the population will get, you can't reduce it. People wont die of hunger, so they don't really need to eat, right? I mean, they'd WANT to eat, their quality of life would surely plummet if there isn't enough food, but they will survive.
They don't really need heat, food, sleep or any other resource that might run out due to overpopulation under the conditions you set, so all they basically NEED is a place to stand on. Of course, it would be a horrible existence, but humans can't be killed so I guess the world would become a violent, deprived and dark place where people constantly fight just to have a piece of space for themselves.
Now, there are also some other things that might just happen. You see, if people don't die, their drive to reproduce might fade. Why create the next generation when you can keep your resources to yourself? You won't die so you would still need them in a generation or so. So though the world will be crowded, it might not end up being severely overpopulated after all.
If you still want to battle overpopulation, even considering the above points, you can always consider expansion. If technology is so advanced, its more than logical that its advanced enough to expand humanity to other planets, which solves the room problem. It's even easier since, as I said, people don't really need food or even oxygen if they are really indestructible as you say.
If it's really the way that you describe, ever-increasing density and off-world colonization might be the ticket. If people can't starve to death there's less need for nutritious food, and if disease doesn't matter then sanitary conditions are less important too. So people just need a place to be. Denser cities will satisfy that.
And off-world efforts become easier when people are completely immortal. It doesn't matter if travel occurs at sublight speeds, passengers will survive. And conditions on the planet/space station/whatever don't need to be as perfect as they would be for mortal humans. Even significant systems failures won't kill the people living there.
I'm still not allowed to comment in order to clarify some stuff, so I will just assume stuff as I write here.
I'm gonna start by saying that true immortality in the sense you mean (against aging, decease and even murder - true immortality) can only be achieved hundreds, maybe thousands of years from now.
In such a future, humans have already mastered biology and genetics to an extent that they no longer need to worry about death, it's only logic to assume that other areas of knowledge - history, geology, philosophy, sociology - have evolved as well. That being said, a future society should be kind of utopic in a sense that humans probably reached a level of societal understanding that ended (or at least mitigated, to a peaceful extent) conflicts about race, religion, politics and stuff like that. There might still be differences, but the general society knows that conflict is not the way to resolve them.
They're a society that has learned to look back and not repeat the same mistakes. There is no murder because they do not murder. There is no decease 'cause they erradicated most deceases. And they live forever 'cause - as I stated before - they mastered aging to an extent that everyone is healthy and young forever. And if a deadly accident happens... well, I'm sure you can figure out a good Altered-Carbon-like explanation to justify those people not dying.
We got to the point where society can only grow.
If we consider that our planet is overpopulated already (and that's really not bound to change in the near future), I'm saying that the next step is reducing the population to a sustainable amount. I'm assuming that even though humans transcend death, they still need to eat and consume stuff. Since the earth has finite resources, there's a maximum amount of humans that the planet supports.
The ethical answer to the constant's problem would be the colonization of enough planets to sustain the given amount. The unethical one would be the random exilation of millions.
Regardless of the approach, once the constant is reached there's a single logical answer: sterilize everyone. This should do it.
But now you have another question to answer: Won't more humans ever be needed?
By answering yes, you state that the population has to grow for some reason.
In Huxley's Brave New World, humans are created in labs. There are bases scattered all around the world where humans are produced via genetic manipulation to perform a deterministic function that will ultimately define their place in that world's society. Let's assume that the social standing problem shown in the book is not present here.
Assuming that some kind of government or organization capable of creating designer babies exist, these people would also have to be responsible for maintaining full control of two variables:
This number of humans needed implies that humanity has a certain objective that demands more people in order to be achieved. From this point you have full narrative liberty to determine a feasible reason for the population to grow.
