One of the biggest 'immortality sucks' issues has always been the question of what to do with the new people being born. Without death, a world's limited resources can't keep up with a never ending increase in population.

Imagine a sci-fi future world where we developed some means of stopping old age, and are even better at combating other common causes of death from disease like heart attack and cancer, but where we also have space travel. Could we expand out to colonize new worlds fast enough to keep up with the constant population growth, to avoid the problem of limited resources? Presuming a government was well aware of the over population concern and real effort was placed into making expansion occur?

I'm specifically thinking a world that is still somewhat near-future, with mostly hard science. With terraforming of planets being difficult but possible, and either no FTL drive, or if I add FTL then one that is difficult enough to exploit to make travel between worlds still relatively difficult or costly.

What would a society like this look like? Would we have difficulty encouraging people to leave their current world for a new one? would strict exportation laws be required to keep from overwhelming a planets resources?

What would new colonists to new planets look like? Would a specific age category be more likely to colonize the new worlds?

Most of all, what sort of hassles and problems would a world like this still have to deal with as a side effect of anti-aging technology?

Keep in mind this is not immorality. Death due to accident, murder, even occasional illness that can't be treated, will still occur. Suicide may also be allowed/tolerated; but the point is people will not live forever. I don't think they would reach the point of wishing they could die out of boredom; if nothing else those who were bored could keep taking more insane risks for fun until one of the risks kill them.


I wanted to add an extra issue I happened to think of after posting this question, just in case it interested anyone. I think there would also be an issue with getting people from earth and it's nearby colonies to newly colonized areas. As more space is colonized the distance (and thus difficulty/expense) from earth to an uncolonized region will increase as more space is colonized. After awhile it may be massively expensive to send people from the center of your colonized space to it's outer region.

This makes the length of time you can go before someone starts to feel the strain of limited resources more limited. Even if there is more then enough uncolonized space to absorb the new population produced by those on the outer regions of colonized space, earth will likely still suffer from population issues because of how prohibitively expensive it can be to ship people all the way along the radius of populated space and out to new unpopulated space.

  • $\begingroup$ FWIW: There is NO old age - heart attacks and cancer are old age come early. Every cause of death can be (and is) given a name and description. Once you have early detection and infinite repair capability you have to deal with "accidents". And suicide. Berak accidents into stupidity and "acts of God". Even aoG are largely stupidity if you are trying to live t say 1,000,000 years old. Death from fire, earthquake, tsunami, avalanche, trenches falling in, transportation, slipping on ice, triopping on shoe laaces, do bite, ... all become stupidity. $\endgroup$ Jun 27, 2015 at 6:11

4 Answers 4


No matter what assumptions you make, you can't handle population growth through colonization alone. To go with some very colonization-friendly assumptions:

  1. No significant change in fertility rates occurs
  2. Interstellar travel is cheap and close enough to light speed that subjective travel time can be ignored
  3. A star system can support 20 billion people
  4. People are willing to colonize, or the government is able to force involuntary colonization

Here on Earth, the annual birth rate is about 1.9%, while the death rate is 0.8%. Reduce the death rate to negligible levels (accidental death rate of 0.04%), and you get a population doubling time of 37 years.

Star systems occur locally at a density of roughly 1 per 300 cubic light years. Available living space grows as the cube of time, since you can (at least initially) expand in three dimensions.

From this, you get two formulas:

$$P = 7*10^9 * 2^{t/37}$$ $$P = 2*10^{10} * (\frac{4}{900} * t^3 + 1)$$

where P is the population, and t is time.

The first is natural population growth (7 billion initially, doubling every 37 years), while the second is available living space. Set them equal, and you get

$$t = 846$$

After 846 years, your population is growing faster than the available living space. No matter what assumptions you go with, this is always true: exponential growth rate beats cubic growth rate. In order to get around this, you need not merely FTL travel, but instantaneous teleportation -- and even then, you'll run into the limited size of the universe in only a few thousand years.

  • $\begingroup$ So Even if we increase rate of expansion by a whole order of magnitude or two it wouldn't have much of a difference on the long term outcome. Still, 800 years of sufficient resources is enough time to have a story in which population density is not considered a significant issue to the population. $\endgroup$
    – dsollen
    Jun 26, 2015 at 22:36
  • 1
    $\begingroup$ Every order-of-magnitude increase in travel speed gains you (if I've done the math right) about 125 years. $\endgroup$
    – Mark
    Jun 26, 2015 at 22:42

Birth rates would drop.

Even expansion to other planets has its limits. Assuming that people stay 'young' enough to have children, if they were to continue doing so, worlds would rapidly become overpopulated. Of course, there's a simple solution to that problem: stop having babies. It seems reasonable, to me, at least, that a society that can cheat death can also cheat birth, and limit the population on any planet by reducing the birth rate to whatever rate people died at due to accidents and disease.

There would be very few young people.

This, of course, would mean very few people who were actually young. Everyone would look, and possibly act, fairly young, but babies and children would be rare. Most people would be of sufficient age to have an established position in adult society, with the 20-something intern age group also dropping significantly in terms of relative portion of the population.

Society would change much more slowly.

The same people with the same ideas and the same way of doing things could remain in their jobs and positions in society for centuries. Things would change at a slower rate because the people would change at a slower rate. The same artists who people listened to as kids would still be the same age and keep making the same sorts of music until accident or illness killed them, but even those things would probably kill people at a slower rate than they do now, given advances in technology.

There would be less focus on the nuclear family.

Rather than being a focus of much of the adult life of an individual, having children would merely be an exercise of a few decades of life, after which the parent could go on with their life. Most people, at any point in time, would not be actively raising children, so there would be less of a concept of 'two parents, house, kids, and a dog,' to drive the image of what a 'family' is in society. Couples would still exist, but the focus would be on couples, rather than nuclear families with kids.

There would be more of a focus on extended family.

On the other hand, grandparents and great-grandparents would be alive and active, having had no aging processes to slow them down. It would be easy, then, for these individuals to keep in touch with their descendants, and on keeping extended families together. I'd expect there to be stronger ties in the extended family as a result of this, especially given the lack of the influence of nuclear family in the lives of most individuals.


If people could live for a significantly longer time, then people would have fewer children in general and likely government restrictions would be placed on how many children someone could actually have. On top of that it could encourage leaving the planet to colonize elsewhere by not having any restrictions on those that leave. So if you want a dozen kids, go somewhere else.

Immigration would need to be tightly controlled, at least on the inbound side.

Over time young people would definitely become less common. The large thing to worry about would be if people became unable to have children as they 'age'. Then making sure there is always enough 'breeding' stock to keep the race going. If people stay fertile for their life, then it isn't as big a deal.

Marriage would like be redefined as a termed contract with options to renew since chances are living to 200-300+ you will likely not expect to stay married for that long. (or it might be your death!).

  • 2
    $\begingroup$ wait marriage isn't already a contract with options to end any time!? someone should tell the divorce lawyers! :P $\endgroup$
    – dsollen
    Jun 26, 2015 at 17:41
  • $\begingroup$ @dsollen :P I think the difference is people will be expecting it to end at some future date vs. 'forever'. $\endgroup$
    – bowlturner
    Jun 26, 2015 at 17:44

"Would we have difficulty encouraging people to leave their current world for a new one?"

Short answer:


Long answer:

I think the best way to answer this question is to look at the great waves of migration throughout human history. We have been in this situation many times before, although at a smaller scale, and here's a few of these occasions:

What do these examples, and probably most other waves of migration with a few notable examples, have in common? The migration was "voluntarily", in the sense that physical force wasn't needed to get all those millions to leave their homes. They had no food, no personal security, no political or religious freedom, or whatever it was that they lacked in your example of choice. Considering migration was a real solution to their problems (or false, as it often turned out to be for thousands of migrants), they left by "free will", if we can use that term when it comes to choices made in order to escape a desperate situation. Meaning that you would probably have no issues with getting millions to line up at the space port check-in desks, if the government make sure that all those migrants can afford the trip and that there are enough seats.

"Could we expand out to colonize new worlds fast enough to keep up with the constant population growth, to avoid the problem of limited resources? Presuming a government was well aware of the over population concern and real effort was placed into making expansion occur?"

That is up to you to decide. As I see it, it depends primarily on four factors:

  • What's the population growth rate?
  • How much resources can be invested in this project?
  • What's the technological level of this culture?
  • What does their space infrastructure look like?

You might want to look into O'Neill cylinders, Stanford toruses, Bishop Rings, McKendree cylinders, and other types of orbital space habitats as well, and not just focus on planet terraforming. Orbital space habitats may or may not be more economical than planetary terraforming, but - depending on your culture's level of technology and space infrastructure - these alternatives would likely be possible to implement much faster than the terraforming of entire planets. Another benefit is that they don't require interstellar expansion, which would reduce the time and energy it takes to provide new homes for all colonists, and it takes a lot less energy to transport people and goods to and from these habitats due to the absence of a deep gravity well. The last argument also makes subterran (sublunar) colonies on moons potentially more interesting than terraforming of planets, at least in a short to medium long perspective.

"What would new colonists to new planets look like? Would a specific age category be more likely to colonize the new worlds?"

Historically, this type of migrants haven't formed part of the upper echelons of their home country. It's the poor, hungry, the sufferers of political/ethnic/religious discrimination and harassment that choose to leave their country. All things equal, I think you could presume that the same would apply to the people in your world.

As for age, I think that the answer would be yes, a specific age category would be more likely to colonize the new worlds. It is quite probable that you would have a significant over representation of young individuals among the colonist, due to the fact that age in many societies have been linked to wealth, status, etc - i.e. older individuals have had a lot more time to attain higher social status and a greater personal wealth than younger individuals. But this is an assumption that your society have at least some degree of social mobility. So again, it can be either way - all depending on how you shape the society.


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