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I see a lot of media describing large space colonies, and am curious as to how they got there. I'll admit, I'm mostly inspired by Interstellar here. So here's the scenario:

A group of 600 settlers, hand picked for genetic diversity and equipped with the latest technologies, land on a Goldilocks planet similar to Earth. Trouble is, Earth has fallen to a catastrophe and they are the only humans left, so they're on their own. Thankfully:

  • They are all young and strong, and none of them are suffering from any genetic conditions that may shorten their life (they are the last hope for humanity after all)
  • In their ranks are skilled scientists, charismatic leaders, brilliant engineers, and generally outstanding people who can contribute to the colonization effort.
  • They have the equipment needed to analyze their new home, avoid most dangers, and figure out their food, water, and shelter.
  • They have means to generate renewable energy
  • They have enough knowledge between them, and written down, to recreate almost all earthen technologies
  • Their ship is outfitted with some technologies that help in mining, farming, metallurgy, and automation, but new ones definitely need to be built to expand the colony. They also have effective ways to locate natural resources.
  • There are no indigenous species smart enough to be competition for them.

The technology they posses is post-modern, but not super futuristic, mostly faster, quicker, more efficient versions of things we already possess. With these ideal conditions, how long would it take for the colony to start building cities? to take over the planet? or do they just not have a chance?

EDIT to make things simple, the planet is considered taken over when at least 25% of habitable land is inhabited (the planet is earth-like in size and geography), there are at least 3 cities on par with Manhattan in size (but not population, no need for so many high rises), and technology is at least the same level as what they started with. I'm not a master at population dynamics but 500 million seems like a good number of people to have in total.

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  • $\begingroup$ There are too many variables and vague terms here to senisbly answer. How are you defining "Building cities"? What population level counts as "taking over the planet"? What's the ratio of males to females? Are they willing to overbreed their women to the extent of damaging their health? $\endgroup$ – Werrf Jul 5 '17 at 20:07
  • $\begingroup$ Six hundred is not enough, by a very large margin. There are more than six hundred kinds of engineers you need to re-create the modern world, and more than six hundred kinds of scientists, and besides scientists and engineers you also need welders and plumbers and tailors and cooks and mechanics and masons and farmers and police and bakers and pilots and potters and smiths and miners and teachers and so many other occupations. Realistically you need about a one or two million people just to keep a reasonably modern economy running, let alone rebuilding it from scratch. $\endgroup$ – AlexP Jul 5 '17 at 20:20
  • $\begingroup$ 600 is small from a genetic diversity standpoint. The chance of inbreeding bad recessive traits is rather large with that small of a starting position. The problem could be alleviated if everyone's second child had to be from stored genetic material. Either that or harsh conditions that kill off the weak. $\endgroup$ – ShadoCat Jul 5 '17 at 21:49
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    $\begingroup$ @Shadocat - Don't all high tech colonies have a few dozen lead-lined thermoses of frozen sperm? $\endgroup$ – Willk Jul 5 '17 at 23:51
  • $\begingroup$ @Will, yes it is very likely but I thought that it should be stated since 600 is a very low number. $\endgroup$ – ShadoCat Jul 6 '17 at 0:00
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Reasonably long. Assuming your colonists have blueprints of every human technology, as well as futuristic 3D printers and self-repairing robotic droids to assist them. A "self-sustainability" gap in this case would not be too big, and your colony would be able to jump it with ease. After that, it only a question of how fast they would multiply. Assuming they would double their population every 30 years, in 300 years the population would be 614,400. In 600 years - 629 million. I think this is enough to call it "Took over a planet".

However, if your colony for any reason fails to become self-sustained, this calculation can be different. Diseases can shrink population, while falling to pre-industrial tech level can, ironically, increase it. If your people would start having more children, they may take over the planet in half the time (say, 300 years), while still struggling to catch up with modern technology.

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  • $\begingroup$ If the colonists have every luxury available, chances are that they will not double their population every 30 years... ;-) $\endgroup$ – Florian Schaetz Jul 6 '17 at 13:22
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How long until they started building cities? According to Wikipedia, a city has a population fo 1,500 or more persons.

Assuming modern-day infant mortality rates, modern medicine and technology, and a heartfelt desire to "be fruitful and multiply" to continue the human race, I would be surprised if the population wouldn't double every 25 years. If fertility medication was used, we could imagine at least a 250% increase every 25 years (with multiple births being more common.)

By every estimate, a city would form within 25 years. Within 400 years, barring cataclysms, plagues, wars, or other negative events, a world population of 157 million to 25 billion would be sufficient to take over.

As a reference, during the Babylonian Empire, the world population was around 150 million and when the United States was founded, the world population was around 750 million.

Year     2X pop            2.5X                3x
  0         600             600               600
 25       1,200           1,500             1,800 
 50       2,400           3,750             5,400
 75       4,800           9,375            16,200
100       9,600          18,750            48,600 
200     153,600         915,527         3,936,600
300   2,457,600      35,762,787       318,864,600
400  39,321,600   1,396,983,862    25,828,032,600
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Modern technology, largely based on electronic, has the huge inconvenience of being not maintainable: once an IC is gone because of interdiffusion, you have no way of restoring it, unless you make a new one. And I doubt they have a 5 nm scanner with them, plust a state of the art litho fab.

Also, I doubt modern engineers and scientist, educated and used to massively rely on computers for any aspect of their activity, would be able to work using paper and ink (find me an engineer who would dare to design the Tour Eiffel with no FEM). Moreover, most of the advanced materials we are used to (steel alloys, magnesium, aluminium, carbon fibers, etc.) might be simply too complex for a stranded culture.

Their only hope is to downgrade to a steam revolution era, where mechanics rules and is more reliable and easily repairable. Then, if they manage to port their knowledge on media which can be used by future generations, they can try to grow and hope their heirs will make more progress.

But, considering how often colonies in remote location were wiped out for lack of support, they have a though time ahead.

So, let's assume that generation 0 manage to downgrade to steam revolution era and to fix their knowledge in written form. Let's assume they have a loss of 50% human capacity (poisoning due to unknown foods, new illnesses, natural disasters, etc). This leave us with a starting set of about 300 people which then try to transmit their knowledge and grow.

Something similar is supposed to be happened in America, when a group of about 60 people walked through the then frozen Bering strict, finding an unpopulated continent. In about 100000 years they managed to expand to the entire continent. A similar time span is what you are looking for.

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    $\begingroup$ This doesn't answer the question. The question isn't "Can they maintain their tech level?", the question is "How long would it take to populate the planet?". $\endgroup$ – Werrf Jul 5 '17 at 20:01
  • $\begingroup$ In this present form, this does not answer the question "How long ...". However the last sentence might hint a "Never". Now, if it can be improved with an additional paragraph ... $\endgroup$ – Vylix Jul 5 '17 at 20:46
  • $\begingroup$ This answer is currently in the low-quality review queue for the reasons already explained by the previous comments. Please edit it to focus on the question about how long it would take them to populate the planet or whether they would not have any chance. It looks like your answer is aimed at "They don't have a chance", but it's not clear in its current form. Otherwise this might get deleted. $\endgroup$ – Secespitus Jul 5 '17 at 21:19
  • $\begingroup$ Despite it not directly addressing the question, I have upvoted this answer because it does exactly what I love most about this site. It gives me specific, factual knowledge that I can use. That IC's suffer from a limited lifespan due to interdiffusion is new knowledge for me and will appear in my future works. Thanks! @LDutch, please make the others happy by clearly stating that the colony must survive technological decline as part of the colonizing process and then throw in an estimate for the steam-to-silicon climb. May I suggest 300 years like it took on Earth. $\endgroup$ – Henry Taylor Jul 5 '17 at 22:46
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    $\begingroup$ Why wouldn't they have a litho-fab on board to replace broken ICs? The question says "equipped with the latest technologies". And it's not like they necessarily need the latest and best chips to prevent falling back into the steam age. $\endgroup$ – Philipp Jul 6 '17 at 7:56
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It all depends on the habitat of the planet. While birth rates and population growth are a fairly easy calculation (see Population Calculator), there is also a factor of how risky life is.

A planet at war will have a lot of 16 to 30 year old men die, often without any children. A planet with dangerous animals (predators or not, think rhinos which are herbivores) may have similar risks. Our Middle Ages had a birth rate of 4 to 6 children per woman, but an average life expectancy of 43.6 for women and 42.5 for men.

Also because you have prime child bearing colonists (young = ages 16 to 40 for men and 16 to 30 for women?), that first generation would also spike with the population grown rate at least for the first 10 to 15 years. If you use the calculator above, at use a 2x or 3x population growth factor during these first 10 to 15 years of colonization. If the planet is harsh, then expect a higher birth rate to remain, but also a much higher death rate that balances it out.

It also depends on social factors such as the family makeup. A society that accepts or even encourages polygamy could grow at a significantly quicker pace (at least for the first generation while there is a female to male imbalance) but this could have many social ramifications that would affect many generations.

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Although artificial wombs aren't a reality today, it will likely become easily doable with the advent of space travel. Which means in the end, it depends on local resource availability. It is highly likely that the colony will engage in controlled population booms by utilizing artificial production of more humans. I would imagine that a ship build for colonization would already have this tech built in to easily expand a colony. Much of the process of raising the new population can be automated and the production of new colonists can be pipelined. Kids can be educated by AI from early on and indoctrinated on being a good colonist.

As for the tech, the ship should have enough documentation from Earth stored there for everything that was ever discovered or invented and even basic AIs today can present that information when humans need it. There would likely be tech on board for manufacturing of robots for general work. The growth of the human population will also depend on the rate of production of these robots. Robots are likely more efficient resource wise to be used for farming, building, manufacturing and gathering raw materials.

Once there is sufficient resources, the new colony could easily grow exponentially. If the planet is truly just like the Earth, there can be a city in 30 years or so with a population of hundreds of thousands. In ~100 years, there could be billions.

I am imagining a very efficient operation with extremely well controlled society governed by people with a common goal of colonization. If the social situation can't be controlled then this method would not work well.

The answer of how long it takes really would come down to how well everything was planned when the ship was built.

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200 years to reach technology requirements, 700 years to reach your city count and 1000 years to reach the population count. So you can reach your target faster if you have cloning technology.


Figuring out minimum time for technology

A space fairing colony starts from zero. The reason? A technologically advanced society has a huge support base. To build a laptop requires an industry of millions of people. So what societal level can 600 people sustain? Then we can figure out how long it took us to upskill from there.

Let's take a quick detour to the cities. Manhatten is 1.636 million people according to google. Rome was 450,000 at it's peak in 25BC. Apparently Baghdad got to around 1 million in 735AD, and with the advent of mechanical help, London and the UK surpassed our 1.6 million threshold in the 1800's. (Data from here). So what technology did they have in the 1800's? And how fast can we boostrap to it? A quick brainstorm tells me that our society should probably have:

  • Horse and Cart
  • Large cross-ocean sailing vessels
  • Trains

All right. What does it take to build a horse and card? A carpenter and some animal keeper. Great, that's easy. The animal keeper is easy. So long as you have a beast of the burden on your space ship and a human on your ship, and your planet doesn't kill them, you can have a horse and rider. Carpentry is a little more involved. Typically you'll need steel tools to build a cart. This means you need:

  • Coal miners
  • Iron miners
  • Someone who understands geology sufficient to find said resources
  • Furnaces capable of reaching melting point of iron

The furnaces will require bricks and mortar, coal and so on.

Then there's the other two. Building a ship is "just" a case of more carpentry. I haven't been able to get good figures on how many people, but it seems that building a "big" sailing ship took at least a few years for the industry in the 18th century. In a Jules Verne novel (the mysterious island), four people started with nothing and built up to about 18th century tech including a small (10 tonne) boat in four years. They had pottery, basic metalworking and carpentry. I suspect he knew more about this sort of thing than the people of today, and so I can conclude that if four people could do it in four years, your 600 people can get to - and maintain this level of technology fairly promptly. Particularly with the help of their spacecraft.

Trains are harder. They require more advanced metalurgy. But it's mostly just a difference in knowledge than requiring anything physically more advanced. You simply require people who knows what a lathe is, and that steam can be used under pressure, and then you can build the industry to make a train.

I think that a 600 person crew can probably bootstrap fairly quickly - as per the Jules Verne example above. HOWEVER - people from today would not have the required skills to bootstrap an 18th century civilisation. But with education and training, they could.

So how do we divide up your 600-person crew? I would say:

  • 300 farmers
  • 100 blacksmiths/"engineers" (as in people who worked on steam engines)
  • 100 miners/geologists
  • 100 carpenters/woodsmen

Voila, within a few years of settling down, you likely have the required industries to create a 1.6 million person city and 18th century tech.

So how long from there? Well it took us two centuries to the current tech level, and it would probably take less due to passed on knowledge (eg math and physics can be taught for a couple generations even if the tech doesn't exist yet). So it comes down to population.


Figuring out the breeding times

With 600 people you're dead. There's a fun article here, and it states that you need around 10,000 for sufficient genertic diversity. Barring issues with that (eg maybe they are genetically engineered people to not have issues with inbreeding) then it's a case of time. Pulling some numbers from wikipedia, the human population went from 2 billion in 1927 to 4 billion in 1974. That means it doubled in about 50 years. A quick sanity check says it took 40 years to go from 3 to 6 billion. Close enough.

For three 1.6 million population cities, we probably require another equal amount in farmers. So let's assume we need to get up to, say, 10 million people. This is doubling 600 a hair over 14 times. At 50 years per doubling it's a total of around 700 years.

However you specify 500 million people as a "good target". A little more math and out pops the number 20 generations, or 1000 years.

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