
How many people does it take to colonize another star system? - arnauddri
http://www.popularmechanics.com/science/space/deep/how-many-people-does-it-take-to-colonize-another-star-system-16654747
======
zaphoyd
A somewhat related question. How many people would it take to sustainably
maintain current levels of technology if given time to prepare, the ability to
bring all of our knowledge (but not realtime communication with Earth), and a
reasonable starting set of tools?

Would a generation ship with 10,000 people still be able to build an iPhone
when they arrived? A GPS satellite? Is it a matter of knowledge/ability to
specialize or is it the economies of scale that make it possible to build
compact high tech items?

~~~
josephagoss
It's less about the people and more about the resource capabilities on the
ship. If the ship has machinery that can rebuild things like a chip Fab for
example, and the knowledge to repair all said machines, it becomes more
feasible. If the ship has no machinery to construct advanced
machines/facilities even 100,000 might not be enough to construct advanced
tech.

~~~
wyager
> even 100,000 might not be enough to construct advanced tech.

I think that's way too large of an estimate. As long as we could continue to
access records of _how_ we did things, and the planet had sufficient relevant
resources, I bet we could bootstrap ourselves from having only primitive
mechanical tools to today's tech in a few generations. Again, that's assuming
the planet is relatively hospitable and has the correct resources available.

~~~
ForHackernews
I'd assumed he was asking about "immediately on arrival", not "within a few a
generations", but I agree with your assessment.

~~~
zaphoyd
Not sure about the parent here, but I was certainly considering longer term. I
would expect early on that there would be high tech tools and items brought on
the ship or built form parts of the ship. Actually setting up local production
from local resources (beyond what could be constructed on the ship) would
probably take some time.

Longer term though.. is it practically/economically feasible to build and run
a chip fab capable of building modern ARM CPUs for the needs of 10,000 people?
What about the rest of the manufacturing chain for these sorts of devices? Or
is the only reason we can buy a smartphone today for a few hundred dollars
because of the economies of scale of building tens of millions of them on a 2
year replacement cycle?

------
grej
It's an interesting thought exercise, but as many of the commenters point out,
the article's premise is a little ridiculous. With modern technology you don't
need to send the entire population. The vast majority of the genetic diversity
could be in the form of frozen sperm and eggs.

~~~
jerf
It's a pity they went that way, because there's a different framing that is
still an interesting question: How far could humanity fall and still be able
to recover? It's essentially the same problem, and it's a lot easier to
imagine that we're talking about a situation in which there's no longer any
technology. We consider the people geographically co-located, but it's not
hard to imagine a pocket of survivors of whatever $DISASTER, either.

~~~
maxerickson
You have to start somewhere more specific than no technology.

Like, no steel to find lying around, or no one that knows how to make charcoal
and that some dirt has iron in it.

Or does anybody remember anything about agriculture?

~~~
tseabrooks
I feel like anything like that has to be predicated on not being able to find
any book. Which is certainly possible, but I feel like $DISASTER will probably
leave behind some libraries and books somewhere. The people would just have to
be dedicated to learning the lost info from books + experimentation.

~~~
gknoy
I worry that such an event would still be devastating. One fire was all it
took to lose all of the wealth of Alexandria's knowledge several thousand
years ago.

------
Ellipsis753
"Whereas in the simulations, the larger populations were allowed to have only
one child per couple".

This seemed a little strange to me. If you have only a single child per couple
wouldn't you expect the population to at least half each generation?

~~~
JoeAltmaier
People have children early in life. Even at that rate, the population can grow
without bound. E.g. if people lived forever its clear the population would
still grow.

~~~
Ellipsis753
Living forever is somewhat an exception. But even if people live forever there
will still be a hard bound. Imagine a population of 8 people (4 couples). With
one child per couple the first 4 couples will have 4 kids. These 4 kids will
have on child per couple giving 2 kids. The 2 kids make a single couple which
can have one more kid. The last kid cannot make a couple with anyone without
someone having had more than one kid. So starting with 16 immortal people
having immortal kids you cannot get a population above 15. (8+4+2+1=15)

So for a stable population in the long run couples need to be having on
average around 2 kids each (assuming they are not immortal, if everyone is
immortal then no kids are required for a stable population).

Of course if we take "couple" very literally then perhaps we might allow
people to have as many kids as they chose provided they have each with a
different partner (to form a new "couple"). This seems like rule bending
though.

Without rule bending one kid per couple just couldn't work in the long run.

------
ctdonath
_When 10,000 people are housed in one starship, there 's a potential for a
giant catastrophe to wipe out almost everyone onboard. But when 10,000 people
are spread out over five ships of 2000 apiece, the damage is limited._

Whatever you do, don't go on the B Ark.

------
rbanffy
First of all, we need better engines. We need better engines and better probes
to be able to investigate candidate systems up close. We won't send humans
before we have thoroughly evaluated the environment and ensured it's, if not
safe, habitable. It's OK if they take centuries to arrive, but it would be
really great if they didn't. They could also be accelerated and decelerated at
much more than 1G, something we would prefer not to do with a live payload.

Second, we need better engines, better robots and better manufacturing
technology. Once the right planet is found, we'll send supplies and robots
that can build the colony mostly from local resources. Hopefully, all that can
withstand much greater accelerations than humans would.

Only then we can send humans, with human-rated engines (we can't do much more
than 1G for any significant part of the trip) and a complete habitat that can
sustain the population for the duration of the trip (as seen from the
passengers - relativistics may apply, depending on our progress with the all-
important engine thing)

So, before we have better engines (and get rid of the bureaucratic problems
with nuclear reactors in space), it's really a waste of time to think about
how large the crew should be. We can have that data if we build marginally
better engines (yes, they are key) and colonize other planetary surfaces and
asteroids. Eventually, some populations may opt to isolate themselves.

Also, don't forget we may end up learning a lot about genetics well before we
can build a relativistic engine. It's perfectly reasonable to imagine we could
reintroduce (or introduce, or remove) any genetic trait we want in the
population at any time we need to.

~~~
dm2
250,000 kph isn't fast enough for you?
[http://en.wikipedia.org/wiki/Helios_probes](http://en.wikipedia.org/wiki/Helios_probes)

DARPA and NASA are working on it. [http://en.wikipedia.org/wiki/Hundred-
Year_Starship](http://en.wikipedia.org/wiki/Hundred-Year_Starship)

What's needed is either a faster-than-light drive or the ability to
cryogenically freeze people and bring them back once the spacecraft arrives.
[http://en.wikipedia.org/wiki/Faster-than-
light](http://en.wikipedia.org/wiki/Faster-than-light) and
[http://en.wikipedia.org/wiki/Alcubierre_drive](http://en.wikipedia.org/wiki/Alcubierre_drive)

If we can't bend space-time (using something like a worm-hole) or travel
faster than light then there will never be any communication between the 2
civilizations.

Wouldn't it be much easier to just mine the planets we have already and build
artificial planets or massive space structures out of existing planets and
resources within our own solar system? Yes, the sun will eventually burn out
but that's not an issue that our generation will face more than likely.

Where should we go?
[http://en.wikipedia.org/wiki/List_of_nearest_terrestrial_exo...](http://en.wikipedia.org/wiki/List_of_nearest_terrestrial_exoplanet_candidates)

~~~
ufmace
250K kph is nowhere near fast enough, by several orders of magnitude. That
gives us a 4k year journey to the nearest star system, which AFAIK is not
thought to have any habitable planets.

And that's a tiny probe, close in to the sun. Leaving the solar system with
that kind of velocity is a whole different problem. Voyager 1 is leaving the
system, doing about 17 kph, reportedly. As far as I know, we don't have
anything right now that can do much better than that.

According to everything I've read, sending anything at all out of the solar
system at a high enough velocity to get to another star system is way beyond
any kind of engine technology we even have on the drawing board. We could
probably build a fission engine if we really wanted to, but even that's still
orders of magnitude less than we need. Much less propelling an actual
starship, meant to contain hundreds or thousands of humans and keep them alive
and happy for the journey, at those speeds.

I do believe that we'll do it someday, but it's going to require propulsion
technology that we can only imagine right now. Anything like FTL or wormholes
or whatever is pure hand-wavyium at this point.

~~~
dm2
Voyager 1 is traveling at about 57,000 kph.
[http://solarsystem.nasa.gov/missions/profile.cfm?MCode=Voyag...](http://solarsystem.nasa.gov/missions/profile.cfm?MCode=Voyager_1)

The 250k being fast enough remark was just a joke.

Yeah, space is inconceivably massive, that's why my main recommendation was
that we focus on staying in our solar system for now. Autonomous robots can
mine and build huge structures in space for us to expand to, or I guess we
could build them on Mars, either way.

Many NASA scientists don't think that a warp drive is impossible
[http://www.space.com/17628-warp-drive-possible-
interstellar-...](http://www.space.com/17628-warp-drive-possible-interstellar-
spaceflight.html)

[http://www.space.com/9882-warp-drives-
wormholes.html](http://www.space.com/9882-warp-drives-wormholes.html)

We can make antimatter, we can see trillions of miles away, we can talk to
people on the other side of the planet instantly, we have computers that can
simulate nuclear weapons, we have nuclear weapons, we can connect and talk to
the human brain, and we can even theorize with pretty good certainty what
happened to start the universe, a warp-drive or worm-hole isn't completely
impossible in the near future.

Humans are not too far off from becoming gods. We can create life, we can put
life on other planets, we can even improve ourselves by fusing with machines,
shits crazy these days. [0]

~~~
ufmace
That site is awfully vague about exactly when it was travelling at that speed.
Every link I can find says that the speed of Voyager 1 right now, having left
the solar system, is 17kph. It was travelling faster earlier, but getting away
from the sun eats up velocity.

That is an interesting link about Alcubierre drive work, but as far as I know,
we still don't have any idea how to get the exotic matter required for it.

~~~
dm2
17 km per SECOND, not hour, if any site says hour then it's wrong.

Here is Voyager 1 and 2s official website, you can see the distance being
updated live, you'll notice that it increases very fast.
[http://voyager.jpl.nasa.gov/](http://voyager.jpl.nasa.gov/)

Make sure you are looking at distance from the sun, not Earth, the earth
travels faster than Voyager 1 so sometimes it will actually be getting closer
to earth.

We do know how to create antimatter, just not how to create amounts large
enough to be used (the LHC generates it I think). I'm not optimistic about
traveling faster than light anytime soon, but it isn't 100% out of the
question.

And if an alien civilization captures one of our spacecraft:
[http://voyager.jpl.nasa.gov/spacecraft/goldenrec_more.html](http://voyager.jpl.nasa.gov/spacecraft/goldenrec_more.html)

~~~
ufmace
Ah, looks like I misread things. 17kps makes a lot more sense - 17kph is like
bicycle speed.

We can create anti-matter all right, but AFAIK, that isn't the exotic matter
required by an Alcubierre drive. Anti-matter could in theory be used to create
the most efficient rocket drive possible, but apparently even that isn't all
that great. According to this
[http://www.nasa.gov/centers/glenn/images/content/84509main_w...](http://www.nasa.gov/centers/glenn/images/content/84509main_warp06.gif)
sobering chart, even a theoretical anti-matter rocket would require 1 million
kg of propellant to send a small capsule past the Centauri cluster in 900
years, without counting stopping. Going back to chemical rockets, there is
apparently not enough mass in the entire universe for that rather
underwhelming plan!

I don't know that FTL is out of the question, but apparently it is impossible
to have it without time travel. I'm not looking for any of that to happen
tomorrow, and I don't think anybody alive now has a clue when anything like
that might be ruled in or out for sure, but with the right theoretical
breakthrough, a lot of interesting stuff could potentially happen very fast.

------
JoeAltmaier
If you could invent a starship, you could also invent a new human, designed
for starting civilizations. Calorie-efficient, hardworking, has litters of
pups for rapid population growth, early maturity (8-10 yrs old), long-lived,
prodigious learning and memory, adaptable and happy with rote work.

~~~
pokpokpok
if you are doing because you believe in the value and beauty of human society,
you wouldn't want to genetically modify their personality...

~~~
JoeAltmaier
Who's personality? Yours? Mine? Why not this new guy, who's really very nice;
nicer than most people we know. Because we made him that way.

------
skywhopper
Very interesting article. There are tons of ethical and practical concerns
above and beyond the genetic situation, which itself might be fixable well
before a ship capable of such a journey was ready.

However, what I found weirdest about the article was not the topic itself, but
this line: "He calculated the trajectory of each population 10 times, then
averaged the results. (With one exception: The starting population of 40,000
is so large that it takes 18 hours to complete each simulation, so he
calculated that trajectory only once.)"

Even without considering the possibility of running the simulation on 10
colleague's computers or spinning up cloud VMs or any number of workarounds,
how rushed was this project that a week's worth of 18 hour MATLAB runs was
considered too much work?

~~~
ForHackernews
That stood out to me too. Maybe they figure they'll have enough time to run
some more simulations between now and 2350 when the starship is built, so it's
not worth wasting a lot of time on what is mostly just a fun thought
experiment.

------
waterlesscloud
Related- The 1 kg Starship, with a lively discussion in the comments, from
cstross among others.

[http://www.centauri-dreams.org/?p=30313](http://www.centauri-
dreams.org/?p=30313)

------
Zigurd
The problem is more-daunting than stated. The mechanics of applying the energy
it takes to accellerate, and decellerate, a plausible generation-ship to two
orders of magnitude higher speeds than currently possible is multiple
technology horizons away. Bio-engineering ourselves into forms required for
millennia or tens of millennia of travel is probably much closer than
acquiring that amount of energy. Indeed by the time such a ship could be
built, the "human" form may be more distantly related to us than chimpanzees
are.

~~~
placeybordeaux
But far before either of those happen we will have an increasing amount of
either remote controlled robots or self guided robots exploring on the fringes
before us.

~~~
Zigurd
That's also true. And another reason to stay away from sci-fi inspired
prognostication, like a lot of comments here where space ships five orders of
magnitude heavier than anything yet built are blithely assumed to be possible.
Most of it requires magical solutions to very hard problems. David Brin is one
of the few writers i have seen take on the "it's really hard, and insanely
expensive, to get anywhere" problem and make a story based on that problem.
The most plausible future doesn't have animals that look like us running
around in it, never mind traveling to other stars. And that makes it hard to
sympathize with, or even imagine, the protagonists of stories about the far
future.

------
mistagiggles
Very interesting, but this raises a point in my mind. If a colonisation trip
takes several generations to reach its destination, would the human rights of
the descendants of the original travellers be infringed?

They would be conceived, born, live out their lives and die without ever
living anywhere but the ship (unless they are part of a generation lucky
enough to reach the destination), and they would have no choice in the matter.

~~~
fennecfoxen
If a couple joins a colonization movement and moves to the middle of nowhere,
with limited chance to survive (make your time) outside the colony, in a land
occupied by dangerous animals and savage heathens - say, New England in the
early 1600s - would you consider the human rights of their children and
grandchildren to be infringed? Isn't the difference just a matter of degree?

(n.b. actual savageness of heathens is left as an exercise to the risk-averse
potential colonist)

~~~
paul_f
I think our understanding of human rights has evolved since the 1600s. This is
a very interesting ethical question.

~~~
bsamuels
At the level of technological sophistication required to send a probe to
another star system, you could probably sequence/modify the genome of the
eggs/sperm to produce humans that have a lust for exploration and pioneering.

Now it's just a question of whether genome modification is ethical.

~~~
JoeAltmaier
Not quite: the 20 generations that are born and die on the ship don't get to
explore anything. You'd want people content to live in a crowded can.

~~~
AOsborn
In a related point - what would the cultural mindset of the final descendants
become, both individually and collectively?

They would have no shared experiences with those who first set off.

Ideals could be passed down, but with cultural evolution through the
generations, would their priorities or preferences even be remotely similar?

~~~
JoeAltmaier
Many science fiction stories written about this. The most popular theme is the
breakdown of civilization and an ignorant crowd of savages set down on the
destination world. Other authors have them undergoing violent revolution a
dozen times over the centuries, recapitulating human history. The resulting
world is populated by whatever form of government is extant at the time of
arrival. Still others imagine them passing serenely by the destination, no
longer interested in their progenitors plans and seeing no other future for
themselves than perpetual ship-board life.

------
kephra
The following idea comes from a SciFi role playing game Traveller™:

The maximum sustainable techlevel of an economy equals the logarithm base 10
of the population. Even if a population of 10k-40k people is genetically
healthy, they would fall back to to techlevel 4 or 5. They would be just able
to sustain a technology of medieval times.

~~~
flatline
I suspect there is a tipping point. If there is sufficient automation and
information available, a very small number of people could potentially
reproduce/rebuild a full high-tech society in a short amount of time. Vinge's
"Marooned in Realtime" engages in similar speculation. IIRC his requirement
for preventing inbreeding was something on the order of 20 people -- much
lower than the parent article's 150 bare minimum, with 10K being more
realistic.

------
jmnicolas
I would think if your technology is advanced enough to send a spaceship for a
1000 years in space, you should be able to manipulate the human genome to
avoid "inbred" diseases.

First let's start by going back to the moon or even Mars ...

~~~
flatline
I would argue that we know a lot more about the physics and engineering
required to build a generational ship than we do about the biology to cure
rare genetic diseases.

~~~
jmnicolas
I would bet that if global warming doesn't destroy us before, we will master
inbreeding before we're able to go for a 1000 years space exploration tour.

------
sentenza
The number could be significantly higher, since genetics might not be the
limit at all. The true question is how many people it takes to maintain the
complete production line of our computers, from dirt and water to boards and
chips.

Anybody interested in interstellar colonization topic (and in particular the
question of how to get hundreds of thousands of colonists there) might also
want to read "Neptune's Brood" by Charles Stross. The society and mechanics he
describes are so far the most realistic I have ever seen.

Don't want to spoil anything, but according to him, the squishy biological
stuff might not be up to the job.

------
EGreg
This is a bit silly. Yes, genetic diversity is important for surviving viruses
and other pathogens that come from Earth. Because we have evolved here, we can
handle the other conditions of this planet. But it's not a guarantee that
we'll survive the subtle changes on other planets - the gravity, magnetic
fields, radiation, light, composition of the atmosphere etc etc.

~~~
JoeAltmaier
A good argument for designing the people that will be sent to colonize.

~~~
JTon
Or simply designing the immunization shots?

------
DominikR
Creating an artificial uterus and sending that device with frozen sperm and
eggs would be more efficient.

I just think that it would be impossible to calculate the risks if real human
beings would be sent on such a journey.

~~~
orkoden
So all the children would then be educated by a robot ai?

------
rivd
Unrelated yet more relevant question:

How many people does it take to properly care for ourselves and the planet we
live on?

------
postit
According to the Bible two and a bunch of animals.

~~~
rbanffy
It's debatable whether their descendants (or those who claim to be their
descendants) can build an advanced civilization.

