# How fast would a civilization with FTL spread out?

Let's say that a civilization has access to FTL. Let's say it is instantaneous so travel time between solar systems isn't a factor. How long would it take for them to spread out from their home solar system? Like how long would it take for them to colonize 1000, 10000 or 100000 solar systems?

Let's say we are talking about future humans. That when that technology was developed they have a population of around 10 billion. As for terraforming technology let's say it would take them a century to terraform Mars. How long it would then take to terraform other planets would be dependent on how different the planet is from earth. But colonizing a solar system doesn't necessarily mean terraforming a planet. It could be establishing space stations in that solar system for habitation or mining/research operations. Or they don't bother terraforming and live in dome habitats or underground cities. Or do that while terraforming. All these would count as colonizing a solar system.

• Depends on how many they are, on why they want to colonize those solar systems, on the available terraforming technology, and on many other factors which you are supposed to come up with as background for your story. As a potentially interesting historical data point, the ancient Greeks established about 300 colonies all around the Mediterranean and the Black Sea in about 200 years, from the 8th to the 6th century BCE, with whatever rudimentary technology they had available at that time. Dec 22, 2019 at 23:04
• I started writing an answer for this, then I realised just how broad this question is. I like the question, but the number of critical factors is absolutely mind boggling, and they all compound one another. Best estimate is anywhere between a hundred and a couple billion years for the first thousand colonies, depending on political will, economic growth, how you define ‘colony’, population statistics, the exact nature of your FTL tech, etc etc... Dec 22, 2019 at 23:10
• @JoeBloggs Updated the question Dec 22, 2019 at 23:19
• @AlexP Updated the question. Also, I didn't know that. I mean I knew they created colonies but that does seem kinda fast. I'll research that more. Dec 22, 2019 at 23:21
• I think the goalposts have been moved. If a single outpost habitat or lone mining-town under a dome now counts as a "colonized" solar system, then we briefly "colonized" the Moon in 1969. Where does the slippery-slope end? Dec 23, 2019 at 6:40

FTL isn't the issue

The problem is finding somewhere to live. The Milky Way has around four hundred billion stars alone so if you look at a star system every second, it will take you over 200 years to get through it all.

Now on top of that, chances are your destination will require terraforming which won't be a quick process nor a cheap process.

This means we're down to living in habitats and ships which comes down to how fast they can be built.

The desire to move will be as fast as other constraints will let them and the speed of travel is only a small part.

• By my calculation for "four hundred billion stars" it would take over 12000 years to check them all at one per second. Dec 23, 2019 at 14:00
• Computers and sufficiently good space-based telescopes can check far faster than that. Dec 23, 2019 at 17:52
• @MichaelKaras - it doesn't have to be the same guy/ship that checks all the systems - you could 'multithread' that easily by sending a thousand or more small ships... Dec 23, 2019 at 19:42
• There will be an expanding "known worlds" bubble and the rate of exploring unexplored star systems will expand out proportional to the surface area if the "settlement front". The number of colonized worlds, and the population, will increase accordingly. Dec 23, 2019 at 22:37
• I feel like the total number of stars in the galaxy is pretty irrelevant. Any attempt to colonize is going to prefer a closer destination, and so will colonize one of the closest candidates. And so the only factor is what percentage of star systems have suitable planets. And as humans grow out from earth, colonization will not be some centrally planned endeavor. It will be decentralized, so the number of planets under consideration by any group looking to expand will not change. Dec 24, 2019 at 3:14

Not long at all, depending on political and economic will.

You have instantaneous FTL and the capacity to build (presumably pretty good) space stations. You can ‘colonise’ literally as fast as you can build cheap stations with a one-shot FTL Drive and pop them to another star.

If the first country to colonise a system gets to claim it you can expect things to get hairy. Does a man and a woman in a tin can ‘space station’ count for political colonisation status? If so then the first thousand systems will be colonised in decades. If you’re a bit more stringent it depends on economic power to build the stations and the availability of willing colonists. Either way: you can expect humanity to colonise very quickly if nationalism gets to spread to space.

• By the time Earthlings are routinely building FTL drives and space stations I would think and hope that we would have a World Government and the things we now call countries would be merely provinces or (Federal) states. Dec 23, 2019 at 10:32
• Your cheap space stations are not colonization, any more than Apollo 11 colonized the moon. Pop one into another star system, and the people aboard will die without ongoing support from the home planet. Dec 23, 2019 at 17:56
• @jamesqf “But colonizing a solar system doesn't necessarily mean terraforming a planet. It could be establishing space stations in that solar system for habitation” - OP Dec 23, 2019 at 22:18
• The political definition of ‘habitation’ is all that matters there. Colonies almost always need support from home for a long time before they’re entirely self sufficient. Dec 23, 2019 at 22:19
• @Joe Bloggs: I suppose it depends on just what is meant by colonization. I'm assuming that a successful colony has to be self-sustaining, at least in basic things like food. Otherwise it becomes a failed colony, like Roanoke: en.wikipedia.org/wiki/Roanoke_Colony I'd certainly argue that a single space habitat (or even multiple ones) is not capable of being self-sustaining. Dec 24, 2019 at 17:52

Since travel is instantaneous, the real question is economic. Basically it is the time and resources it takes to build FTL vehicles, and the time it takes to transport sufficient personnel, materiel and equipment to settle a solar system.

Essentially assume a long-term economic growth of around one percent (1%) per annum. This is, from memory, the long-term economic growth rate for the human rate over human history. Effectively doubling every century.

Therefore, the settle any number of solar systems will be derived from considering the two major settlement parameters, mentioned in paragraph one, against the amount of economic growth.

For example, if it takes two centuries to settle one solar system, then economic growth will have quadrupled over that time span. Therefore, to settle another solar system should take less than one century or roughly fifty years.

Economic factors aside, there is a matter of political will. if a civilization is less committed to settling other solar systems, the rate of colonization will decline proportionally.

In conclusion, it is economic and political factors that will ultimately determine the settlement of solar systems. Adjust your suit, and the answers for different rates of settlement in different epochs will fall out out of the equations. This analysis isn't very sophisticated, but it doesn't need to be to give rule of thumb estimates.

• 1% per year is 270% per 100y. It doubles every 70y. Dec 23, 2019 at 9:10
• @ksbes Thank you for the trend correction. Dec 23, 2019 at 12:11

Basically, with instantaneous FTL, there isn't a question. The only answer is that we will spread out as fast as possible in whatever system we lay our eyes on. we will travel from the milky way to 13 billion lightyears in months because there would be nothing stopping us. The question is how fast would we fill out the territory we take? basically forever, but it doesn't matter. But if FTL does have a certain speed, if it even has a sort of geography, the answer is much different and more interesting.

Warp Drive

I am currently going to define warp-drive as an FTL tech that has a speed limit but no need to travel along specific routes. In this scenario, humanity would travel as fast as the warp drive lets them. If the fuel of the warp drive is really expensive to create, we may not use it to expand, but rather to simply travel between pre-existent colonies light-years away. If we are able to produce warp-feul in reasonable quantities, we would likely travel and skip to stars we think might have habitable worlds and travel until we find one. As ages pass by, empires will form as spheres with the largest ones having their edges around the 2 week travel range. If it ever takes more than 2 weeks to travel from the center of the empire to its edge, it will generally be difficult to hold onto that territory, though those kinds of situations have happened throughout history.

Hyperspace

Basically, I am calling hyper-space, or hyper-lanes, any sort of region of space that you can travel through faster than light which lets you stop at any point along the route and get on at any point. Basically, we would stop at every star the lane happened to be near enough to let us colonize it, and if the lane had an end, we would quickly find it. if not, we would continue along with it forever. However, empires would still tend to have their borders at the 2 weeks from the capitol terminator.

Wormholes

Basically, if we could create the wormholes but their locations were random, we would simply open them until we found one that let us travel somewhere we wanted to go. Depending on how common the material is we can make them out of, and the amount that can usually be recycled from failed wormholes, you will have entirely we will go at different speeds. Commonplace materials and easy recyclability will cause fast expansion, rare materials and difficult recyclability will slow expansion. pretty simple ig. if all wormholes are naturally occurring that do exist, we will just travel where they take us and see if there is anything on the other side we want to colonize. FTL travel is pretty complicated and the system should be pretty stringent when you are trying to figure this stuff out. But generally, we just go where-ever our road lets us go and we always like to try and get to the very end of it if we can. The harder it is to get there, the more we will try, the longer it takes, the longer we will journey because one-day we think we can get there. That's really it. When is your story set? that would be really helpful.

** But for what you are doing right now**

the answer is really simple. on the extremes, if FTL is as cheap as spacecraft today, it will only take less than a century to expand to 100000 systems. If making on FTL jump is about as cheap as making on a kilogram of Oggannesson, it could easily take millennia to colonize 100 systems with FTL, it would almost be a faster expansion method not to use it! How expensive is it? But for your answer, I will say it's about a gram of Oggannesson just for the answer. It may take 3 millennia to reach 100000 and no less than that. Maybe, with a lot of money, some sort of connection between systems is also possible. I mean, even a gram of Oggannesson would be ridiculous as a price measure for this thing. I am just going to say that a single FTL jump cost 3.78 Quadrillion dollars just to make this measurable. I am going to say it may take 3 millennia to reach 100,000 systems, each fiercely independent with their own gene pool and identity, likely hidden from one another. The first faction that is able to make regular jumps between multiple systems (2 per 2 weeks per non-capitol system controlled) will be the first major empire. I think it may be reasonable for you to maybe have instantaneous travel, but put a limit on the amount of distance you can travel per jump and estimate the cost of each jump to roughly decide the cost of a given journey, but considering how many star systems can be in a relatively small volume of space, using this method, you don't need to expand to many million galaxies to reach this number. For this kind of instant-travel, you should maybe look at 2B2T teleportation exploits. 2B2T is a Minecraft server, but it's bed teleport exploit is where my idea comes from. I may edit this answer later, I am likely slightly unintelligible.

Assume exponential expansion. For a reasonable upper limit assume that 100 colonies will be founded in the first 10 years after FTL is discovered and then double every 30 years or so. Assume that habitable planets can easily be found and moving there is no harder than moving to a different country here on Earth. A lot depends on your culture, if it's very expansionist and encourages its citizens to get 15 children per woman and move to a new planet as soon as you're old enough it will be faster than a conservative culture.

• Any expansion like this is basically exponential. So far this is the only answer which uses this very important word.
– hyde
Dec 23, 2019 at 11:31
• Of course it requires that the colonies get self-sufficient and expand on their own. If you expand from Earth alone you won't get exponential growth. Dec 23, 2019 at 17:08

I suspect the limiting factor here is going to be societal, not technological. People are social; they like to cluster together, and remain within easy distance of friends and families. We wouldn't have a problem finding planets to colonize — there are always individuals who are drawn to the solitary life of an explorer, wandering off to look for discoveries and opportunities — but people only choose to emigrate because of social pressures. The three most prominent types of emigrants are:

• Refugees, who flee violence, deprivation, or oppression (e.g., modern Syrians dispersing into Europe)
• Sectarians, who reject the rules and structures of a given society and want to establish their own independent community (e.g., the Mormons settling Utah)
• Exiles or other forced deportations (e.g., the settlement of Australia with convicted criminals)

Barring such conditions, people will prefer to stay where they are. I can imagine that at the very beginning of of FTL travel, there would be a wave of colonization efforts. Perhaps as many as a dozen of the most congenial planets discovered will be colonized as people push away from undesirable situations on earth (or perhaps as nations rid themselves of people they deem undesirable). But after that initial wave, social pressures will decrease. On earth, social and political tensions will drop, resources will be less strained, and in general the standard of living and the quality of life will increase; on colonies vast new challenges and resources will keep settlers happy and occupied. It would take generations before population sizes increase again, new social pressures develop, and new possibilities on colonies are exhausted. It's safe to anticipate 300 years or more between major colonization efforts.

Of course, there will likely be small commercial colonies scattered out anywhere there is some unique resource to be tapped, often on planets that are farther out and less habitable — the nature of those would depend on the interstellar economic system — but those kinds of colonies are usually not settlements. They are more like the occupying force in the movie Avatar: a corporate/military enclave that is semi-permanent at best. They are likely to be abandoned when the unique resource is exhausted or loses its value.

To recap Douglas Adams: space is big. You just won't believe how vastly, hugely, mind- bogglingly big it is. I mean, you may think it's a long way down the road to the chemist's, but that's just peanuts to space.

It's all very well being able to get somewhere fast, but you want to have an idea of where you're going (literally where you're going - even if you pick a specific star in Andromeda, where you see that star isn't where it is now, it's where it was 2 million years ago). Now, for a given astronomical capability, that practically limits you to colonising no more than a certain distance from your current boundary. We have good knowledge about exoplanets up to about 50 pc from Earth (well, when I say good I really mean extremely scant, but possibly enough rudimentary knowledge about planet size and possible atmospheric composition then maybe enough data to start sending FTL probes).

And once you have a colony established it will take some time before it grows and develops to the point where it's ready to start sending out colonists of its own. Let's be generous and assume every colony is benign and supports population doubling in a short human generation of 20 years, starting from an initial colony of 1000 (hopefully enough to support genetic diversity). It will take 10 generations to reach a million, or 20 generations to reach a billion, so around 400 years. Somewhere in that population range seems a likely timescale to become sufficiently well established to be ready to start colonisation activities of their own. Say 300 years on average. This limitation constrains the radius of the human sphere to grow linearly, and while the population of individual colonies will grow exponentially for a while before reaching an equilibrium, the overall growth of the human population will be proportional to $$r^2$$ (or equivalently, proportional to $$t^2$$ since the radius grows proportional to time.

Now the Milky Way is 60 kpc across. It would therefore take roughly 1200 years to colonise the entire galaxy (slightly more, because we're not starting from the middle). Once the galaxy is filled there's the question of other galaxies. Even the Magellanic clouds are 50-60 kpc away: crossing that kind of gulf could well be much more difficult than just hopping a few tens of parsecs to a suitable colony star system. Andromeda is 780 kpc away.

If the technology available in your universe allows for bridging those kinds of vast distance, then you start again but this time you're populating concentric shells of galaxies with a 1200 year "ready time" before looking to expand again rather than concentric shells of stars with a 300 year "ready time".

All this is probably rather optimistic, it assumes optimal colonisation, no distractions from outward expansion and unlimited technology and resources. In reality, politics and war may act as a drag on expansion as star systems fight among themselves.

In my post number 8 in a discussion of colonizing other star systems with slower than light travel: https://historum.com/threads/generation-or-sleeper-ships-which-would-be-the-better-more-realistic-option-for-space-travel.181701/1

I wrote:

It is possible to build artificial space habitats with materials from small solar system objects like asteroids and comets.

So eventually there could be tens, hundreds, thousands, tens of thousands, hundreds of thousands, millions, etc. of such space habitats with populations of thousands of persons each.

And of course adding an engine and fuel supply, etc., to such a space habitat would turn it into a vast generation ship.

So I can imagine that a fleet of several such generation ships might be sent to colonize some region in the outer cometary halo of our solar system. At a speed of one percent of the speed of light, it would take such a fleet 100 years to reach a part of the cometary halo 1 light year from the Sun. At a speed of 2 percent of the speed of light it would take such a fleet 50 years to make the journey, at a speed of 3 percent it would take 33.333 years, at a speed of 4 percent it would take 25 years, at a speed of 5 percent it would take 20 years.

If a fleet of several such generation ships is sent to colonize some region in the outer cometary halo of our solar system. At a speed of two percent of the speed of light, it would take such a fleet 100 years to reach a part of the cometary halo 2 light years from the Sun. At a speed of 3 percent of the speed of light it would take such a fleet 66.666 years to make the journey, at a speed of 4 percent it would take 50 years, at a speed of 5 percent it would take 40 years, at a speed of 6 percent it would take 33.333 years.

So possibly several fleets would be sent from the inner solar system to colonize various regions in the cometary halo. And after expanding in the cometary halo for a period, perhaps centuries, each such colony there might send out one or more fleets of generation ships to colonize another, and farther, region of the cometary halo.

The average distance between a star and its nearest neighbor is about five light years in our part of the galaxy. At a speed of about 1 percent to 10 percent of the speed of light, it would take about 50 to 500 years for a generation ship to travel straight from the inner solar system of one star to the inner solar system of the other star, and about 1,000,000 to 10,000,000 years to go from side to sie of the disc of the Milky Way Galaxy.. But if generation ships make voyages of 1 light year each to colonize regions of the cometary halos, and take 100 to 300 years to each the stage to send out long distance colonizing expeditions of their own, the colonizers could reach the inner solar system of a star 5 light years away in about 450 to 1,700 years.

And travelling at about 100 to 300 years between jumps, and jumps of 1 light year each at a speed of 1 percent to 10 percent of the speed of light, a society could expand in all directions at an average speed of about 110 to 400 years per light year of distance. Thus such a society could eventually colonize the entire galactic disc of the Milky way Galaxy, 100,000 light years in diameter, in about 11,000,000 to 40,000,000 years, if they started from an outer rim of the galactic disc.

If the inhabitants of such space habitats expect that they and their descendants will live in space habitats forever, and have no desire to land on any habitable planets they might possibly find, Generation ships made of such space habitats could make much longer distances.

Possibly some generation ship fleets might travel 10 light years in a single voyage, taking 100 to 1,000 years. And if such voyages are successful, some generation ship fleets might later travel 100 light years in a single voyage taking 1,000 to 10,000 years. And eventually generation ship fleets might make voyages of 50,000 light years, taking 500,000 to 5,000,000 years, reaching and beginning to colonize distant regions of the galaxy.

With a faster than light (FTL) space drive the galaxy could theoretically be colonized much faster than with slower than light (STL) methods of propulsion.

I stated that colonists with STL travel might take 100 to 300 years after colonizing a region to start sending out colonizing expeditions of their own, and that their ships might travel at 1 percent to 10 percent of the speed of light, thus traveling at about 10 to 100 years per light year, thus expanding at a rate of about 110 to 400 years of time per light year of distance.

With a FTL drive capable of instantaneous travel to any distance, the travel time part of the equation would drop to zero, so it would all depend on the average time a colony planet would take to send out colonies of its own and how many colony planets each colony planet founds on the average.

Assume that each and every planet, including Earth, sends out two and only two colony expeditions, 100 to 1,000 years after being founded by a colony expedition.

If the average interval is only 100 years, the planets or solar systems inhabited by humans will number:

3 including Earth at first.

5 after 100 years.

9 after 200 years.

17 after 300 years.

33 after 400 years.

65 after 500 years.

129 after 600 years.

257 after 700 years.

513 after 800 years.

1,025 after 900 years.

2,049 after 1,000 years.

4,097 after 1,100 years.

8,193 after 1,200 years.

16,385 after 1,300 years.

32,769 after 1,400 years.

65,537 after 1,500 years.

131,073 after 1,600 years.

262,145 after 1,700 years.

524,289 after 1,800 years.

1,048,577 after 1,900 years.

2,097,153 after 2,000 years.

And if the average colony world takes a multiple of 100 years to send out its colony expeditions, one can multiply that by the amounts of time in the list to get the necessary time.

For example, if it takes 1,000 years for the average colony to send out it colony expeditions, the times to reach a specific number of colony worlds will be ten times longer.

And of course the average colony world might send out three or four, or some other number, of colony expeditions instead of two. And the average colony world might send out one colony expedition every 127.5 years, for example, for as many centuries or millennia as that colony world exists, instead of sending out all its colony expeditions at once.

But it seems simple to make reasonable assumptions about the average rate of colonization that will make it simple to calculate how long it will take for a specific number of worlds and solar systems to be colonized.

I suspect a lot of it will depend on how small you can make your FTL engine, and how good your nanotech is. In which case, simply imagine an effectively infinite-sized earth and ask yourself how humanity would spread.

Imagine you've got a database in front of you with 100 billion rows of data. In that data is a column called "Percentage" - with a value between 0.000% and 100.0000%. You're looking for a value close to 100% (the closer the better) but there's one catch: reading a row of data, no matter where in the 100 billion rows, will always take 1 second.

So, how long will it take you to find values extremely close to 100%?

The answer is: you wouldn't. You'd program something to do it for you. Or somethings - you'd have several cooperative processes (threads) looking through it for you, compiling an index of the closest values.

Well, your FTL civilization is in the same boat. Travelling anywhere in the universe is trivially quick (just like looking up any one record will only take a second.) Finding someplace worth travelling is much slower, as is terraforming a less-than-ideal planet.

So the immediate first answer is: send out a swarm of FTL bots to start indexing. Spend a year, going star to star to star, and cataloging the planets - and then report back the data.

The problem is, there are 100,000,000,000 stars in our galaxy alone (there was a reason I choose 100 billion as the number of database records.) A thousand bots taking an hour per star would only chew through 0.01% of them. And then someone things: hey, we're not the only galaxy... in fact, there's an estimated 100,000,000,000 galaxies in our observable slice of the universe.

Which brings a second facet of the answer: bots that can assemble copies of themselves. That way, you're not trying to solve this linearly. You're going to let the bots assemble all that information in a relatively small amount of time. Within a year of two, there are bots FTL'ing every which way before reporting back and spitting out the data.

Which would be the values in that "Percentage of Complete Idealness For Colonization" that are as close to 100.0000% as possible.

Which, with that huge of a database, you're going to get back a LOT of results very close to 100%. You're going to get near-earths, mega-earths, idyllic paradises, resource-laden meadowlands with frollicking fauna, etc.

And since neither getting there or settling it will be difficult at all? You can imagine that humanity's going to spread awfully freaking fast. At least until we've got all the 99.999% planets colonized.

# Bottleneck

Since you removed travel time as the bottleneck, the new bottleneck becomes population growth. You posited a starting population of about 10 billion souls. The Milky Way contains about 250 billion stars. So even if every last soul on earth claimed their own star system, that generation could only colonize about 4% of all stars. Given that your civilization has FTL capability, we are going to assume that they can either make the available planets livable, or are satisfied with living in artificial structures, merely using the star as the ultimate giant battery. Thus, we will assume that your civilization will attempt to populate every star system in the galaxy.

# Growth Rate

Currently, human females are capable of producing at least 10 children each, on average. The historical sustained high rate is about 6-7 children, but this is almost certainly limited by nutrition and medical advancement. Many women have been recorded to have more than 20 children, and they certainly have the eggs and reproductive longevity for such. One of the big downers in population growth is that half your children will be somewhat useless non-child-bearing males. You can mitigate this with sex-biased IVF, so that you produce, say, 80-90% females, assuming that they are ok with not all having (exclusive) male partners. Assuming slightly more than 10 children per woman, we can estimate that each woman has 10 female children, so that the generational growth rate is 10x.

In one generation, you can go from 10 billion to 100 billion souls, and in two, you can top out at a trillion souls. That's more than 4 souls per star, but again, 4 is well below a robust "minimum viable population". If we assume a target closer to 4000 souls, then you just need to wait three more generations. If you assume each generation is about 30 years (on average, women start bearing children at 20, and have one every year or two until 40, uniformly distributed), then you have "colonized" the entire galaxy in just 5 x 30 = 150 years. Less than two centuries!!! Of course, this assumes along with the FTL tech that your civilization can either bring what they need to support such a colony, or can exploit whatever materials are available at their destination system.

# Mining

Obviously, you probably don't want to disassemble Earth to build 250 billion colony bases on alien worlds. But you don't need to. You said FTL was instantaneous, so you can steal asteroids, clean out the Kuiper belt, and strip-mine any new rocky planets you find around new stars, and move the raw materials to your new colony worlds. The only trick, of course, is what powers your FTL drives. You may, in fact, find that fuel is the bottleneck, depending on what kind of handwavium actually makes them go. If they use an Alcubierre-style warp drive, they may be able to traverse the galaxy in hours, but require the mass of Jupiter to do so, rendering your colonization program moot, because if you use an entire planet to jump between the stars, there will soon be no planets left to colonize.

If, on the other hand, your FTL drive is fast, but travel time is still linear or even polynomial in the distance and/or mass, then resources become a much bigger factor. It may no longer be feasible to move an entire colony base with you to a new star, and if your destination star lacks suitable raw materials, you may need to send some from another star which does.