A machine world (or forge world, or industrial world, or factory world, etc. etc. etc.), as I will define it for the purposes of this question, is a planet (or sufficiently large moon or asteroid) whose resources, surface area, and governmental apparatus are entirely devoted to fabricating some good, using a massive and constant influx of resources from other planets to continuously producing something(s) and pouring out a virtually-endless supply of machined materials; a machine world, even one that was originally barren of resources, might have millions of tons per second of iron ore delivered from elsewhere in the system every second and churn out millions of tons of raw steel to be delivered back to orbit, and another might take in all that raw steel to then craft an endless supply of spaceships for the civilization that controls it. Whatever the case, this is definitely a Kardashev type 2 civilization that controls the machine worlds.

While an excellent setting for cyberpunk or steampunk storytelling and a fantastic plot device for when you need to justify a until-recently-pacifist group suddenly just having a hundred thousand warships at the ready, they really don't seem that logistically valid. Sure, you have an entire planet's resources and area to build endless factories and data centers and assembly lines and quarries, but still,

  • delivering supplies when necessary from orbit gets crowded, especially if the machine world doesn't have the resources it needs on the surface to do its job: if a supercarrier can haul around a thousand tons of supplies, then feeding a machine world might take hundreds or thousands of supermassive ships entering and leaving orbit every second, each one having to send out hundreds of drop ships to deliver the supplies down to the planet;
  • getting finished product off of the machine world after one of the trillions of assembly lines finishes its job is nigh impossible without equally-massive orbital launch systems launched on the hour that carry millions of tons of supplies into orbit, making the machine world expensive both in terms of resources and financial costs;
  • even though a nuclear bomb delivered to the planet's surface won't really deal any considerable damage, doing security checks for drugs or guns or bombs or anything on every one of the thousands of shipping containers on every one of the thousands of supercarriers would either a) have to be very, very slow and almost 100% effective or b) have to be reasonably fast but not 100% effective and allow for nukes, drugs, or other illicit materials down to the planet's surface frequently and thus making the machine world into a dangerous, highly-criminally-active place (maybe that's a plus, depending on what kind of setting you're going for, but still); and
  • finding viable worlds for terraformation is difficult. It might be more effective to just reserve a space on a bunch of the more common worlds for factories instead of having one planet have all the factories on it; if the factories are more spread out, then the air pollution on those planets goes up a little bit, but if the factories are all on one planet, then the air on that planet will be filled with toxic smoke and render what might have been a habitable home into an industrial wasteland. Not a very good thing for PR.

The thing is (in the universe in which I have this problem), the Empire has nineteen machine worlds already that produce 99.9999% of all the non-agricultural goods for many hundreds of trillions of their species, and I can't think of a reason why the factories wouldn't be more evenly distributed across the planets.

So, what makes machine worlds the only viable option for supplying the many-trillion-strong Empire with its goods?

For the record:

  • in this universe, there is FTL travel, so once a ship gets into high orbit of a planet (almost outside its Hill sphere), it can almost-instantaneously jump to wherever it needs to go, but warp drives don't work deep inside the planet's gravity well; interplanetary and interstellar travel logistics can be handwaved aside

  • interstellar colonization has expanded to a decent fraction of the galaxy; there are five million planets which at least house some colonies, and while the majority of them are just some outposts with total populations under one million people, there are around five thousand planets that have reached Earth-like development and have large populations

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    $\begingroup$ You mentioned terraforming and pollution - is it an established fact in your world that these machine worlds have breathable atmospheres? I think there's a reasonable answer if they could be airless rocks instead - if that's a possibility let me know and I'll post it. $\endgroup$
    – N. Virgo
    Commented Apr 21 at 10:25
  • $\begingroup$ @N.Virgo that's fair - I'll allow the construction of a machine world on any planet that holds itself together (airless ones included) $\endgroup$ Commented Apr 21 at 18:29
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    $\begingroup$ What else are we going do with an airless rock? $\endgroup$ Commented Apr 21 at 21:50
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    $\begingroup$ On earth we also have massive fabrication hubs and vast areas with little to no mass-production industrial activity. Why should the factors that lead to this phenomenon differ on a galactic scale? machine worlds - to me - are just a natural outcome of how humans do things $\endgroup$
    – Hobbamok
    Commented Apr 22 at 10:48
  • $\begingroup$ Why would you drop all that mass down a gravity well just to have to lift it out again? The only way this would make sense if they had gravity manipulation, or energy production so cheap it did not matter, which in its self both solutions bring their own god power problems. $\endgroup$
    – Gillgamesh
    Commented Apr 22 at 18:42

10 Answers 10


Because there are some products that require a planet-sized facility to make.

This isn't even that absurd of an idea. Faster-than-light travel and other far-future technology might rely on forms of exotic matter that need to be manufactured in particle accelerators, and the maximum attainable energy of such an accelerator is limited by its size. Since current accelerators presumably can't make the heavy particles required for FTL, perhaps the most practical option is to scale them up, pumping obscene amounts of Dyson-sphere-beamed power (K2, right?) into constant peta- or exa-electronvolt scale collisions.

Imagine a facility that produces FTL drives for starships. It needs, perhaps, not one but many of these world-sized accelerator rings, perhaps stacked up into a column or draped around the planet like so many necklaces, to produce the specialized materials in sufficient quantity (these things might be slow!). It needs all of the tools, replacement parts, and staff to keep these accelerators running. It needs the heavy-duty factories that can safely handle unstable heavy particles and store them up in engine shells for later manufacturing steps (which for economic reasons might as well be on-site). And it needs the infrastructure to move all of this stuff in and out (at this scale you might want to consider orbital rings instead of puny thousand-ton haulers to move things up and down).

Now what do you have? You have a huge network of spaceports, an enormous power grid, and the housing and support needed for the army of people who keep all this stuff running. Why not use this well-established industrial zone, that you needed just for one exotic-matter product, for other stuff?

Sounds like a machine world to me.

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    $\begingroup$ This factory may also require (close to) the entire energy output of a very bright star. So it needs to be in one of the few stellar systems with such a star and you can't have much else in that system. $\endgroup$
    – quarague
    Commented Apr 22 at 7:27
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    $\begingroup$ Metastable quark matter /n/ a.k.a. MsQM, a self-stabilizing volume of hadrons that have exceeded the Hagedorn temperature, resulting in their dissociation into a mass of quarks which, aside from being metastable at high temperatures, is extremely sensitive to electromagnetic and gravitational fields, making it ideal for use as fuel in warp drives. Requires circular accelerators consuming exawatts of power and thousands of kilometers in circumference in order to accelerate protons to the energy necessary to produce MsQM. (Fantastic answer.) $\endgroup$ Commented Apr 22 at 16:57
  • $\begingroup$ Could you build a particle accelerator in orbit? You get a near-vacuum for free, and you can put ring of magnets (or charged plates to deflect particles electrostatically?) far from each other so they don't have to bend their path very much; huge diameter of ring that just needs wires to carry power and lightweight structure. (Or beam power and do station-keeping somehow to maintain shape). Might need some future tech to focus the beam onto the next stage, if they're so far from each other than it's not tightly collimated when it arrives at a stage. $\endgroup$ Commented Apr 23 at 18:36
  • $\begingroup$ @PeterCordes Oh, almost certainly, and I've upvoted some answers saying that there's no need to do this stuff on planets at K2 to begin with. But OP was pretty specific about the alternative to concentrated machine worlds being factories spread out on many planets; whether or not it's "realistic", I was running with "infrastructure is built on planet surfaces" as more-or-less a setting rule. $\endgroup$
    – parasoup
    Commented Apr 23 at 19:37
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    $\begingroup$ Right, I like this answer, just particle accelerators might not be the best example. Other answers point out things like dust buildup being mitigated by gravity for industrial processes. $\endgroup$ Commented Apr 23 at 20:06

Economies of scale

There's a huge advantage to having lots of things in one place. If you can have the widget factory and the wotsit factory right next to the factory that turns widgets and wotsits into doohickeys, then you don't have to pay the cost of transporting widgets and wotsits all over the place, and the factories' activities can be coordinated for maximum output. If the widget factory uses a lot of energy and it happens that bigger hyperfusion plants are generally more efficient than smaller ones, then it makes sense to have one giant hyperfusion plant next to one giant widget factory, rather than lots of small ones scattered across the empire. And given that, it makes sense to go big with the wotsit and doohickey factories too, as well as everything that uses them.

Given that, the main question is why put all this stuff on a planet, rather than, say an O'Neill cylinder, or just floating in space, perhaps held together by trusses. I can think of two main reasons:

  1. Planets have resources. Granted, by the time things reach the kind of scale you're talking about, those resources might all be used up. But the resources were there initially, and at that time it made sense to put factories on the planet, next to all the mines. The factories are there now because that's where they were historically - the economies of scale make it hard to move them.

  2. Don't underestimate the value of a solid surface. If your factories are just floating in space then they're going to move around every time something docks with them, and that's going to be happening a lot. There will be a huge amount of logistics involved in making sure the whole thing doesn't accumulate momentum and end up in the wrong orbit, or accumulate angular momentum and start spinning around the wrong axis. Vibrations will also be an issue. It could end up just being a lot more practical to put things on solid ground that doesn't move.

You mentioned the difficulty of getting to and from orbit, but for a Kardashev 2 civilisation (or even Kardashev 1) this is barely an issue - you can have all the launch loops, skyhooks, space elevators, rail launchers etc. that you need, and these will make the orbital costs negligible, compared to the scale of energy that such a civilisation deals with.

You probably wouldn't choose a planet with an atmosphere for this, and you might be inclined to go for one with a relatively low gravity. (Any population would live indoors.) So realistically they might be more like machine moons than machine planets. They might end up with (very much non-breathable) atmospheres after a while though, due to a build-up of gaseous industrial side products.



Even when, as in our case life is gathered on a single planet, gathering, processing and using resources to produce heavy-goods is a dirty business for a single country. Then there's all the energy production costs (to the atmosphere and water) and toxic mess generated by all the chemical-processing plants, the airborne particulates, soot. A dirty business for a single country, and the planet's environs get pretty nasty when every country in a world is doing it. Who'd want to live somewhere like that?

So, in a civilization comprising many planets, the more acceptable choice is to keep all that mess out of sight. To keep all the other planets pristine you can nominate a single one, not hospitable to begin with, but in possession of raw materials to kick-start the venture.

It can be used as a dump for all the galaxy's unmentionables, the waste packaging, the worn-out goods - much of which can be recycled to as-good-as-new. This might go for the workers too, criminals and general undesirables would be sent here to earn their way back into civilization, or die trying. It's a way better idea than wasting-away in prison and more economically efficient.

If it comes to it as the planet becomes increasingly unable to support human life through the nasties in the air/water, atmospheric soot/dust or radioactivity etc., the industry can up-sticks and relocate to a virgin planet.

Over the millennia, the "dead-zone" of disused industrial planets might be of interest to scavengers and criminal gangs seeking a home-base. With all those chemicals and radioactive waste, who knows what mutations might arise among the indigenous lifeforms - and the criminals.

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    $\begingroup$ Eh, with FTL you can put your hazardous wastes and undesirables anywhere you like. Radioactives are readily denatured once you've mastered fusion power, and toxic chemicals can be exposed to unfiltered sunlight in close orbit around a star til they've learned to behave. That said, just creating dust is a potentially dangerous and polluting thing, if done in space. Smelting and ore processing in a gravity well helps keep the micrometeroid flux down. $\endgroup$ Commented Apr 20 at 20:54
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    $\begingroup$ You're right, it wasn't a very well thought out answer, thanks for the bit about dust/soot, I've added that now. @StarfishPrime $\endgroup$ Commented Apr 21 at 18:11

Anything you can do on a planet, you can do better in a Dyson swarm, as long as you have the materials. If you are shipping materials in, then this is even less of an issue.


The one thing that a planet has that can't be easily reproduced by a space-based facility is gravity. You can do most gravity things with centrifugal force, but then you have to pay to spin things up and down between processes. There are a few ways to make gravity a requirement of your production facilities.

If you riddle your planet full of tunnels that make a straight shot from one point on the planet to another, it'll take about 38 minutes to send materials from anywhere on the planet to anywhere else on the planet. It would take some serious engineering to accomplish this, but if you're talking Kardashev 2, that shouldn't be a problem.

Reality warping, or some other super-advanced manufacturing technique might require a minimum relativistic gradient in order to function.

Fractional distillation can be done in a centrifuge, but why bother when gravity is free?

I'll add more gravity-based processes if I can think of them. If you still have humans manning the forges, then it may just be more practical to have them in a gravity well instead of in orbit.


Space wants to kill you

I guess it's a lack of experience -- who here has ever lived in space? -- so I'll put the reminder here: space wants to kill you.

Space is extremely inimical to life: no atmosphere to breathe, no easy to warm up/cool down, radiations, high-velocity particles (and bigger debris), ...

Building a factory in space -- space station, O'Neill cylinder, etc... -- means having to contend with all of that, and while those are solvable problems, the solutions require maintenance -- which has a cost -- and are generally fallible -- which means losing people, and materials.

By comparison, even a modest moon or planet can do so much for you!

A good magnetic field can help keep radiations at bay, an atmosphere (even if not a breathable one) will shield you from most particles and debris, temperature of equipment and habitat can be regulated by exchanging it with the (massive in comparison) moon/planet, etc...

The only one issue, really, is the gravity well, but it shouldn't be much of an issue for a Kardashev II civilization: surely at this stage they've got working Space Elevators. At least for low-gravity worlds.

Machine-only world

Would you terraform Mercury? Or Titan? The surface temperature doesn't really lend itself to creating an habitable world...

Would you want to live on a planet where factories blacken the sky and set rivers on fire?

I have a solution for you! It's easy, really:

  • Reserve moons/planets in the Goldilock zone for living, and terraform them.
  • Use moons/planets outside the Goldilock zone for factories, and save the cost of terraforming them -- the atmosphere wouldn't remain breathable for long anyway.

Full world

Why a single world, and not splitting across many?

Well, first of all, not every moon/planet already has a solid magnetic field and an atmosphere thick enough to protect folks and machinery from space. Add in a relatively low-gravity and ground as a requirement, and there aren't that many candidates.

And from there it's all about economies of scale.

Why, in our current world, do you have megalopoles with 10s of millions of people living all crammed together instead of a uniformly distributed population? Same, same.

There's a cost to maintaining a space elevator, and having only the one leaves you open to maintenance windows. So you'd want 3 or 4 at least. It's not viable to have 3 or 4 for a single factory!

There's a cost to shipping materials left and right (to manufacture X here sir, we'll need shipments of Y and Z). There's a cost to moving specialists (architects, engineers, ...) left and right (for repairs, maintenances, audits, design). There's a cost to transferring products left and right (much cheaper within a world than across worlds). There's a cost to innovating (ASML anyone?).

The more worlds you have factories on, the more the cost pile up. It's much cheaper to concentrate them. The only limits are how much you can cram in one planet -- energy-wise, transfer-wise -- and how many eggs you're willing to put in a single basket.

Lone world

It shouldn't be the only machine world, though. There should be several of them (eggs/basket), or whoever's in charge is fairly inept.

There needn't be that many, though, and they should be spread about -- to prevent a catastrophe wiping them all at once. No need to have one here, if there's one in the neighbouring solar system already, it's a short enough hop.


Hmm... I find that my suspension of disbelief works quite well with this explanation:

It's just a naturally-occurring congregation of similar services into one spot. Like, ages ago it wasn't a machine-world, it was just a big factory on some backwater useless planet that wasn't good for much else. But the location was relatively close to the mining operation and the trade routes, so it made sense to put the factory there.

As time went on, more factories were built next to it, because, again - that was just the most logical place at the time. For example, the supply chains for the advanced manufactured goods are pretty long, so keeping the relevant factories close cuts down drastically on overall transport costs. And many superfreighters are already going to the world, not all of them at 100% capacity at all times, so it's cheaper to just add your load to them. Etc.

And so, after a few hundred years, you get a machine-world.

I wouldn't bother about the orbital mechanics too much. Since we're talking about Kardashev 2 interstellar travel and commerce, ships are unlikely to want to hang around in orbit. That's just time wasted. They'll just want to get down, unload, reload, and back again to faraway places. Cuts down on fuel usage too.

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    $\begingroup$ Exactly. If 9/10 parts suppliers (and their raw material refiners plus manufacturing infrastructure) are on planet X, where are you gonna build that spaceship factory? Definitely not on planet Y where you'd have to ship everything first. $\endgroup$
    – Hobbamok
    Commented Apr 22 at 8:16

Business, ownership, security, politics

Many of our current cities have Central Business Districts, or Industrial Centres, where a concentrated area of production is not only viable but desired from an Political and a Business point of view.

So having a machine world would have these benefits:

  • Security With all manufacturing occurring in one place, there is less chance of theft, infiltration, or surveillance, than on distributed smaller facilities spread over a wide area. For a certain amount of security force, it is more effective if it is concentrated, than divided many times over many locations.
  • Intellectual Property Having one area where innovation, research, manufacturing all occurs allows IP to be concentrated physically in an area, and means it is not 'sent' all over a large area and easily lost control over.
  • Logistics Having a central machine planet will prevent the need for logistics between different manufacturing processes. Ie - in Guangzhou, aluminium extrusion and smelting is often close to aluminium powder coating and window manufacturing to reduce the need for logistics in shipping products between processes. The same benefits would occur on your machine planet.
  • Politics and Competition A planet of machines also is politically concentrated - meaning rules, governance and ownership are more easily manageable. If they were distributed (for instance over many star systems), the benefits would be too and these areas would be far more likely to 'break away' or become a separate region of governance or sold off as a different entity. It is often better to concentrate these to be a more cohesive unit that is more powerful when in competition with other smaller facilities.
  • Simpler supply, Simpler waste Supply to a central location allows for a large investment in an efficient big 'port' facility in lieu of investing in multiple port facilities over thousands of planets, and simple mass trade routes in lieu of a more complicated web of supply routes to different facilities. Similarly, waste products can also be simpler, rather than dealing with waste from a thousand planets, you only need to transport waste away from one.
  • Marketing: Having a physical concentration renown for the creation of certain products allows specialisation, and many customers would simply find it the 'goto' for that kind of product.
  • $\begingroup$ The politics part also becomes relevant with standards (in parts, specs and so on). Because everyone on that planet will use the same type of screws, data interfaces and the same way to specify how material quality is measured/specified and so on. This makes planning a production much easier since everyone working on the project is in the same space of definitions, which I'd assume can drift in a large interstellar civilisation $\endgroup$
    – Hobbamok
    Commented Apr 22 at 8:19

The same reasons why we have industrial centers on earth

Open up Google maps and hit some random spots. The chance is insanely high that there's no large factory within quite a stretch.

Because our production is highly clustered too So not having machine worlds (while still having megaprojects or massive ships) would be way harder to believe

Machine worlds would be no difference, except it's easy to see why the effects would be even more pronounced:

  • Interstellar-capable logistics setups would be incredibly expensive for that large scale (you'd likely need in-orbit unloading of superfreighters, industrial grade space elevators and so on, ideally multiple), so you want to max out their useage (aka make individual shipments cheap)

  • shipping works best when you have clear flows from one hub to hub t distributor, with the (presumed) expense of space-shipping per launch (yet close to 0 per distance) it makes perfect sense to want to get all your manufactured goods from one place. This gives any factory located at that hub a huge advantage

  • being located near your suppliers (or B2B customers) is another huge advantage due to lower shipping costs. A machine world could also be completely integrated and permeated with logistics projects further lowering cost.

  • (assuming a somewhat federated civilisation): everyone being in the exact same locale enables an easily (historically) shared set of standards / ways to do buisness etc. While this doesn't force a singular machine planet it heavily encourages centralization within one general economic/political space.

  • furthermore having all industry in one place makes it easier to regulate/control, so politics is motivated to order or incentivise centralisation

  • Megaprojects (like starships, dyson-sphere components) require an immense throughput, something hard to coordinate with distributed manufacturing (especially logistically), having a planet with the infrastructure to move the required mass (and produce energy) already is a huge advantage.

  • Large starships (the Star Wars star destroyers come to mind) already need a megascale shipyard infrastructure just to produce single/individual items. Why not locate the supply infrastructure nearby? (or build the shipyard where the sources are concentrated?)


Essentially the same argument by Robert Rapplean (planets have gravity) above, in detail:

The reason why warp drives only work when local space is flat enough is that the hyperspatial interface leaks energy from higher-order dimensions. The leak effect is more or less the same as trying to walk in a stream: you can do it easily enough if the stream is slow and shallow enough, but otherwise you'll fall and even get swept away.

Human ingenuity on the other hand soon realized that there was a colossal opportunity here: by properly initiating a controlled warp jump that goes nowhere deep inside a gravity well, and running coils through the interface, you can get all the energy you want, for free. The First Law of Thermodynamics only applies to closed systems, after all.

The availability of infinite energy (even if you'll need some way of dumping the waste heat) will trump whatever limitations a planet may offer.

Indeed, once you have set up a core tap (this is the name of the device in David Weber's Empire from the Ashes) on a planet, you'll find it especially convenient to locate all the industries possible on the same planet.


One possibility is to start by looking at how stuff gets to/from the planet surface.

The way we do it today on earth is hugely inefficient - stuff we need to get down to the surface from orbit comes into the atmosphere so fast that air resistance creates massive amounts of (wasted) heat, and stuff we need to get up into orbit from the surface uses enormous amounts of energy to accelerate the payload, and also to accelerate the fuel for later stages etc.

Hypothetical future technologies such as an astronomically expensive (in terms of initial construction cost) "space-elevator" allow for a simpler route in and out of the surface, but with caveat - the energy to put material "into orbit" must be balanced by material being de-orbited.

Once can imagine the following stages:

  1. Planet contains significant quantities of a very valuable resource (gold, platinum, "unobtainium", etc.), which the civilisation wants to relocate elsewhere.
  2. First factories are built on planet using "traditional techniques" in order to build rockets to get the valuable resource off the planet.
  3. This quickly uses up the readily-available resources that are common elsewhere in the galaxy (steel needed for the factories), but to get more of the valuable resource off the planet, it's economical to ship in more common materials.
  4. Massive construction project for "space elevator" or similar to efficiently get new materials for factories in, and valuable resources out. Indeed, as the economics of this are the same throughout the planet, many space elevators are constructed by competing investors keen to maximise the amount of the valuable resource they can extract.
  5. Due to nature of the "space elevator", all the valuable resources being exported need to be balanced by something arriving, so raw material imports are heavily subsidised making industry very economical. Export costs are expensive, so most of the imported material goes into building more industry rather than being exported.
  6. As the valuable resource becomes depleted and eventually exhausted, export costs and import costs become balanced. The astronomical costs of the space elevators were paid for by the export of the now-exhausted resource. The huge industrial complexes that are already built, coupled a low marginal cost of importing and exporting materials from the world makes a heavy industry the most economical use of the planet in its current condition.

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