The Best of Orion’s Arm

There are two types of fandom: the creative and the systematizing1. The creatives write fan fiction and draw fan art, the systematizers write the huge wikis, like Star Wars’ Wookiepedia or Star Trek’s Memory Alpha, where everything down to the life story of the cobbler who made Han Solo’s boots is neatly documented. But the franchise comes first: the books or the movies or TV show form the canon from which the facts are extracted and catalogued.

The Orion’s Arm Universe Project is a wiki without a franchise: it is a vast, sprawling, Borgesian wiki documenting the next ten thousand years of posthuman history. It’s been going twenty years, I’ve been reading it on and off since I was a teenager, since around 2009, and every time I visit the website I’ll find some article I’ve never read, scroll down, and see that it was published in 2001. The ratio of worldbuilding to storytelling is the highest of anything like it other than maybe SCP: there are a few stories, here and there, but the overwhelming majority of the content is in the form of wiki entries, describing history, places, technology, factions and science.

It’s mostly—for the first few thousand years, at least—hard science fiction, and it’s been a huge influence on how I view the future. The technologies and their consequences to the development of civilization are described so rigorously that it leaves little room for argument. The great thing about hard science fiction is it’s basically physics plus repeated application of modus ponens: two authors, starting with the same knowledge of physical law, and thinking with equal rigour, will reach more or less identical conclusions, because reality overconstrains everything.

The setting of Orion’s Arm is a vast, diverse galactic ecology, where baseline humans, transhumans, posthumans, uplifted animals, artificial intelligences all live in their ecological niches. A small number of incomprehensibly posthuman intelligences, the archailects, sit at the evolutionary apex. Terragen (Earth-originated) intelligence has settled a roughly spherical volume 14,000 light years across, and made the universe into a garden. It’s a refreshing change from the misanthropy and catastrophism of most popular science fiction.

The worldbuilding of The Epiphany of Gliese 581 was heavily inspired by the setting of Orion’s Arm. In fact, other than when choosing the place names and the names of the characters and the details of culture, I never felt that I was worldbuilding. Most of the tech tree is Orion’s Arm-inspired, but the more speculative things from OA (wormholes and reactionless propulsion) left over.

This article is an index of my favorite topics from the Orion’s Arm wiki.


  • The Argus Array: a vast interferometric telescope, made up of thousands of individual telescopes spread out across a thousand light year-wide volume. Each telescope is a supercooled black sphere 20AU across, absorption photons in every frequency, for a combined light gathering area of 1027 m2.

    … the light emitted from a one metre, sunlit object in Andromeda is sufficient to build an image in the Argus Array over a period of three standard years. Larger objects can be imaged more quickly- at the same distance, a 10km object can be seen by collecting photons over a period of just 10 seconds. This allows large-scale phenomena to be observed on the surfaces of planets, such as weather patterns”

  • Mass-Stream Technology: structures far beyond the tensile or compressive strength of any material can be built by having a stream of fast-moving particles traveling in a constant loop, exchanging momentum with the structure when they change direction at either end. Based on dynamic compression members by Paul Birch.
  • Conversion Drive: propulsion using monopole-catalyzed matter-to-energy conversion.
  • Boostbeam: a beam of charged particles that pushes a magnetic sail. A source of propulsion that avoids the tyranny of the rocket equation, since the ships don’t have to carry fuel themselves.
  • Angelnet: a pervasive utility fog surveillance and control system to protect sapients from accidents and violence. “All of the major modern archailect-ruled worlds and capitals are heavily angelnetted.”
  • Star Lifting: stars are inefficient, their light and heat is thrown away into space, and the larger they are, the less efficient they are, the larger stars consuming their store of hydrogen in mere tens of millions of years. Technological civilization can’t accept this waste. Star lifting is the removal of matter from a star, either as an exploitable natural resource or to extend the star’s life.

    At the limit you get a matrioshka hypernode, where the star is completely disassembled and its fuel is burned, efficiently, in fusion reactors, extending the star’s effective life past even the coldest-burning red dwarfs. At the limit of the limit, you get artificially-optimized galaxies, where the stars across an entire galaxy are starlifted to prolong their useful life.

  • Matrioshka Brain: a Dyson swarm dedicated entire to computation, built in concentric layers, each layer running off the waste heat of the more interior one.
  • Matrioshka Hypernode: while a Matrioshka brain runs off a star’s natural light output, in a Matrioshka hypernode the star is dismantled, and the energy comes from burning hydrogen in fusion or conversion reactors in a controlled manner.
  • Nicoll-Dyson Beams: phased-array lasers powered by the total power output of a Dyson sphere, capable of destroying objects tens of light years away.


  • Artificially Optimised Galaxies: distant galaxies that alien species have optimized for long-term habitation, using the stars’ own power to starlift hydrogen into gas giants and brown dwarfs, so it can be burned efficiently (in fusion or conversion reactors) and last far longer than stellar fusion.
  • Lazurogenics: recreation of extinct species from the genetic, fossil, or historical record.

  • The Tranquility Calendar: the calendar system used in Orion’s Arm counts time from the moon landing, from the moment of the transmission: “Houston, Tranquility Base here. The Eagle has landed”. Dates are given in AT and BT.

  • Cliotelescopy: the use of high-resolution telescopy to study the past.


  • Duxed: a moon of a gas giant with an extreme tidal range, with tides reaching two kilometers up.
  • Wadai: a small ringworld around the white dwarf Eggen-Greenstein 471, built entirely without exotic matter and held together by dynamic compression members.
  • Black Acropolis: an abandoned Dyson swarm built by an extinct alien civilization.
  • Oceanus Ultimata: ringworld + waterworld. A dense ring of immense water droplets floating around a star, protected from vacuum by membranes of nanotechnology. They bump and merge and come apart and are filled with alien life.
  • Earth: largely depopulated and under the control of the local deity, bent on restoring and preserving the ecosystem as it was before the Holocene.


  • The Tragedy of the G995: a starwisp carrying uploaded humans is blown off course. The ship coasts for centuries, unseen, and the crew are unable to change the VR environment’s clock rate or put their minds in hibernation.

Alien Civilizations

Much of this was merged from another world-building project from the early 2000’s, the website of the Hamilton Institute of Exopalentology, which was translated into Orion’s Arm with the name intact.

The alien civilizations and artifacts are some of my favorite content from Orion’s Arm, despite being the most speculative. This is the part of the worldbuilding with the highest concentration of Lovecraftian horror.

  • Asoka’s Pillar: a cylindrical Dyson shell around a lone star floating high above the galaxy, broadcasting a signal saying it is the center of a vast galaxy-spanning empire. If such an empire existed, it no longer does. Perhaps it never did. Who broadcasts the message? An automated system? A mad superintelligence?
  • The Empire of Screaming Skulls: this has to be my favorite. An alien species in a galaxy 200 million light years away, known only from remote observations. Their space habitats are shaped like the head of an insect, with four empty eye sockets and mandible-like appendages. They are observed in pairs, orbiting their common barycenter and facing each other.
  • SMBH Civilisation: an alien civilization, living around the black hole at the center of a galaxy 200 million light years away. Around the black hole are over a million artificial planets, orbiting one after the other in hundreds of distinct orbits, like a Bohr atom, and each moves at 5% of the speed of light.
  • Daidarabotchi Megadyson: fourteen billion light years away, a Dyson shell almost 300 light years in diameter, moving at half the speed of light, a centikelvin above the temperature of the cosmic microwave background. Occasionally a star punches a hole through it, and the shell rebuilds itself in place.
  • Leo Hyperobject 1: an artificial object in a galaxy 300 million light years away, twice the mass of the Milky Way, 1.2 light years in diameter.
  • The Deep Traveler: a Dyson shell, millions of light years away, moving at half the speed of light through intergalactic space.
  • Dead Drifter: a dead alien in a space suit, dated to 190 megayears before present, the holotype of an extinct alien species known only from this single space burial.
  • Makers: an extinct alien species, the first to be discovered by humans, in the form of a derelict probe floating near Epsilon Sculptoris.
  • HIE-236-PPE: an extinct alien species known only from their efforts to terraform various planets into Titan-like ecologies. Nothing else is known about them.
  • Batholith Civilization: an extinct alien civilization whose planet was irradiated by a gamma ray burst. They took refuge in tunnels in a granite batholith, and gradually died out.
  • The Trader: a fleet of six alien spacecraft traveling in close formation, using a Lorentz force tether to travel in a circular trajectory around the galaxy.
  • The Iahi Daon Empire: an extinct alien civilization, known from the derelict generation ships they sent out before collapsing.
  • Ultima Gate: an alien wormhole, guarded by a heavily armed alien fleet, whose destination is unknown.


  1. I read this on Tumblr somewhere.