Megastructures

We humans can build some big stuff. The Great Wall of China. The Burj Khalifa. The Hoover Dam. But for truly big structures – megastructures, if you will – we must turn to science fiction.

Megastructures in science fiction dwarf anything we’ve built on Earth. We might be able to build some of these theoretical structures in the future. Some might already exist out there in the galaxy, built by alien civilizations.

Let’s take a look at some science fiction megastructures.

ORBITAL RING

An orbital ring is a theoretical, ring-shaped structure that orbits around a central point. The inner surface of the ring provides living area. If the ring is large enough, living space is quite ample, greatly surpassing the surface area of Earth. Cities, forests, fields, lakes—they can all fit on the inner surface of the ring.

Meanwhile, the ring will spin, generating centrifugal force. This will create artificial gravity. The centrifugal force will also negate the need for a “roof.” By spinning, the ring can maintain an atmosphere. The air will “cling” to the ring like water clings to the bottom of a spinning bucket.

Orbital rings were popularized by Larry Niven’s seminal novel Ringworld. Other science fiction authors have included orbital rings in their universes. Banks Orbitals, a smaller version of Ringworlds, feature prominently in the Culture series. Bishop Rings, proposed by Forrest Bishop of the Institute of Atomic-Scale Engineering, are small orbitals with enough living space for millions of people.

O’NEILL CYLINDER

O'Neill Cylinders are theoretical “tube” habitats. Space colonists would live on the inner surface of the cylinder. The entire structure would spin, generating centrifugal force and thereby providing artificial gravity.

The interior of an O’Neill cylinder would be curved. Standing inside one, you would see the horizons curve upward. Far above, you would see colonists on the “roof,” walking upside down. If the cylinder’s radius were large enough, however, you would barely notice the curve. The surface would seem flat. The inside of the cylinder could support fields, gardens, rivers, and cities.

A famous O’Neill cylinder in science fiction is Rama, featured in Arthur C. Clark’s novel Rendezvous with Rama.

TOPOPOLIS

A topopolis is a cross between an Orbital Ring and an O’Neill Cylinder. In a sense, it’s an extremely long O’Neill cylinder which loops around a star. It can even loop around several times, forming a torus knot.

A topopolis would require massive amounts of matter to construct. Its total mass could equal or even eclipse the mass of a planet. But its inner surface area would be far larger than that of a planet, providing enough living space for trillions of humans (or aliens).

A topopolis appears in the 2008 novel Matter by Iain M. Banks. The 2020 novel Heaven’s River by Dennis E. Taylor prominently features a topopolis that is home to sentient, otter-like aliens.

ALDERSON DISK

An Alderson disk (named after its originator, Dan Alderson) is a massive artificial disk circling a star. It looks like a giant record, with the star fitting in the central hole. The disk will orbit the star, absorbing its energy. Living space can exist on either side of the disk.

The disk would stretch across a solar system like a solid ecliptic plane. Such a structure would include more mass than in the star it orbits, requiring matter collected from other solar systems.

An Alderson disk appears in Ian McDonald's novel Empress of the Sun.

WORMHOLE

A wormhole is a theoretical tunnel connecting two places in spacetime, allowing for faster-than-light travel. Starships could travel down the wormhole, crossing vast distances in short periods of time. In science fiction, wormholes serve a similar function to warp drive, allowing characters to travel through interstellar space.

Wormholes are, in a sense, a highway system between the stars.

DYSON SPHERE

A Dyson sphere is a megastructure designed to capture the full energy output of a star. It is a solid, artificial sphere the size of a solar system, completely enclosing a star. Solar panels (or analogous technology) along the inner surface capture the sun’s released energy.

The inner surface can also provide living space. The surface area will be millions of times larger than any planet offers.

A Dyson sphere would allow a civilization to fully harvest the energy of its star. Normally, only a very small percentage of a star’s solar energy reaches any particular planet. The rest is lost. A Dyson sphere would solve that problem. A sufficiently advanced, spacefaring civilization might construct Dyson spheres to meet its massive energy needs.

A spherical structure around a star was first proposed by Olaf Stapledon in his 1937 novel Star Maker. Freeman Dyson popularized the concept in his 1960 paper "Search for Artificial Stellar Sources of Infrared Radiation." Dyson proposed that alien civilizations might build such spheres, and that in the search for alien life, we should attempt to find them.

A Dyson swarm is an alternate version of a Dyson sphere, involving a large number of smaller structures (e.g. satellites with solar panels) that swarm around a star.

MATRIOSHKA BRAIN

A Matrioshka brain was proposed by Robert J. Bradbury in the anthology Year Million: Science at the Far Edge of Knowledge. The name is based on Matryoshka dolls, also known as Russian nesting dolls.

The Matryoshka is a megastructure on a truly enormous scale. It's comprised of nested Dyson spheres. The innermost sphere surrounds a star, absorbing its energy, which powers a central computer. This inner sphere releases huge amounts of waste heat. An enclosing sphere absorbs the waste energy, using it for its own computational purposes. It releases its own waste heat to the next layer, and so on. Sphere within sphere. The innermost sphere would run at nearly the temperature of the enclosed star, while each enclosing sphere would be a little cooler.

Know any other megastructures? Mention them in the comments!