Superstructure of the Week: Alderson Disk

Named after Dan Alderson, a NASA scientist who had a love for science fiction, the Alderson Disk is probably the most ambitious megastructure ever conceived. This theoretical structure is shaped in the form of a compact disk – but blown up to nearly incomprehensible proportions. With billions of time the surface area of Earth, the Alderson Disk is able to house trillions of life forms. One science fiction author, Charles Stross, decided to use this megastructure as the setting for his novella Missile Gap.

Stross, Charles - Missile GapIn Stross’s story, the world of Cold War politics is turned upside down when everyone wakes up one day to find that the world is completely flat. What was once the Earth has now been transposed onto a flat surface that extends millions of miles in every direction. One of the most notable things is that the nuclear stockpile both the Soviet Union and the United States have is nearly useless. This is a result in gravity not following in concordance to the inverse square law, but rather constant when perpendicular to the surface. Number of other unusual instances come up as well – off in the distance is a large flame that comes up every day to simulate the day and night cycle of humanity’s original terrestrial planet. It is soon discovered that humans are not the only ones on the disk – a constantly evolving insect like creature also shares the surface with them.

The Malibu Comics Ultraverse series touched on the Alderson Disk in their series called Godwheel. In it, the Godwheel was a flat plane that had a diameter that started from 48 million kilometers and extended outward to 640 million kilometers. The primary arc of the story takes place on one side of the disk – on this side magic reigns supreme but is noted that on the opposing side is a robot based civilization that follows science. The center of the Godwheel contains a binary star system that serves to give heat and light to the inhabitants. Much of this Alderson Disk remains unknown and is heavily implied that the civilization that built it had collapsed long ago.

In Robert Freitas’ 1975 book Xenology: A Study of Extraterrestrial Life, Intelligence Civilization, he devotes an entire chapter to the calculations of theoretical superstructures. Calculated at an outer limit of 600 million kilometers – approximately area spanning from our sun to the area between the asteroid belt and Jupiter – and a thickness of 5000 kilometers, Freitas surmises that an Alderson Disk of this size would have a mass of 6 decillion (6 x 10^36) kilograms. Despite being so massive, such an object would only have a gravitational pull of .14 of that of Earth, or approximately the gravity of the moon. An atmospheric wall of a 1000 km or more would have to be erected around the center and outer rim, along with a series of wall delineating off different tropic zones of the disk.

Could this be built?

To call this a massive undertaking would be an understatement. The primary issue that comes with creating the Alderson Disk is that the vast majority of the surface would be uninhabitable by any single species. A collection of dozens, potentially hundreds, of highly advanced species would have to come together to create such an object. Because of its gargantuan size, the Alderson Disk would be subject to the constant threat of ripping itself apart. An exotic substance, similar to scirth from Larry Niven’s Ringworld, would be needed to keep it together. If such an object were to be created, the matter of hundreds of star systems would be needed. Robert Freitas’ calculates that about 500 tredecillion (5 x 10^44) joules worth of energy would go into just putting the Alderson Disk together. With so many powerful civilizations into building the Alderson Disk – or just one ludicrously advanced one – this energy expenditure would probably be trivial.

The final logistical challenge comes from the star itself. Typically a star makes up the vast majority of the mass in any solar system – our own star, Sol, makes up over 99% of our solar system’s mass. With the creation of the Alderson Disk, this mass distribution is turned on its head. In relative to the supermassive structure itself, the star could wander and damage the inside of the disk and disrupt its ecology. Because of this the star would have to be moved back into place – Freitas recommends a series of machines that would keep the star in a central point. In addition to this, these machines would serve to bob the star up and down giving the effect of a day and night cycle.

Admittedly, with such ridiculous numbers and overwhelming logistics that go into to creating the Alderson Disk the question is begged: Is it worth it? Even in the world of science fiction, the Alderson Disk is considered a ridiculous engineering feat. Ultimately a series of interconnected smaller structures might be more economically and technologically feasible than one enormous one. If such a civilization, or multiple civilizations, were ambitious enough to tackle such a project it would probably serve a dual purpose: The first advantage is immediately obvious, such an object would be able to cradle thousands of different civilizations and trillions of organisms on it. The second purpose would be that of propaganda. A fully functioning Alderson Disk would serve as a rallying point – such a civilization or alliance of civilizations that created such a mind boggling piece of engineering would be a force to be reckoned with.

Article by Logan LePage

Featured Image: Neil Blevins

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