User:Viriditas/Computing megastructure

Matrioshka brain
A matrioshka brain is a hypothetical megastructure, based on the Dyson sphere, of immense computational capacity. It is an example of a Class B stellar engine, employing the entire energy output of a star to drive computer systems. This structure has clear structural analogies to Russian Matrioshka dolls, from which the concept derives its name.

Such a structure would be composed of one or more (typically more) Dyson spheres built around a star, and nested one inside another. A significant percentage of the shells would be composed of nanoscale computers (see molecular-scale computronium). These computers would be at least partly powered by the energy exchange between the star and interstellar space. A shell (or component, should a Dyson swarm be the design model used) would absorb energy radiated onto its inner surface, utilize that energy to power its computer systems, and re-radiate the energy outwards. The nanoscale computers of each shell would be designed to run at different temperatures; shells or components at the core could be nearly as hot as the central star, while the outer layer of the matrioshka brain could be almost as cool as interstellar space.

The ideal mechanism for extracting usable energy as it passes "through" a shell or component, the number of shells (or orbital levels) that could be supported in such a manner, the ideal size of the shells to be constructed, and other details, are all issues of speculation.

The idea of the matrioshka brain violates none of the currently known laws of physics, although the engineering details of building such a structure would be staggering, as such a project would require the "disassembly" of significant portions (if not all) of the planetary system of the star for construction materials.

The term matrioshka brain was invented by Robert Bradbury as an alternative to the Jupiter Brain - a concept similar to the matrioshka brain, but on a smaller planetary scale and optimized for minimum signal propagation delay. A matrioshka brain design is concentrated on sheer capacity and the maximum amount of energy extracted from its source the star, while a Jupiter Brain more on computational speed.

The possible uses of such an immense computational resource tax the imagination. One idea suggested by Charles Stross, in his novel Accelerando, would be to use it to run perfect simulations or "uploads" of human minds into virtual reality spaces supported by the Matrioshka brain. Stross even went so far as to suggest that a sufficiently godlike species utilizing enough raw processing power could launch attacks upon, and manipulate, the structure of the universe itself. In Godplayers (2005), Damien Broderick surmises that a matrioshka brain would allow simulating entire alternate universes.

Jupiter brain
A Jupiter brain is a theoretical computing megastructure the size of a planet. Unlike a matrioshka brain, a Jupiter brain is optimized for minimum signal propagation delay, and so has a compact structure. Power generation and heat dissipation are formidable concerns for a Jupiter brain implementation.

While a rigid solid object the size and mass of a rocky planet or gas giant could not be built using any known material, such a structure could be built as a low-density lattice with a mass comparable to a large moon or a small rocky planet but a far larger volume, or as a solid but non-rigid structure with the mass and density of a planet (as long as the internal heat gradient is carefully controlled to prevent convection).

Fiction
In addition, Marvin the Paranoid Android from the same series complains of having a "brain the size of a planet" but not having any use for it, and thus being terminally bored. He may be indulging in hyperbole, but in the DVD edition of the 1981 television series it is implied that his brain is indeed the size of a planet; it's just not inside his body. In Life, the Universe and Everything, also by Douglas Adams, Hactar is a planet-sized computer who was ordered to construct a weapon of universal destruction. However, he found the idea distasteful and deliberately introduced a flaw into the design he came up with. When his masters learned of this, they pulverized Hactar, greatly diminishing his powers but failing to destroy his consciousness in the process.
 * Earth is a form of Jupiter brain in The Hitchhiker's Guide to the Galaxy by Douglas Adams. Built by the Magratheans and commissioned by mice, it is frequently mistaken for a planet by its inhabitants (who are part of the program to determine the question of "Life, the Universe and Everything", given the answer 42 found by Deep Thought).


 * One of the main "characters" in Ken MacLeod's The Cassini Division is the planet Jupiter, which is the home of transhumanists who uploaded their personalities.


 * In The Well of Souls series by Jack L. Chalker, the Well of Souls is a Jupiter brain which is tasked with maintaining the physical state of the current universe.


 * In Revelation Space by Alastair Reynolds, the neutron star Hades is a Jupiter brain which stored the minds of and so preserved the corporeally extinct race of the Amarantin.


 * In The Last Question by Isaac Asimov, the Multivac predecessor is the size of a planet.


 * In The Dark Side of the Sun by Terry Pratchett, the First Syrian Bank is a sentient computer/planet, composed of silicon formations that have gradually evolved into natural synapses.


 * In the MMOFPS PlanetSide, the planet Auraxis is revealed to be an artificial construct created by the ancient Vanu.


 * In DC comics, Mogo of the Green Lantern Corps is a sentient planet, though it is not clear whether he is a Jupiter Brain or simply a natural planet-bodied lifeform.