A matrioshka brain is a hypothetical megastructure proposed by Robert Bradbury, 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 concept derives its name from Russian Matrioshka dolls. The concept was deployed by its inventor, Robert Bradbury, in the anthology Year Million: Science at the Far Edge of Knowledge, and attracted interest from reviewers in the Los Angeles Times and the Wall Street Journal.
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Concept
A "matrioshka brain" comes from the idea of using Dyson spheres around a star as a gigantic computer. Matrioshka dolls are Russian nested dolls, where smaller ones fit inside larger ones; similarly, the brain would be nested Dyson spheres, drawing most or all of their power from the star and propagating it up out through the shells. The inner shells could run at almost the same temperature as the star itself, while the outer ones would be almost at the temperature of interstellar space. The engineering requirements and resources needed for this would be enormous.
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 minimal signal propagation delay. A matrioshka brain design is concentrated on sheer capacity and the maximum amount of energy extracted from its source star, while a Jupiter brain is more optimized for computational speed.
Possible uses
Some possible uses of such an immense computational resource have been proposed. 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 powerful 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. The futurist and transhumanist author Anders Sandberg wrote an essay speculating on implications of computing on the massive scale of machines such as the matrioshka brain, published by the Institute for Ethics and Emerging Technologies.