A Matryoshka Brain is a theoretical type of megastructure built around using the sheer power output of a Dyson Swarm-like construction, but rather than use that power to create food and sustain life it would all be used to power a computer… a computer so vast with so many interconnected circuits that it would need to compartmentalize its processes to avoid problems with relativity and time lag, and uses the vastness of its construction as a form of cooling, radiating away excess energy after it has already been used to power calculations.
Named after the Russian Nesting Dolls because of their construction, a Matrioshka Brain would be several Dyson Swarms nested inside one another. The innermost Dyson Swarm of the Matrioshka Brain would draw energy directly from the star it surrounds and give off large amounts of waste heat while computing at a high temperature. The next surrounding Dyson Swarm would absorb this waste heat and use it for its computational purposes, all while giving off waste heat of its own. This heat would be absorbed by the next sphere, and so on, with each sphere radiating at a lower temperature than the one before it. For this reason, Matrioshka brains with more nested Dyson Swarms would tend to be more efficient, as they would waste less heat energy, and also more powerful as the outermost layer will always be the most powerful, and the more layers there are the larger and more efficient that final layer will be. Ideally, the outer layer’s temperature would be close to that of ambient interstellar space.
The sheer amount of processing power possible using one of these defies imagination. More than one scientist has noted that simulating whole realities is easily within the capabilities of such computing power – this is the origin point of Supposition 1 of Nick Bostrum’s famous Simulation Hypothesis, which we will not be going into here. Many more things are possible with this degree of usable calculation.