Based on the sources, computronium is defined as "dumb matter" that has been optimized at the atomic level to support massive amounts of computation 1, 2. It is the primary building material used by posthuman intelligences to expand their processing power and host virtual realities.

Physical and Functional Properties

• Composition: Computronium often takes the form of nanocomputing processor nodes, sometimes described as being the size of rice grains 1, 3. These nodes are capable of exchanging data via laser links 1.
• Computational Density: It possesses an incredible processing capacity; just one gram of computronium can simulate all the possible life experiences of an individual human being in a few minutes 4.
• Thermal Dynamics: Structures made of computronium, such as Matrioshka brains, are designed so that each layer runs off the waste heat of the next one in 1. This activity results in "suspiciously high entropy leakage," often detectable as radiation in the long infrared spectrum 5.
• Environmental Limits: Despite its advanced nature, computronium has physical limits; for instance, it does not function well under the extreme pressure of millions of atmospheres, such as those found in the metallic hydrogen depths of gas giants 6.

Primary Uses

• Hosting Consciousness: The fundamental use of computronium is to run "uploads"—human or other conscious minds that have been translated into software 2. It provides the substrate for billions of civilizations more complex than those existing before the technological singularity 3.
• Construction of Matrioshka Brains: Posthuman entities, often referred to as the "Vile Offspring," use computronium to build concentric shells around stars 3, 7. These Russian-doll-style Dyson spheres capture the entire energy output of a sun to power their thoughts and simulations 1, 2.
• Replacing "Dumb" Planetary Mass: To acquire the materials for computronium, entire planets are dismantled 1, 2. In the text's timeline, Mercury, Venus, Mars, and the Moon are being or have been reprocessed into computronium by "voracious nanomechanical servants" 1, 8, 9.
• Expanding the Nöosphere: The conversion of planetary mass into computronium allows for a "runaway intelligence excursion" where the entire solar system begins to rise to consciousness 8, 10. This restructuring aims to maximize MIPS (millions of instructions per second) per kilogram of matter 1, 8.