Permutation City is a 1994 science-fiction novel by Greg Egan that explores many concepts, including quantum ontology, through various philosophical aspects of artificial life and simulated reality. Sections of the story were adapted from Egan's 1992 short story "Dust", which dealt with many of the same philosophical themes. Permutation City won the John W. Campbell Award for the best science-fiction novel of the year in 1995 and was nominated for the Philip K. Dick Award the same year. The novel was also cited in a 2003 Scientific American article on multiverses by Max Tegmark.
Themes and setting Permutation City asks whether there is a difference between a computer simulation of a person and a "real" person. It focuses on a model of consciousness and reality, the Dust Theory, similar to the Ultimate Ensemble Mathematical Universe hypothesis proposed by Max Tegmark. It uses the assumption that human consciousness is Turing-computable: that consciousness can be produced by a computer program. The book deals with consequences of human consciousness being amenable to mathematical manipulation, as well as some consequences of simulated realities. In this way, Egan attempts to deconstruct notions of self, memory, and mortality, and of physical reality. The Autoverse is an artificial life simulator based on a cellular automaton complex enough to represent the substratum of an artificial chemistry. It is deterministic, internally consistent and vaguely resembles real chemistry. Tiny environments, simulated in the Autoverse and filled with populations of a simple, designed lifeform, Autobacterium lamberti, are maintained by a community of enthusiasts obsessed with getting A. lamberti to evolve, something the Autoverse chemistry seems to make extremely difficult. Related explorations go on in virtual realities (VR), which make extensive use of patchwork heuristics to crudely simulate immersive and convincing physical environments, albeit at a maximal speed of seventeen times slower than "real" time, limited by the optical crystal computing technology used at the time of the story. Larger VR environments, covering a greater internal volume in greater detail, are cost-prohibitive even though VR worlds are computed selectively for inhabitants, reducing redundancy and extraneous objects and places to the minimal details required to provide a convincing experience to those inhabitants; for example, a mirror not being looked at would be reduced to a reflection value, with details being "filled in" as necessary if its owner were to turn their model-of-a-head towards it. Within the story, "Copies" – digital renderings of human brains with complete subjective consciousness, the technical descendants of ever more comprehensive medical simulations – live within VR environments after a process of "scanning". Copies are the only objects within VR environments that are simulated in full detail, everything else being produced with varying levels of generalisation, lossy compression, and hashing at all times. Copies form the conceptual spine of the story, and much of the plot deals directly with the "lived" experience of Copies, most of whom are copies of billionaires suffering terminal illnesses or fatal accidents, who spend their existences in VR worlds of their creating, usually maintained by trust funds, which independently own and operate large computing resources for their sakes, separated physically and economically from most of the rest of the world's computing power, which is privatized as a fungible commodity. Although the wealthiest copies face no financial difficulties, they can still be threatened because copies lack political and legal rights (they are considered software), especially where the global economy is in recession. Hence they cannot afford to retreat into solipsism and ignore what is happening in the real world. At the opposite end from the wealthy Copies are those who can only afford to live in the virtual equivalent of "Slums", being bounced around the globe to the cheapest physical computing available at any given time in order to save money, while running at much slower speeds compared to the wealthy Copies. Their slowdown rate depends on how much computer power their meager assets can afford, as computer power is traded on a global exchange and goes to the highest bidder at any point in time. When they cannot afford to be "run" at all, they can be frozen as a "snapshot" until computer power is relatively affordable again. A Copy whose financial assets can only generate sufficient interest to run at a very slow rate is stuck in a rut because he/she/it becomes unemployable and is unable to generate new income, which may lead to a downward spiral. By creating this scenario, Egan postulates a world where economic inequality can persist even in one's (virtual) afterlife. The concept of solipsism is also examined prominently, with many less-wealthy Copies attending social functions called Slow Clubs, where socialising Copies agree to synchronise with the slowest person present. Many of these less-wealthy Copies become completely deracinated from their former lives and from world events, or else become Witnesses, who spend their time observing (at considerable time lapse) world events unfold, at the cost of any meaningful relationships with their fellow Copies. A subculture of lower/middle-class Copies, calling themselves Solipsist Nation after a philosophical work by their nominal founder, choose to completely repudiate the "real" world and any Copies still attached to it, reprogramming their models-of-brains and their VR environments in order to design themselves into their own personal vision of paradise, of whatever size and detail, disregarding slowdown in the process. Egan's later novels Diaspora and Schild's Ladder deal with related issues from other perspectives.
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