The simulation hypothesis or simulation theory is the proposal that all of reality, including the Earth and the rest of the universe, could in fact be an artificial simulation, such as a computer simulation. Some versions rely on the development of a simulated reality, a proposed technology that would be able to convince its inhabitants that the simulation was "real". The simulation hypothesis bears a close resemblance to various other skeptical scenarios from throughout the history of philosophy. The hypothesis was popularized in its current form by Nick Bostrom. The suggestion that such a hypothesis is compatible with all of our perceptual experiences is thought to have significant epistemological consequences in the form of philosophical skepticism. Versions of the hypothesis have also been featured in science fiction, appearing as a central plot device in many stories and films.
Origins
There is a long philosophical and scientific history to the underlying thesis that reality is an illusion. This skeptical hypothesis can be traced back to antiquity; for example, to the "Butterfly Dream" of Zhuangzi, or the Indian philosophy of Maya, or in Ancient Greek philosophy Anaxarchus and Monimus likened existing things to a scene-painting and supposed them to resemble the impressions experienced in sleep or madness.
A version of the hypothesis was also theorised as a part of a philosophical argument by René Descartes.
Simulation hypothesis
Nick Bostrom's premise:
Many works of science fiction as well as some forecasts by serious technologists and futurologists predict that enormous amounts of computing power will be available in the future. Let us suppose for a moment that these predictions are correct. One thing that later generations might do with their super-powerful computers is run detailed simulations of their forebears or of people like their forebears. Because their computers would be so powerful, they could run a great many such simulations. Suppose that these simulated people are conscious (as they would be if the simulations were sufficiently fine-grained and if a certain quite widely accepted position in the philosophy of mind is correct). Then it could be the case that the vast majority of minds like ours do not belong to the original race but rather to people simulated by the advanced descendants of an original race.
Nick Bostrom's conclusion:
It is then possible to argue that, if this were the case, we would be rational to think that we are likely among the simulated minds rather than among the original biological ones.
Therefore, if we don't think that we are currently living in a computer simulation, we are not entitled to believe that we will have descendants who will run lots of such simulations of their forebears.
— Nick Bostrom, Are you living in a computer simulation?, 2003
The simulation argument
In 2003, philosopher Nick Bostrom proposed a trilemma that he called "the simulation argument". Despite the name, Bostrom's "simulation argument" does not directly argue that we live in a simulation; instead, Bostrom's trilemma argues that one of three unlikely-seeming propositions is almost certainly true:
- "The fraction of human-level civilizations that reach a posthuman stage (that is, one capable of running high-fidelity ancestor simulations) is very close to zero", or
- "The fraction of posthuman civilizations that are interested in running simulations of their evolutionary history, or variations thereof, is very close to zero", or
- "The fraction of all people with our kind of experiences that are living in a simulation is very close to one."
The trilemma points out that a technologically mature "posthuman" civilization would have enormous computing power; if even a tiny percentage of them were to run "ancestor simulations" (that is, "high-fidelity" simulations of ancestral life that would be indistinguishable from reality to the simulated ancestor), the total number of simulated ancestors, or "Sims", in the universe (or multiverse, if it exists) would greatly exceed the total number of actual ancestors.
Bostrom goes on to use a type of anthropic reasoning to claim that, if the third proposition is the one of those three that is true, and almost all people with our kind of experiences live in simulations, then we are almost certainly living in a simulation.
Bostrom claims his argument goes beyond the classical ancient "skeptical hypothesis", claiming that "...we have interesting empirical reasons to believe that a certain disjunctive claim about the world is true", the third of the three disjunctive propositions being that we are almost certainly living in a simulation. Thus, Bostrom, and writers in agreement with Bostrom such as David Chalmers, argue there might be empirical reasons for the "simulation hypothesis", and that therefore the simulation hypothesis is not a skeptical hypothesis but rather a "metaphysical hypothesis". Bostrom states he personally sees no strong argument as to which of the three trilemma propositions is the true one: "If (1) is true, then we will almost certainly go extinct before reaching posthumanity. If (2) is true, then there must be a strong convergence among the courses of advanced civilizations so that virtually none contains any individuals who desire to run ancestor-simulations and are free to do so. If (3) is true, then we almost certainly live in a simulation. In the dark forest of our current ignorance, it seems sensible to apportion one's credence roughly evenly between (1), (2), and (3)... I note that people who hear about the simulation argument often react by saying, 'Yes, I accept the argument, and it is obvious that it is possibility #n that obtains.' But different people pick a different n. Some think it obvious that (1) is true, others that (2) is true, yet others that (3) is true."
As a corollary to the trilemma, Bostrom states that "Unless we are now living in a simulation, our descendants will almost certainly never run an ancestor-simulation."
Criticism of Bostrom's anthropic reasoning
Bostrom argues that if "the fraction of all people with our kind of experiences that are living in a simulation is very close to one", then it follows that we probably live in a simulation. Some philosophers disagree, proposing that perhaps "Sims" do not have conscious experiences the same way that unsimulated humans do, or that it can otherwise be self-evident to a human that they are a human rather than a Sim. Philosopher Barry Dainton modifies Bostrom's trilemma by substituting "neural ancestor simulations" (ranging from literal brains in a vat, to far-future humans with induced high-fidelity hallucinations that they are their own distant ancestors) for Bostrom's "ancestor simulations", on the grounds that every philosophical school of thought can agree that sufficiently high-tech neural ancestor simulation experiences would be indistinguishable from non-simulated experiences. Even if high-fidelity computer Sims are never conscious, Dainton's reasoning leads to the following conclusion: either the fraction of human-level civilizations that reach a posthuman stage and are able and willing to run large numbers of neural ancestor simulations is close to zero, or we are in some kind of (possibly neural) ancestor simulation.
Some scholars categorically reject—or are uninterested in—anthropic reasoning, dismissing it as "merely philosophical", unfalsifiable, or inherently unscientific.
Some critics propose that we could be in the first generation, and all the simulated people that will one day be created do not yet exist.
The cosmologist Sean M. Carroll argues that the simulation hypothesis leads to a contradiction: if a civilization is capable of performing simulations, then it will likely perform many simulations, which implies that we are most likely at the lowest level of simulation (from which point one's impression will be that it is impossible to perform a simulation), which contradicts the arguer's assumption that it is easy for us to foresee that advanced civilizations can most likely perform simulations.
Arguments, within the trilemma, against the simulation hypothesis
Some scholars accept the trilemma, and argue that the first or second of the propositions are true, and that the third proposition (the proposition that we live in a simulation) is false. Physicist Paul Davies deploys Bostrom's trilemma as part of one possible argument against a near-infinite multiverse. This argument runs as follows: if there were a near-infinite multiverse, there would be posthuman civilizations running ancestor simulations, and therefore we would come to the untenable and scientifically self-defeating conclusion that we live in a simulation; therefore, by reductio ad absurdum, existing multiverse theories are likely false. (Unlike Bostrom and Chalmers, Davies (among others) considers the simulation hypothesis to be self-defeating.)
Some point out that there is currently no proof of technology which would facilitate the existence of sufficiently high-fidelity ancestor simulation. Additionally, there is no proof that it is physically possible or feasible for a posthuman civilization to create such a simulation, and therefore for the present, the first proposition must be true. Additionally there are limits of computation.
Consequences of living in a simulation
Economist Robin Hanson argues a self-interested high-fidelity Sim should strive to be entertaining and praiseworthy in order to avoid being turned off or being shunted into a non-conscious low-fidelity part of the simulation. Hanson additionally speculates that someone who is aware that he might be a Sim might care less about others and live more for today: "your motivation to save for retirement, or to help the poor in Ethiopia, might be muted by realizing that in your simulation, you will never retire and there is no Ethiopia."
Testing the hypothesis physically
A method to test one type of simulation hypothesis was proposed in 2012 in a joint paper by physicists Silas R. Beane from the University of Bonn (now at the University of Washington, Seattle), and Zohreh Davoudi and Martin J. Savage from the University of Washington, Seattle. Under the assumption of finite computational resources, the simulation of the universe would be performed by dividing the continuum space-time into a discrete set of points. In analogy with the mini-simulations that lattice-gauge theorists run today to build up nuclei from the underlying theory of strong interactions (known as quantum chromodynamics), several observational consequences of a grid-like space-time have been studied in their work. Among proposed signatures is an anisotropy in the distribution of ultra-high-energy cosmic rays, that, if observed, would be consistent with the simulation hypothesis according to these physicists. In 2017, Campbell et al. proposed several experiments aimed at testing the simulation hypothesis in their paper "On Testing the Simulation Theory".
In 2019, philosopher Preston Greene suggested that it may be best not to find out if we're living in a simulation since, if it were found to be true, such knowing may end the simulation.
Other uses of the simulation hypothesis in philosophy
Besides attempting to assess whether the simulation hypothesis is true or false, philosophers have also used it to illustrate other philosophical problems, especially in metaphysics and epistemology. David Chalmers has argued that simulated beings might wonder whether their mental lives are governed by the physics of their environment, when in fact these mental lives are simulated separately (and are thus, in fact, not governed by the simulated physics). They might eventually find that their thoughts fail to be physically caused. Chalmers argues that this means that Cartesian dualism is not necessarily as problematic of a philosophical view as is commonly supposed, though he does not endorse it.
In popular culture
The first to state the basic concept of reality as a simulation was Plato in 380BCE, in the famous Allegory of the Cave, describing people imprisoned since childhood (but not since birth) led to believe that artificial light-based representations of reality were truly real when, in fact, they were a fabricated illusion.
Science fiction themes
Science fiction has highlighted themes such as virtual reality, artificial intelligence and computer gaming for more than fifty years. Simulacron-3 (1964) by Daniel F. Galouye (alternative title: Counterfeit World) tells the story of a virtual city developed as a computer simulation for market research purposes, in which the simulated inhabitants possess consciousness; all but one of the inhabitants are unaware of the true nature of their world. The book was made into a German made-for-TV film called World on a Wire (1973) directed by Rainer Werner Fassbinder. The movie The Thirteenth Floor (1999) was also loosely based on this book. "We Can Remember It for You Wholesale" is a short story by American writer Philip K. Dick, first published in The Magazine of Fantasy & Science Fiction in April 1966, and was the basis for Total Recall (1990 film) and Total Recall (2012 film). In Overdrawn at the Memory Bank, a 1983 television movie, the main character pays to have his mind connected to a simulation.
The 1993 Star Trek: The Next Generation episode "Ship in a Bottle" explores the idea of people being unaware they are living in simulation, with Picard postulating at the end that perhaps they are also in a simulation playing out in a box on a table. This is also a possible use of dramatic irony, with both the actors and audience aware the television programme is indeed a simulation of sorts.
The same theme was repeated in the 1999 film The Matrix, which depicted a world in which artificially intelligent robots enslaved humanity within a simulation set in the contemporary world. The 2012 play World of Wires was partially inspired by the Bostrom essay on the simulation hypothesis. In the episode "Extremis" (broadcast on 20 May 2017 on BBC One) of the science fiction series Doctor Who, aliens called "The Monks" plan an invasion of Earth by running and studying a holographic simulation of Earth with conscious inhabitants. When the virtual Doctor finds out about the simulation he sends an email about the simulation to his real self so that the real Doctor can save the world. In the first season of Rick and Morty, a science-fiction animated comedy, the episode "M. Night Shaym-Aliens!" (2014) aliens trap the lead role (Rick) in a simulated reality in order to trick him into revealing his formula for concentrated dark matter. The hypothesis also serves as the climax of No Man's Sky's overarching plot, in which it was revealed that the game's setting itself was a simulation and that the player character is a member of a race made to explore it. In the game Xenoblade Chronicles, it is revealed that the whole world of the gods Bionis and Mechonis was a simulation run by Alvis, the administrative computer of a phase transition experiment facility (heavily implied to be "Ontos" in Xenoblade Chronicles 2) after Klaus destroyed the universe in a multiverse experiment.
