Simulation hypothesis


The simulation hypothesis proposes that what one experiences as the real world is actually a simulated reality, such as a computer simulation in which humans are constructs. There has been much debate over this topic in the philosophical discourse, and regarding practical applications in computing.
Variations of the simulation hypothesis essentially originate from, or are offshoots of, the dream hypothesis popularized by ancient philosophers like Zhuangzi and early modern philosophers like René Descartes. In 2003, philosopher Nick Bostrom proposed the simulation argument suggesting that if a civilization becomes capable of creating conscious simulations, it could generate so many simulated beings that a randomly chosen conscious entity would almost certainly be in a simulation. This argument presents a trilemma:
  1. either such simulations are not created because of technological limitations or self-destruction;
  2. advanced civilizations choose not to create them;
  3. if advanced civilizations do create them, the number of simulations would far exceed base reality and we would therefore almost certainly be living in one.
This assumes that consciousness is not uniquely tied to biological brains but can arise from any system that implements the right computational structures and processes.
The hypothesis is preceded by many earlier versions, and variations on the idea have also been featured in science fiction, appearing as a central plot device in many stories and films, such as Simulacron-3 and The Matrix.

Origins

Human history is full of thinkers who observed the difference between how things seem and how they might actually be, with dreams, illusions, and hallucinations providing poetic and philosophical metaphors. For example, the "Butterfly Dream" of Zhuangzi from ancient China, or the Indian philosophy of Maya, or in ancient Greek philosophy, where Anaxarchus and Monimus likened existing things to a scene-painting and supposed them to resemble the impressions experienced in sleep or madness. Aztec philosophical texts theorized that the world was a painting or book written by the Teotl. A common theme in the spiritual philosophy of the religious movements collectively referred to by scholars as Gnosticism was the belief that reality as we experience it is the creation of a lesser, possibly malevolent, deity, from which humanity should seek to escape.
In the Western philosophical tradition, Plato's allegory of the cave analogized human beings to chained prisoners unable to see reality. René Descartes' evil demon philosophically formalized these epistemic doubts, to be followed by a large literature with subsequent variations like brain in a vat. In 1969, Konrad Zuse published his book Calculating Space on automata theory, in which he proposed the idea that the universe was fundamentally computational, a concept which became known as digital physics. Later, roboticist Hans Moravec explored related themes through the lens of artificial intelligence, discussing concepts like mind uploading and speculating that our current reality might itself be a computer simulation created by future intelligences.

Simulation argument

's premise:
Bostrom's conclusion:

Expanded argument

In 2003, Bostrom proposed a trilemma that he called "the simulation argument". Despite its name, the "simulation argument" does not directly argue that humans live in a simulation; instead, it argues that one of three unlikely-seeming propositions is almost certainly true:
  1. "The fraction of human-level civilizations that reach a posthuman stage is very close to zero", or
  2. "The fraction of posthuman civilizations that are interested in running simulations of their evolutionary history, or variations thereof, is very close to zero", or
  3. "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 "ancestor simulations" were run, the total number of simulated ancestors, or "Sims", in the universe would greatly exceed the total number of actual ancestors.
Bostrom uses 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 live in simulations, then humans are almost certainly living in a simulation.
Bostrom's argument rests on the premise that given sufficiently advanced technology, it would be possible to represent the populated surface of the Earth without recourse to digital physics; that the qualia experienced by a simulated consciousness are comparable or equivalent to those of a naturally occurring human consciousness, and that one or more levels of simulation within simulations would be feasible given only a modest expenditure of computational resources in the real world.
Bostrom argues that if one assumes that humans will not be destroyed nor destroy themselves before developing such a technology, and that human descendants will have no overriding legal restrictions or moral compunctions against simulating biospheres or their own historical biosphere, then it would be unreasonable to count ourselves among the small minority of genuine organisms who, sooner or later, will be vastly outnumbered by artificial simulations.
Epistemologically, it is not impossible for humans to tell whether they are living in a simulation. For example, Bostrom suggests that a window could pop up saying: "You are living in a simulation. Click here for more information." However, imperfections in a simulated environment might be difficult for the native inhabitants to identify and for purposes of authenticity, even the simulated memory of a blatant revelation might be purged by a programme. But if any evidence came to light, either for or against the skeptical hypothesis, it would radically alter the aforementioned probability.
Bostrom claims that 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 humans 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 says he sees no strong argument for which of the three trilemma propositions is the true one: "If is true, then we will almost certainly go extinct before reaching posthumanity. If 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 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,, and ... 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 is true, others that is true, yet others that 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 humans 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" 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 some kind of ancestor simulation exists.
The hypothesis has received criticism from some physicists, such as Sabine Hossenfelder, who considers that it is physically impossible to simulate the universe without producing measurable inconsistencies, and called it pseudoscience and religion. Cosmologist George F. R. Ellis, who stated that " is totally impracticable from a technical viewpoint", and that "late-night pub discussion is not a viable theory". Some scholars categorically reject—or are uninterested in—anthropic reasoning, dismissing it as "merely philosophical", unfalsifiable, or inherently unscientific.
Some critics propose that the simulation could be in the first generation, and all the simulated people that will one day be created do not yet exist, in accordance with philosophical presentism.
The cosmologist Sean M. Carroll argues that the simulation hypothesis leads to a contradiction: if humans are typical, as it is assumed, and not capable of performing simulations, this contradicts the arguer's assumption that it is easy for us to foresee that other civilizations can most likely perform simulations.
Physicist Frank Wilczek raises an empirical objection, saying that the laws of the universe have hidden complexity which is "not used for anything" and the laws are constrained by time and location—all of this being unnecessary and extraneous in a simulation. He further argues that the simulation argument amounts to "begging the question," due to the "embarrassing question" of the nature of the underlying reality in which this universe is simulated. "Okay if this is a simulated world, what is the thing in which it is simulated made out of? What are the laws for that?"
Brian Eggleston has argued that the future humans of our universe cannot be the ones performing the simulation, since the simulation argument considers our universe to be the one being simulated. In other words, it has been argued that the probability that humans live in a simulated universe is not independent of the prior probability that is assigned to the existence of other universes.