Nick Bostrom'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: 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 (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." 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 some kind of (possibly neural) 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 "[the hypothesis] 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. 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.
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 humans live in a simulation) is false. Physicist
Paul Davies uses 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, which would lead to the untenable and scientifically self-defeating conclusion that humans 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 that 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 taken to be true. Physicist
Marcelo Gleiser objects to the notion that posthumans would have a reason to run simulated universes: "...being so advanced they would have collected enough knowledge about their past to have little interest in this kind of simulation. ...They may have virtual-reality museums, where they could go and experience the lives and tribulations of their ancestors. But a full-fledged, resource-consuming simulation of an
entire universe? Sounds like a colossal waste of time". Gleiser also points out that there is no plausible reason to stop at one level of simulation, so that the simulated ancestors might also be simulating their ancestors, and so on, creating an infinite regress akin to the "
problem of the First Cause". In 2019, philosopher Preston Greene suggested that it may be best not to find out if we are living in a simulation, since, if it were found to be true, such knowing might end the simulation.
Economist Robin Hanson argues that a self-interested occupant of a high-fidelity simulation 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 in a simulation 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". 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). Chalmers claims that they might eventually find that their thoughts fail to be physically
caused, and 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. Similar arguments have been made for philosophical views about
personal identity that say that an individual could have been another human being in the past, as well as views about
qualia that say that colors could have appeared differently than they do (the
inverted spectrum scenario). In both cases, the claim is that all this would require is hooking up the mental lives to the simulated physics in a different way.
Computationalism Computationalism is a
philosophy of mind theory stating that
cognition is a form of
computation. It is relevant to the simulation hypothesis in that it illustrates how a simulation could contain conscious subjects, as required by a "virtual people" simulation. For example, it is well known that physical systems can be simulated to some degree of accuracy. If computationalism is correct and if there is no
problem in generating
artificial consciousness or cognition, it would establish the theoretical possibility of a simulated reality. Nevertheless, the relationship between cognition and phenomenal
qualia of consciousness is
disputed. It is possible that
consciousness requires a
vital substrate that a computer cannot provide and that simulated people, while behaving appropriately, would be
philosophical zombies. This would undermine
Nick Bostrom's simulation argument; humans cannot be a simulated consciousness, if consciousness, as humans understand it, cannot be simulated. The skeptical hypothesis remains intact, however, and humans could still be
vatted brains, existing as conscious beings within a simulated environment, even if consciousness cannot be simulated. It has been suggested that whereas
virtual reality would enable a participant to experience only three senses (sight, sound and optionally smell), simulated reality would enable all five (including taste and touch). Some theorists have argued that if the "consciousness-is-computation" version of
computationalism and
mathematical realism (or radical
mathematical Platonism) are true, then consciousness
is computation, which in principle is
platform independent and thus admits of simulation. This argument states that a "
Platonic realm" or
ultimate ensemble would contain every algorithm, including those that implement consciousness.
Hans Moravec has explored the simulation hypothesis and has argued for a kind of mathematical Platonism according to which every object (including, for example, a stone) can be regarded as implementing every possible computation. == In physics ==