Simulated reality hypothesis

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Simulated reality is the idea that reality could be simulated — usually computer-simulated — to a degree indistinguishable from 'true' reality. It could contain conscious minds which may or may not know that they are living inside a simulation. In its strongest form, the "Simulation Hypothesis" claims we actually are living in such a simulation.

This is different from the current, technologically achievable concept of virtual reality. Virtual reality is easily distinguished from the experience of 'true' reality; participants are never in doubt about the nature of what they experience. Simulated reality, by contrast, would be hard or impossible to distinguish from 'true' reality.

Practical or not, the idea raises three vexing questions:

• Is it possible, even in principle, to tell whether we are in a simulated reality?
• Is there any difference between a simulated reality versus a 'real' one?
• How should we behave if we knew that we were living in a simulated reality?

Types of simulation

For the purpose of discussion, there are four categories of simulation:

Brain-computer interface

In a brain-computer interface simulation, each participant enters from outside, directly connecting their brain to the simulation computer. The computer transfers sensory data to them and reads their desires and actions back; in this manner they interact with the simulated world and receive feedback from it. The participant may even receive adjustment in order to temporarily forget that they are inside a virtual realm (e.g. "passing through the veil"). While inside the simulation, the participant's consciousness is represented by an avatar, which could look very different from the participant's actual appearance.

The Cyberpunk genre is an example of a brain-computer interface simulated reality.

Virtual people

In a virtual-people simulation, every inhabitant is a native of the simulated world. They do not have a 'real' body in the 'outside' reality. Rather, each is a fully simulated entity, possessing an appropriate level of consciousness that is implemented using the simulation's own logic (i.e. using its own physics). As such, they could be downloaded from one simulation to another, or even archived and resurrected at a later date. It is also possible that a simulated entity could be moved out of the simulation entirely by means of mind transfer into a synthetic body.

This category subdivides into two further types:

• Virtual people-virtual world, in which an external reality is simulated separately to the artificial consciousnesses;

and

• Solipsistic simulation in which consciousness is simulated and the "world" participants perceive exists only within their minds.

Emigration

In an emigration simulation, the participant enters the simulation from the outer reality, as in the brain-computer interface simulation, but to a much greater degree. On entry, the participant uses mind transfer to temporarily relocate their mental processing into a virtual-person. (Presumably, their outside-world body remains in stasis during the simulation.) After the simulation is over, the participant's mind is transferred back into their outer-reality body, along with all new memories and wisdom gained within.

Intermingled

File:SimulatedReality MorpheusAndNeoInSmallSimulation.jpg

Morpheus teaches Neo inside a small simulated reality

An intermingled simulation supports both types of consciousness: players from the outer reality who are visiting (as a brain-computer interface simulation) or emigrating, and virtual-people who are natives of the simulation and hence lack any physical body in the outer reality.

The Matrix movie features an intermingled type of simulation: it contains not only human minds (with their physical brains remaining outside), but also the 'agents', who are sovereign software programs indigenous to the computed realm.

Philosophical arguments that our reality might be simulated

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 from cognition, it would establish the theoretical possibility of a simulated reality. However, the relationship between cognition and phenomenal consciousness is disputed. It is possible that consciousness requires a substrate of "real" physics, and simulated people, while behaving appropriately, would be philosophical zombies.

Bostrom's "Simulation Argument"

The philosopher Nick Bostrom investigated the possibility that we may be living in a simulation. His argument attempts to prove the disjunction of three hypotheses (that is, that at least one of the following three propositions must be true), that:

either

1. intelligent races will never reach a level of technology where they can run simulations of reality so detailed they can be mistaken for reality; or
2. races who do reach such a level do not tend to run such simulations; or
3. we are almost certainly living in such a simulation.

Bostrom's argument uses the premise that given sufficiently advanced technology, it is possible to simulate entire inhabited planets or even larger habitats or even entire universes as quantum simulations in time/space pockets, including all the people on them, on a computer, and that simulated people can be fully conscious, and are as much persons as non-simulated people are.

If we then assume that the human race could reach such a technological level without destroying themselves in the process (i.e. we deny the first hypothesis); and that once we reached such a level we would still be interested in history, the past, and our ancestors, and that there would be no legal or moral strictures on running such simulations (we deny the second hypothesis) - then

• it is likely that we would run a very large number of so-called ancestor simulations;
• and that, by the same line of reasoning, many of these simulations would in turn run other sub-simulations, and so on;
• and that given the fact that right now it is impossible to tell whether we are living in one of the vast number of simulations or the original ancestor universe, the likelihood is that the former is true.

Assumptions as to whether the human race (or another intelligent species) could reach such a technological level without destroying themselves depend greatly on the value of the Drake equation, which gives the number of intelligent technological species communicating via radio in a galaxy at any given point in time. The expanded equation looks to the number of posthuman civilizations that ever would exist in any given universe. If the average for all universes, real or simulated, is greater than or equal to one such civilization existing in each universe's entire history, then odds are rather overwhelmingly in favor of the proposition that the average such civilization is living in a simulation, assuming that such simulated universes are possible and such civilizations would want to run such simulations.

Criticism

Bostrom's argument relies on probability when not all possible outcomes are known. The conclusion that we might be living in a simulated universe makes the assumption "there can be large number of simulated universes and one physical universe" is not necessarily true. There are other possibilities and hence probability cannot be applied to only a subset of the outcomes.

Frank Tipler's Omega Point

Physicisist Frank Tipler envisages a similar scenario to Nick Bostrom's argument: a hypothetical cosmological scenario where, as the Universe comes to an end in a Big Crunch, the computational capacity of the Universe is capable of increasing at a sufficient rate that this computation rate is accelerating exponentially faster than time runs out. In principle, a simulation run on this Universe-computer can thus continue forever in its own terms, even though the external Universe lasts only a finite time.

The implication of this theory for present-day humans is that this ultimate cosmic computer will essentially be able to resurrect everyone who has ever lived, by recreating all possible quantum brain states within the master simulation. This would manifest as a "emigration "or "virtual person" simulated reality. From the perspective of the inhabitant, the Omega Point represents an infinite-duration afterlife, which could take any imaginable form due to its virtual nature. At first glance, Tipler's hypothesis requires some means by which the inhabitants of the far future can recover historical information in order to reincarnate their ancestors into a simulated afterlife. However, if they really have access to infinite computing power, that is no problem at all -- they can just simulate "all possible worlds". (This line of thought is continued in Platonic simulation theories).

Recent observations suggesting an accelerating universe mean that the Big Crunch, on which the theory was originally predicated, is now thought an unlikely scenario. Also, recent ideas in modern physics suggest that time and space are not infinitely divisible, but instead have a discrete nature. Should these ideas turn out to be true, it would constitute a serious, even insurmountable, hurdle to the Omega point idea, which relies heavily on the (assumed) existence of increasingly small intervals of time and space.

Platonic simulation theories

A few people , have argued that if the "consciousness-is-computation" version of computationalism and mathematical realism (also known as mathematical Platonism) are both true our consciousnesses must be inside a simulation. This argument states that a "Plato's heaven" or ultimate ensemble would contain every algorithm, including those which implement consciousness. Platonic simulation theories are also subsets of the multiverse theories and theories of everything.

Dreaming

In order to demonstrate the possibility that what we accept as reality is a simulation there should be some evidence that we could point to in order to extrapolate that it is in fact an illusion. Dreaming is one such example where ordinary people are fooled into believing a simulated reality (a dream) is the ‘true’ reality.

Unlike recent philosophical analysis that require readers to imagine future generations that may create simulated realities, dreaming requires no such leap of faith. All that is required for the observer to realize he has been fooled is the simple act of waking up.

Since dreams are commonplace, and most people are fooled by them, the "reality" of dreams should silence the critics who argue that simulations are theoretical or that humans are too intelligent to be easily fooled by them. As a result, left open is the question of whether we’re being fooled when our eyes are wide open.

Boredom & immortality

If intelligent life achieves immortality, either through salvation or through technology or through the slow march of evolution, then a serious problem of boredom could arise. Immortality implies the absence of needs and threats, and so immortal creatures need not seek any values, nor any knowledge at all (if knowledge is understood as information about how values may be obtained). If the immortal creatures' intelligence is nevertheless of a goal-directed nature, then they will be plagued with boredom. (This is called the "I am sick of playing this harp" conjecture, which is a reference to certain religious portrayals of heaven in which ascended souls are shown spending all their time singing praises to God.)

In order to satiate their desire for goal-directed activity, the immortal creatures may design devices or simulations that constrain their own immortality, omniscience, and/or invulnerability. With the help of these devices or simulations, the immortal creatures would be able to once again experience curiosity, goals, peril, uncertainty, danger, adventure, perhaps even death.

The argument, then, is that bored immortal creatures will eventually experiment with such "adventures in mortality", and so in infinite time such experiments will inevitably occur. This is support for Bostrom's conjecture that advanced intelligences will "run a very large number of so-called ancestor simulations". They will be driven to do so not only by curiosity, but by the sheer boredom of being perfectly safe. They will create and enter virtual worlds for the exact same reason that humans play video games today.

The rest of Bostrom's argument then follows. The argument predicts that this turn of events has almost certainly already occurred, and that we are now inside such a simulation. (We may have willed ourselves to forget that we have entered a simulation in order to keep it exciting.)

However, this argument rests on a series of "what ifs". We might not achieve immortality. If we do, we might find another way of alleviating boredom.

Quasi-religious arguments

Prayers. A simulation may have been built for the purpose of its inhabitants, and so it may respond to their wishes if properly expressed. (This is the secular version of having one's prayers answered if delivered using the correct ritual.) If any sort of prayer or wishing is found to be effective, and is verified to be scientifically inexplicable, then it is grounds to suspect that reality is being simulated.

Interventions. The director of the simulation may choose to intervene from time to time in a way that violates the simulation's normal rules. The director may even choose to manifest him/her/itself to the inhabitants. (This is another secular version of a common religious meme, and of course many believe that this has already occurred.)

Past lives. The inhabitants may have entered the simulation after living for a period of time in an outer world or in a previous simulation, and so they may possess recoverable "past life" memories. If such memories can be proven to be both accurate and inexplicable, then reality may be simulation which inhabitants can visit multiple times. Deja vu is a similar concept such inhabitants may experience for the same reasons.

All three arguments suffer from the same two problems.

• The evidence for the religious phenomena appealed to is debatable
• If true, these phenomena can be also explained theologically. They are not evidence for simulated reality over and above other hypotheses.

Scientific and technological approaches.

Software Bugs

File:SimulatedReality VoidInTheSimulation.jpg

A void in a holodeck simulation, as seen in the movie "Star Trek Insurrection".

A computed simulation may have voids or other errors that manifest inside. If one can be found and tested, and if the observers survive its discovery, then it may reveal the underlying computational substrate. However, lapses in physical law could be attributed to other explanations, for instance divine intervention, or inherent instability in the nature of reality.

In fact, bugs could be very common. An interesting question is whether knowledge of bugs or loopholes in a sufficiently powerful simulation are instantly erased the minute they're observed since presumably all thoughts and experiences in a simulated world could be carefully monitored. Of course, if this is the case we'll never be able to act on our discovery of bugs!

Hidden messages or "Easter eggs"

The simulation may contain secret messages or exits, placed there by the designer, or by other inhabitants who have solved the riddle, in the way that computer games and other media sometimes do. People have already spent considerable effort searching for patterns or messages within the endless decimal places of the fundamental constants such as e and pi. In Carl Sagan's science fiction novel Contact, Sagan contemplates the possibility of finding a signature embedded in pi (in its base-11 expansion) by the creators of the universe.

However, such messages have not been found, and the argument relies on the messages being truthful. As usual, other far-fetched hypotheses could explain the same evidence.

Connection problems

If the inhabitants are mentally living in the simulation while their bodies remain outside, then the connection between the two may have detectable vulnerabilities. For example, certain mental stimulation or certain levels of pain may cause the inhabitant's real (outside) body to respond or disconnect in some way, akin to an epileptic seizure. However, epileptic seizures can be explained without the Simulation Hypothesis.

Processing power

A computer simulation would be limited to the processing power of its host computer, and so there may be aspects of the simulation that are not computed at a fine-grained (e.g. subatomic) level. this might show up as a limitation on the accuracy of information that can be obtained in particle physics.

However, this argument, like many others, assumes that accurate judgements about the simulating computer can be made from within the simulation. If we are being simulated, we might be misled about the nature of computers.

Also, the point can be turned round. If we are in a simulation run on limited hardware, why is it so detailed? Why bother with atoms at all? After all, humans went for thousand of years without knowing anything about atoms.

Taken one step further, the "fine grained" elements of our world could themselves be simulated since we never see the sub-atomic particles due to our inherent physical limitations. In order to see such particles we rely on other instruments which appear to magnify or translate that information into a format our limited senses are able to view: computer print out, lens of a microscope, etc. Therefore, we essentially take on faith that they're an accurate portrayal of the fine grained world which appears to exist in a realm beyond our natural senses. Assuming the sub-atomic could also be simulated then the processing power required to generate a realistic world would then be greatly reduced.

But not reduced as far as simulating a world where microscopes just don't do anything interesting. People who have never heard of atoms do not find their experienced world to be unrealistic. Who knows what reality ought to be like?

Heisenberg Uncertainty Principle

German physicist, Werner Heisenberg, discovered that in the quantum world observers cannot obtain perfect information about every aspect of a system: “The more precisely the position is determined, the less precisely momentum is known in this instant, and vice versa.” – Heisenberg, uncertainty paper, 1927.

This is often, but inaccurately,stated as meaning that "the observer has an effect on the observed"

This "disturbance" interpretation of the uncertainty principle is similar to how scenes are sometimes rendered in video games, where computational resources are limited. Some areas of the simulation may not be rendered until a participant looks at them. This might resemble "observer effect" to a participant.

However, the Heisenberg uncertainty principle and observer effect can be explained without the Simulation Hypothesis. The universe could just be that way, as most physicists think.

Digital Physics and Cellular Automata

Proponents of digital physics and cellular automata such as Ed Fredkin, Stephen Wolfram and Konrad Zuse believe the current laws of physics, should be replaced by new laws involving finite or countably infinite elements. (Note that there is no workable digital theory in physics itself — digital physics is more of a philosophical proposal). This approach is often coupled with the claim that the universe is a computer (for instance, by Zuse, Seth Lloyd and Wolfram). This is of course not the same as the claim that the universe is computer-simulated, but is at least related. A computer can always be computer-simulated, according to the Church-Turing thesis.

It can be argued that the use of continua in physics constitutes a possible argument against the simulation of a physical universe. Removing the real numbers and uncountable infinities would counter some of the objections noted above, and at least make computer simulation a possibility. However, digital physics needs overcome objections. For instance, cellular automata would appear to be a poor model for the non-locality of quantum mechanics.

Objections

Computability of Physics

A refutation of claims that what we perceive as external reality is computer-simulated would be the discovery of some uncomputable physics. If reality is doing something no computer can do, it cannot be a computer simulation. In fact, known physics is held to be computable, making the Simulation Hypothesis safe — if lending no positive support to it.

The statement "physics is computable" needs to be qualified in various ways. A number — thinking particularly of a real number, one with an infinite number of digits -- is said to be computable if a Turing machine will continue to spit out digits endlessly. In other words, there is no question of getting to the "last digit". But this sits uncomfortably with the idea of simulating physics in real time (or any plausible kind of time). Known physical laws (including those of quantum mechanics)are very much infused with real numbers and continua, and the universe seems to be able decide on their values on on a moment-by-moment basis. As Richard Feynman put it:

"It always bothers me that, according to the laws as we understand them today, it takes a computing machine an infinite number of logical operations to figure out what goes on in no matter how tiny a region of space, and no matter how tiny a region of time. How can all that be going on in that tiny space? Why should it take an infinite amount of logic to figure out what one tiny piece of space/time is going to do? So I have often made the hypotheses that ultimately physics will not require a mathematical statement, that in the end the machinery will be revealed, and the laws will turn out to be simple, like the chequer board with all its apparent complexities".

page 57.

The objection could be made that the simulation does not have to run in "real time". But it misses an important point: the shortfall is not linear, rather it is a matter of performing an infinite number of computational steps in a finite time.

(It could be objected that we can simulate physical systems already. But what is currently being discussed is the simulation of "real physics". Flight simulators and the like are relatively coarse-grained. It requires supercomputers to calculate the "real physics" of a few quarks.)

Another way round the problem would be to argue that the universe is not a Turing machine but an analogue computer or a hypercomputer. The problem now is that there is no evidence that can conceivably be produced to show that the universe is not any kind of computer, making the Simulation Hypothesis unfalsifiable and therefore scientifically unacceptable, at least by Popperian standards.

Computational load

As of 2006, the computational requirements for Molecular dynamics are such that it takes several months of computing time on the world's fastest computers to simulate 1/10th of one second of the folding of a single protein molecule. To simulate an entire galaxy would require more computing power than can presently be envisioned, assuming that no shortcuts are taken when simulating areas that nobody is observing.

In answer to this objection, Bostrom calculated that the whole of human history would require roughly 10³³ to 10³⁶ calculations to simulate. He further calculated that a planet-sized computer built using known nanotechnological methods would perform about 10⁴² calculations per second -- and a planet-sized computer is not inherently impossible to build, (although the speed of light could severely constrain the speed at which its subprocessors share data).

In any case, it is erroneous to apply our current sense of feasibility to projects undertaken in an outer reality, where resources and physical laws may be very different. It also assumes designers would need to simulate reality beyond our natural senses.

Also, a simulated reality need not run in realtime. The inhabitants of a simulated universe would have no way of knowing that one day of subjective time actually required a billion years to calculate in their host computer, or vice-versa.

Rand's "Primacy of Existence"

This is a philosophical version of the problem raised by the "observer changes reality" findings of quantum mechanics. It is implied by Ayn Rand's philosophy of Objectivism. Objectivism holds that reality is objective and that it has Primacy over consciousness:

The basic fact implicit in all [...] observations is that consciousness, like every other kind of entity, acts in a certain way and only in that way. In adult, philosophic terms, we refer to this fact as the "primacy of existence," a principle that is fundamental to the metaphysics of Objectivism.

Existence, this principle declares, comes first. Things are what they are independent of consciousness -- of anyone's perceptions, images, ideas, feelings. Consciousness, by contrast, is dependent. Its function is not to create or control existence, but to be a spectator: to look out, to perceive, to grasp that which is. (Peikoff 1991)

In other words, consciousness axiomatically requires lawful external independent entities with which to become aware. Therefore, if our reality turns out to be directly controlled by consciousness, then the axiom of consciousness is violated. In that event the observer's reality must be declared to be a simulation, while the outer reality (in which the simulation is running) remains in conformity with the axiom.

The point can be carried further in this way: Existence necessarily has Primacy only in the outermost level of reality; all inner simulations can be programmed to grant Primacy to the consciousnesses within or without. In a simulated world, wishing can make it so, because identities within a simulated world are malleable.

By way of a thought experiment, imagine playing a computer game like The Sims and rearranging its reality according to the observations (not actions) of the simulated people inside. If the simulated people were intelligent enough, they might infer that their consciousness had primacy over their world, and that their world was therefore simulated.

Criticism

The argument is flawed because it takes an empirical observation from our reality (or pseudo-reality) -- that entities behave in a lawful manner — and takes it as applying apriori to any reality, to any possible world. Moreover, it cannot be argued that any simulation will necessarily be programmed to give primacy to consciousness. The inhabitants of a primacy-of-reality simulation — a simulation in which there are some kind of mind-independent physical laws, rather than magic — will not be able to apply this approach to tell that they are in a simulation. So, while Objectivism may "hold" that reality is objective, it cannot decisively prove it.

Lack of originality

Some consider the idea of Simulated Reality to be little more than a modern, and perhaps more plausible, rehashing of ideas put forth in earlier eras:

• Aboriginal Australian mythology includes a concept called the Dreamtime which is abstractly similar to the idea of simulated reality.
• Buddhism has long posited that reality is illusory, as a dream.
• In ancient Athens, Plato proposed the Allegory of the Cave in the seventh book of his Republic. Plato composed it in order to illustrate a person's epistemological progress via "a series of 'conversions' from a less adequate to a more adequate cognitive state" (Copleston 1946). Even so, the allegory is often mentioned as an early example of "Is our reality real?" inquiry.
• Zeno of Elea, a Greek philosopher and student of Parmenides, proposed that the world must be an illusion at the conclusion of his famous paradoxes. Thus the concept that the world is not as it seems is hardly a new one.
• During the middle ages, René Descartes considered whether his perceived existence was systematically warped or false:

  Yet it is possible, given a metaphysical hypothesis, to doubt even the propositions of mathematics. For I can suppose that "some evil genius, no less powerful than deceitful, has employed his whole energies in deceiving me". In other words, by a voluntary effort I can envisage the possibility of my having been so constituted that I am deceived even in thinking that those propositions are true which inevitably appear to me to be certain. (Copleston 1960)

• In later times, this core idea was resurrected as a thought experiment called the "brain-in-a-vat" scenario.

Irrelevance

Others see the proposition itself as being irrelevant. It has no real-life applicability because the claim is essentially unprovable in any concrete sense: any "evidence" that is directly observed could be another simulation itself. In other words, there is an infinite regress problem with the argument. Even if we are a simulated reality, there is no way to be sure the people running the simulation are not themselves a simulation, and the operators of that simulation are not a simulation, ad infinitum. Given the premises of the simulation argument, any reality, even one running a simulation, has no better or worse chances of being a simulation than any other.

Unless the knowledge of a reality as simulation alters the control or abilities of its inhabitants, that knowledge is irrelevant.

Occam's razor

"All things being equal, the simplest solution tends to be the best one." -Occam's Razor

It has been noted that there is no definitive way to tell whether one is in a simulation, simulation-of-a-simulation and so on. It is in fact generally the case that any number of hypotheses can explain the same evidence. That situation prompted the formulation of a heuristic rule called Occam's razor, which instructs us to prefer simpler explanations over more complex ones. (Since it is a heuristic rule, it does not dictate what is ultimately true, but only what is best to believe, all other things being equal). The Razor would tell us to reject the simulation-of-a-simulation hypothesis as being too complex...but it would also tell us to reject the Simulation Hypothesis, in favour of reality being what it appears to be.

Critics of this analysis point out that all things are not equal, as evidenced by our dreams, and that even if they were equal Occam's Razor is not a natural law. Often the complex answer is the correct one. Galileo's observation that the Earth was round and not flat is an example where the simple answer was wrong.

However, the amount of evidence supporting the round earth theory was not the same as that supporting the flat earth theory, so things were not equal, and the razor therefore would not have applied anyway.

Reality is perception

Another criticism of the idea of Simulated Reality is that reality is always whatever we perceive as reality. So, even if we are in a simulation, it is still the only reality we have ever known, and anyway we have no counterexamples, so this is still "reality" as we understand it. Reality simply becomes defined down to a narrower scope, with a bigger super-reality outside it.

For example, even if this were not a simulation in our brains it is still a simulation since our neurons are converting information from the outside world (light, sound, etc.) and creating a simulated world in our minds. We don't, for example, see ultraviolet light or microwaves even though they exist because our brains are selectively editing the information for our biological purposes.

It's similar to what happens when we take a picture with our digital camera. The photo is not the actual event. It's a representation of that event. And our brains work in a similar fashion.

Moral lease

Widespread acceptance of the idea of Simulated Reality may create a hazardous situation: if everyone believes that reality is a an illusion, then they may feel free to commit crimes and atrocities. Released from the empathetic restraint of their knowledge that life is precious and irreplaceable, would-be criminals might run rampant. They might even feel virtuous in doing so, thinking that they are simply making the game more interesting for the other players.

A similar moral shakeup is instigated by the idea that some or most of the other people inside the simulation may actually be bots.

However, if we assume that a simulation may consist of multiple participants not unlike today's most popular massively multiplayer online games with millions of players, then some concept of ethics and morality may still apply. For example, if during a simulation a participant picks up a hammer and smashes the hand of another participant, resulting in pain that is identical in all ways neurologically to 'real' pain, then there may still be negative consequences when they awake, albeit the hand would not actually have been smashed.

In addition, the behavior of children and adults playing video games who are aware that it is a virtual environment seem to point toward ethics and moral codes still applying. Although anecdotal at best, game designers go to great lengths to control player killers who do precisely what is outlined earlier in this section: wantonly killing other players, breaking social norms already established among players, etc. On a lesser scale, the editors of wikipedia provide a similar function by policing for SPAM and other abuses, even though it's voluntary and uncompensated.

Other issues

The simulation may defend itself

A simulated reality may be programmed to prevent its inhabitants from discovering its nature. The creators of a simulation would probably add such defensive programming in order to protect their simulation from spoilage.

Assuming that discovery of the simulation is even possible, the inhabitant that does so might be subsequently memory-wiped, punished, killed, or removed from the simulation altogether. The other inhabitants would therefore have no way of learning about the discovery.

The discovery might even cause the simulation to reboot itself, ending the lives and goals of all of its inhabitants. Therefore, any investigation into the question will imperil the continued existence of the entire cosmos.

However, the fact that we're all still alive would seem to bring this theory into question.

Spoiling the fun

If reality is being simulated for our entertainment, then there must have been a reason for us to have no knowledge that we are in a simulation. This would be the case if, for example, we had entered this simulation in order to experience the fun of risk, quest, and mystery. That fun -- and therefore the entire purpose of the simulation -- would be ruined by the discovery that we are indeed inside a game.

There is a religious version of this objection: "The Creator has denied you knowledge of Him/Her/Itself in order to give you the opportunity for faith. Proof precludes faith, so no proof of the Creator should ever be sought."

The alternative explanation is that part of the "fun" is unraveling the mystery of how the world works even if it turns out to be a simulation. This is feasible since it would be possible for a simulation to auto detect thoughts that would lead to discovery of the truth and immediately erase them.

Humanity itself

Much attention has been given the question of whether we are humans in the future enjoying a simulated environment or human minds uploaded or created in the simulation itself. However, another possibility is that we’re not human at all.

If this experience is an accurate depiction of actual events in “real time” then it is conceivable that any number of alien civilizations could have intercepted or discovered “humanity” and sought to replicate it for their own purposes.

The archival efforts of Wikipedia, the human genome, and radio and television signals being broadcast through the darkness of space offer no shortage of building blocks upon which to build a simulation. Not to mention human heads being cryogenically frozen and sent into space on rockets, providing the potential for memory extraction.

Doomsday theorists who predict the end of humanity may have been correct and what we’re experiencing is the equivalent of life as a dinosaur. A long extinct race of carbon based life forms called humans who were on the brink of leaving their solar system only to be snuffed out by their own impulses.

Non-player characters or "bots"

Some of the people in a simulated reality may be automatons, philosophical zombies, or 'bots' added to the simulation to make it more realistic or interesting or challenging. Indeed, it is conceivable that every person other than oneself is a bot. Bostrom called this a "me-simulation", in which oneself is the only sovereign lifeform, or at least the only inhabitant who entered the simulation from outside.

Bostrom further elaborated on the idea of bots:

In addition to ancestor-simulations, one may also consider the possibility of more selective simulations that include only a small group of humans or a single individual. The rest of humanity would then be zombies or “shadow-people” – humans simulated only at a level sufficient for the fully simulated people not to notice anything suspicious. It is not clear how much [computationally] cheaper shadow-people would be to simulate than real people. It is not even obvious that it is possible for an entity to behave indistinguishably from a real human and yet lack conscious experience.

The idea of "zombies" may have been borrowed from the video game industry where computer generated characters are known as Non-Player Characters ("NPCs"). The term 'bots' is short for 'robots'. The usage originated as the name given to the simple AI opponents of modern video games.

Moral implications of bots

If some or most inhabitants of a simulation are indeed bots, then it may be necessary for the sovereign inhabitants to revise the moral calculus of free-riding, murder, and the like.

If the basis of a moral code is deontological (i.e. duty-based), then bots will require different treatment than sovereign inhabitants because bots cannot demand the same duty of care that other sovereigns can. For example, one might conclude that the commandment "You shall not murder" applies only to victims who have souls.

An egoistic moral code, on the other hand, would probably not change at all in the presence of bots. This is so because one's interactions with bots are already indistinguishable from one's interactions with sovereigns... and if interactions with bots have the same yield as those with sovereigns, then self-interest demands that one treat both types of people the same.

Birth

File:SimulatedReality BabyInVat.jpg

A newborn baby is interfaced with the simulation in the movie "The Matrix"

Simulated reality raises the question of what would happen if a human is 'born' in simulated reality. This does not mean the physical process of creating a human in reality, but rather interfacing an infant from the outer universe with the simulation. The simulation would not have to be as realistic, or even close, to reality, because the human will grow to accept it. If the human subject has no memories of 'actual' reality, he or she will assume the simulation is true, as there is no basis for comparison.

It is difficult to speculate how a human, having grown accustomed to a particular reality (irrespective of whether it is real or fake), would react to being brought into another reality. Thus, simulations designed for humans to be born into need not incorporate full detail as the people inside will have no referential reality to compare the simulation to. It is likely then that such a simulation (generated using computers) could have lower detail levels and omit content which the people inside would probably not discover (e.g. core of the Earth) and simply use a simpler algorithm to generate the symptoms of the omitted content (e.g. heat and magnetic field from Earth's core)

Subjective time

A brain-computer interface simulated reality may be required to progress at a rate that is near realtime; that is, time within it may be required to pass at approximately the same rate as the outer reality which contains it. This might be the case because the players are interacting with the simulation using brains which still reside in the outer reality. Therefore, if the simulation were to run faster or slower, those brains could notice because they were not contained with it.

It is possible that time passes slower or quicker for brains in a dream state (i.e. in a brain-computer interface trance); however, the point is that they still function at a finite, biological speed, and the simulation must track with them. Unless those interacting with the simulation are augmented and capable of processing information at the same rate as the simulation itself.

A virtual-people or emigration simulated reality, on the other hand, need not. This is because its inhabitants are using the simulation's own physics in order to experience, think, and react. If the simulation were slowed down or sped up, so also would the inhabitants' own senses, brains, and muscles, as well as every other molecule inside. The inhabitants would perceive no change in the passage of time, simply because their method of measuring time is dependent on the cosmic clock that they are seeking to measure. (They could perform the measurement only if they had some access to data from the outer reality.)

For that matter, they could not even detect whether the simulation had been completely halted: a pause in the simulation would pause every life and mind within it. When the simulation was later resumed, the inhabitants would continue exactly as they were before the pause, completely unaware that (for example) their cosmos had been paused and archived for a billion years before being resumed by a completely different director.

One practical implication of this is that a virtual-people or a hybrid simulation does not require a computer powerful enough to model its entire cosmos at full speed. Per the Turing completeness theorem, a simulation can progress at whatever speed its host computer can manage; it would be constrained by available memory but not by computation rate.

Recursive simulations

A simulated reality could contain a computer that is running a simulated reality. The 'parent' simulator would be simulating all of the atoms of the computer, atoms which happen to be calculating a 'child' simulation. By way of illustration: imagine that a human is playing a game of The Sims in which one of the player's Sims (simulated people) is playing a computer game in the game. Or consider the "hall of mirrors" effect observed when pointing a videocamera at its own monitor.

This recursion could continue to infinitely many levels -- a simulation containing a computer running a simulation containing a computer running a simulation and so on. The recursion is subject only to one constraint: each 'nested' simulation must be:

• smaller than its parent reality, because its own memory must be a subset of the parent's;

...and must be at least one of the following:

• slower than its parent reality, because its own calculations must be a subset of the parent's; or
• less complex than its parent reality, via simplifications of processes that are computationally intensive in the parent reality; or
• less complete than its parent reality, via approximations of objects that nobody is observing.

The latter is the basis of the idea that quantum uncertainties are circumstantial evidence that our own reality is a simulation.

Simulated reality in fiction

Simulated reality is a theme that pre-dates science fiction. In Medieval and Renaissance religious theatre, the concept of the world as a theater is frequent. Works, early and contemporary, include:

Literature

• Accelerando (2005) by Charles Stross
• The Cookie Monster (2004), by Vernor Vinge
• Darwinia (1998) by Robert Charles Wilson
• Diaspora (1997)) by Greg Egan
• Discourse on Method (1637) by René Descartes
• Feersum Endjinn (1994) by Iain M. Banks (his later novel, The Algebraist, posits a religion that believes our universe is virtual)
• Forever Free (1999) by Joe Haldeman
• Get Real: A Philosophical Adventure in Virtual Reality (1998) by Philip Zhai
• The Girl Who Was Plugged In (1974) by James Tiptree Jr.
• Illusions (1977) by Richard Bach
• Jorge Luis Borges's many short stories (and essays)
• Neuromancer (1984) and Mona Lisa Overdrive (1988) by William Gibson
• Otherland (1998) by Tad Williams
• Permutation City (1994) by Greg Egan
• Loop (1998) by Koji Suzuki
• Riverworld (1979) by Philip José Farmer
• Simulacron 3 (1964) by Daniel F. Galouye
• Sophie's World (1991) by Jostein Gaarder
• The Three Stigmata of Palmer Eldritch (1965) by Philip K. Dick
• Time Out of Joint (1959) by Philip K. Dick
• Ubik (1969) by Philip K. Dick
• Valis (1981) by Philip K. Dick
• The Wonderland Gambit (1995) by Jack L. Chalker

Film, plays & TV series

• .hack//SIGN an anime cartoon about a person whose mind is trapped in a computer game
• Avalon by Mamoru Oshii
• Better Than Life in Red Dwarf, by Rob Grant and Doug Naylor
• The Big O by Hajime Yatate and Chiaki J. Konaka NB the reality in question has not been confirmed as simulated, but it is extremely likely
• Brainscan by John Flynn
• "The Cage" and "The Menagerie", the unaired pilot and later episodes (respectively) of Star Trek, screenplays by Gene Roddenberry
• Dark City by Alex Proyas
• "The Deadly Assassin," an episode of Doctor Who written by Robert Holmes
• eXistenZ by David Cronenberg
• Good Bye Lenin!, by Wolfgang Becker, a Berlin family tries to make the feeble mother believe that East Germany did not fall.
• The Island, directed by Michael Bay
• The Truman Show, directed by Peter Weir
• La vida es sueño (Life is a Dream), a Spanish play by Pedro Calderón de la Barca (1600-1681) that evolved from the legends of the early years of Siddhartha Gautama, the Buddha
• The Matrix trilogy by the Wachowski brothers
• In the Doctor Who universe, the eponymous hero's race, the Time Lords of Gallifrey, developed the APC Net AKA 'the Matrix', into which all their memories and experience were placed at the point of death or – it was later implied – constantly throughout their existence. When it was first depicted in The Deadly Assassin (1976), the Doctor's brain was connected so that he could enter the virtual world of the Matrix to do battle with the titular villain, spending over an entire episode in the fantasy landscape devised by, as it transpired, his old enemy the Master and containing such diverse elements as First World War nightmare images, a deadly jungle and desert, strange beasts and even an evil clown and surgeon. The concept was expanded in later serials, with the Doctor reentering the Matrix in Arc of Infinity (1981) and again – somehow physically – in The Trial of a Time Lord (1986), this time finding a largely Victorian dreamscape devised by an evil aspect of himself: the Valeyard. By the time of the relaunched series starring Christopher Eccleston (2005), Gallifrey and the Doctor's race were destroyed and the fate of their Matrix is not known
• Paranoia Agent by Satoshi Kon
• Possible Worlds, both the play and the 2000 film adaptation of that play
• Serial Experiments Lain by Chiaki J. Konaka
• "Ship in a Bottle" episode of Star Trek: The Next Generation, in which the fictional Professor Moriarty of Sir Arthur Conan Doyle's Sherlock Holmes stories is allowed to exist in a simulation of the world
• In the Star Trek fictional universe, particularly in and since the series Star Trek: The Next Generation, holodecks are simulators aboard starships and other facilities used for training and recreation
• The 13th Floor by Josef Rusnak
• Tron (1982) by Walt Disney
• Vanilla Sky by Cameron Crowe (a remake of Abre los ojos by Alejandro Amenábar)
• "The X-Files" has featured a number of episodes involving simulated realities of some sort.

Interactive fiction

• A Mind Forever Voyaging by Steve Meretzky

Video games

• Final Fantasy X by Yoshinori Kitase
• Final Fantasy VII
• Star Ocean 3: Till the End of Time by Minato Koio
• Sid Meier's Alpha Centauri
• Silent Hill
• Metal Gear Solid 2: Sons of Liberty and Metal Gear Solid 3: Snake Eater by Hideo Kojima
• .hack series.
• Custom Robo
• Kingdom Hearts II
• Second Life
• The Sims
• The Sims 2
• The Legend of Zelda: Link's Awakening
• Torment

See also

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• Artificial consciousness
• Artificial intelligence
• Artificial reality
• Augmented reality
• Brain-in-a-vat A brain-computer interface scenario discussed by philosophers.
• Computational universe theory
• Consensus reality
• Cyberpunk
• Digital philosophy
• Digital physics
• Holodeck
• Hyperreality
• Mind Transfer
• Mixed reality
• The Matrix movie, which popularized the idea that reality could be simulated
• Tipler's "Omega point", the hypothetical point at which the cosmos achieves infinite computing power
• Reality
• Virtual Reality
• Zeno's paradoxes

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• Major contributing thinkers:

• Nick Bostrom
• René Descartes
• David Deutsch
• Edward Fredkin
• Raymond Kurzweil
• Seth Lloyd
• Plato
• Frank Tipler
• Zeno of Elea
• Konrad Zuse

Bibliography

• Copleston, Frederick (1993) [1946]. "XIX Theory of Knowledge". A History of Philosophy, Volume I: Greece and Rome. New York: Image Books (Doubleday). p. 160. ISBN 0-385-46843-1.

• Copleston, Frederick (1994) [1960]. "II Descartes (I)". A History of Philosophy, Volume IV: Modern Philosophy. New York: Image Books (Doubleday). p. 86. ISBN 0-385-47041-X.

• Deutsch, David (1997) [1997]. The Fabric of Reality. London: Penguin Science(Allen Lane). ISBN 0-14-014690-3. {{cite book}}: Cite has empty unknown parameters: |1= and |2= (help)

• Lloyd, Seth (2006). Programming the Universe: A Quantum Computer Scientist Takes On the Cosmos. Knopf. ISBN 978-1400040926.

• Peikoff, Leonard (1993) [1991]. "Reality". Objectivism: The Philosophy of Ayn Rand. New York: Meridian. pp. 17–23. ISBN 0-452-01101-9.

• Tipler, Frank (1994) [1994]. TThe Physics of Immortality. Doubleday. ISBN 0-385-46799-0. {{cite book}}: Cite has empty unknown parameters: |1=, |2=, and |3= (help)

External links

• Computationalism: The Very Idea, an overview of computationalism by David Davenport.
• The Cutting Edge of Haptics, an article in MIT's Technology review on touch illusion technology by Duncan Graham-Rowe.
• http://www.digitalphilosophy.org, Edward Fredkin's website about his pursuit of proof that reality is running on a digital substrate.
• http://whatisthematrix.warnerbros.com/rl_cmp/phi.html The philosophy of "The Matrix"
• http://www.channel4.com/science/microsites/W/what_we_still_dont_know/textonly/to_arewereal.html#a6 British Astronomer Royal Sir Martin Rees.
• http://www.simulation-argument.com, Nick Bostrom's website about the Simulation Argument
• http://www.simulism.org, a wiki devoted to the possibility that our reality is a simulation.
• "That Mysterious Flow"". Davies, Paul, (Sept. (2002) Scientific American. 287 (3): 40–45. {{cite journal}}: Cite has empty unknown parameter: |1= (help)
• http://www.wired.com/wired/archive/10.12/holytech.html "Wired" article
• "Zombies" - Philosophical zombie article by Robert Kirk on the Stanford Encyclopedia of Philosophy.