hn-classics/_stories/2003/9054846.md

---
created_at: '2015-02-16T01:09:48.000Z'
title: Are You Living In a Computer Simulation? (2003)
url: http://simulation-argument.com/simulation.html
author: theunamedguy
points: 52
story_text: 
comment_text: 
num_comments: 60
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created_at_i: 1424048988
_tags:
- story
- author_theunamedguy
- story_9054846
objectID: '9054846'
year: 2003

---
# 

ARE YOU LIVING IN A COMPUTER SIMULATION?

 

BY NICK BOSTROM

 

#### 

ABSTRACT

 

 

#### 

I. INTRODUCTION

 

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. 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. That is the basic idea. The rest of this paper will spell it
out more carefully.

            Apart form the interest this thesis may hold for those who
are engaged in futuristic speculation, there are also more purely
theoretical rewards. The argument provides a stimulus for formulating
some methodological and metaphysical questions, and it suggests
naturalistic analogies to certain traditional religious conceptions,
which some may find amusing or thought-provoking.

            The structure of the paper is as follows. First, we
formulate an assumption that we need to import from the philosophy of
mind in order to get the argument started. Second, we consider some
empirical reasons for thinking that running vastly many simulations of
human minds would be within the capability of a future civilization that
has developed many of those technologies that can already be shown to be
compatible with known physical laws and engineering constraints. This
part is not philosophically necessary but it provides an incentive for
paying attention to the rest. Then follows the core of the argument,
which makes use of some simple probability theory, and a section
providing support for a weak indifference principle that the argument
employs. Lastly, we discuss some interpretations of the disjunction,
mentioned in the abstract, that forms the conclusion of the simulation
argument.

 

#### 

II. THE ASSUMPTION OF SUBSTRATE-INDEPENDENCE

 

A common assumption in the philosophy of mind is that of
*substrate-independence*. The idea is that mental states can supervene
on any of a broad class of physical substrates. Provided a system
implements the right sort of computational structures and processes, it
can be associated with conscious experiences. It is not an essential
property of consciousness that it is implemented on carbon-based
biological neural networks inside a cranium: silicon-based processors
inside a computer could in principle do the trick as well.

Arguments for this thesis have been given in the literature, and
although it is not entirely uncontroversial, we shall here take it as a
given.

The argument we shall present does not, however, depend on any very
strong version of functionalism or computationalism. For example, we
need not assume that the thesis of substrate-independence is
*necessarily* true (either analytically or metaphysically) – just that,
in fact, a computer running a suitable program would be conscious.
Moreover, we need not assume that in order to create a mind on a
computer it would be sufficient to program it in such a way that it
behaves like a human in all situations, including passing the Turing
test etc. We need only the weaker assumption that it would suffice for
the generation of subjective experiences that the computational
processes of a human brain are structurally replicated in suitably
fine-grained detail, such as on the level of individual synapses. This
attenuated version of substrate-independence is quite widely accepted.

Neurotransmitters, nerve growth factors, and other chemicals that are
smaller than a synapse clearly play a role in human cognition and
learning. The substrate-independence thesis is not that the effects of
these chemicals are small or irrelevant, but rather that they affect
subjective experience only *via* their direct or indirect influence on
computational activities. For example, if there can be no difference in
subjective experience without there also being a difference in synaptic
discharges, then the requisite detail of simulation is at the synaptic
level (or higher).

 

**III. THE TECHNOLOGICAL LIMITS OF COMPUTATION**

****

 

At our current stage of technological development, we have neither
sufficiently powerful hardware nor the requisite software to create
conscious minds in computers. But persuasive arguments have been given
to the effect that *if* technological progress continues unabated *then*
these shortcomings will eventually be overcome. Some authors argue that
this stage may be only a few decades away.[](#_ftn1) Yet present
purposes require no assumptions about the time-scale. The simulation
argument works equally well for those who think that it will take
hundreds of thousands of years to reach a “posthuman” stage of
civilization, where humankind has acquired most of the technological
capabilities that one can currently show to be consistent with physical
laws and with material and energy constraints.

Such a mature stage of technological development will make it possible
to convert planets and other astronomical resources into enormously
powerful computers. It is currently hard to be confident in any upper
bound on the computing power that may be available to posthuman
civilizations. As we are still lacking a “theory of everything”, we
cannot rule out the possibility that novel physical phenomena, not
allowed for in current physical theories, may be utilized to transcend
those constraints[](#_ftn2) that in our current understanding impose
theoretical limits on the information processing attainable in a given
lump of matter. We can with much greater confidence establish *lower*
bounds on posthuman computation, by assuming only mechanisms that are
already understood. For example, Eric Drexler has outlined a design for
a system the size of a sugar cube (excluding cooling and power supply)
that would perform 1021 instructions per second.[](#_ftn3) Another
author gives a rough estimate of 1042 operations per second for a
computer with a mass on order of a large planet.[](#_ftn4) (If we could
create quantum computers, or learn to build computers out of nuclear
matter or plasma, we could push closer to the theoretical limits. Seth
Lloyd calculates an upper bound for a 1 kg computer of 5\*1050 logical
operations per second carried out on ~1031 bits.[](#_ftn5) However, it
suffices for our purposes to use the more conservative estimate that
presupposes only currently known design-principles.)

The amount of computing power needed to emulate a human mind can
likewise be roughly estimated. One estimate, based on how
computationally expensive it is to replicate the functionality of a
piece of nervous tissue that we have already understood and whose
functionality has been replicated *in silico*, contrast enhancement in
the retina, yields a figure of ~1014 operations per second for the
entire human brain.[](#_ftn6) An alternative estimate, based the number
of synapses in the brain and their firing frequency, gives a figure of
~1016-1017 operations per second.[](#_ftn7) Conceivably, even more could
be required if we want to simulate in detail the internal workings of
synapses and dendritic trees. However, it is likely that the human
central nervous system has a high degree of redundancy on the mircoscale
to compensate for the unreliability and noisiness of its neuronal
components. One would therefore expect a substantial efficiency gain
when using more reliable and versatile non-biological processors.

Memory seems to be a no more stringent constraint than processing
power.[](#_ftn8) Moreover, since the maximum human sensory bandwidth is
~108 bits per second, simulating all sensory events incurs a negligible
cost compared to simulating the cortical activity. We can therefore use
the processing power required to simulate the central nervous system as
an estimate of the total computational cost of simulating a human mind.

If the environment is included in the simulation, this will require
additional computing power – how much depends on the scope and
granularity of the simulation. Simulating the entire universe down to
the quantum level is obviously infeasible, unless radically new physics
is discovered. But in order to get a realistic simulation of human
experience, much less is needed – only whatever is required to ensure
that the simulated humans, interacting in normal human ways with their
simulated environment, don’t notice any irregularities. The microscopic
structure of the inside of the Earth can be safely omitted. Distant
astronomical objects can have highly compressed representations:
verisimilitude need extend to the narrow band of properties that we can
observe from our planet or solar system spacecraft. On the surface of
Earth, macroscopic objects in inhabited areas may need to be
continuously simulated, but microscopic phenomena could likely be filled
in *ad hoc*. What you see through an electron microscope needs to look
unsuspicious, but you usually have no way of confirming its coherence
with unobserved parts of the microscopic world. Exceptions arise when we
deliberately design systems to harness unobserved microscopic phenomena
that operate in accordance with known principles to get results that we
are able to independently verify. The paradigmatic case of this is a
computer. The simulation may therefore need to include a continuous
representation of computers down to the level of individual logic
elements. This presents no problem, since our current computing power is
negligible by posthuman standards.

Moreover, a posthuman simulator would have enough computing power to
keep track of the detailed belief-states in all human brains at all
times. Therefore, when it saw that a human was about to make an
observation of the microscopic world, it could fill in sufficient detail
in the simulation in the appropriate domain on an as-needed basis.
Should any error occur, the director could easily edit the states of any
brains that have become aware of an anomaly before it spoils the
simulation. Alternatively, the director could skip back a few seconds
and rerun the simulation in a way that avoids the problem.

            It thus seems plausible that the main computational cost in
creating simulations that are indistinguishable from physical reality
for human minds in the simulation resides in simulating organic brains
down to the neuronal or sub-neuronal level.[](#_ftn9) While it is not
possible to get a very exact estimate of the cost of a realistic
simulation of human history, we can use ~1033 - 1036 operations as a
rough estimate[](#_ftn10). As we gain more experience with virtual
reality, we will get a better grasp of the computational requirements
for making such worlds appear realistic to their visitors. But in any
case, even if our estimate is off by several orders of magnitude, this
does not matter much for our argument. We noted that a rough
approximation of the computational power of a planetary-mass computer is
1042 operations per second, and that assumes only already known
nanotechnological designs, which are probably far from optimal. A single
such a computer could simulate the entire mental history of humankind
(call this an *ancestor-simulation*) by using less than one millionth of
its processing power for one second. A posthuman civilization may
eventually build an astronomical number of such computers. We can
conclude that the computing power available to a posthuman civilization
is sufficient to run a huge number of ancestor-simulations even it
allocates only a minute fraction of its resources to that purpose. We
can draw this conclusion even while leaving a substantial margin of
error in all our estimates.

 

·         Posthuman civilizations would have enough computing power to
run hugely many ancestor-simulations even while using only a tiny
fraction of their resources for that purpose.

****

 

**IV. THE CORE OF THE SIMULATION ARGUMENT**

## 

 

The basic idea of this paper can be expressed roughly as follows: If
there were a substantial chance that our civilization will ever get to
the posthuman stage and run many ancestor-simulations, then how come you
are not living in such a simulation?

            We shall develop this idea into a rigorous argument. Let us
introduce the following notation:

 

![](simargtemp_files/image002.gif) : Fraction of all human-level
technological civilizations that survive to reach a posthuman stage

 

![](simargtemp_files/image004.gif) : Average number of
ancestor-simulations run by a posthuman civilization

 

![\*](simargtemp_files/image006.gif) : Average number of individuals
that have lived in a civilization before it reaches a posthuman stage

 

The actual fraction of all observers with human-type experiences that
live in simulations is then

 

![](simargtemp_files/image008.gif) 

 

Writing ![](simargtemp_files/image010.gif) for the fraction of posthuman
civilizations that are interested in running ancestor-simulations (or
that contain at least some individuals who are interested in that and
have sufficient resources to run a significant number of such
simulations), and ![](simargtemp_files/image012.gif) for the average
number of ancestor-simulations run by such interested civilizations, we
have

 

![](simargtemp_files/image014.gif)

 

and thus:

 

![](simargtemp_files/image016.gif)                                      
 (\*)

 

Because of the immense computing power of posthuman civilizations,
![](simargtemp_files/image012.gif) is extremely large, as we saw in the
previous section. By inspecting (\*) we can then see that *at least one*
of the following three propositions must be true:

 

(1)        ![](simargtemp_files/image018.gif)

(2)        ![](simargtemp_files/image020.gif)

(3)        ![](simargtemp_files/image022.gif)

 

#### 

V. A BLAND INDIFFERENCE PRINCIPLE

 

We can take a further step and conclude that conditional on the truth of
(3), one’s credence in the hypothesis that one is in a simulation should
be close to unity. More generally, if we knew that a fraction *x* of all
observers with human-type experiences live in simulations, and we don’t
have any information that indicate that our own particular experiences
are any more or less likely than other human-type experiences to have
been implemented *in vivo* rather than *in machina*, then our credence
that we are in a simulation should equal *x*:

 

![](simargtemp_files/image024.gif)                                   
(\#)

 

This step is sanctioned by a very weak indifference principle. Let us
distinguish two cases. The first case, which is the easiest, is where
all the minds in question are like your own in the sense that they are
exactly qualitatively identical to yours: they have exactly the same
information and the same experiences that you have. The second case is
where the minds are “like” each other only in the loose sense of being
the sort of minds that are typical of human creatures, but they are
qualitatively distinct from one another and each has a distinct set of
experiences. I maintain that even in the latter case, where the minds
are qualitatively different, the simulation argument still works,
provided that you have no information that bears on the question of
which of the various minds are simulated and which are implemented
biologically.

            A detailed defense of a stronger principle, which implies
the above stance for both cases as trivial special instances, has been
given in the literature.[](#_ftn11) Space does not permit a
recapitulation of that defense here, but we can bring out one of the
underlying intuitions by bringing to our attention to an analogous
situation of a more familiar kind. Suppose that *x*% of the population
has a certain genetic sequence *S* within the part of their DNA commonly
designated as “junk DNA”. Suppose, further, that there are no
manifestations of *S* (short of what would turn up in a gene assay) and
that there are no known correlations between having *S* and any
observable characteristic. Then, quite clearly, unless you have had your
DNA sequenced, it is rational to assign a credence of *x*% to the
hypothesis that you have *S*. And this is so quite irrespective of the
fact that the people who have *S* have qualitatively different minds and
experiences from the people who don’t have *S*. (They are different
simply because all humans have different experiences from one another,
not because of any known link between *S* and what kind of experiences
one has.)

The same reasoning holds if *S* is not the property of having a certain
genetic sequence but instead the property of being in a simulation,
assuming only that we have no information that enables us to predict any
differences between the experiences of simulated minds and those of the
original biological minds.

It should be stressed that the bland indifference principle expressed by
(\#) prescribes indifference only between hypotheses about which
observer you are, when you have no information about which of these
observers you are. It does not in general prescribe indifference between
hypotheses when you lack specific information about which of the
hypotheses is true. In contrast to Laplacean and other more ambitious
principles of indifference, it is therefore immune to Bertrand’s paradox
and similar predicaments that tend to plague indifference principles of
unrestricted scope.

Readers familiar with the Doomsday argument[](#_ftn12) may worry that
the bland principle of indifference invoked here is the same assumption
that is responsible for getting the Doomsday argument off the ground,
and that the counterintuitiveness of some of the implications of the
latter incriminates or casts doubt on the validity of the former. This
is not so. The Doomsday argument rests on a *much* stronger and more
controversial premiss, namely that one should reason as if one were a
random sample from the set of all people who will ever have lived (past,
present, and future) *even though we know that we are living in the
early twenty-first century* rather than at some point in the distant
past or the future. The bland indifference principle, by contrast,
applies only to cases where we have no information about which group of
people we belong to.

If betting odds provide some guidance to rational belief, it may also be
worth to ponder that if everybody were to place a bet on whether they
are in a simulation or not, then if people use the bland principle of
indifference, and consequently place their money on being in a
simulation if they know that that’s where almost all people are, then
almost everyone will win their bets. If they bet on *not* being in a
simulation, then almost everyone will lose. It seems better that the
bland indifference principle be heeded.

Further, one can consider a sequence of possible situations in which an
increasing fraction of all people live in simulations: 98%, 99%, 99.9%,
99.9999%, and so on. As one approaches the limiting case in which
*everybody* is in a simulation (from which one can *deductively* infer
that one is in a simulation oneself), it is plausible to require that
the credence one assigns to being in a simulation gradually approach the
limiting case of complete certainty in a matching manner.

 

**VI. INTERPRETATION**

## 

 

The possibility represented by proposition (1) is fairly
straightforward. If (1) is true, then humankind will almost certainly
fail to reach a posthuman level; for virtually no species at our level
of development become posthuman, and it is hard to see any justification
for thinking that our own species will be especially privileged or
protected from future disasters. Conditional on (1), therefore, we must
give a high credence to *DOOM*, the hypothesis that humankind will go
extinct before reaching a posthuman level:

![](simargtemp_files/image026.gif)

 

One can imagine hypothetical situations were we have such evidence as
would trump knowledge of ![](simargtemp_files/image002.gif) . For
example, if we discovered that we were about to be hit by a giant
meteor, this might suggest that we had been exceptionally unlucky. We
could then assign a credence to *DOOM* larger than our expectation of
the fraction of human-level civilizations that fail to reach
posthumanity. In the actual case, however, we seem to lack evidence for
thinking that we are special in this regard, for better or worse.

            Proposition (1) doesn’t by itself imply that we are likely
to go extinct soon, only that we are unlikely to reach a posthuman
stage. This possibility is compatible with us remaining at, or somewhat
above, our current level of technological development for a long time
before going extinct. Another way for (1) to be true is if it is likely
that technological civilization will collapse. Primitive human societies
might then remain on Earth indefinitely.

There are many ways in which humanity could become extinct before
reaching posthumanity. Perhaps the most natural interpretation of (1) is
that we are likely to go extinct as a result of the development of some
powerful but dangerous technology.[](#_ftn13) One candidate is molecular
nanotechnology, which in its mature stage would enable the construction
of self-replicating nanobots capable of feeding on dirt and organic
matter – a kind of mechanical bacteria. Such nanobots, designed for
malicious ends, could cause the extinction of all life on our
planet.[](#_ftn14)

            The second alternative in the simulation argument’s
conclusion is that the fraction of posthuman civilizations that are
interested in running ancestor-simulation is negligibly small. In order
for (2) to be true, there must be a strong *convergence* among the
courses of advanced civilizations. If the number of ancestor-simulations
created by the interested civilizations is extremely large, the rarity
of such civilizations must be correspondingly extreme. Virtually no
posthuman civilizations decide to use their resources to run large
numbers of ancestor-simulations. Furthermore, virtually all posthuman
civilizations lack individuals who have sufficient resources and
interest to run ancestor-simulations; or else they have reliably
enforced laws that prevent such individuals from acting on their
desires.

            What force could bring about such convergence? One can
speculate that advanced civilizations all develop along a trajectory
that leads to the recognition of an ethical prohibition against running
ancestor-simulations because of the suffering that is inflicted on the
inhabitants of the simulation. However, from our present point of view,
it is not clear that creating a human race is immoral. On the contrary,
we tend to view the existence of our race as constituting a great
ethical value. Moreover, convergence on an ethical view of the
immorality of running ancestor-simulations is not enough: it must be
combined with convergence on a civilization-wide social structure that
enables activities considered immoral to be effectively banned.

            Another possible convergence point is that almost all
individual posthumans in virtually all posthuman civilizations develop
in a direction where they lose their desires to run
ancestor-simulations. This would require significant changes to the
motivations driving their human predecessors, for there are certainly
many humans who would like to run ancestor-simulations if they could
afford to do so. But perhaps many of our human desires will be regarded
as silly by anyone who becomes a posthuman. Maybe the scientific value
of ancestor-simulations to a posthuman civilization is negligible (which
is not too implausible given its unfathomable intellectual superiority),
and maybe posthumans regard recreational activities as merely a very
inefficient way of getting pleasure – which can be obtained much more
cheaply by direct stimulation of the brain’s reward centers. One
conclusion that follows from (2) is that posthuman societies will be
very different from human societies: they will not contain relatively
wealthy independent agents who have the full gamut of human-like desires
and are free to act on them.

            The possibility expressed by alternative (3) is the
conceptually most intriguing one. If we are living in a simulation, then
the cosmos that we are observing is just a tiny piece of the totality of
physical existence. The physics in the universe where the computer is
situated that is running the simulation may or may not resemble the
physics of the world that we observe. While the world we see is in some
sense “real”, it is not located at the fundamental level of reality.

            It may be possible for simulated civilizations to become
posthuman. They may then run their own ancestor-simulations on powerful
computers they build in their simulated universe. Such computers would
be “virtual machines”, a familiar concept in computer science. (Java
script web-applets, for instance, run on a virtual machine – a simulated
computer – inside your desktop.) Virtual machines can be stacked: it’s
possible to simulate a machine simulating another machine, and so on, in
arbitrarily many steps of iteration. If we do go on to create our own
ancestor-simulations, this would be strong evidence against (1) and (2),
and we would therefore have to conclude that we live in a simulation.
Moreover, we would have to suspect that the posthumans running our
simulation are themselves simulated beings; and their creators, in turn,
may also be simulated beings.

            Reality may thus contain many levels. Even if it is
necessary for the hierarchy to bottom out at some stage – the
metaphysical status of this claim is somewhat obscure – there may be
room for a large number of levels of reality, and the number could be
increasing over time. (One consideration that counts against the
multi-level hypothesis is that the computational cost for the
basement-level simulators would be very great. Simulating even a single
posthuman civilization might be prohibitively expensive. If so, then we
should expect our simulation to be terminated when we are about to
become posthuman.)

            Although all the elements of such a system can be
naturalistic, even physical, it is possible to draw some loose analogies
with religious conceptions of the world. In some ways, the posthumans
running a simulation are like gods in relation to the people inhabiting
the simulation: the posthumans created the world we see; they are of
superior intelligence; they are “omnipotent” in the sense that they can
interfere in the workings of our world even in ways that violate its
physical laws; and they are “omniscient” in the sense that they can
monitor everything that happens. However, all the demigods except those
at the fundamental level of reality are subject to sanctions by the more
powerful gods living at lower levels.

Further rumination on these themes could climax in a *naturalistic
theogony* that would study the structure of this hierarchy, and the
constraints imposed on its inhabitants by the possibility that their
actions on their own level may affect the treatment they receive from
dwellers of deeper levels. For example, if nobody can be sure that they
are at the basement-level, then everybody would have to consider the
possibility that their actions will be rewarded or punished, based
perhaps on moral criteria, by their simulators. An afterlife would be a
real possibility. Because of this fundamental uncertainty, even the
basement civilization may have a reason to behave ethically. The fact
that it has such a reason for moral behavior would of course add to
everybody else’s reason for behaving morally, and so on, in truly
virtuous circle. One might get a kind of universal ethical imperative,
which it would be in everybody’s self-interest to obey, as it were “from
nowhere”.

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 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. Even if there are such selective simulations, you
should not think that you are in one of them unless you think they are
much more numerous than complete simulations. There would have to be
about 100 billion times as many “me-simulations” (simulations of the
life of only a single mind) as there are ancestor-simulations in order
for most simulated persons to be in me-simulations.

There is also the possibility of simulators abridging certain parts of
the mental lives of simulated beings and giving them false memories of
the sort of experiences that they would typically have had during the
omitted interval. If so, one can consider the following (farfetched)
solution to the problem of evil: that there is no suffering in the world
and all memories of suffering are illusions. Of course, this hypothesis
can be seriously entertained only at those times when you are not
currently suffering.

            Supposing we live in a simulation, what are the implications
for us humans? The foregoing remarks notwithstanding, the implications
are not all that radical. Our best guide to how our posthuman creators
have chosen to set up our world is the standard empirical study of the
universe we see. The revisions to most parts of our belief networks
would be rather slight and subtle – in proportion to our lack of
confidence in our ability to understand the ways of posthumans. Properly
understood, therefore, the truth of (3) should have no tendency to make
us “go crazy” or to prevent us from going about our business and making
plans and predictions for tomorrow. The chief empirical importance of
(3) at the current time seems to lie in its role in the tripartite
conclusion established above.[](#_ftn15) We may hope that (3) is true
since that would decrease the probability of (1), although if
computational constraints make it likely that simulators would terminate
a simulation before it reaches a posthuman level, then out best hope
would be that (2) is true.

If we learn more about posthuman motivations and resource constraints,
maybe as a result of developing towards becoming posthumans ourselves,
then the hypothesis that we are simulated will come to have a much
richer set of empirical implications.

 

**VII. CONCLUSION**

## 

 

A technologically mature “posthuman” civilization would have enormous
computing power. Based on this empirical fact, the simulation argument
shows that *at least one* of the following propositions is true: (1) The
fraction of human-level civilizations that reach a posthuman stage is
very close to zero; (2) The fraction of posthuman civilizations that are
interested in running ancestor-simulations is very close to zero; (3)
The fraction of all people with our kind of experiences that are living
in a simulation is very close to 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 relatively wealthy 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).

Unless we are now living in a simulation, our descendants will almost
certainly never run an ancestor-simulation.

 

 

## 

Acknowledgements

I’m grateful to many people for comments, and especially to Amara
Angelica, Robert Bradbury, Milan Cirkovic, Robin Hanson, Hal Finney,
Robert A. Freitas Jr., John Leslie, Mitch Porter, Keith DeRose, Mike
Treder, Mark Walker, Eliezer Yudkowsky, and several anonymous referees.

 

\[Nick Bostrom's academic homepage:
[www.nickbostrom.com](http://www.nickbostrom.com)\]  
\[More on the simulation argument:
[www.simulation-argument.com](http://www.simulation-argument.com)\]