Physicists say there may be a way
to prove that we live in a computer simulation
by 
George Dvorsky
George Dvorsky Back in 2003, Oxford professor Nick Bostrom suggested that we may be living in a computer simulation [see below]. In his paper, Bostrom offered very little science to support his hypothesis — though he did calculate the computational requirements needed to pull off such a feat. And indeed, a philosophical claim is one thing, actually proving it is quite another. But now, a team of physicists say proof might be possible, and that it's a matter of finding a cosmological signature that would serve as the proverbial Red Pill from the Matrix. And they think they know what it is.
According to Silas Beane and his team at the University of Bonn in Germany, a simulation of the universe should still have constraints, no matter how powerful. These limitations, they argue, would be observed by the people within the simulation as a kind of constraint on physical processes.
So,
how could we ever hope to identify these constraints? Easy: We just need build
our own simulation of the universe and find out. And in fact, this is fairly
close to what the physicists are actually trying to do. To that end, they've
created an ultra-small version of the universe that's down to the femto-scale
(which is even smaller than the nano-scale).
Interestingly, the researchers consider their simulation to be a forerunner to more powerful versions in which molecules, cells, and even humans themselves might someday be generated. But for now, they're interested in creating accurate models of cosmological processes — and finding out which ones might represent hard limits for simulations.
To that end, they have investigated the Greisen–Zatsepin–Kuzmin limit (or GZK cut-off) as a candidate — a cut-off in the spectrum of high energy particles. The GZK cut-off is particularly promising because it behaves quite interestingly within the QCD model.
According to the Physics arXiv blog, this cut-off is well known and comes about when high energy particles interact with the cosmic microwave background, thus losing energy as they travel long distances. The researchers have calculated that the lattice spacing imposes some additional features on the spectrum, namely that the angular distribution of the highest energy components should exhibit cubic symmetry in the rest of the lattice (causing it to deviate significantly from isotropy).
"In other words," write the arXiv bloggers, "the cosmic rays would travel preferentially along the axes of the lattice, so we wouldn't see them equally in all directions."
And that would be the kind of reveal the physicists are looking for — an indication that there is indeed a man hiding behind the curtain.
And what's particularly fascinating about this is that we can make this measurement now with our current level of technology. As the researchers point out, finding this effect would be the same as 'seeing' the orientation of the lattice on which our own universe is simulated.
That said, the researchers caution that future computer models may utilize completely different paradigms, ones that are outside of our comprehension. Moreover, this will only work if the lattice cut-off remains consistent with what we see in nature.
At any rate, it's a remarkable suggestion — one that could serve as an important forerunner to further research and insights into this fasinating possibility.
The entire study can be found at Physics arXiv.
Are You Living in a Computer Simulation?
By NICK BOSTROM
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 from 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.1 Yet present purposes require no new 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 constraints2 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.3 Another
author gives a rough estimate of 1042 operations per second for a computer with
a mass on order of a large planet.4 (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.5 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.6 An alternative estimate, based the number of synapses in the
brain and their firing frequency, gives a figure of ~1016-1017 operations per
second.7
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.8 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.9 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 estimate10.
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:
Pf: Fraction of all
human-level technological civilizations that survive to reach a posthuman stage
N: Average number
of ancestor-simulations run by a posthuman civilization
H: Average number
of individuals that have lived in a civilization before it reaches a posthuman
stage
Writing 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 IfIN
for the average number of ancestor-simulations run by such interested
civilizations, we have11
In e.g. N. Bostrom, “The Doomsday argument, Adam & Eve, UN++, and Quantum
Joe.” Synthese 127(3): 359-387 (2001); and most fully in my book Anthropic
Bias: Observation Selection Effects in Science and Philosophy, Routledge,
New York, 2002.
[For complete equations see original link below]
Because of the immense computing power of
posthuman civilizations, IN 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) 0≈fP
(2) 0≈fI
(3) 1≈ f sim
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:
Cr(SIM / sim = x) = x (#)
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. 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 is 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 argumentv12 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 premise, 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 worthwhile 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:
Cr (DOOM | fP ≈1)≈1
One
can imagine hypothetical situations where we have such evidence as would trump
knowledge of fP. 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.13
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.14
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.15 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
Notes
1 See e.g. K. E. Drexler, Engines of Creation: The
Coming Era of Nanotechnology, London, Forth Estate, 1985; N. Bostrom, “How
Long Before Superintelligence?” International Journal of Futures Studies, vol.
2, (1998); R. Kurzweil, The Age of Spiritual Machines: When computers exceed
human intelligence, York, Viking Press, 1999; H. Moravec, Robot: Mere
Machine to Transcendent Mind, Oxford University Press, 1999.
2 Such as the Bremermann-Bekenstein bound and the black
hole limit (H. J. Bremermann, “Minimum energy requirements of information
transfer and computing.” International Journal of Theoretical Physics 21:
203-217 (1982); J. D. Bekenstein, “Entropy content and information flow in
systems with limited energy.” Physical Review D 30: 1669-1679 (1984); A.
Sandberg, “The Physics of Information Processing Superobjects: The Daily Life
among the Jupiter Brains.” Journal of Evolution and Technology, vol. 5
(1999)).
3 K. E. Drexler, Nanosystems: Molecular Machinery,
Manufacturing, and Computation, New York, John Wiley & Sons, Inc.,
1992.
4 R. J. Bradbury, “Matrioshka Brains.” Working
manuscript (2002),
http://www.aeiveos.com/~bradbury/MatrioshkaBrains/MatrioshkaBrains.html.
5 S. Lloyd, “Ultimate physical limits to computation.” Nature
406 (31 August): 1047-1054 (2000).
6 H. Moravec, Mind Children, Harvard University
Press (1989).
7 Bostrom (1998), op. cit. 8 See
references in foregoing footnotes
9 As we build more and faster computers, the cost of
simulating our machines might eventually come to dominate the cost of
simulating nervous systems.
10 100
billion humans×50 years/human 30 million secs/year×[1014, 1017] operations in
each human brain per second [1033, 1036] operations.
11
Space does not permit a recapitulation of that defense here, but we can bring
out one of the underlying intuitions
12 See e.g. J. Leslie, “Is the End of the World Nigh? ” Philosophical Quarterly 40, 158: 65-72 (1990).
12 See e.g.
J. Leslie, “Is the End of the World Nigh? ” Philosophical Quarterly 40, 158:
65-72 (1990).
13 See my paper “Existential
Risks: Analyzing Human Extinction Scenarios and Related Hazards.” Journal of
Evolution and Technology, vol. 9 (2001) for a survey and analysis of the
present and anticipated future threats to human survival.
14 See e.g.
Drexler (1985) op cit., and R. A. Freitas Jr., “Some Limits to Global Ecophagy
by Biovorous Nanoreplicators, with Public Policy Recommendations.” Zyvex
preprint April (2000), http://www.foresight.org/NanoRev/Ecophagy.html
.
[Published in Philosophical Quarterly (2003)
Vol. 53, No. 211, pp. 243-255. (First version: 2001)]
From http://people.uncw.edu/guinnc/courses/Spring11/517/Simulation.pdf
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