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					  do we live in a                                                                                                                  futurologists think it will happen
                                                                                                                                   within the next 50 years. But even if it
                                                                                                                                   takes10 million years, it makes no

  computer simulation?                                                                                                             difference to the argument.
                                                                                                                                      Let me state what the conclusion of
                                                                                                                                   the argument is. The conclusion is that
  NICK BOSTROM                                                                                                                     at least one of the following three
                                                                                                                                   propositions must be true:

                                                                                                                                   1 Almost all civilisations at our level
  SCIENCE has revealed much about the       infrastructure. Our habitat is now           without mathematics. It starts with       of development become extinct
  world and our position within it.         largely one of human making. The             the assumption that future civilisa-      before becoming technologically
  Generally, the findings have been         fact of technological progress is also in    tions will have enough computing          mature.
  humbling. The Earth is not the centre     a sense humbling. It suggests that the       power and programming skills to be        2 The fraction of technologically
  of the universe. Our species              most advanced technology we have             able to create what I call “ancestor      mature civilisations that are interested
  descended from brutes. We are made        today is extremely limited and               simulations”. These would be detailed     in creating ancestor simulations is
  of the same stuff as mud. We are          primitive compared with what our             simulations of the simulators’            almost zero.
  moved by neurophysiological signals       descendants will have.                       predecessors – detailed enough for        3 You are almost certainly living in a
  and subject to a variety of biological,       If we extrapolate these expected         the simulated minds to be conscious       computer simulation.
  psychological and sociological            technological advances, and think            and have the same kinds of
  influences over which we have limited     through some of their logical                experiences we have. Think of an              How do we reach this conclusion?
  control and little understanding.         implications, we arrive at another           ancestor simulation as a very realistic   Suppose first that the first proposition
     One of our remaining sources of        humbling conclusion: the “simulation         virtual reality environment, but one      is false. Then a significant fraction of
  pride is technological progress. Like     argument”, which has caused some             where the brains inhabiting the world     civilisations at our level of develop-
  the polyps that over time create coral    stir since I published it three years ago.   are themselves part of the simulation.    ment eventually become technologi-
  reefs, the many generations of                The formal version of the argument          The simulation argument makes no       cally mature. Suppose, too, that the
  humans that have come before us           requires some probability theory, but        assumption about how long it will         second proposition is false. Then a
  have built up a vast technological        the underlying idea can be grasped           take to develop this capacity. Some       significant fraction of these civilisa-

 | NewScientist | 00 Month 2006                                                                                                            
tions run ancestor simulations.               It should be emphasised that the          If this were true, it would be an          predicting what will happen next are
Therefore, if both one and two are         simulation argument does not show            interesting constraint on the future       still the familiar ones – extrapolation
false, there will be simulated minds       that you are living in a simulation. The     evolution of intelligent life.             of past trends, scientific modelling and
like ours.                                 conclusion is simply that at least one           The third possibility is philosophi-   common sense. To a first approxima-
   If we work out the numbers, we          of the three propositions is true. It        cally the most intriguing. If it is        tion, if you thought you were in a
find that there would be vastly many       does not tell us which one.                  correct, you are almost certainly living   simulation, you should get on with
more simulated minds than non-                In reality, we don’t have much            in a computer simulation that was          your life in much the same way as if
simulated minds. We assume that            specific information to tell us which of     created by some advanced civilisation.     you were convinced that you were
technologically mature civilisations       the three propositions might be true.        What Copernicus and Darwin and             leading a non-simulated life at the
would have access to enormous              In this situation, it might be               latter-day scientists have been            “bottom” level of reality.
amounts of computing power.                reasonable to distribute our credence        discovering are the laws and workings          If we are in a simulation, could ever
   So enormous, in fact, that by           roughly evenly between them.                 of the simulated reality. These laws       know for certain? If the simulators
devoting even a tiny fraction to              Let us consider the options in a little   might or might not be identical to         don’t want us to find out, we probably
ancestor simulations, they would be        more detail. Proposition one is              those operating at the more                never will. But if they choose to reveal
able to implement billions of              straightforward. For example, maybe          fundamental level of reality where the     themselves, they could certainly do
simulations, each containing as many       there is some technology that every          computer that is running our               so. Another event that would let us
people as have ever existed. In other      advanced civilisation eventually             simulation exists (which, of course,       conclude with a high degree of
words, almost all minds like yours         develops and which then destroys             may itself be a simulation). In a way,     confidence that we are in a simulation
would be simulated. Therefore, by a        them. Let us hope this is not the case.      our place in the world would be even       is if we ever reach a point when we
very weak principle of indifference,       Proposition two requires that there is       humbler than we thought.                   are about to switch on our own
you would have to assume that you          a strong convergence among all                   What kind of implications would        ancestor simulations. That would be
are probably one of these simulated        advanced civilisations, such that            this have? How should it change the        very strong evidence against the first
minds rather than one of the ones          almost none of them are interested in        way you live your life?                    two propositions, leaving us only with
that are not simulated.                    running ancestor simulations. One can            Your first reaction might think that   the third.
   Hence, if you think that propositions   imagine various reasons that may lead        if three is true, then all bets are off
one and two are both false, you            civilisations to make this choice. Yet       and you would go crazy. To reason          Nick Bostrom is the director of the
should accept the third. It is not         for proposition two to be true, virtually    thus would be an error. Even if we are     Future of Humanity Institute at the
coherent to reject all three.              all civilisations would have to refrain.     in a simulation, the best methods of       University of Oxford                                                                                                                            00 Month 2006 | NewScientist | 

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