I came across Nick Bostrom's paper called Are You Living in a Computer Simulation?. The paper argues that at least one of the following propositions is true:

  1. The human species is likely to go extinct before reaching the "posthuman" stage (posthuman stage meaning the stage at which humankind has acquired most of the technical abilities constistent with physical laws and with material and energy constraints),
  2. Any posthuman civilization is extremely unlikely to run a significant number of simulations of their evolutionary history (or variations thereof),
  3. We are almost certainly living in a computer simulation.

When I first read this paper it made a lot of sense to me; if there exist trillions and trillions of simulated worlds that are similar to ours and there is only one real world, we are probably living in a simulated world. However, now that I've thought about it a bit longer I don't feel so sure anymore.

Suppose that tomorrow through a series of unexpected scientific breakthroughs we are all of a sudden able to simulate our own lives and the lives of our ancestors. We have two options:

  1. Simulating our lives and those of our ancestors on a massive scale.
  2. Not simulating our lives and those of our ancestors on a massive scale.

If we decide against running simulations nothing happens, but if we decide to start simulating our ancestors lives and our own lives on a massive scale, then according to Bostrom's simulation argument, we are probably living inside a simulation.

Question: If the claim that one of the three mentioned propositions is true holds, the example I gave should hold as well, but why would it? Why would pressing a button determine whether or not we're living inside a simulation? (The mathematics Bostrom uses to justify his argument are very simple and not really convincing.)


  • 2
    When you play a video game, do you think the characters are self-aware? Why do you think Bostrom glides past this obvious refutation without mentioning it?
    – user4894
    Aug 26, 2018 at 17:01
  • @user4894 Thanks for your comment! No I don't think they are, but why does that refute his argument? It's possible that mankind will be able to simulate self-awareness or consciousness in the future, right? Aug 26, 2018 at 17:18
  • Simulate? Sure. Implement? No. What's the difference? Well, if I simulate gravity on my computer, the simulation does not attract nearby bowling balls. If I implement gravity, it does. A simulation of a mind is not self-aware. We have no theory of mind that would allow us to even begin to imagine how we would implement a mind. Bostrom's fatal error.
    – user4894
    Aug 26, 2018 at 17:30
  • 1
    To be honest, any argumentation that gives you a couple of pre-determined suggestions is immediately flagged as flawed for me. You should ask yourself, are the 3 suggestions Bostrom gives the only possible ways the argumentation could go? Are the 2 suggestions you yourself give the only two possible ways your argument could go? Aug 26, 2018 at 18:09
  • 1
    @Mr.President well, in the most basic sense, sure, but you can't allow yourself to strict yourself to these basic propositions. Where would a "simulating a small percentage of our current lives on a small scale" come in? It wouldn't necessarily imply that we're living in a simulation. Aug 26, 2018 at 19:34

3 Answers 3


I have paraphrased Nick Bostrum's three options in the chart below. A posthuman stage is when we are able to make sims. A sim is a human being simulated by a computer that is indistinguishable from ourselves.

 | A posthuman state is not possible. | 1. We CAN'T make sims. |
 | A posthuman state is possible.     | 2. We DON'T make sims. |
 |                                    | 3. We DO make sims.    |

The OP notes the following about the probability of us being sims.

...if there exist trillions and trillions of simulated worlds that are similar to ours and there is only one real world, we are probably living in a simulated world.

Bostrum observes something similar (page 6):

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.

Bostrum's calculation for the fraction of sims is the following (page 7):

fsim = fp N H / ((fp N H) + H)

fp is the fraction of civilizations able to make sims. This would be 0 if option 1 holds. N is the average number of simulations per civilization. This would be 0 if option 1 holds. H is the average number of humans who lived in the civilization prior to reaching posthuman stage. And fsim is the fraction of sims out of all humans, simulated or real. Again, this would be 0 if option 1 holds.

Assume also the "blind indifference principle" that "you have no information that bears on the question of which of the various minds are simulated and which are implemented biologically" (page 8), then the chance of any of us being a sim is high.

Now consider the OP's questions:

If the claim that one of the three mentioned propositions is true holds, the example I gave should hold as well, but why would it? Why would pressing a button determine whether or not we're living inside a simulation?

If we actually CAN press a button and therefore DO want to turn on a simulation capable of making a sim as defined above, then that is evidence that we are in option 3. If that should happen, by assumption we can make a lot of sims. If that should happen, by assumption we cannot tell sims from real people, that is, we would not be able tell whether we are sims or not.

Given the large number of sims compared to real humans and our inability to distinguish between the sim and the real human, we are more likely to be sims than real.

Some things need to be noted:

  1. No one has made any sims to date.
  2. John Searle's Chinese Room Argument suggests that we cannot make sims.
  3. Michael Rescorla raises further issues about the underlying computational theory of mind:

Advances in computing raise the prospect that the mind itself is a computational system—a position known as the computational theory of mind (CTM). Computationalists are researchers who endorse CTM, at least as applied to certain important mental processes. CTM played a central role within cognitive science during the 1960s and 1970s. For many years, it enjoyed orthodox status. More recently, it has come under pressure from various rival paradigms. A key task facing computationalists is to explain what one means when one says that the mind “computes”. A second task is to argue that the mind “computes” in the relevant sense. A third task is to elucidate how computational description relates to other common types of description, especially neurophysiological description (which cites neurophysiological properties of the organism’s brain or body) and intentional description (which cites representational properties of mental states).

Given these three points above, of the three options Bostrum presents only option 1 appears to be possible.


Bostrom, N. (2003). Are we living in a computer simulation?. The Philosophical Quarterly, 53(211), 243-255.

Rescorla, Michael, "The Computational Theory of Mind", The Stanford Encyclopedia of Philosophy (Spring 2017 Edition), Edward N. Zalta (ed.), URL = https://plato.stanford.edu/archives/spr2017/entries/computational-mind/.

John Searle, "Minds, Brains and Programs" reprinted in Haugeland, John, ed. Mind design II: philosophy, psychology, artificial intelligence. MIT press, 1997.

  • A sim is a human being simulated by a computer that is indistinguishable from ourselves. -- But this is a BEHAVIORAL standard. We can't distinguish a sim from a human. Yet the human is self-aware and the sim as far as you know is a philosophical zombie, having behavior but no consciousness. Your definition of a sim bakes into it all the wrong ideas of the simulation hypothesis. You forgot to give your sims a mind.
    – user4894
    Aug 27, 2018 at 0:22
  • @user4894 As I understand the computational theory of mind, the program gives them a mind. I don't agree with this view of mind, but these sims are assumed to have minds. It's a big assumption and I don't agree with it. My view is that option 1 is the only option possible, that is, that we cannot make such sims. Aug 27, 2018 at 0:26
  • Ok so are saying the assumption that creating a sim instantiates a mind; and that you agree this is an assumption; and it's NOT one you agree with; but that this assumption is necessary to Bostrom's argument. That much, I agree with. BUT!!! Doesn't it bother anyone that the claim is that when we play Ms. PacMan, she has an inner life as she gobbles white dots and runs from monsters? Why am I the only one troubled by the absurdity of the assumption that someday we'll create video games with self-aware characters?
    – user4894
    Aug 27, 2018 at 0:30
  • ps -- Ok I get it. The people who think the Chinese room is sentient think Ms. PacMan or her technological descendent is sentient. This is just the same old argument. If a video game can have an inner life, then the simulation argument works.
    – user4894
    Aug 27, 2018 at 0:43
  • @user4894 I agree. Neither the Chinese room nor Ms PacMan are sentient. The assumption is absurd. However, there are people who take it seriously, but based on Rescorla's information it is not as popular as it used to be. Aug 27, 2018 at 1:40

One issue to be careful about in your argument is the distinction between correlation and causation. If we decide to simulate ancestors, then this is, in a statistical sense, evidence that other civilizations would do the same, and as a result (if one buys into Bostrom's argument) evidence that we ourselves are simulated. But we don't thereby cause ourselves to be simulated.


"David Chalmers has argued that we should consider the 'simulation hypothesis' not as a skeptical hypothesis that threatens our having knowledge of the external world but as a metaphysical hypothesis regarding what our world is actually made of. " http://philosophycommons.typepad.com/flickers_of_freedom/2014/08/the-case-for-libertarian-compatibilism-a-brief-overview.html

It is meaningless really, whether we are in a simulation or not if they are truly equivalent. It would be unfalsifiable.

The vague way the simulation is presented, like Bostrom's version, is really kin to Zhuanzhi asking if he is a man dreaming of being a butterfly or vice versa, or Descartes considering the possibility of an evil demon. Just dressed up for now. I say vague, because computational and informational specifics are lacking. Ideas like the uncertainty principle are suggested to ve explained, and other computational simplifiers, but we have every reason to think them fundamental - 11 dimensions is far more promising than 4.

Bostrom's approach is like trying to do thermodynamics when you don't understand the system. Occam's razor says it is outside science just like Descartes answer, until there is evidence. I hope to see tge simulation argument developed towards that, and especially more attention to the wider nature of information. But I don't see anything truly new on the table. It just 'Could I be dreaming right now?', which is to say, describe realness.

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