I recently read an article that suggested we might be able to determine if we are part of a computer simulation run by our descendants. The idea seemed far-fetched, but after looking around, I see that it has been argued for by at least one philosopher. Notably, this abstract from "Are You Living In a Computer Simulation?":

This paper argues that at least one of the following propositions is true: (1) the human species is very likely to go extinct before reaching a “posthuman” stage; (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. It follows that the belief that there is a significant chance that we will one day become posthumans who run ancestor-simulations is false, unless we are currently living in a simulation. A number of other consequences of this result are also discussed.—Nick Bostrom. Philosophical Quarterly, 2003, Vol. 53, No. 211, pp. 243-255.

Wikipedia points out:

The concept is reminiscent of René Descartes' Evil Genius but posits a more futuristic simulated reality.

As I think about it, however, I can't think of any material difference except that the generic "demon" (which is a stand-in for any powerful being) is replaced with a specific candidate: our own decedents. While it certainly makes for some wonderful science fiction (and even seems inspired by it), there doesn't seem to be anything about the ontological and epistemological aspects of the theory that weren't anticipated by Descartes.

Is there some aspect of the Simulation Argument that improves on the Evil Genius? Would not the same limitations on proving (or disproving) this sort of existence apply equally to both?

  • Well, you can come up with all sorts of fun and utterly unproveable statements like, "Quantum mechanics is like jpeg artifacts--it's because our simulators didn't want to have to keep track of infinite precision arithmetic!" Otherwise, no, they're identical IMO.
    – Rex Kerr
    Dec 14, 2012 at 0:09
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    @Rex Kerr: I tend to agree. I discovered, by the way, that mine is an FAQ. It's not answered to my satisfaction, however. I don't see how this is true: "Thus, the simulation argument is not best thought of as a skeptical argument that would have us be more agnostic, but rather as an argument that would have us increase our credence in one particular disjunction (and decrease our credence in its negation). It aims to tell us something about the world rather than to advise us that we know less about the world than we thought we did." Dec 14, 2012 at 0:25
  • It isn't true. Raising the Evil Demon tells us that we should increase our credence that an evil demon is doing everything at its whim and decrease our credence in its negation. It's exactly the same. Except for the fun unprovable statements, which I have to admit, are a nice bonus.
    – Rex Kerr
    Dec 14, 2012 at 0:33
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    The main difference between both arguments is that NB is arguing that either some substantial empirical questions are resolved in a particular way, or we are actually living in an evil-genius kind of situation. Descartes tried nothing like that; he was merely interested in the logical possibility of such a scenario.
    – Schiphol
    Dec 14, 2012 at 15:17
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    I have a lovely detailing of the simulation argument in this other answer. The simulation argument does not say that we are living in a simulated universe. It only says we should ponder our intuitions on whether we do. Jan 17, 2013 at 16:12

2 Answers 2


If the simulation trilemma is correct, it is also trivial

Reading through the Bostrom paper the first time, I missed his definition of "posthuman". Thankfully, the term is defined:

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.

For the purposes of the paper, the critical stage is the moment when humanity is able to harness the essentially unlimited computational power that Bostrom assumes is physically possible. So the first proposition asserts that this will likely never happen either because of some unforeseen limitation or because civilizations such as our own will become extinct. (Or, really, for both reasons at the same time.) The second proposition asserts that posthumanity will be willing to conduct the sorts of simulations that are contemplated in the third proposition. If we eliminate two of the possibilities, according to Bostrom, the third must be true.

To rephrase the trilemma:

A. If a civilization can obtain unlimited computational power,
B. And there are no self-imposed restrictions to using it,
C. Then it will be used.

Bostrom further argues from C that statistically speaking, we must assume that we are part of a simulation. In order for the simulation argument to work, you must push the number of simulations as if there are essentially no resource limits. But the sticking point isn't whether any civilization will achieve this particular posthuman state, but whether such a state is possible. Once I swallow the elephant of limitless power, the gnat of this particular science fiction scenario should go down well enough.

In his FAQ, Bostrom mentions that the argument may be generalized. So, if you plug in unlimited time travel for unlimited computational power, you could formulate an argument that you are most likely the decedent of your ancestor. At the moment, unlimited time travel lacks empirical evidence, however. Or you could plug in unlimited capacity for causing suffering and arrive at the conclusion that our ancestors are certain to become sadists. If you begin with the assumption that X is potentially unlimited, then, given enough time and an agent who willing to activate it, X is certain to have extreme influence.

Our universe need not provide us the relevant evidence

Much of the paper is dedicated to describing research that considers the limits of computational power. While that research is fascinating, it's also entirely irrelevant to the argument. The easiest way to verify this is to consider the relationship between our computers and the simulations we run on them. An obvious observation is that we simulate a restricted portions of the universe. Professionally, I deal with weather simulations and while there are some that consider the entire atmosphere, most consider only a portion of the atmosphere (say the troposphere over North America) and have limited duration.

While it's true limited computational power plays a role in limiting our simulations, a bigger problem is simulation drift. Edward Norton Lorenz discovered small deviations in initial conditions will result in radically different results over time. He expressed it with the fanciful idea that a butterfly could cause a tornado. In practice, because our measurement of atmospheric properties is inexact, simulations must be reset with new input parameters on a regular basis. Increasing computational power cannot mitigate against this problem. Due to the nature of measurement, it's also impossible for us to improve our measurements to the point that we can run perpetually accurate simulations; the act of measurement produces tiny, unpredictable changes on the properties we are trying to measure.

More troubling, a case can be made that the vast majority of our simulations are of fictional scenarios, i.e. video games. The evidence of our current activities would suggest that simulations with important variables changed for no other reason than to provide entertainment far outweigh "realist" simulations. There's no reason to not conclude that the fickle tastes of the civilization that is simulating us are stimulated by giving us the illusion that computing power could be virtually unlimited. There's no reason to assume that the most prolific posthuman simulations authors aren't their generation's Jules Verne, H. G. Wells, and Issac Asimov.

The simulation argument ignores epistemological problems

From Bostrom's FAQ:

The purpose of the simulation argument is different: not to set up a skeptical problem as a challenge to epistemological theories and common sense, but rather to argue that we have interesting empirical reasons to believe that a certain disjunctive claim about the world is true (that is, (1)v(2)v(3)). The simulation argument relies crucially on non-obvious empirical premises about future technological abilities. And the conclusion of the simulation argument is not simply that we cannot be certain that we are not living in a simulation. If we knew that fSIM (the faction of all human-like beings who are simulated) was very small but non-zero, we might not be able to be completely certain that we are not in a simulation, but this would not be a very interesting contention.

In other words, among many other assumptions, the argument assumes that we can trust our empirical observations. If we take the Aristotelian assumption that the world around us is the only reality that exists, then we have no choice in the matter. But a simulation inhabited by human-like beings must contain a reality greater than its own. If we are to know anything about that other reality, we must develop an epistemology of transcendence. Our model ought to be Plato, not Aristotle. Our a priori assumptions must include some way of relating knowledge obtained empirically to knowledge of the transcendent reality. Bostrom, in his reply to Brian Weatherson [PDF], sweeps the issue under the rug; he argues that the simulated human is only likely to be wrong when it comes to the question of whether or not they are simulated and in all other respects are epistemologically competent.

But the critical question is not whether the simulated human can have transcendental knowledge, but whether observations about computational power, human psychology, and statistical certainty are transferable from this reality to any potential transcendent reality. I would argue that if they are transferable, they must endure some sort of transformation themselves. If as a species we create a certain ratio of descendants that happen to reside in computer simulations to descendants that live in physical space, it tells us little to nothing about the ratio of descendants our creators have spawned of each type. Any conclusions we draw from this ratio must be tempered by humility.


As I read the paper, I kept waiting for the punchline. But it never came. Nick Bostrom seems sincere in his belief that the castle in the air that he has constructed is supported by empirical evidence even though our current observations show that no human-like being has ever been simulated on a computer and 100% of the people known to exist are part of the same reality that we inhabit. Therefore, if we are simulated, we have been deceived by someone very powerful and of questionable morality.



This question can be cast in many forms. The problem is that there are several "possibilities" that are ontologically distinguishable: Firstly Descartes' demon, where we have some entity with powers beyond our comprehension that can manipulate our senses to create any kind of reality in our minds. Closely related we have the brain-in-a-vat, This time the "entity" is replaced by some sort of technology, thereby dispensing with the need for "powers beyond our comprehension". The brain is real, physical reality is real, only our senses are presented with a manufactured manifestation. Thirdly Last Thursdayism, the idea the God created everything mere days ago. In this case everything is real except history.

Or, we could simply be dreaming: no need for arcane forces, only the magic and mystery of our own minds. But then what if the reality in which we are sleeping is also a dream? Edgar Allen Poe's "dream within a dream"? Now nothing is real but the dreamer. Or perhaps dreams are the substance of reality.

Finally simulation, which also comes in two flavors. The consciousness is technologically transposed into a simulated environment; this one is pretty much the brain-in-a-vat without the vat. Or everything is simulated, our very minds are constructed with software. But there is an "outside" reality where the machinery that runs the simulation exist, a presumably more "real" kind of existence...


Now naturally one is tempted to ask "how can we know?", and it is precisely when we start thinking epistemologically that the whole thing collapses into one concept. The kinds of question we ask, the experiments we try to devise; if we compare them we find them the same in all these scenarios. What we want to look at, is not what we can see, but what is behind the physical. The metaphysical.

As with anything metaphysical the first question we should ask is: "Can we know?" (actually trying to devise experiments for Last Thursdayism should already give pause) The idea that we cannot gain metaphysical knowledge is old and widely accepted. Yet for the simulation argument there have been attempts to do just that. The idea is, inside the simulation certain physical measurements should deviate from their predicted values, i.e. zooming in on reality will yield ever increasing levels of detail while zooming in on a photograph eventually produces pixelation.

However it is unclear how our predictions, from within a simulated reality, could apply to the paradigm that created the simulation. Think again of the granulation inherent in a photo, now imagine we could produce a perfect photo capturing all of a particular slice of reality. Now we zoom in on it and do find granulation. Does this mean we are in a simulation or did we just find we the limits of producing perfect photographs?


There are some additional caveats that sometimes muddies the issue: such as the assumption that simulator computers have the same operating principles that we are familiar with. Worth to point out here that we couldn't possibly know every type of computing device. Also, we don't know that the laws of physics are the same in- and outside of simulation, so the set of possible operating principles may not even match.

Another untestable assumption is that there need be some "higher intelligence" involved in the creation of the simulation. But it is also possible that reality as we know it is the product of some algorithmic process. (and here)

And the most sweeping assumption of all? that it makes a difference whether or not we are simulated. After all our very biology presents a simulation to our minds. So the more perennial question is: Why am I in a simulation? Maybe I can just wake up! Or, it is my own "higher self" that really wants to win at Goodest Sim. Or, I am on trial, with my brain in a vat, so my decisions can be evaluated, without my knowing, in order to determine my eternal fate...

So is there anything scientifically or philosophically interesting here, some purpose to creating these thought experiments? Well this is exactly where the diversity of the formulations come from: their purpose or context

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