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July 26th, 2004

Philosophy in the News

This is sort of a follow up to Brian Leiter’s post on philosophy blogs in Newsweek. And equally belated.

Last week the Sydney Morning Herald ran an article by Paul Davies about the possibility that our universe is a simulation. What was interesting, to me at least, was that the article cited Nick Bostrom’s argument to this effect in The Philosophical Quarterly. (An online version of Bostrom’s paper is here.) It isn’t every day you see a philosophy journal cited in the morning newspaper. Sadly Davies didn’t cite, or even talk about, my refutation of Bostrom’s argument also in The Philosophical Quarterly. So I thought I may as well take the chance to revisit that debate and say what I thought was most important about it. Anyone who wants to write to the SMH making either of the points below is much more than welcome!

(Blog history note: I first found out about Bostrom’s paper through a chain of links starting with Instapundit, which probably makes my paper the first philosophy paper to be the result of a blog entry.)

The core of Bostrom’s argument is fairly simple. Given some plausible assumptions it is likely that there will be many more simulated conscious beings than material conscious beings over the course of the history of the world. (Bostrom makes all his conclusions conditional on these assumptions, but it makes life easier to just assume they are true, and I won’t question any of the assumptions in any case.) Now if we accept that we’re just as likely to be any one of the simulees as one of the material entities, it follows that we’re more likely to be a simulation than a material entity.

There are two problems with this argument, both due in different ways to the fact that we actually have quite a bit of evidence about just what our place in the universe is.

First, I know right now that I’m not feeling cold. So it’s not just as likely that I’m one of the people as any other, because I’m not one of the ones feeling cold. A much more plausible principle is that for any of the conscious beings whose conscious experiences are indiscriminable from mine I’m just as likely to be any one as any other. (I think even that’s not true, but let’s grant it for now.) The problem is that the assumptions don’t give us the conclusion that there are likely to more simulees than materials with conscious experiences indiscriminable from mine. Indeed, when we think about the vast variety of conscious experiences it starts to seem unlikely that there is any other being, simulation or material, with the same experiences as I have. So for all the argument has told us, the proportion of beings with conscious experiences indiscriminable from mine who are material is 1. And then applying the more plausible principle, we get that the probability that I’m material is 1.

To get the original argument to work, Bostrom has to come up with stronger principles than the plausible one I listed. But these principles all seem either ad hoc or inconsistent for reasons related to Goodman’s ‘grue’ paradox. I won’t go into the detail, because what really seems important is that the makeup of classes of beings that I know I’m not in just doesn’t seem that relevant to what probability I should assign to my being material or simulated.

The other point is that part of Bostrom’s argument relies on a principle of indiscriminability that is importantly false. I said above that Bostrom-style arguments can’t affect the probability I assign to being cold, because I can just tell that I’m not cold. Most modern theorists of perception would say the same thing about the probability I should assign to being a material being. I can just look at see that I’m material, whatever other philosophers would tell us.

Why wouldn’t we believe this? One intuitive reason turns out to be quite bad, for reasons Tim Williamson has recently stressed. It’s intuitive to think that if we were simulees rather than material beings we couldn’t tell the difference, which I guess is true. And it’s intuitive to think that this implies if we are material rather than simulees that we couldn’t tell the difference. But this doesn’t follow, because ‘is indiscriminable from’ is not symmetric.

We can make this intuitive by considering real-life cases. After 2 martinis there’s all sorts of things I can safely do, e.g. walk down steep steps, that I can’t safely do after 4 martinis. But when I’ve had 4 martinis I can’t tell the difference between by abilities and what they were when I’d only had 2 martinis. My ability to tell what’s happening is deteriorating as what is happening changes. That in no way means that after the first 2 martinis I can’t tell that I can safely walk down the steps.

The point generalises. Just because I can’t tell A from B when in situation A doesn’t mean I can’t tell A from B when in situation B if my capacities are greater in B than in A. And that’s just what happens in the simulation/material case. True, I can’t tell if I’m a simulee that I’m the product of a simulation rather than material. But if I’m material I have epistemic capacities that I don’t have if I’m a simulation. E.g. I can easily form reliable beliefs by perception. So nothing follows about what I can and can’t detect as a material being by thinking about what happens if I’m the product of simulation. The catchphrase version of this is that what happens in bad scenarios is not that relevant to what I can and can’t know by perception if I’m actually in a good scenario.

The upshot of all this is that we don’t need to worry about philosophical arguments talking us out of our naive belief that we are material beings any more than we could possibly worry about philosophical arguments talking us out of our naive beliefs that we are feeling warm (if we are). Compare: even if we knew that 99.999% of conscious beings feel cold, if we feel warm we just won’t be moved to change our beliefs by any philosophical arguments based on that statistic. I’m inclined to think that questions about whether we are material or a simulation are similar.

Posted by Brian Weatherson in Uncategorized

6 Comments »

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6 Responses to “Philosophy in the News”

  1. Istvan Aranyosi says:

    Regarding the newspaper feature, it is indeed a pity that the guy didn’t mention your response to Bostrom. It usually happens with newspapers that a topic is not presented in all its aspects.

    But regarding your response, it relies on externalism in epistemology, which in my opinion is precisely the contested kind of approach in cases like the simulation argument. See for example Dave Chalmers’ “Matrix as metaphysics”, which I personally agree with. You can’t simply say that “if I’m material I have epistemic capacities that I don’t have if I’m a simulation”. That’s precisely what the others and I dispute: one’s epistemic capacities, by assumption, are the same in both scenarios, first because one’s subjective perspective is exactly the same in both, and second because one’s objective environment is different in the two scenarios, but in aspects that don’t make a difference to one’s knowledge (e.g. if you are simulated, you still have hands as in the case you’re not, just that hands are not composed of atoms as in the physical reality, but of information bits. But you still have hands.)

    What seems to me the problem with Bostrom’s argument is not the indiscriminability thesis or the indifference principle, but something simpler, namely that from his premises one can draw this much of a conclusion:

    If we are simulated, then we will have attained a posthuman stage.

    From which:

    Our not attaining a posthuman stage implies our not being simulated.

    But not what Bostrom concludes:

    WE are not simulated only if we don’t attain a posthuman stage.

    (footnote: not attaining a posthuman stage is the same as the disjunction of human extinction and lack of further tech development)

  2. Brad Weslake says:

    Summarising from my rambling post at the time I first saw the article:

    Why assume that it is future humans who developed the simulation of our world? If we are in a simulation, then the concept of our future selves is irrelevant metaphysically, since what “really” exists is outside of our entire simulation. We may as well assume that it is God running the simulation (Bostrom mentions something like this towards the end, but from the angle that we should consider the posthumans that are running our simulations as God. But I say, why consider the God(s) who created our simulations as posthumans?). Or we might assume that the simulation is an accident that happened when a bunch of Platonic-silicon fell off a Platonic-cliff in the Platonic-”Real World” and made a Platonic-computer. That is, if we concede the possibility of a simulation we must also concede there is nothing inside the simulation that could possibly tell us anything about what is outside the simulation. Substitute “evil demon” for “simulation”; all we have here is an updated Descartes.

  3. P.D. Magnus says:

    I agree with Brad on this point, although I think of it the other way round. If you have an answer to Cartesian demon scenarios, then (mutatis mutandis) you have an answer to the simulation argument. This holds regardless of your preferred answer to the evil demon. Any respectable epistemology has some answer to the evil demon. Therefore, the simulation argument is only a problem if you lack a respectable epistemology.

    On a sociological note: I’m not sure how, but Bostrom has managed to pull off a coup of self-promotion. The simulation argument has been bandied about widely and in the least likely of places.

  4. Brad Weslake says:

    P.D.,

    That’s the way round I was thinking. On Bostrom and self-promotion, I think it would have at least something to do with his website. Or maybe it’s the endless optimism of the transhumanists that’s infectious…

  5. Keith says:

    all we have here is an updated Descartes

    Without explaining/arguing the point (sorry about that), I’ll just here state my opinion FWIW: I disagree with Brad & P.D.:
    Bostrom’s argument is significantly different & very different from the standard ways that arguments from skeptical hypotheses have been run.

  6. walker says:

    Beware the breathless optimists…………….