NOTE: One of the members of my Facebook group had some questions about Daniel Dennett’s dismissal of the possibility of “Descartes’ demon”, who could create virutal reality like the “Matrix” and fool the “Cogito” about the external world. We had a great discussion about it, which I have edited and posted below. While a lot of my blog posts are adapted from Facebook discussions, this one seems rather hard to change into a monologue. As a result, I am going to experiment with posting in this cleaned-up dialogue version. Thanks to all my great interlocutors. Enjoy!
Q: There seem to be some problems with the following line of reasoning from Dennett: “Might you be nothing but a brain in a vat? Might you have always been just a brain in a vat?”
Dennett’s answer (in brief): “Descartes was wise to endow his demon with *infinite* powers of trickery. Although the task is not, strictly speaking, infinite, the amount of information obtainable in short order by an inquisitive human being is staggeringly large…Throw a skeptic a dubious coin, and in a second or two of hefting, scratching, ringing, tasting, and just plain looking at how the sun glints on its surface, the skeptic will consume more bits of information than a Cray computer can organize in a year. Making a real but counterfeit coin is child’s play; making a simulated coin out of nothing but organized nerve simulations is beyond human technology now and probably forever. One conclusion we can draw from this is that we are not brains in vats — in case you were worried.” ( Consciousness Explained, page 7)
(Facepalm..) Just seems like a non-sequitur. x would be very difficult to achieve, therefore not x, but there’s even a deeper fallacy here. Our brains are creating a simulation of the universe all the time…? So, clearly that can be done. However, the implicit part of the argument sort-of makes sense, to rephrase it “The universe is, like, really complex. So, it’d be, like, really a lot of effort to fake it”. You still need a universe, and universes are kinda big. Of course, it also raises the question – if our universe is simulated, what practical difference does it make?
Adam Voight’s Reply: This is a very good question and really gets to the heart of what separates modern and premodern scepticism / science.
Let’s start with skepticism: ancient skepticism simply doubted everything and found correctly that if you do this, then that means everything “can” be doubted and that therefore there is no knowledge. This is true and yet “trivial” as mathematicians say. It’s not “interesting” and you can’t really do anything with it. Fortunately, natural selection tends to eliminate those who act in accordance with this trivial truth. Others ignore it in practice but pay lip service to it, and they are difficult to answer when they bring it up.
Modern skepticism takes many many forms, but all of them accept some form of modern science, meaning that while any one particular fact can be doubted, you cannot doubt everything at once. Every scientific theory accepts some set of truths as premises, but what they all accept are Aristotle’s Three Laws of Thought and all of their corrolaries, e.g. arithmetic, geometry, et cetera.
While it is logically permissible to doubt the reality of the external world, the truths of physics are true even if the external world is an illusion. For example, even if the Earth and Moon are “not real”, physics and engineering will still let you know how to get to the Moon and back. Even if the Moon is an illusion, you can still die from having your rocket miss it and go hurling through deep space. In either case, physics is just a well founded as it needs to be. There is no better-founded form of knowledge about the Earth and Moon available. It is useless to criticize it like some ancient skeptic or neo-Platonist. Useless, but not logically inconsistent. It is conceivable that someday someone can restate skepticism in an interesting form.
Now here is where we get to Dennett. Dennett is assuming that humans are living things, and that living things are physical objects and that physical objects “are” in the way that Aristotle or Descartes might define: subject to change, extended in space and time, et cetera. It’s logically possible to doubt the existence of the external world and all of these other premises, even though this would require redefining “existence”. Certainly a philosopher should at the very least entertain these thoughts, and if any theory could deal with them in a better way than Aristotle did, it would be one point in its favor.
However, physics can be true about physical objects regardless of the ultimate nature of these objects in the same way that evolutionary theory is true not only of “real” life but also virtual life existing in computer simulations. Even if it were found that we live in a simulation, physics and biology would still be just as true. Why? For the following two reasons:
1) Physics is not only the study of physical objects, it’s also the study of models of physical objects. Now if the our entire universe were shown to be model, then it would still fall within the purview of physics.
2) It is in fact possible that our universe is a simulation. However, the only way to prove that this is true or false is through the study of physics as it is currently done. Philosophy and physics can cooperate to define this question, and ask what sorts of answers are possible or satisfactory. Simulation theory is a possible physical theory, so long as it has practical effects. If it has no practical effects, then it’s meaningless. If it does have practical effects, then physics can study it.
Just because physics assumes the reality of the external world does not mean it is false if the world is a simulation. Newton’s theory of space and time were wrong, but his theory was good physics, because it consisted of well-defined concepts that were derived from experience. That’s why it led somewhere, and by “somewhere” I mean the NEXT theory.
Question: “My issue isn’t with Dennett’s “quasi-skepticism” (for lack of a better term) — it’s with his tautology. I do see your point, that if we want to get anywhere, we need to take *some* things for granted. Call them the Rules Of The Game. But to take data obtained using this method, and hereby try to prove that your founding assumptions are valid, is a tautology. All Dennett has really shown is the following: ‘If all possible worlds have the same physics, chemistry, biology and information science that ours does, then we are (probably) not brains in vats.’ (Actually, he hasn’t even demonstrated THIS very well IMHO — after all, he’s assuming that his imaginary mad scientists would be at our level of technological development, which seems odd given that, among other things, computing power doubles every decade — or is it faster now? But to continue…)
This is a perfectly valid conclusion, as far as it goes. But to extrapolate from this conclusion to the wider conclusion (that we are not brains in vats, full stop) is unwarranted and, moreover, misleading. After all, if we ARE brains in vats, then surely the validity of our scientific information is one of the first things we should be doubting! (I disagree with your conclusion that physics is physics; it’s trivially easy to invent a possible physics that differs wildly from ours — e.g. where an object initially at rest will gradually accelerate, or where both poles of magnets attract, or where “light speed” does not exist as an upper limit to velocity…) Essentially he’s using a clever sleight of hand to conceal a tautology from the unsuspecting reader, and all within the first seven pages, so as (I think) to dazzle them with his supposed brilliance before they have a chance to get their mental guards up. This is insidious, and unworthy of his training as a philosopher. An honest philosopher would explicitly spell out what he was doing (“For the purposes of argument, we will assume X”) and discuss the limitations of his conclusion. Dennett goes out of his way to hide them, like a magician pulling a carrot out of somebody’s ear. Unlike the magic trick, though, people read Dennett’s books (presumably) to seek truth and knowledge, not entertainment, and it’s dishonest to pull the wool over his audience’s eyes in this way.”
Adam Voight: “If it were me writing the same book, I would do it differently. He doesn’t really need to show that we’re not in a cosmic simulation, only that literal ‘brains in vats’ would not be lucid like we are now (they would not be able to read or write or think logically, for example), but I think that this section is very important to include because it looks at consciousness as a physical system, and you can’t do a science of consciousness without considering how mind is supervenient on life and life is supervenient on physics.
(Note to neophytes: “Supervenient” means based on but not reducible to the lower level. “Reducible to” means being an emergent phenomenon originating completely from a lower substrate while exhibiting characteristics that are physically impossible to deduce from the substrate.)
However, once you show that it’s physically impossible to create a single brain in a vat, this possibility becomes a LOT less interesting. It’s actually more likely that our entire universe is a simulation than that any single person’s qualia within a universe is. A true brain in a vat would not have access to the same consciousness that we do; it would be like a dream. Now they might not realize it that they were dreaming, but it is possible to know for sure that you are not dreaming if you’re awake, and he shows how this is true.
In conclusion, Dennett’s argument is not as circular as it might seem. With all of its assumptions openly stated, it goes like this: “Given our current knowledge of physics, it is impossible to implement ‘Descartes’ Demon’ within a Universe. So as far as we know, the way around this is for a civilization to implement an entire universe as a simulation. Since this is a radically different situation from a simulation at the individual level, Descartes’ thought-experiment becomes much less interesting and compelling.”
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