A scientific response to the Brain in a Vat

Scientia Salon is an enjoyable webzine discussing philosophical matters, which recently addressed an old conundrum: how do we know we are not a brain in a vat? As I see it, this question is straightforwardly answered by the usual scientific method, so here I’ll summarise the argument that I advanced in the Scientia Salon discussion.

The Matrix-style scenario, which dates back to the skepticism of Descartes, supposes that we are a brain kept alive in a vat, being fed with a stream of inputs generated by an Evil Genius. Everything that we experience as sense data is not real, but is artificially simulated and fed to us. Since, ex hypothesi, our stream of experiences is identical to that in the “real world” explanation, we cannot know for sure whether or not we are such a brain in a vat.

How to respond? First, the whole point of science is to make sense of our “stream of experiences”. We do that by looking for regularities and patterns in those experiences, and we develop those into descriptions and explanations of the world (I’ll use the term “world” here for the sum of those experiences, regardless of whether they derive from our contact with a real world, or from a simulated world being fed to us).

Science attempts to build the best models of that world, meaning the most parsimonious explanations with the greatest explanatory and predictive power. The more parsimonious the description and the greater the predictive power the more likely the model is to be close to the true state of affairs. I’ve previously written a post justifying parsimony, but the main point is that the set of all true statements is vastly smaller than the set of all possible statements, and thus we are only likely to alight on a true statement when guided to it by evidence. Any statement not supported by evidence is most likely to be wrong and thus should be discarded. Thus science’s task is finding the model with the least information content that adequately describes the world.

Now suppose that we are a brain in a vat. Science’s task is still to describe and model everything, including the “stream of experiences”. Regardless of whether the “world” is real or simulated, the standard scientific “real-world model” gives the greatest parsimony and predictive power in describing that world. Any departure from that standard model would result in a worse account (one that is less parsimonious and less predictive about that stream of experiences). That’s because science’s models do work very well about our world and are the best that we have.

One might object that in a “brain in vat” scenario the Evil Genius could feed us any stream of experience he liked, with no rhyme or reason to it, no regularities and no predictability. That is indeed possible, but then the stream of experiences could only be described essentially as a streamed video tape, which is the most information-hungry type of model and one that would be totally useless at predicting anything.

In contrast the “real world” model is very compact in that all one needs are the basic laws of physics and all else follows from that. This model has a vast amount of predictive power, as we know from the fact that engineering works, and planes we build fly, and predictions we make for solar eclipses come true.

biv2

The brain-in-vat model has no capacity to make any predictions at all about the stream of experiences, unless we make all sorts of assumptions about the Evil Genius and why he is feeding us the stream of experiences. Yet, ex hypothesi, we can never have any information about the Evil Genius or his doings.

The only way of regaining any degree of parsimony or predictive power is to build the real-world model into the brain-in-vat model. Thus, we can consider three competing models:

(1) The standard scientific real-world model.

(2) A brain in a vat being fed the {standard scientific real-world model}.

(3) A brain in a vat being fed a video-tape stream of information.

The first of these is by far the most parsimonious. The third is the worst, being vastly less parsimonious than the second. The second is worse than the first since it encompasses everything in the first but then adds a wrapper of additional content. Nor is the additional content trivial, since any explanation would have to describe the Evil Genius and the vat and the brain, and give an explanation of where the Genius came from and why he is acting as he is. This will amount to a whole meta-reality, and since that is going to take a quantity of information akin to that of the standard real-world model, the second scenario is going to involve an information content of order double that of the real-world model.

Thus the brain-in-vat model is invoking that vast increase in information content to explain absolutely nothing at all; it is pointed to by literally no evidence whatsoever, since, ex hypothesi, the brain-in-vat scenario envisages that we have exactly the same stream-of-experiences, and thus evidence, that we have in the real-world model. It is thus a hypothesis bad enough to make William of Occam faint with horror, and can be excised by the merest glance towards his razor.

Indeed, this real-world-plus-meta-reality idea is one of a class of models that all fail for the same reason. We can suppose that all sorts of things could be added to our model of the world (parallel dimensions; Narnia-like realities; orbiting teapots à la Russell; Flying Spaghetti Monsters, et cetera) yet if there is no actual evidence for them then the scientific method simply discounts them.

The in-a-vat wrapper to the real-world model is along the same lines, a vast and needless complication that doesn’t in any way improve the model’s fit to evidence. We could just as well imagine any number of other parallel meta-realities that make no difference to what we experience. Since there are an infinite number of such possibilities the chances of any random one of them being actually true is infinitessimal.

Thus, by the adoption of the usual scientific method, invoking Occam’s razor and principles of parsimony and the need for predictive power, we can reject brain-in-a-vat scenarios. That, of course, does not mean that they can be absolutely ruled out, any more than we can rule out any other hypothesis designed to leave no discernible trace at all on our experience of the world (apophatic theologians are particularly good at inventing these), but the chances of any such suggestion being true is too low to merit taking it seriously.

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11 thoughts on “A scientific response to the Brain in a Vat

  1. Pingback: Brain in a Vat | Ramblings

    1. Coel Post author

      Hi Ron,
      I’ve written a reply to your reply on your blog. Here’s the ending to it:

      We’re mostly in agreement, in that we both appeal to parsimony to dispense with the BIV wrapper. I’m then going one step further and trying to justify parsimony in terms of a probabilistic argument. That’s the big difference between us, since you don’t regard my argument as valid. However, from what you’ve said here I don’t see how you are countering my argument.

      Essentially the BIV wrapper is one of an infinite number of conceivable meta-realities for which there is zero evidence, since they are hypothesized as making no discernable difference to what we experience.

      For any one of these meta-realities that is actually true (if any), I can list a very large number of alternative meta-realities (possibly an infinite number of alternatives) that are not true. Would you agree with that?

      If so, then I list all the possible meta-realities, pick one at random and say, “that meta-reality is indeed true”. Would you agree that, more likely than not, that statement is false (which follows from the previous paragraph)?

      Cheers, Coel.

  2. Joe

    Hi Coel
    I didn’t know you had a blog. I am glad to see you do.

    It seems to me that science requires some assumptions. 1) we have sense impressions 2) that there is a world outside of our sense impressions and 3) that outside world somehow interacts with our sense impressions.

    Now I think parsimony could suggest we only need to adopt 1 as being true. But adding 2 and 3 is just adding beliefs that are beyond our experience and violates parsimony.

    We don’t need to assume there are others tweaking our brain we just need to assume we have sense impressions. Maybe like a dream or any way. But to go beyond the sense impressions and to start believing in things outside of them – well then you are just adding stuff you can’t verify.

    As far as predictions being a ground to believe in an objective reality well that doesn’t really work either. Our memories are just more sense impressions. I can say I have had dreams where in the dream I remember things happening. But it was all just part of the dream. I can wake up and go back to sleep and have a completely different history in the same night. All of it seems perfectly consistent.

    I can also say on the other end that some things in this world don’t really fit with how we would predict or make sense. Issues involving the infinite and quantum mechanics come to mind.

    I am not saying we should believe we are just dreaming or are brains in a vat. But I do think this problem is more difficult to deal with than you suggest.

    Reply
    1. Coel Post author

      Hi Joe,
      Thanks for commenting:

      It seems to me that science requires some assumptions. 1) we have sense impressions …

      Or, more basically, that we experience a stream of experiences. Whether these result from our senses is then a conclusion that we work out. I’d think that the starting point that we are experiencing experiences is a pretty solid one.

      … 2) that there is a world outside of our sense impressions and 3) that outside world somehow interacts with our sense impressions.

      As I see it, these are not assumptions. These are part of the “world view” that we develop by trying to understand and model the stream of experiences. If a world model in which we were brains in a vat actually worked better (in terms of explanatory and predictive power), then we’d adopt that instead. In the article I argue that that is not the case.

      I can say I have had dreams where in the dream I remember things happening. But it was all just part of the dream. … All of it seems perfectly consistent.

      This is true, but the “everything is a dream” model has essentially zero explanatory and predictive power. The “everything is a dream” idea can only model the stream-of-experiences essentially as a video-tape stream. That is the most information-hungry, the least parsimonious and the least explanatory sort of model.

    2. Joe

      Hi Coel

      In understanding the Cartesian argument you should understand that we believe we have internal thoughts and there exists an external world. That is we have impressions of things that we think exist outside of our thoughts.

      The dream argument clearly demonstrates that the external world does not need to exist for us to hold these beliefs. (I am assuming you do not think there is an external world that corresponds to your dreams.) Accordingly parsimony would say we reject the notion that there is an external world.

      I am not sure why you say the everything is a dream is essentially a video tape stream. I think most people know what a dream is. For me to believe that there is an external world corresponding to my dream would clearly violate parsimony.

      The dream model without an external world can entirely explain our experiences. As far as predictions it completely explains those as well. Because when you are in a dream you think you are talking to people. You think things are happening just as you predict. Maybe when you wake up you see there were logical gaps but when you are in the dream you don’t necessarily see them. That is the point. You can’t know that for sure.

      We are something that involves ideas and thoughts. But to think those thoughts correspond with an external world cuts against parsimony.

      And just because you say 2 and 3 are part of your worldview that does not mean they are not assumptions. The brain in a vat/dream model would explain everything we think and account for all of our predictions. Understand that as a brain in a vat what you think are memories of things could change in an instant just like they can in dreams. Your impressions of everything acting consistently and predictably would be just as they are now.

    3. Coel Post author

      Hi Joe,

      But to think those thoughts correspond with an external world cuts against parsimony.

      Parsimony is about the amount of information needed to explain and describe something. Suppose everything was indeed a dream. How would you then produce a parsimonious model of that stream of experiences? Since dreams have no rhyme or reason to them, you couldn’t. You couldn’t, for example, make predictions using “laws of physics” because there is no necessity for a dream to comply with them.

      Thus your model would just be a video-tape style frame-by-frame account of the dream. That is the most information-hungry type of model, and thus the least parsimonious, and it has no predictive power. From the history of the dream up until now one could not predict what happened next, because dreams are not like that.

      The only way of producing a parsimonious account of the stream-of-experiences is by building in the “real-world model”, because the real-world model has been developed exactly as our best and most parsimonious model of everything we experience, complete with parsimonious laws of physics that allow us to make predictions.

      But, if you’re going to adopt the model of “we are dreaming the {real-world model}” then it becomes more parsimonious to simply drop the “we are dreaming”, which adds nothing to the explanatory and predictive power of the model, and just have the {real-world model}. Thus, having an external reality is actually by far the most parsimonious account we have.

      If you disagree, show how adopting the “we are dreaming” model can produce better predictions of what we’ll experience in the future. If it can’t do that, we can excise that idea as having no explanatory or predictive power.

    4. Joe

      “Parsimony is about the amount of information needed to explain and describe something. Suppose everything was indeed a dream. How would you then produce a parsimonious model of that stream of experiences? Since dreams have no rhyme or reason to them, you couldn’t. ”

      Coel

      I am not sure you really understand the power of the Cartesian argument. When you wake up you realize dreams seem to have no rhyme or reason but that is not necessarily the case when you are in the dream. The model for the stream of experiences is that we are just dreaming them. Just like when we are asleep we dream.

      Let me ask you this. 1) When you sleep and dream are you not having a sequence of experiences? 2) Do you think there is an actual external world that corresponds with those dream experiences?

      Of course not. Believing there is an external world that corresponds with those experiences is unnecessary. It would violate parsimony. Would you agree?

      Well then what is it about what we think of as our waking experience that makes you think parsimony wouldn’t rule out an external world there too. It too could be entirely explained just as the dreaming experiences are. Namely without resorting to a whole bunch of things that have independent existence.

      The real world model is the assumption we make about our experiences. Just like when we are dreaming we assume there is an external world there too. E.g., When we dream we assume we really are talking to other people etc. But of course we realize that we can have those experiences without there actually being that external world.

      The external world model was not built based on considerations of parsimony. We just naturally think its there just like we think its there when we are dreaming. If we actually used parsimony we would reject the notion that there are all these other things actually existing and corresponding with our internal beliefs/sensations.

      “If you disagree, show how adopting the “we are dreaming” model can produce better predictions of what we’ll experience in the future. If it can’t do that, we can excise that idea as having no explanatory or predictive power.”

      When I dream I often find no difficulties with the predictions or explanations of things. When you say our predictions must come true you are sort of begging the question against the argument. Sure if we are actually always dreaming our predictions are not coming true because our memories might be constantly shifting and there is no correspondence with an external world. But that doesn’t mean we are not dreaming because even when I dream things *seem* to be consistent. That is all that is required. We can’t break free of our own existence to see how things really are. We just have our experiences.

    5. Coel Post author

      Hi Joe,
      Sorry for delayed response, owing to work and press-release stuff:

      Let me ask you this. 1) When you sleep and dream are you not having a sequence of experiences?

      Yes.

      2) Do you think there is an actual external world that corresponds with those dream experiences?

      No, I don’t. Invoking an external world corresponding to the dream would not improve the explanation of and understanding of the dream experience.

      It would violate parsimony. Would you agree?

      Yes, in that case it would. It would not improve the model, and so adding it would be un-parsimonious.

      Well then what is it about what we think of as our waking experience that makes you think parsimony wouldn’t rule out an external world there too. It too could be entirely explained just as the dreaming experiences are.

      Yes, the waking experience could indeed be entirely explained just as the dreaming experiences are. That explanation has two features: firstly, the dream makes no real sense, it’s just an fairly nonsensical stream of occurrences, and second: there is some meta-reality, outside the dream, that explains why the dream is occurring, why the person is dreaming.

      Now, the point of science is to produce the best explanation of our stream of experiences, which I’ll call the WakingExperience/Dream or WE/D (leaving aside which it is until later). By “best” we mean the most parsimonious and having the most explanatory and predictive power about that WE/D. That means concise yet powerful explanations.

      By that standard, the above “dream” explanation of the WE/D is hopeless. Suppose we ask, why does the WE/D contain regularities such as day/night cycles, seasonal cycles, and all the other regularities about how the WE/D proceeds that we call “laws of nature”?

      One answer is “it’s just a dream, that’s just how it is”. That is about the worst an answer can be (“worst” by the above standard).

      Another answer is the “real world model”. That is *vastly* better in every respect, where by “better” we mean parsimony and explanatory and predictive power. That explains huge amounts about the WE/D and gives huge amount of predictive power about the experiences in the WE/D.

      For example, if we were to ask when the next solar eclipse will occur in the WE/D, then the “it’s just a dream” model gives no answer, whereas the “real world model” gives a very good and reliable answer.

      Now, you might say, a-hah, I’ll now claim that we are dreaming the real-world-model. The real-world-model *is* what we are dreaming. Therefore we can adopt and make use of all of the explanatory and predictive power of the real-world model. That’s the only hope of getting any sort of explanatory and predictive power into the “it’s a dream” model.

      This model is then: there is a meta-reality that is dreaming the {real-world model}.

      Now, let’s compare *that* to the simple: {real-world-model}.

      On that comparison, the phrase “there is a meta-reality that is dreaming the … ” adds absolutely nothing to the explanation of anything we actually experience. The bit of the model that does the explaining is the {real-world model} bit. Yet that is sufficient on its own. Everything that we actually experience is dealt with by the {real-world model} aspect.

      At *that* point the phrase “there is a meta-reality that is dreaming the …” becomes superfluous. It adds nothing at all to the explanation. Yet in invokes a whole meta-reality that is entirely unexplained.

      It is the worst sort of violation of parsimony, invoking an entire meta-reality for no explanatory or predictive gain of any aspect of the WE/D. Thus, by parsimony, we simply omit that phrase as unwarranted and superfluous and explanatorily useless.

      At that point we’re left with: {real-world model}.

      If we actually used parsimony we would reject the notion that there are all these other things actually existing and corresponding with our internal beliefs/sensations.

      Parsimony is not about the number of entities that exist. It’s about the information content of the explanation.

      In terms of information content:
      Option 1: {real-world model},
      is vastly more parsimonious than:
      Option 2: there is a meta-reality that is dreaming the {real-world model},
      because any information needed to specify that meta-reality is additional, yet adds nothing to the explanation of the WE/D.

      When I dream I often find no difficulties with the predictions or explanations of things.

      If you think that, then please predict the content of your next dream! I bet I can predict the time of the next sunrise much more accurately than you can predict the time and content of your next dream.

      Further, if you think that the WE/D is a dream, then predict the time of the next solar eclipse. If you use the {real-world model} to do that then you’ll run straight into my above argument.

      When you say our predictions must come true …

      I’m not saying that. I’m saying that quite demonstrably the {real-world model} does have a lot of predictive power about the WE/D.

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