The brain in a vat: what if we live in a simulation?

Thought experiments are imaginary scenarios that help us rethink our ideas and develop new ones. They are tools that scientists, economists, historians, and thinkers have used to elicit "a heartfelt intuition that knocks the table," as philosopher Daniel Dennett writes. In this series of articles we examine some of the best-known philosophical thought experiments.

Imagine that an evil scientist has removed a brain from the body and placed it in a bucket of nutrients that keep it alive. The nerve endings have been connected to a computer that gives that person the illusion that everything is perfectly normal. He wakes up every day to go to work, goes to have a few beers with friends, meets his partner at night. Everything the same as always, he does not suspect that anything has changed. "The victim may even believe that he is sitting, reading these same words about the assumption, amusing, if quite absurd, that there is a diabolical scientist who extracts brains from bodies and places them in a bucket."

The quote is from Reason, Truth and History , a book by the American philosopher Hilary Putnam, published in 1981. The goal of this thought experiment is to suggest that everything can be an illusion and inoculate us with a good dose of skepticism. It is an idea that has been around for centuries and has also served as inspiration for science fiction books and movies, such as The Matrix . And that is as extravagant as it is difficult to disprove.

Life is simulation

The same idea can be found in Plato's myth of the cave; in Life is a Dream, by Calderón de la Barca; in the veil of Maya of Hinduism, and in the evil genius of Descartes, as Jesús Zamora Bonilla reminds us over the phone, author of In search of the self: a philosophy of the brain and professor of Philosophy of Science at UNED. The idea is that if our perceptions and brain activity take place in the brain, "caused by external stimuli", they could "come from a source other than the real world, be it a mad scientist or an evil demon, and we could not distinguish them" .

The argument, he explains, is impossible to refute one hundred percent, because in the end it is “an empirical fact: either we are brains in a bucket or we are not”. Another difficulty in refuting these claims is that this evil scientist is often given almost absolute power. For example, you could have created the whole world, including our memories, five minutes ago, as you suggested, without taking it too seriously, Bertrand Russell. Or every midnight it could start all over from scratch, like in the movie Dark City.

Putnam himself exposes this idea in his book precisely to try to refute it by means of a logical argument: if in our universe we were all brains in a bucket, there would be no external world to which our language could refer, so the phrase “we are brains in a bucket ”wouldn't even make sense. As the reader can guess, this proposal has left many philosophers dissatisfied, even though practically all of humanity agrees with it in the conclusion.

The most modern versions of the experiment suggest that we could be living in a simulation, along the lines of the Matrix . The philosopher Nick Bostrom, author of the book Superintelligence, pointed to this possibility in an article published in 2003. His argument is based on two premises: the first, that consciousness could be simulated by computer. The second, that future civilizations could have access to an enormous amount of computational power. In such a case, these civilizations could program simulations of millions of entire worlds. If so, there would be many more simulated universes than real ones, so we would be more likely to live in a simulation than in a real world. Like the Sims , but with uglier houses.

Kiefer Sutherland and Rufus Sewell in Dark City, 1998 film directed by Alex Proyas

So nothing is real?

Just because it is almost impossible to completely refute these hypotheses does not mean that they are necessarily true. Nor can we rule out (at least for now) that the universe has the same shape as Homer Simpson's face, although there is very little probability that this is the case.

In his book, Zamora Bonilla points out that it is very difficult to think that such a detailed virtual world can be designed: “Not only is the necessary computational capacity beyond what is technologically possible, but it is likely that we will never be able to find out, with all the necessary detail, the code that converts a chain of synaptic connections and nervous impulses into a specific mental experience ”.

On the other hand, there is the question of why an evil genius would do something like that, with all the work that it takes. Just because he's crazy? And in the Matrix, would it not pay more to use lithium batteries? But, of course, perhaps the Sim we removed the pool stairs to is also wondering why so much cruelty.

However, the thought experiment is not only intended to make us believe that everything is an illusion. Probably, Bostrom doesn't even think about it, since he published his article in 2003 and since then he continues to work and publish books, as if the universe existed. But it helps us better understand how our relationship with the world works. In this sense, Zamora Bonilla recalls that in a certain way we are brains in a bucket. Or in a skull: "What we perceive is not the real world without more, but we reproduce the real world through a physical process."

For example, our eyes are not video cameras that capture reality as it is, but we interpret and rework all the information that comes to us from our senses. Continuing with the example of sight and as the neuroscientist Ignacio Morgado writes in The Illusions Factory, “the light and the colors that we see are only the reading that our brain and our conscious mind make of what is truly outside of us, which is nothing other than matter and energy ”. Everything indicates that this information is reliable, since we have been using it for tens of thousands of years to survive, but there is no total and absolute correspondence between that real world and our mental activity.

As philosopher Thomas Nagel writes in A View from Nowhere, the skepticism that distills the idea of ​​the brain in a vat (and movies like Dark City ) helps us realize that “our ideas about the world, however sophisticated, they are the result of the interaction of one part of the world with part of the rest, in ways that we do not understand very well ”. Thus, this skepticism is actually a way of recognizing our limits, without for that reason we go to think that our life is nothing more than a mirage.

That is, it may seem that the experiment casts doubt on whether there is anything else in the universe other than ME, which was Descartes's starting point. But in the end it turns out that it is the other way around: the world exists and, in any case, what is in doubt is what I know about it.

Other thought experiments:

- Theseus's ship: what a rebuilt ship teaches us about identity

- The Chinese room: can a machine think?

- The lifeboat: who should I help?

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