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How I Can Be a Brain in a Vat

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The brain in a vat thought experiment is a scenario designed to make you think skeptically about the world around you. In the scenario, the world you are in is perfectly simulated by a computer that is connected to your brain which is floating in a vat. Once you consider the scenario, you must ask yourself if it is possible that you are a brain in a vat. I propose that it is possible that I am a brain in a vat because I can imagine this to be true.

Your brain is not in your head connected to your body, instead it is in a vat of nutrients connected to an extremely sophisticated computer. This computer, let’s call her Codey, is generating all the sensory inputs you have, are, or will ever experience in your life. She responds to the signals that your brain sends out, like the signal to move your arms to adjust your chair. Codey processes this signal like your nervous system would, except it doesn’t actually move your body ‒ because you do not have one. She then shows you the reaction that would have happened if it was real, giving you the complete illusion that you are sitting in a chair and you just accidentally pinched your finger trying to raise it a little higher.

On top of generating the world you are immersed in, along with all your actions in it, Codey can make you experience things that do not comply with the laws of physics. She could manifest a gravity-defying, super-sparkly, rainbow-haired unicorn in front of you. Such an event may seem like a fast track way to destroy the illusion, but Codey can ease you seamlessly into any new scenario. Make the world believable enough and she would leave you having no context to believe that this is a new environment and that anything impossible is happening.

This thought experiment is often used on a larger scale by considering the possibility that it is not just your brain in a vat, but everyone’s brain is in their own vats. All beings that have sentience in this scenario are connected to Codey. We all co-exist in the same simulated world and communicate with each other, but we each experience it through our own perspectives. We also do not technically communicate in the usual sense, instead we only have the illusion that we are communicating since it is facilitated and controlled by Codey. Now think about the scenario described and ask yourself, “is it possible that I am just a brain in a vat?” How do you know?

The reason for considering all of these hypotheticals is to think about global skepticism, whether or not we can be sure that anything we know is true or false. This questioning of knowledge is the main idea that the brains in vats thought experiment explores and is often applied to our understanding of truth, consciousness, meaning, and more. To understand this concept, you can break the problem down into a simple example: Take the observation that the sky is blue. If you know the sky is blue, then you know that you are not a brain in a vat. However, if you do not know that you are not a brain in a vat, then you do not know for certain that the sky is blue. By this logic, all of science may be founded on a misconception, and we would be forced to reevaluate all that we think we know.

There are many philosophers that have pursued a counter argument to the claim that it is possible that we are brains in vats. Hillary Putnam was one of the first, and most famous, to entertain such an argument in his essay “Reason, Truth and History” (1981). He explains the argument that if we are brains-in-vats, we would not be able to think that we are. This is shown through his claim that someone in the real world and a brain in a vat would appear to share the same language, but what the words used by the brain-in-vat refer to cannot possibly be referring to the same things that exist in the real world. A brain in a vat would have only the concept of what a chair was and be able to experience it in a conceptual way, but because it is a vat-world chair, it is not the same as a real chair.

Entertaining this philosophical problem has grown further than just philosophers, it has also made its way into mainstream media. A famous example of this is “The Truman Show.” This was a movie released in 1998 about a man named Truman who is born and grows up in a world completely invented for him. The people there are all actors pretending to be his wife, neighbors, even the mailman, and it is all secretly filmed for what we would now call a reality TV show. Truman starts to discover that things are not adding up, and he attempts to break free and escape from the set.

Exactly like the brain in the vat theory, his whole world around him is simulated, even if it is done through physical props rather than a system of virtual reality that affects his disembodied brain. For almost all his life, Truman is oblivious that his world is a facade, and he has no reason to think that it might be otherwise until anomalies that he cannot explain begin to occur. His interactions with others can be, and are, orchestrated just like a simulation, just like Codey does to the brains in vats. Truman starts to believe that he is being systematically deceived and, unlike us, he tries to prove that he is and escape.

The novel, City of Ember, also portrays aspects of the brains in vats thought experiment. The story takes place in a world completely surrounded by darkness. There is electricity, food, and water, but they are running out quickly. Two kids find a mysterious box containing damaged instructions and tools which they piece together helping them to discover a secret tunnel out of their city. They follow it and end up in the outside world; They then realize that their town was simply just under the ground the entire time (DuPrau).

Their town relates to the theory because it is, in a way, a simulation created by their ancestors to keep them safe. It is a simulation that everyone believes to be real, and their knowledge is completely based on this belief, much like our knowledge on our beliefs. The kids find a way out of the simulation, but only because they find a paper written by an architect of their dwelling before the town moved underground and everyone forgot about the outside world.

It is possible that I am a brain in a vat because I can imagine this to be true. If I think about the perception of my finger, then I can break my knowledge of its existence down into all the sensory input I receive from it. If there is no other form of perception other than the physical, then this is the only way in which I know that my finger is real. If there was a super computer that could simulate all these sensory inputs exactly as I am experiencing them now, I can imagine that as a brain in a vat I would experience everything exactly the same. I can imagine then that I am a brain in a vat, so it is possible that it is true.

By applying a modal theory we can see how likely it is that other worlds are real and that we may just be in a different world than we think we are. There is a theory of modality called modal realism that makes the brain-in-vat thought experiment easier to understand. It also makes it easier to consider the brain-in-vat thought experiment an actual possibility. The concept of modality is a philosophical tool used to ask questions about what is possible and what is necessary for a possible world to be true. Modal realism is the viewpoint that if a world is possible, then it is real. This means that there are infinite worlds that all exist independently of one another. There is only one mandate to this theory; aAll worlds must exist both spatially and temporally isolated from one another. Other than this, there is no difference between the actuality of our world and other worlds. We can take the modal realism theory one step further and say that if we can imagine a world to be possible, then it is real.

A world in which the inhabitants of the world are brains-in-vats is one that we cannot interact with, but we can still argue that it does exist through the modal realist theory. The next step is to take what we know and ask ourselves, “could our world be that brains-in-vats world?” The answer is, “yes!” Since we can imagine that it is possible that we are brains in vats, then it is possible we are in that world currently. This is because there is no difference between the way in which we would experience our world as brains-in-vats, or as embodied brains.

This theory of modality also then allows us to speculate that not only does the brains-in-vats scenario exist, but all of its variations exist too as their own separate worlds. “The Truman Show” and “City of Ember” are just two of the infinite worlds similar to the brains-in-vats world that exist. Truman is alive, in the same sense that we are alive, but he exists in a spatiotemporally separate world. He is discovering that there are inconsistencies in his reality, and venturing out to explore them. It does not take much creativity to imagine that one might be Truman in their own “The Truman Show” world. Therefore it is a possibility that we are, or, at least, in some personalized version of it.

Our own world is much more similar to the world in which “The City of Ember” exists. Though they live underground and very much have the tools to explore the limits of their world, they choose to accept their subjective reality unquestioningly. This is the same way that we often accept our own reality, never imagining that what we are experiencing may not be the whole truth of our world. In the world with the City of Ember, they have the tools to figure out whether their experience of their world is true. We do not have tools as tangible they do, but we do have the modal realist theory and others like it to help us find our way “above ground.”

The claim that we are possibly brains in vats can be disproved if we were to discover a way in which we can differentiate between the way a brain in a vat would experience and how an embodied brain would experience. This problem was addressed by Dr. Ofra Magidor, the current Waynflete Professor of Metaphysical Philosophy at the University of Oxford. In her paper “How both you and the brain-in-a-vat can know whether or not you are envatted,” she discusses the epistemic externalist response to the brains in vats scenario. Epistemic externalists believe that facts that are external to the agent’s awareness can still justify their belief.

This view is applied to mean that the BIV-you is not in a position to know the proper evidence, as real-world-you does, to support their beliefs. The evidence, as Magidor provides it, is as follows: real-world-you proposes that you are perceiving hands, while brain-in-vat-you proposes that they appear to have hands or the sensation of them. The result of this is that real-world-you has sufficient support for knowledge unlike brain-in-vat-you and, since I can propose that I am perceiving hands, I know I am not a brain in a vat.

The problem that I find with her reasoning is that the experience of perceiving and the experience of sensing would not be differentiable. Let us consider the sensation of my finger once again, although it is important to note that this explanation can be applied to any body part or interaction with our world. If all that I have ever known is my finger through my senses, then by definition I can propose that I am sensing it. However, sensing my finger has lead me to believe that I am conscious of, or perceiving, its existence.

When I imagine that all that I know is being simulated by a super computer, then I imagine that everything is completely the same except that the way in which I am interacting with my world on an unconscious level is different. In other words, there is no perceivable difference between my world and the brains in vat’s world. So, if everything is the exact same, it is possible that I am a brain in a vat right now. 

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How I Can Be A Brain In A Vat. (2021, December 16). GradesFixer. Retrieved January 31, 2023, from
“How I Can Be A Brain In A Vat.” GradesFixer, 16 Dec. 2021,
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