Brain In A Vat Hypothesis Statement

"Brain in a jar" redirects here. For other uses, see Brain in a Jar (Dungeons & Dragons). For the biology of brain in a vat, see isolated brain.

In philosophy, the brain in a vat (alternately known as brain in a jar) is a scenario used in a variety of thought experiments intended to draw out certain features of human conceptions of knowledge, reality, truth, mind, consciousness and meaning. It is an updated version of René Descartes' evil demon thought experiment originated by Gilbert Harman.[1] Common to many science fiction stories, it outlines a scenario in which a mad scientist, machine, or other entity might remove a person's brain from the body, suspend it in a vat of life-sustaining liquid, and connect its neurons by wires to a supercomputer which would provide it with electrical impulses identical to those the brain normally receives.[2] According to such stories, the computer would then be simulating reality (including appropriate responses to the brain's own output) and the "disembodied" brain would continue to have perfectly normal conscious experiences, such as those of a person with an embodied brain, without these being related to objects or events in the real world.


The simplest use of brain-in-a-vat scenarios is as an argument for philosophical skepticism[3] and solipsism. A simple version of this runs as follows: Since the brain in a vat gives and receives exactly the same impulses as it would if it were in a skull, and since these are its only way of interacting with its environment, then it is not possible to tell, from the perspective of that brain, whether it is in a skull or a vat. Yet in the first case most of the person's beliefs may be true (if they believe, say, that they are walking down the street, or eating ice-cream); in the latter case their beliefs are false. Since the argument says one cannot know whether one is a brain in a vat, then one cannot know whether most of one's beliefs might be completely false. Since, in principle, it is impossible to rule out oneself being a brain in a vat, there cannot be good grounds for believing any of the things one believes; a skeptical argument would contend that one certainly cannot know them, raising issues with the definition of knowledge.

The brain in a vat is a contemporary version of the argument given in HinduMaya illusion, Plato's Allegory of the Cave, Zhuangzi's "Zhuangzi dreamed he was a butterfly", and the evil demon in René Descartes' Meditations on First Philosophy.

Philosophical debates[edit]

While the disembodied brain (the brain in a vat/BIV) can be seen as a helpful thought experiment, there are several philosophical debates surrounding the plausibility of the thought experiment. If these debates conclude that the thought experiment is implausible, a possible consequence would be that we are no closer to knowledge, truth, consciousness, representation, etc. than we were prior to the experiment.

Argument from biology[edit]

One argument against the BIV thought experiment derives from the idea that the BIV is not and cannot be biologically similar to that of an embodied brain (that is, a brain found in a person). Since the BIV is disembodied, it follows that it does not have a similar biology to that of an embodied brain. That is, the BIV lacks the connections from the body to the brain, which renders the BIV neither neuroanatomically nor neurophysiologically similar to that of an embodied brain.[4][5] If this is the case, we cannot say that it is even possible for the BIV to have similar experiences to the embodied brain, since the brains are not equal.

Argument from (ultra-)externalism[edit]

A second argument deals directly with the stimuli coming into the brain. This is often referred to as the account from externalism or ultra-externalism.[6] In the BIV, the brain receives stimuli from a machine. In an embodied brain, however, the brain receives the stimuli from the sensors found in the body (via touching, tasting, smelling, etc.) which receive their input from the external environment. This argument oftentimes leads to the conclusion that there is a difference between what the BIV is representing and what the embodied brain is representing. This debate has been hashed out, but remains unresolved, by several philosophers including Uriah Kriegel,[7]Colin McGinn,[8] and Robert Rupert.[9] This debate has ramifications for philosophy of mind discussions on (but not limited to) representation, consciousness, content, cognition, and embodied cognition.[10]

In fiction[edit]

Main article: Isolated brain § In fiction

See also: Simulated reality in fiction

  • Agents of S.H.I.E.L.D., Season 4
  • "The Brain of Colonel Barham", a 1965 episode of the TV series The Outer Limits
  • The Brain of Morbius
  • Brainstorm
  • Caprica
  • The City of Lost Children
  • Cold Lazarus
  • Dark Star
  • Donovan's Brain
  • Fallout
  • Futurama
  • Gangers in Doctor Who
  • Inception
  • The Man with Two Brains
  • The Matrix film series
  • "Out of Time", an episode of Red Dwarf
  • Old World Blues, an expansion pack for Fallout: New Vegas
  • Possible Worlds
  • Psycho-Pass
  • Repo Men
  • RoboCop (most obvious with Cain in RoboCop 2)
  • Saints Row IV
  • "Ship in a Bottle", an episode of Star Trek: The Next Generation
  • Sid Meier's Alpha Centauri
  • Soma
  • Source Code
  • "Spock's Brain", an episode of Star Trek: The Original Series
  • Strange Days
  • The Thirteenth Floor
  • Transcendence
  • "The Vacation Goo", an episode of American Dad!
  • Welt am Draht
  • The Whisperer in Darkness
  • Where am I?, written by Daniel Dennett
  • William and Mary by Roald Dahl
  • "White Christmas - Part II", an episode of Black Mirror

See also[edit]


External links[edit]

A brain in a vat that believes it is walking
  1. ^Harman, Gilbert 1973: Thought, Princeton/NJ, p.5.
  2. ^Putnam, Hilary. "Brains in a Vat"(PDF). Retrieved 21 April 2015. 
  3. ^Klein, Peter (2 June 2015). "Skepticism". Stanford Encyclopedia of Philosophy. Retrieved 7 January 2017. 
  4. ^Heylighen, Francis (2012). "A Brain in a Vat Cannot Break Out: Why the Singularity Must be Extended, Embedded, and Embodied". Journal of Consciousness Studies. University of Cincinnati. 19 (1–2): 126–142. 
  5. ^Thompson, Evan; Cosmelli, Diego (Spring 2011). "Brain in a Vat or Body in a World? Brainbound versus Enactive Views of Experience". Philosophical Topics. University of Arkansas. 39 (1): 163–180. 
  6. ^Kirk, Robert (1997). "Consciousness, Information and External Relations". Communication and Cognition. 30 (3–4). 
  7. ^Kriegel, Uriah (2014). Current Controversies in Philosophy of Mind. Routledge. pp. 180–95. 
  8. ^McGinn, Colin (1988). "Consciousness and Content". Proceedings of the British Academy. 76: 219–39. 
  9. ^Rupert, Robert (2014). The Sufficiency of Objective Representation. Current Controversies in Philosophy of Mind. Routledge. pp. 180–95. 
  10. ^Shapiro, Lawrence (2014). When Is Cognition Embodied. Current Controversies in Philosophy of Mind. Routledge. pp. 73–90. 

There is an important distinction between reality-is-a-simulation and brain-in-a-vat, namely that in the former one's brain is simulated, whereas in the latter one's brain exists outside of the simulation and only one's experience is simulated.

Because of this "stitching together" of two realities, brain-in-a-vat offers far more opportunities to discover the simulation.

But first, we must ask some questions:

  • How different is the "real" reality from the simulated one? (Perhaps entities in the "real" reality are not human. Maybe they are advanced beings seeking to understand simpler life forms or vastly different laws of physics.)
  • Why is my brain in the vat? (Entertainment? Research? Healthcare? Space travel? Imprisonment?)
  • What percentage of other people in this simulation are also brains-in-vats? (If I am the only one, the simulation can do a lot to both hide itself from me, and to only simulate very small parts of the world at a time.)

The easiest way to determine that you ARE a brain in a vat is to be "brought back" into the real world. Short of dying in the simulation, your best bet at doing this is to find a way to force the simulation to do a lot of work, using a lot of processor power, which might annoy your captors sufficiently to get you out. (For example if you build a huge room lined with TVs displaying detailed real-time satellite images of populated parts of the Earth it might force the simulation to make sure that all those areas are simulated in high detail so that you don't notice any discrepancies. Maybe you will be watching pre-recorded footage but if you try enough such ideas you may find something the simulation can't cope with.

There may be some sort of failsafe "get me out of here" thing you can do, but that seems a bit pointless if we aren't given the memory of what it is. On the other hand one might argue that those who have "transcended" or "ascended" through meditation have found the secret to breaking out of this existence. Perhaps when we stop paying attention to our senses we can start to sense the vat we are in---or perhaps it is necessary to disconnect ourselves from our senses in order to be safely disconnected from the simulation!

If you are a brain in a vat, then your simulated brain will appear to contradict the laws of physics at times. If you get a knock on the head in the simulated world, this cannot be reproduced exactly in the real world, and so either your brain and the simulated brain respond differently, or the simulated brain mirrors the real brain and therefore seems to contradict the laws of physics. This might be very hard to detect, but it will be there. Of course, can you really trust the MRI machine or the neurosurgeon not to be manipulated by the simulation so that everything seems fine? Perhaps your best bet is to build your own brain imaging machine. Even then, the simulation could twist reality to lie to you, but the bigger the lies, the greater the chance an inconsistency will arise.

Onto your next question: if I'm a brain in a vat, can I in theory experience the real world?

Sure! If technology exists to feed your senses with an artificial world, it should be even easier to feed your senses with input from a camera, microphone, touch and motion sensors, etc.

Of course, you could be told that you are visiting the real world but are in fact in another simulation. But that's beside the point.

If the real world is utterly different from the simulated one (e.g. it's 6 dimensional, there's no light or sound, and objects can overlap) there might be some serious challenges in interfacing it with a brain that is designed for our world. But consider that we can use infra-red goggles to sense a somewhat unfamiliar world. If we are slowly introduced to a weird universe perhaps we can adapt.

If the universe is just a computer simulation, we cannot tell who is running it or why. Any discrepancies or artifacts of simulation might give us clues, but at the end of the day, we can't be completely sure of anything. The simulation designers have full control of what it's like inside the simulation, so they can hide ALL of their tracks and put in red herrings if they like.

answered Dec 29 '15 at 0:02

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