Brain in a vat

In philosophy, the brain in a vat (BIV; 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's evil demon thought experiment originated by Gilbert Harman. 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. 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 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 Hindu Maya 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. Brain-in-a-vat scenarios—or closely related scenarios in which the protagonist is in a virtual reality simulation and unaware of this fact—have also been used for purposes other than skeptical arguments. For example, Vincent Conitzer uses such a scenario to illuminate further facts—facts that do not follow logically from the physical facts—about qualia (what it is like to have specific experiences), indexicality (what time it is now and who I am), and personal identity. As an example, a person in the real world may observe a simulated world on a screen, from the perspective of one of the simulated agents in it. The person observing knows that besides the code responsible for the physics of the simulation, there must be additional code that determines in which colors the simulation is displayed on the screen, and which agent's perspective is displayed. (These questions are related to the inverted spectrum scenario and whether there are further facts about personal identity.) That is, the person can conclude that the facts about the physics of the simulation (which are completely determined by the code governing the physics) do not fully determine his experience on their own. But then, Conitzer argues, one could imagine a person who has become so engrossed in a VR simulation that he has forgotten that it is a simulation he is watching. That person could still reach the same conclusion, which means that our own conclusions about our own daily lives may be questionable.