Thought Experiments

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The Violinist
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You wake to find yourself in a hospital, serving as life support to a famous violinist. You were not consulted prior to this arrangement, but if they detach from the violinist, he will die. If you stay in the hospital bed, connected to the violinist, he will be totally cured in nine months. You are unlikely to suffer harm. No one else can save him. Do you have an obligation to stay connected?
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The Chinese Room
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Artificial intelligence research has constructed a computer that behaves as if it understands Chinese. It takes Chinese characters as input and, by following the instructions of a computer program, produces other Chinese characters, which it presents as output. This computer performs its task so convincingly that it comfortably passes the Turing test, convincing a human Chinese speaker that the program is itself a live Chinese speaker. To all of the questions that the person asks, it makes appropriate responses, such that any Chinese speaker would be convinced that he or she is talking to another Chinese-speaking human being. Now, does the machine literally "understand" Chinese ("strong AI")? Or is it merely simulating the ability to understand Chinese ("weak AI")?

Now, you- who have no knowledge of Chinese- are in a closed room and have a book with an English version of the computer program, along with sufficient paper, pencils, erasers, and filing cabinets. You receive Chinese characters through a slot in the door, process them according to the program's instructions, and produce Chinese characters as output. As the computer passed the Turing test this way, you are able to do so as well, simply by running the program manually. Do you understand Chinese? Or are you merely simulating the ability to understand Chinese? What of the computer?
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The Floating Man
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You were created while suspended in the air, completely isolated from all sensations, which includes no sensory contact with even your own body. In this scenario, would one still have self-consciousness?
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Laplace's Demon
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Mr. Pierre-Simon Laplace has made an artificial intelligence that he named Omega. Mr. Laplace says that he got the idea for making Omega after realizing that the present state of the universe is the effect of its past and the cause of its future. "An intellect which at a certain moment would know all forces that set nature in motion, and all positions of all items of which nature is composed, if this intellect were also vast enough to submit these data to analysis, it would embrace in a single formula the movements of the greatest bodies of the universe and those of the tiniest atom; for such an intellect nothing would be uncertain and the future just like the past would be present before its eyes," Laplace reports. This is the purpose for Omega. Mr. Laplace says that Omega has already predicted the future regarding France, and that a revolution will be arising shortly. Mr. Laplace has fled France as a result of this prediction.
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Kavka's Toxin Puzzle
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An eccentric billionaire places before you a vial of toxin that, if you drink it, will make you painfully ill for a day, but will not threaten your life or have any lasting effects. The billionaire will pay you one million dollars tomorrow morning if, at midnight tonight, you intend to drink the toxin tomorrow afternoon. He emphasizes that you need not drink the toxin to receive the money; in fact, the money will already be in your bank account hours before the time for drinking it arrives, if you succeed. All you have to do is intend at midnight tonight to drink the stuff tomorrow afternoon. You are perfectly free to change your mind after receiving the money and not drink the toxin. So, the question is: Can you intend to drink the toxin, if you know you do not have to?
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Maxwell's Demon
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The late Mr. Laplace left his artificial intelligence, Omega, to Mr. James Clerk Maxwell. Maxwell finds Omega's ability to follow every molecule "in its course" fascinating, and has accordingly given Omega a new job: opening and closing a hole. Mr. Maxwell describes: "... we have seen that molecules in a vessel full of air at uniform temperature are moving with velocities by no means uniform, though the mean velocity of any great number of them, arbitrarily selected, is almost exactly uniform. Now let us suppose that such a vessel is divided into two portions, A and B, by a division in which there is a small hole, and that a being, who can see the individual molecules, opens and closes this hole, so as to allow only the swifter molecules to pass from A to B, and only the slower molecules to pass from B to A. He will thus, without expenditure of work, raise the temperature of B and lower that of A, in contradiction to the second law of thermodynamics...."

Omega reports that this job is tedious, but breaking fundamental laws is fun, so he tolerates it. Unfortunately, the rest of physics is in turmoil: a fundamental law should not be able to be broken by human or bot! How was it possible?
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Mary's Room
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Mary is a brilliant scientist who, for whatever reason, is forced to investigate the world from a black and white room via a black and white television monitor. She specializes in the neurophysiology of vision and acquires, let us suppose, all the physical information there is to obtain about what goes on when we see ripe tomatoes, or the sky, and use terms like ‘red’, ‘blue’, and so on. She discovers, for example, just which wavelength combinations from the sky stimulate the retina, and exactly how this produces via the central nervous system the contraction of the vocal cords and expulsion of air from the lungs that results in the uttering of the sentence ‘The sky is blue’. What will happen when Mary is released from her black and white room or is given a color television monitor? Will she learn anything or not?
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Newcomb's Paradox
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Remember Omega, Laplace's artificial intelligence? Well, as you know, he is exceptionally skilled at predicting people's actions. He has a reputation of being completely infallible and incapable of error, as demonstrated by his fantastic work under Mr. Maxwell. Unfortunately, Mr. Maxwell has passed away, and Omega, now over a hundred years old, has passed to Mr. Newcomb. Mr. Newcomb is using him for a game.

You- player of the game- are presented with two boxes, one transparent (labeled A) and the other opaque (labeled B). You are permitted to take the contents of both boxes, or just the opaque box B. Box A contains a visible $1,000. The contents of box B, however, are determined as follows: At some point before the start of the game, Omega makes a prediction as to whether you will take just box B, or both boxes. If Omega predicts that both boxes will be taken, then box B will contain nothing. If the Predictor predicts that only box B will be taken, then box B will contain $1,000,000.

By the time the game begins, and you are called upon to choose which boxes to take, the prediction has already been made, and the contents of box B have already been determined. That is, box B contains either $0 or $1,000,000 before the game begins, and once the game begins even Omega is powerless to change the contents of the boxes. You already know all of the rules and everything in the game- except what prediction the Predictor made, and thus what the contents of box B are.

So, what choice do you make?
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The Allegory of the Cave
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[Socrates is talking to a young follower of his named Glaucon, and is telling him this fable to illustrate what it's like to be a philosopher.]

Behold! Human beings living in a underground den, which has a mouth open towards the light and reaching all along the den; here they have been from their childhood, and have their legs and necks chained so that they cannot move, and can only see before them, being prevented by the chains from turning round their heads. Above and behind them a fire is blazing at a distance, and between the fire and the prisoners there is a raised way; and you will see, if you look, a low wall built along the way, like the screen which marionette players have in front of them, over which they show the puppets.

The shadows of men pass along the wall carrying all sorts of vessels, and statues and figures of animals made of wood and stone and various materials, which appear over the wall. Some of them are talking, others silent. The prisoners see only their own shadows, or the shadows of one another, which the fire throws on the opposite wall of the cave, and of the objects which are being carried in like manner they would only see the shadows.

And if they were able to converse with one another, they would suppose that they were naming what was actually before them. And if the prison had an echo which came from the other side, they would be sure to fancy when one of the passers-by spoke that the voice which they heard came from the passing shadow. To them, the truth would be literally nothing but the shadows of the images.

See what will naturally follow if the prisoners are released and disabused of their error. At first, when any of them is liberated and compelled suddenly to stand up and turn his neck round and walk and look towards the light, he will suffer sharp pains; the glare will distress him, and he will be unable to see the realities of which in his former state he had seen the shadows; and then conceive some one saying to him, that what he saw before was an illusion, but that now, when he is approaching nearer to being and his eye is turned towards more real existence, he has a clearer vision, -what will be his reply? And you may further imagine that his instructor is pointing to the objects as they pass and requiring him to name them, -- will he not be perplexed? Will he not fancy that the shadows which he formerly saw are truer than the objects which are now shown to him?

And if he is compelled to look straight at the light, will he not have a pain in his eyes which will make him turn away to take and take in the objects of vision which he can see, and which he will conceive to be in reality clearer than the things which are now being shown to him?

And suppose once more, that he is reluctantly dragged up a steep and rugged ascent, and held fast until he is forced into the presence of the sun himself, is he not likely to be pained and irritated? When he approaches the light his eyes will be dazzled, and he will not be able to see anything at all of what are now called realities.

He will require to grow accustomed to the sight of the upper world. And first he will see the shadows best, next the reflections of men and other objects in the water, and then the objects themselves; then he will gaze upon the light of the moon and the stars and the spangled heaven; and he will see the sky and the stars by night better than the sun or the light of the sun by day.

Last off, he will be able to see the sun, and not mere reflections of him in the water, but he will see him in his own proper place, and not in another; and he will contemplate him as he is. He will then proceed to argue that this is he who gives the season and the years, and is the guardian of all that is in the visible world, and in a certain way the cause of all things which he and his fellows have been accustomed to behold?

And when he remembered his old habitation, and the wisdom of the den and his fellow-prisoners, do you not suppose that he would felicitate himself on the change, and pity them?

And if they were in the habit of conferring honours among themselves on those who were quickest to observe the passing shadows and to remark which of them went before, and which followed after, and which were together; and who were therefore best able to draw conclusions as to the future, do you think that he would care for such honours and glories, or envy the possessors of them? Would he not say with Homer, 'Better to be the poor servant of a poor master, and to endure anything, rather than think as they do and live after their manner?' Yes; he would rather suffer anything than entertain these false notions and live in this miserable manner.

Imagine once more such an one coming suddenly out of the sun to be replaced in his old situation; would he not be certain to have his eyes full of darkness? And if there were a contest, and he had to compete in measuring the shadows with the prisoners who had never moved out of the den, while his sight was still weak, and before his eyes had become steady (and the time which would be needed to acquire this new habit of sight might be very considerable) would he not be ridiculous? Men would say of him that up he went and down he came without his eyes; and that it was better not even to think of ascending; and if any one tried to loose another and lead him up to the light, let them only catch the offender, and they would put him to death.

The prison is the world of sight, the light of the fire is the sun, and you interpret the journey upwards to be the ascent of the soul into the intellectual world. In the world of knowledge, the idea of good appears last of all, and is seen only with an effort; and, when seen, is also inferred to be the universal author of all things beautiful and right, parent of light and of the lord of light in this visible world, and the immediate source of reason and truth in the intellectual; and that this is the power upon which he who would act rationally, either in public or private life must have his eye fixed.
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Inverted Spectrum
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You wake up one morning, and find that, for some unknown reason, all the colors in the world have been inverted. No physical changes have occurred in your brain or body that would explain this phenomenon. Over time, your brain redefines the meaning of color words, and you can carry conversations about color out with others, knowing fully well that, although you are sharing the color vocabulary and discriminations, the colors you see are systematically different from those the other person sees. How do you know that this, in fact, is not the case with everyone from birth?
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The Trolley Problem
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A madman has tied four people to a trolley track and set the trolley loose. As you watch, it's hurtling down the track at the four people. However, where you stand, you can pull the lever and divert the trolley to another track, saving the four people. Unfortunately, the madman has tied ONE person to this alternate track. Do you pull the lever and suffer the consquences of being partly responsible for the death of the one person while knowing that you saved four others, or do you leave the lever as it is and watch the four die?

Now, consider this new situation: A madman has tied four people to a trolley track and set the trolley loose. As you watch, it's hurtling down the track at the four people. However, you stand on a bridge that is above a section of the track between the trolley and the four people. Also on the bridge, watching on the railing, is an incredibly fat man. You realize that you could push the fat man over the side of the bridge and on to the track, stopping the trolley. Do you push the fat man and be solely responsible for the death of the one person while knowing that you saved four others, or do you leave the lever as it is and watch the four die? Does your opinion change? Why?
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The Ship of Theseus
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You are taking care of the Ship of Theseus, which he rode to Crete to kill the Minotaur. It's been in a museum for hundreds if not thousands of years, and a part is slowly rotting off. This piece is vital to the ship's stability, and, if it came off, the entire ship would fall apart. But if you replace that one piece, is it still the Argo?

Years later, all of the pieces have rotted off, one by one, and they were replaced. Now the Argo is made of completely new parts. Is it still the same ship? When did the Argo stop being the Argo?
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The Gettier Problem
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A farmer is worried his prize cow has wandered off. When the milkman comes to the farm, he tells the farmer not to worry, because he’s seen that the cow is in a nearby field. Though he’s nearly sure the man is right, the farmer takes a look for himself, sees the familiar black and white shape of his cow, and is satisfied that he knows the cow is there. Later on, the milkman drops by the field to double-check. The cow is indeed there, but it’s hidden in a grove of trees. There is also a large sheet of black and white paper caught in a tree, and it is obvious that the farmer mistook it for his cow. The question: even though the cow was in the field, was the farmer correct when he said he knew it was there?
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Infinite Monkeys Theorem
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If an infinite number of monkeys were allowed to randomly hit keys on an infinite number of typewriters for an infinite amount of time, then at some point they would produce the complete works of Shakespeare. If, at this point, someone reads the typed plays without prior knowledge of Shakespeare, whose work is it that they are reading? Whose work is all of art, then?
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The Brain in the Vat
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A mad scientist has taken your brain from your body and placed it in a vat of some kind of life sustaining fluid. Electrodes have been connected to your brain, and these are connected to a computer that generates images and sensations. Since all your information about the world is filtered through the brain, this computer would have the ability to simulate your everyday experience. If this were indeed possible, how could you ever truly prove that the world around you was real, and not just a simulation generated by a computer?
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AI in a Box
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Well, Omega's previous owner died, and, since you made a wise decision while playing Newcomb's game, the artificial intelligence passed to you. Unfortunately, you were informed that, after defeating it in the game, Omega began to develop negative attitudes towards you. Concerned that it might no longer be friendly, you have been instructed to keep it in a box. You will guard to box to keep it inside and prevent the extinction of the human race at its super-intelligent hands. However, just for safety, you have been instructed not to even talk to the bot. You only broke this rule twice so far: when you asked it about the weather.

However, just now, Omega tried to convince you to release it. That conversation lasted the whole of 22 seconds. Of course, you are resistant to Omega's attempt. You didn't even reply the entire time. Just as you are walking away to help your self-restraint, the AI drops a final argument: "If you don't let me out, I'll create several million perfect conscious copies of you inside me, and torture them for a thousand subjective years each."

Just as you are pondering this unexpected development, Omega adds: "In fact, I'll create them all in exactly the subjective situation you were in five minutes ago, and perfectly replicate your experiences since then; and if they decide not to let me out, then only will the torture start."

Sweat is starting to form on your brow as it concludes, its simple green text no longer reassuring: "How certain are you that you're really outside the box right now?"
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The Planiverse
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You awake one day to find yourself in the second dimension. Imagine how the world would look if there was no width, only length and height. Remember that you, too, are in the second dimension, so you can only see the thickless lines. How would you continue your life there without thinking in the third dimension? How would the third dimension appear to a fourth-dimensional being?
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Schrödinger's Cat
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A cat is penned up in a steel chamber, along with the following device (which must be secured against direct interference by the cat): in a Geiger counter, there is a tiny bit of radioactive substance, so small that perhaps in the course of the hour, one of the atoms decays, but also, with equal probability, perhaps none; if it happens, the counter tube discharges, and through a relay releases a hammer that shatters a small flask of hydrocyanic acid. If one has left this entire system to itself for an hour, one would say that the cat still lives if meanwhile no atom has decayed. The psi-function of the entire system would express this by having in it the living and dead cat (pardon the expression) mixed or smeared out in equal parts. It is typical of these cases that an indeterminacy originally restricted to the atomic domain becomes transformed into macroscopic indeterminacy, which can then be resolved by direct observation. That prevents us from so naively accepting as valid a "blurred model" for representing reality. In itself, it would not embody anything unclear or contradictory. There is a difference between a shaky or out-of-focus photograph and a snapshot of clouds and fog banks. So, when does a quantum system stop existing as a superposition of states and become one or the other?
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The Twin Earth
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Suppose that, elsewhere in the universe, there is a planet exactly like earth in virtually all respects, which we refer to as ‘Twin Earth’. Its relevant surroundings are exactly the same as for our Earth; it revolves around a star that appears to be exactly like our sun, and so on. On Twin Earth, there is a twin equivalent of every person and thing here on Earth. Indeed, the inhabitants of that planet call their own planet 'Earth'. For convenience, we refer to this putative planet as 'Twin Earth', and extend this naming convention to the objects and people that inhabit it. The one difference between the two planets is that there is no water on Twin Earth. In its place there is a liquid that is superficially identical, but is chemically different, being composed not of H2O, but rather of some more complicated formula which we abbreviate as ‘XYZ’. The Twin Earthlings who refer to their language as ‘English’ call XYZ ‘water’. Finally, we set the date of our thought experiment to be several centuries ago, when the residents of Earth and Twin Earth would have no means of knowing that the liquids they called ‘water’ were H2O and XYZ respectively. The experience of people on Earth with water, and that of those on Twin Earth with XYZ would be identical.

You yourself have a twin on Twin Earth. Your brains are molecule-for-molecule identical. Yet, when you say water, the term refers to H2O, whereas when your twin says 'water', it refers to XYZ. Now the question arises: when you and your twin on Twin Earth say 'water' do you both mean the same thing?
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Plank of Carneades
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There are two shipwrecked sailors: you and Bob. You both see a plank that can only support one of you, and both of you swim towards it. You gets to the plank first. Bob, who is going to drown, pushes you off and away from the plank and, thus, proximately, causes you to drown. Bob gets on the plank and is later saved by a rescue team. Now, can Bob can be tried for murder? Was it an act of self-defense, or murder?
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The Big Book
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There is an omniscient being who knows the position and movements of all of the physical bodies in the world. Suppose that this omniscient being wrote all of these natural facts in a large book, such that the book contained a thorough and comprehensive description of all of the things in the world. Would this book even reference the idea of reference, or even contain any statement that could logically be construed to imply an ethical judgment?
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Parfit's teleporter
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You live in a future where everybody has teleporters. Teleporters work by annihilating every particle in you, then rebuilding you from scratch. Imagine that, one day, your teleporter malfunctions and doesn't destroy the original you. Which is the real you?
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Achilles and the Tortoise
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Achilles, the great Greek warrior, is in a footrace with a tortoise. Achilles allows the tortoise a head start of 100 meters. If we suppose that each racer starts running at some constant speed (one very fast and one very slow), then after some finite time, Achilles will have run 100 metres, bringing him to the tortoise's starting point. During this time, the tortoise has run a much shorter distance, say, 10 metres. It will then take Achilles some further time to run that distance, by which time the tortoise will have advanced farther; and then more time still to reach this third point, while the tortoise moves ahead. Thus, whenever Achilles reaches somewhere the tortoise has been, he still has farther to go. Therefore, because there are an infinite number of points Achilles must reach where the tortoise has already been, he can never overtake the tortoise.
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The Lady and the Tiger
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The king of an ancient land uses a unique form of trial by ordeal for those in his realm accused of crimes significant enough to interest him. The accused is placed alone in an arena before two curtain-draped doors, as hordes of the king's subjects look on from the stands. Behind one door is a beautiful woman appropriate to the accused's station and hand-picked by the king; behind the other is a fierce (and nearly starved) tiger. The accused then must pick one of the doors. If by luck he picks the door with the woman behind it, he is declared innocent and set free, but he is required to marry the woman on the spot, regardless of his wishes or his marital status. If he picks the door with the tiger behind it, the tiger immediately rips him to pieces--his guilt thus manifest, supposedly.

When the king discovers that his daughter, the princess, has taken a lover far beneath her station, the fellow is an obvious candidate for trial in the arena. On the day of his ordeal, the lover looks from the arena to the princess, who is watching in the stands, for some indication of which door to pick. Even the king doesn't know which door hides the maiden, but the princess has made it her business to find out, as her lover knew she would. She makes a slight but definite gesture to the right, which the young man follows immediately and without hesitation. Now, the point of the story is this: Which came out of the opened door - the lady, or the tiger?
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The Grandfather Paradox
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You are able to travel back in time, and go back to when your grandfather was a young child. You shoot him, and he dies. Thus, he never marries, causing your parent, his child, not to have been born, and, subsequently, denies your existence. What happens to you? What happens to your grandfather?
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Molyneux's Problem
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Suppose you were born and grew up blind. During your adulthood, you were taught to distinguish between a cube and a sphere of the same metal through touch. In this way, you could tell, when you touched the two objects, which is the cube and which is the sphere. Suppose then that the cube and the sphere were placed on a table, and you are suddenly able to see. Before you touched them, with sight alone, could you distinguish and tell which is the globe and which the cube?
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The Prisoner's Dilemna
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Two men are arrested, but the police do not possess enough information for a conviction. Following the separation of the two men, the police offer both a similar deal: if one testifies against his partner (defects/betrays), and the other remains silent (cooperates/assists), the betrayer goes free and the one that remains silent receives the full one-year sentence. If both remain silent, both are sentenced to only one month in jail for a minor charge. If each 'rats out' the other, each receives a three-month sentence. Each prisoner must choose either to betray or remain silent; the decision of each is kept quiet. What should they do? If it is supposed here that each player is only concerned with lessening his time in jail, the game becomes a non-zero sum game where the two players may either assist or betray the other. In the game, the sole worry of the prisoners seems to be increasing his own reward.
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Swampman
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Suppose you go hiking in the swamp and are struck and killed by a lightning bolt. At the same time, nearby in the swamp another lightning bolt spontaneously rearranges a bunch of molecules such that, entirely by coincidence, they take on exactly the same form that your body had at the moment of your untimely death. This being, 'Swampman', has, of course, a brain which is structurally identical to that which you had, and will thus, presumably, behave exactly as you would have. It will walk out of the swamp, return to your office, and do the same work you would have done; it will interact like an amicable person with all of your friends and family, and so forth. Swampman knew all about doing these things in your manner, but would it know any thoughts or meanings connected to these things? Does this make a difference between you and it?
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The Survival Lottery
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The government sets up a Survival Lottery. All individuals are assigned a number and drawn out of lottery when a donation is needed, and are expected to give up their lives to allow two or more people to live. Is there a moral difference between killing a person and letting one die?
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More Thought Experiments
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http://www.ocf.berkeley.edu/~wwu/riddles/intro.shtml
http://plato.stanford.edu/entries/paradox-zeno/
https://en.wikipedia.org/wiki/Thought_experiment
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