The field of philosophy makes extensive use of thought experiments and I have trawled the web to bring you some of my favourites:
The Trolley problem
A trolley is running out of control down a track. In its path are 5 people who have been tied to the track. Fortunately, you can flip a switch, which will lead the trolley down a different track to safety. Unfortunately, there is a single person tied to that track. Should you flip the switch? Consider another, similar dilemma. You’re walking along the track again, you notice the trolley is out of control, although this time there is no auxiliary track. But there is a man within arm’s reach, between you and the track. He’s large enough to stop the runaway trolley. You can save the five people on the trolley by pushing him onto the tracks, stopping the out-of-control vehicle, but you’ll kill the man by using him to stop the trolley. Again, what do you do?
The brain in a vat is an element used in a variety of thought experiments intended to draw out certain features of our ideas of knowledge, reality, truth, mind, and meaning. It is drawn from the idea, common to many science fiction stories, that a mad scientist 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 a virtual reality (including appropriate responses to the brain’s own output) and the person with the “disembodied” brain would continue to have perfectly normal conscious experiences without these being related to objects or events in the real world.
How many men?
How many men? is a thought experiment often used by anarcho-capitalists as a moral argument for showing that taxation is theft. There are many variations of it, but one begins with the example of a man stealing a car, which most people would regard as unethical. It then proceeds to make slight changes to the equation, with the identity of the aggressor gradually shifting from one man, to a gang of five men, to a gang of ten men who take a vote (allowing the victim to vote as well) on whether to steal the car before stealing it; to a gang of twenty men who not only take votes but have specialization of labour; to one hundred men who take the car and give the victim back a bicycle; to two hundred men who not only give the victim back a bicycle but buy a poor person a bicycle as well. It ultimately challenges the reader to say how big a group needs to be, and what characteristics it needs to have, before the immorality of theft become the alleged morality of taxation. The argument may be seen as an example of the Sorites Paradox. In a classic example of this paradox, removing one hair from a person’s head does not make them bald, but by the time the last hair is removed, they have become bald.
Mary is a brilliant scientist who is, for whatever reason, 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 colour television monitor? Will she learn anything or not?
Plank of Carneades
There are two shipwrecked sailors, A and B. They both see a plank that can only support one of them and both of them swim towards it. Sailor A gets to the plank first. Sailor B, who is going to drown, pushes A off and away from the plank and, thus, ultimately, causes A to drown. Sailor B gets on the plank and is later saved by a rescue team. The thought experiment poses the question of whether Sailor B can be tried for murder because if B had to kill A in order to live, then it would arguably be in self-defence. The English case of R. v. Dudley and Stephens (1884) established that necessity is no defence against a charge of murder.
Ticking time bomb scenario
The ticking time bomb scenario is a thought experiment that has been used in the ethics debate over whether torture can ever be justified. Simply stated, the consequentialist argument is that nations, even those such as the United States that legally disallow torture, can justify its use if they have a suspect in custody whom they feel sure possesses critical knowledge, such as the location of a time bomb or a weapon of mass destruction that will soon explode and cause great loss of life.
The infinite monkey theorem
The infinite monkey theorem states that a monkey hitting keys at random on a typewriter keyboard for an infinite amount of time will almost surely type a given text, such as the complete works of William Shakespeare. In this context, “almost surely” is a mathematical term with a precise meaning, and the “monkey” is not an actual monkey; rather, it is a metaphor for an abstract device that produces a random sequence of letters ad infinitum. The theorem illustrates the perils of reasoning about infinity by imagining a vast but finite number, and vice versa. The probability of a monkey typing a given string of text exactly, as long as, for example, Shakespeare’s Hamlet, is so tiny that, were the experiment conducted, the chance of it actually occurring during a span of time of the order of the age of the universe is minuscule but not zero. Variants of the theorem include multiple and even infinitely many typists, and the target text varies between an entire library and a single sentence. The history of these statements can be traced back to Aristotle’s On Generation and Corruption and Cicero’s De natura deorum, through Blaise Pascal and Jonathan Swift, and finally to modern statements with their iconic typewriters. In the early 20th century, Émile Borel and Arthur Eddington used the theorem to illustrate the timescales implicit in the foundations of statistical mechanics. Various Christian apologists on the one hand, and Richard Dawkins on the other, have argued about the appropriateness of the monkeys as a metaphor for evolution. Today, popular interest in the typing monkeys is sustained by numerous appearances in literature, television, radio, music, and the Internet. In 2003, an experiment was performed with six Celebes Crested Macaques, but their literary contribution was five pages consisting largely of the letter ‘S’
The Experience Machine
Suppose there were an experience machine that would give you any experience you desired. Superduper neuropsychologists could stimulate your brain so that you would think and feel you were writing a great novel, or making a friend, or reading an interesting book. All the time you would be floating in a tank, with electrodes attached to your brain. Should you plug into this machine for life, pre-programming your life’s desires?…Of course, while in the tank you won’t know that you’re there; you’ll think it’s all actually happening. Others can also plug in to have the experiences they want, so there’s no need to stay unplugged to serve them. (Ignore problems such as who will service the machines if everyone plugs in.) Would you plug in? What else can matter to us, other than how our lives feel from the inside?