Thought experiment
A thought experiment is an imaginary scenario that is meant to elucidate or test an argument or theory. It is often an experiment that would be hard, impossible, or unethical to actually perform. It can also be an abstract hypothetical that is meant to test our intuitions about morality or other fundamental philosophical questions.
History
The ancient Greek, "was the most ancient pattern of mathematical proof", and existed before Euclidean mathematics, where the emphasis was on the conceptual, rather than on the experimental part of a thought experiment.Johann Witt-Hansen established that Hans Christian Ørsted was the first to use the equivalent German term Gedankenexperiment. Ørsted was also the first to use the equivalent term Gedankenversuch in 1820.
By 1883, Ernst Mach used Gedankenexperiment in a different sense, to denote exclusively the conduct of a experiment that would be subsequently performed as a by his students. Physical and mental experimentation could then be contrasted: Mach asked his students to provide him with explanations whenever the results from their subsequent, real, physical experiment differed from those of their prior, imaginary experiment.
The English term thought experiment was coined as a calque of Gedankenexperiment, and it first appeared in the 1897 English translation of one of Mach's papers. Prior to its emergence, the activity of posing hypothetical questions that employed subjunctive reasoning had existed for a very long time for both scientists and philosophers. The irrealis moods are ways to categorize it or to speak about it. This helps explain the extremely wide and diverse range of the application of the term thought experiment once it had been introduced into English.
Galileo's demonstration that falling objects must fall at the same rate regardless of their masses was a significant step forward in the history of modern science. This is widely thought to have been a straightforward physical demonstration, involving climbing up the Leaning Tower of Pisa and dropping two heavy weights off it, whereas in fact, it was a logical demonstration, using the thought experiment technique. The experiment is described by Galileo in his 1638 work Two New Sciences thus:
Uses
Thought experiments may be used to explore a hypothesis and the implementation of theories around it. They are also used in education, or for personal entertainment.Examples of thought experiments include Schrödinger's cat, that was meant to attack the Copenhagen Interpretation of quantum mechanics by showing that its assumptions could lead to the seemingly absurd condition of a cat being simultaneously alive and dead, and Maxwell's demon, which attempts to demonstrate the ability of a hypothetical finite being to violate the 2nd law of thermodynamics.
It is a common element of science-fiction stories.
Thought experiments, which are well-structured, well-defined hypothetical questions that employ subjunctive reasoning – "What might happen if... " – have been used to pose questions in philosophy at least since Greek antiquity, some pre-dating Socrates. In physics and other sciences many thought experiments date from the 19th and especially the 20th Century, but examples can be found at least as early as Galileo.
In thought experiments, we gain new information by rearranging or reorganizing empirical data in a new way and drawing new inferences from them, or by looking at these data from a different and unusual perspective. In Galileo's thought experiment, for example, the rearrangement of empirical experience consists of the original idea of combining bodies of different weights.
Thought experiments have been used in philosophy, physics, and other fields. In law, the synonym "hypothetical" is frequently used for such experiments.
Regardless of their intended goal, all thought experiments display a patterned way of thinking that is designed to allow us to explain, predict, and control events in a better and more productive way.
Theoretical consequences
In terms of their theoretical consequences, thought experiments generally:- challenge a prevailing theory, often involving the device known as reductio ad absurdum,,
- confirm a prevailing theory,
- establish a new theory, or
- simultaneously refute a prevailing theory and establish a new theory through a process of mutual exclusion
Practical applications
In terms of their practical application, thought experiments are generally created to:
- challenge the prevailing status quo, identify flaws in the argument presented, to preserve
- extrapolate beyond the boundaries of already established fact
- predict and forecast the indefinite and unknowable future
- explain the past
- facilitate the retrodiction, postdiction and hindcasting of the otherwise indefinite and unknowable past
- facilitate decision making, choice, and strategy selection
- solve problems, and generate ideas;
- move current unsolved problems into another more productive problem space
- attribute causation, preventability, blame, and responsibility for specific outcomes
- assess culpability and compensatory damages in social and legal contexts
- ensure the repeat of past success
- examine the extent to which past events might have occurred differently
- ensure the future avoidance of past failures
Fields
Philosophy
In philosophy, a thought experiment typically presents an imagined scenario with the intention of eliciting an intuitive or reasoned response about the way things are in the thought experiment. The scenario will typically be designed to target a particular philosophical notion, such as morality, or the nature of the mind or linguistic reference. The response to the imagined scenario is supposed to tell us about the nature of that notion in any scenario, real or imagined.For example, a thought experiment might present a situation in which an agent intentionally kills an innocent for the benefit of others. Here, the relevant question is not whether the action is moral or not, but more broadly whether a moral theory is correct that says morality is determined solely by an action's consequences. John Searle imagines a man in a locked room who receives written sentences in Chinese, and returns written sentences in Chinese, according to a sophisticated instruction manual. Here, the relevant question is not whether or not the man understands Chinese, but more broadly, whether a functionalist theory of mind is correct.
It is generally hoped that there is universal agreement about the intuitions that a thought experiment elicits. A successful thought experiment will be one in which intuitions about it are widely shared. But often, philosophers differ in their intuitions about the scenario.
Other philosophical uses of imagined scenarios arguably are thought experiments also. In one use of scenarios, philosophers might imagine persons in a particular situation, and ask what they would do.
For example, in the veil of ignorance, John Rawls asks us to imagine a group of persons in a situation where they know nothing about themselves, and are charged with devising a social or political organization. The use of the state of nature to imagine the origins of government, as by Thomas Hobbes and John Locke, may also be considered a thought experiment. Søren Kierkegaard explored the possible ethical and religious implications of Abraham's binding of Isaac in Fear and Trembling. Similarly, Friedrich Nietzsche, in On the Genealogy of Morals, speculated about the historical development of Judeo-Christian morality, with the intent of questioning its legitimacy.
An early written thought experiment was Plato's allegory of the cave. Another historic thought experiment was Avicenna's "Floating Man" thought experiment in the 11th century. He asked his readers to imagine themselves suspended in the air isolated from all sensations in order to demonstrate human self-awareness and self-consciousness, and the substantiality of the soul.
Science
Scientists tend to use thought experiments as imaginary, "proxy" experiments prior to a real, "physical" experiment. In these cases, the result of the "proxy" experiment will often be so clear that there will be no need to conduct a physical experiment at all.Scientists also use thought experiments when particular physical experiments are impossible to conduct, such as Einstein's thought experiment of chasing a light beam, leading to special relativity. This is a unique use of a scientific thought experiment, in that it was never carried out, but led to a successful theory, proven by other empirical means.
Properties
Further categorization of thought experiments can be attributed to specific properties.Possibility
In many thought experiments, the scenario would be nomologically possible, or possible according to the laws of nature. John Searle's Chinese room is nomologically possible.Some thought experiments present scenarios that are not nomologically possible. In his Twin Earth thought experiment, Hilary Putnam asks us to imagine a scenario in which there is a substance with all of the observable properties of water, but is chemically different from water. It has been argued that this thought experiment is not nomologically possible, although it may be possible in some other sense, such as metaphysical possibility. It is debatable whether the nomological impossibility of a thought experiment renders intuitions about it moot.
In some cases, the hypothetical scenario might be considered metaphysically impossible, or impossible in any sense at all. David Chalmers says that we can imagine that there are zombies, or persons who are physically identical to us in every way but who lack consciousness. This is supposed to show that physicalism is false. However, some argue that zombies are inconceivable: we can no more imagine a zombie than we can imagine that 1+1=3. Others have claimed that the conceivability of a scenario may not entail its possibility.