Thought experiment
A thought experiment is a hypothetical situation in which a hypothesis, theory,[a] or principle is laid out for the purpose of thinking through its consequences.
The concept is also referred to using the German-language term Gedankenexperiment within the work of the physicist Ernst Mach[2] and includes thoughts about what may have occurred if a different course of action were taken.
[11] 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.
This helps explain the extremely wide and diverse range of the application of the term thought experiment once it had been introduced into English.
Examples of thought experiments include Schrödinger's cat, illustrating quantum indeterminacy through the manipulation of a perfectly sealed environment and a tiny bit of radioactive substance, and Maxwell's demon, which attempts to demonstrate the ability of a hypothetical finite being to violate the 2nd law of thermodynamics.
[15] 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.
[21][22] Counterfactual (contrary to established fact) thought experiments – the term counterfactual was coined by Nelson Goodman in 1947,[24] extending Roderick Chisholm's (1946) notion of a "contrary-to-fact conditional"[25] – speculate on the possible outcomes of a different past;[26] and ask "What might have happened if A had happened instead of B?"
[43][44] According to David Sarewitz and Roger Pielke (1999, p123), scientific prediction takes two forms: Although they perform different social and scientific functions, the only difference between the qualitatively identical activities of predicting, forecasting, and nowcasting is the distance of the speculated future from the present moment occupied by the user.
[46] Whilst the activity of nowcasting, defined as "a detailed description of the current weather along with forecasts obtained by extrapolation up to 2 hours ahead", is essentially concerned with describing the current state of affairs, it is common practice to extend the term "to cover very-short-range forecasting up to 12 hours ahead" (Browning, 1982, p.ix).
[43][44] The activity of retrodiction (or postdiction) involves moving backward in time, step-by-step, in as many stages as are considered necessary, from the present into the speculated past to establish the ultimate cause of a specific event (e.g., reverse engineering and forensics).
[50][44] Given that retrodiction is a process in which "past observations, events, add and data are used as evidence to infer the process(es) that produced them" and that diagnosis "involve[s] going from visible effects such as symptoms, signs and the like to their prior causes",[51] the essential balance between prediction and retrodiction could be characterized as: regardless of whether the prognosis is of the course of the disease in the absence of treatment, or of the application of a specific treatment regimen to a specific disorder in a particular patient.
Conversely, the reasoning behind "backcasting" is: on the basis of an interconnecting picture of demands technology must meet in the future – "sustainability criteria" – to direct and determine the process that technology development must take and possibly also the pace at which this development process must take effect.
Backcasting [is] both an important aid in determining the direction technology development must take and in specifying the targets to be set for this purpose.
[60] In physics and other sciences, notable thought experiments date from the 19th and, especially, the 20th century; but examples can be found at least as early as Galileo.
(Philosophers might also supplement their thought experiments with theoretical reasoning designed to support the desired intuitive response.)
The scenario will typically be designed to target a particular philosophical notion, such as morality, or the nature of the mind or linguistic reference.
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.
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.
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.
In this paper, starting from certain philosophical assumptions,[64] on the basis of a rigorous analysis of a certain, complicated, but in the meantime assertedly realizable model, he came to the conclusion that quantum mechanics should be described as "incomplete".
The above-mentioned EPR philosophical starting assumptions were considered to be falsified by the empirical fact (e.g. by the optical real experiments of Alain Aspect).
