---
title: "Thought experiment"
chunk: 1/3
source: "https://en.wikipedia.org/wiki/Thought_experiment"
category: "reference"
tags: "science, encyclopedia"
date_saved: "2026-05-05T03:12:59.237630+00:00"
instance: "kb-cron"
---

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 δείκνυμι, deiknymi, 'thought experiment', "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 c. 1812. 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 imaginary conduct of a real experiment that would be subsequently performed as a real physical experiment 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:

Salviati: If then we take two bodies whose natural speeds are different, it is clear that on uniting the two, the more rapid one will be partly retarded by the slower, and the slower will be somewhat hastened by the swifter. Do you not agree with me in this opinion?Simplicio: You are unquestionably right.Salviati: But if this is true, and if a large stone moves with a speed of, say, eight while a smaller moves with a speed of four, then when they are united, the system will move with a speed less than eight; but the two stones when tied together make a stone larger than that which before moved with a speed of eight. Hence the heavier body moves with less speed than the lighter; an effect which is contrary to your supposition. Thus you see how, from your assumption that the heavier body moves more rapidly than the lighter one, I infer that the heavier body moves more slowly.

== 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 (irrealis moods) – "What might happen (or, what might have happened) 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 (especially ethics), physics, and other fields (such as cognitive psychology, history, political science, economics, social psychology, law, organizational studies, marketing, and epidemiology).  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 (or even refute) a prevailing theory, often involving the device known as reductio ad absurdum, (as in Galileo's original argument, a proof by contradiction),
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 ===
Thought experiments can produce some very important and different outlooks on previously unknown or unaccepted theories. However, they may make those theories themselves irrelevant, and could possibly create new problems that are just as difficult, or possibly more difficult to resolve.
In terms of their practical application, thought experiments are generally created to: