In philosophy, physics, and other fields, a thought experiment (from the German Gedankenexperiment) is an attempt to solve a problem using the power of human imagination. These experiments are used to attempt to understand something about the universe. Thought experiments have been used to pose questions in philosophy at least since Greek antiquity; a famous example is Plato's cave, but others pre-date Socrates. In physics and other sciences many famous thought experiments date from the nineteenth and especially the twentieth century, but examples can be found at least as early as Galileo.

Many thought experiments include apparent paradoxes about the known or accepted, that with time have led to the reformulation or precision of theories.

Famous thought experiments

Physics

Thought experiments are popular in physics and include:

• Brownian ratchet (Richard Feynman's "perpetual motion" machine which does not violate the second law, and does not work)
• Casimir cones (Basis for almost perpetual motion machine fueled by entropy)
• Galileo's ship (classical relativity principle) 1632
• GHZ experiment (quantum mechanics)
• EPR paradox (quantum mechanics) (forms of this have actually been performed)
• Maxwell's demon (thermodynamics) 1871
• Plato's theory of refraction (optics)
• Quantum suicide (quantum mechanics)
• Schrödinger's cat (quantum mechanics)
• Twin paradox (special relativity)
• Wigner's friend (quantum mechanics)
• Wittgenstein's rod (engineering mechanics)- an exercise in visualization
• Bucket argument- argues that space is absolute, not relational

Philosophy

The field of philosophy makes extensive use of thought experiments:

• Brain-in-a-vat (epistemology)
• Chinese room (philosophy of mind, artificial intelligence, cognitive science)
• Coherence (philosophical gambling strategy)
• Dining Philosophers (computer science)
• God's Debris (religion and awareness)
• Hilary Putnam's Twin Earth thought experiment in the philosophy of language
• Mary's room (philosophy of mind)
• Original position (politics)
• The Ship of Theseus (concept of identity)
• Simulated reality (philosophy, computer science, cognitive science)
• Swamp man (personal identity)
• Trolley problem (ethics)
• Zeno's paradoxes (classical Greek problems of the infinite)

Miscellaneous

• Braitenberg vehicles (robotics, neural control and sensing systems)
• Doomsday argument (anthropic principle)
• Infinite monkey theorem (probability, infinity)

External links

• http://www.people.cornell.edu/pages/tsg3/thoughtexperimententry.pdf
• http://plato.stanford.edu/entries/thought-experiment/