Schrödinger's Cat: every hour, there is a 50% chance that the poisonous gas will be released and kill the cat.

Schrödinger's cat is a seemingly paradoxical thought experiment devised by Erwin Schrödinger that attempts to illustrate the incompleteness of the theory of quantum mechanics when going from subatomic to macroscopic systems. The experiment proposes: Download high resolution version (1168x740, 367 KB)I created this file myself for the Schrodingers cat article. ... Download high resolution version (1168x740, 367 KB)I created this file myself for the Schrodingers cat article. ... A physical paradox is an apparent contradiction relating to physical descriptions of the universe. ... 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. ... Erwin Schrödinger, as depicted on the former Austrian 1000 Schilling bank note. ... Fig. ...

A cat is placed in a sealed box. Attached to the box is an apparatus containing a radioactive nucleus and a canister of poison gas. The experiment is set up so that there is a 50% chance of the nucleus decaying in one hour. If the nucleus decays, it will emit a particle that triggers the apparatus, which opens the canister and kills the cat. According to quantum mechanics, the unobserved nucleus is described as a superposition (mixture) of "decayed nucleus" and "undecayed nucleus". However, when the box is opened the experimenter sees only a "decayed nucleus/dead cat" or a "undecayed nucleus/living cat."

The question is: when does the system stop existing as a mixture of states and become one or the other? The purpose of the experiment is to illustrate that quantum mechanics is incomplete without some rules to describe when the wavefunction collapses and the cat becomes dead or remains alive instead of a mixture of both.

Contrary to popular belief, Schrödinger did not intend this thought experiment to indicate that he believed that the dead-alive cat would actually exist; rather he considered the quantum mechanical theory to be incomplete and not representative of reality in this case. Since a cat clearly must either be alive or dead (there is no state between alive and dead, e.g. half-dead) surely the same must be true of the nucleus. It must be either decayed or not decayed. Trinomial name Felis silvestris catus Schreber, 1775 The cat (also called domestic cat or house cat) is a small feline carnivorous mammal. ... The nucleus (atomic nucleus) is the center of an atom. ... Radioactive decay is the set of various processes by which unstable atomic nuclei (nuclides) emit subatomic particles. ... Quantum superposition is the application of superposition principle to quantum mechanics. ... In certain interpretations of quantum mechanics, wavefunction collapse is one of two processes by which quantum systems apparently evolve according to the laws of quantum mechanics. ...

The original article appeared in the German magazine Naturwissenschaften ("Natural Sciences") in 1935: E. Schrödinger: "Die gegenwärtige Situation in der Quantenmechanik" ("The present situation in quantum mechanics"), Naturwissenschaften, 48, 807, 49, 823, 50, 844 (November 1935). It was intended as a discussion of the EPR article published by Einstein, Podolsky and Rosen in the same year. Apart from introducing the cat, Schrödinger also coined the term "entanglement" (German: Verschränkung) in his article. In quantum mechanics, the EPR paradox is a thought experiment which demonstrates that the result of a measurement performed on one part of a quantum system can have an instantaneous effect on the result of a measurement performed on another part, regardless of the distance separating the two parts. ... Quantum entanglement is a quantum mechanical phenomenon in which the quantum states of two or more objects have to be described with reference to each other, even though the individual objects may be spatially separated. ...

Copenhagen interpretation

In the Copenhagen interpretation, a system stops being a mixture of states and becomes either one or the other when an observation takes place. This experiment makes apparent the fact that the nature of measurement, or observation, is not well defined in this interpretation. Some interpret the experiment to mean that while the box is closed, the system simultaneously exists in a mixed superposition of the states "decayed nucleus/dead cat" and "undecayed nucleus/living cat", and that only when the box is opened and an observation performed does the wave function collapse into one of the two states. More intuitively, some feel that the "observation" is taken when a particle from the nucleus hits the detector. However (and this is a key point of the thought experiment), there isn't any rule within the Copenhagen interpretation that says one way or the other, and this interpretation of quantum mechanics is incomplete without such rules and explanations for how such rules come to exist. The Copenhagen interpretation is an interpretation of quantum mechanics formulated by Niels Bohr and Werner Heisenberg while collaborating in Copenhagen around 1927. ... For railroad use of the term observation, see observation car. ... The framework of quantum mechanics requires a careful definition of measurement, and a thorough discussion of its practical and philosophical implications. ...

Everett many-worlds interpretation & consistent histories

In the many-worlds interpretation of quantum mechanics, which does not single out observation as a special process, both states persist, but decohere. When an observer opens the box, he becomes entangled with the cat, so observer-states corresponding to the cat being alive and dead are formed, and each can have no interaction with the other. The same mechanism of quantum decoherence is also important for the interpretation in terms of Consistent Histories. Only the "dead cat" or "alive cat" can be a part of a consistent history in this neo-Copenhagen interpretation. The many-worlds interpretation (or MWI) is an interpretation of quantum mechanics that averts the special role played by the measurement process in the Copenhagen interpretation by proposing several key ideas. ... Quantum decoherence is the general term for the consequences of irreversible quantum entanglement. ... Quantum entanglement is a quantum mechanical phenomenon in which the quantum states of two or more objects have to be described with reference to each other, even though the individual objects may be spatially separated. ... In quantum mechanics, the consistent histories approach is intended to give a modern interpretation of quantum mechanics, generalising the conventional Copenhagen interpretation and providing a natural interpretation of quantum cosmology. ...

Practical applications

Curiously, all of this has some practical use in quantum computing and quantum cryptography. It is possible to send light that is in a superposition of states down a fiber optic cable. Placing a wiretap in the middle of the cable which intercepts and retransmits the transmission will collapse the wavefunction (in the Copenhagen interpretation, "perform an observation") and cause the light to fall into one state or another. By performing statistical tests on the light received at the other end of the cable, one can tell whether it remains in the superposition of states or has already been observed and retransmitted. In principle, this allows the development of communication systems that cannot be tapped without being noticed at the other end. This experiment (which can be performed, though a workable quantum cryptographic communications system which can transmit large quantities of data has not yet been constructed) also illustrates that "observation" in the Copenhagen interpretation has nothing to do with consciousness, in that a perfectly unconscious wiretap will cause the statistics at the end of the wire to be different. Molecule of alanine used in NMR implementation of error correction. ... Quantum cryptography is an approach to securing communications based on certain phenomena of quantum physics. ... Optical fibers An optical fiber is a transparent thin fiber, usually made of glass, for transmitting light. ...

In quantum computing, the phrase "cat state" often refers to the special entanglement of qubits where the qubits are in an equal superposition of all being 0 and all being 1, i.e. |00...0>+|11...1>. Molecule of alanine used in NMR implementation of error correction. ... In quantum computing, the cat state, named after Schrödingers cat, is the special state where where the qubits are in an equal superposition of all being |0> and all being |1>, i. ... Quantum entanglement is a quantum mechanical phenomenon in which the quantum states of two or more objects have to be described with reference to each other, even though the individual objects may be spatially separated. ... A quantum bit, or qubit is a unit of quantum information. ... The term superposition can have several meanings: Quantum superposition Law of superposition in geology and archaeology Superposition principle for vector fields Superposition Calculus is used for equational first-order reasoning This is a disambiguation page — a navigational aid which lists other pages that might otherwise share the same title. ...

An interesting variant of the Schrödinger's Cat experiment known as the quantum suicide machine has been proposed by cosmologist Max Tegmark. It asks the question, what does the Schrödinger's Cat experiment look like from the point of view of the cat, and argues that this question may be able to distinguish between the Copenhagen interpretation and many worlds. Another variant on the experiment is Wigner's friend. Quantum suicide is a thought experiment which has been independently proposed in 1987 by Hans Moravec, in 1988 by Bruno Marchal and in 1998 by Max Tegmark that attempts to distinguish between the Copenhagen interpretation of quantum mechanics and the Everett many-worlds interpretation by means of a variation of... Max Tegmark, born in Sweden, is a cosmologist formerly at the University of Pennsylvania but now at the Massachusetts Institute of Technology as an Associate Professor. ... Wigners friend is a thought experiment proposed by the physicist Eugene Wigner; it is an extension of the Schrödingers cat experiment designed as a point of departure for discussing the mind-body problem as viewed by the Copenhagen interpretation of quantum mechanics. ...

Physicist Stephen Hawking once exclaimed, "When I hear of Schrödinger's cat, I reach for my gun," paraphrasing Hermann Göring's anti-intellectual quote, "When I hear the word 'culture', I reach for my Browning", which Göring quoted from a play by German playwright and Nazi Poet Laureate, Hanns Johst. Stephen William Hawking, CH, CBE, FRS (born January 8, 1942) is one of the worlds leading theoretical physicists. ... Hermann Göring Hermann Wilhelm Göring (also Goering or Goring in English) (January 12, 1893 – October 15, 1946) was an early member of the Nazi party, founder of the Gestapo, and one of the main perpetrators of Nazi Germany. ... Anti-intellectualism is a term that in one sense describes a hostility towards, or mistrust of, intellectuals and intellectual pursuits. ... Play – literature / theatre A play (noun) is a common form of literature, usually consisting chiefly of dialog between characters, and usually intended for performance rather than reading. ... A Poet Laureate is a poet officially appointed by a government and often expected to compose poems for state occasions and other government events. ... Hanns Johst (July 8, 1890 - November 23, 1978) was a German playwright and Nazi Poet Laureate. ...

Related humor

The term "Schrödinger's Terrorist" has been used to humorously label "terrorists" whose status as living or dead is unknown and/or subject to contradictory rumors. Notable persons in this status have been Yasser Arafat, in the comatose period before his death, and Osama bin laden. Terrorism is a controversial and subjective term with multiple definitions. ... A rumor (British English: rumour) is a piece of purportedly true information that is circulated without substantiating evidence. ... Yasser Arafat Yasser Arafat (August 4 or August 24, 1929 – November 11, 2004), born Muhammad `Abd ar-Rauf al-Qudwa al-Husayni (Arabic محمد عبد الرؤوف القدوة الحسيني) and also known as Abu `Ammar (ابو عمّار), was co-founder and Chairman of the Palestine Liberation Organization (PLO) (1969–2004... Osama bin Laden Usāmah bin Muhammad bin `Awad bin Lādin (born July 30 or March 10, 1957) (Arabic: ), commonly known as Osama bin Laden (Arabic: ), is the figurehead of al-Qaeda, an Islamist movement that has been involved in attacks against civilians and military targets around the world. ...

The slightly humorous online database website "Dead People Server", keeping track of which famous people were still alive and which had died, lists Schrödinger's cat as <blink>not</blink> alive. The "blink" HTML tag causes the word "not" to blink, causing the text to alternate between "alive" and "not alive". This might be one of the very few legitimate uses of the notorious "blink" tag. This article is about HTML elements. ...

Schrödinger's cat in fiction

• "Schrodinger's Cat" is a science fiction story written by Ursula K. Le Guin in 1974. It appeared in The Compass Rose, published in 1982. The story deals with Schrödinger's Cat, stoves and quantum decoherence.

• The Schrödinger's Cat trilogy is the name commonly given to a trilogy of science fiction/conspiracy theory novels written by Robert Anton Wilson. It consists of The Universe Next Door, The Trick Top Hat and The Homing Pigeons.

• In Lords and Ladies, by Terry Pratchett, the cat Greebo is placed in a box and enters a superposition of being Alive, Dead and Bloody Furious.

• In the manga of Hellsing, there is a werewolf named Schrödinger.

• In the roguelike computer game NetHack, monsters known as quantum mechanics may carry a chest containing Schrödinger's cat. When opened, there is a 50% chance of finding it dead and a 50% chance of it jumping out alive.

• A cat named Schrodinger appears as a semi-recurring character in Checkerboard Nightmare, a web comic by Kristofer Straub. Schrodinger can see all possible states of existence at once, and as a result is very much insane, as detailed in his first appearance (http://checkerboardnightmare.com/d/20010319.html).

• A cat named Schrödinger appeared in the television series Stargate SG-1.

• A cat named Schrödinger also appeared in the television program Sliders. His owner, Quinn Mallory, studied Quantum Theory and invented a device to travel to other dimensions.

• A cat named Pixel in the classic Robert Heinlein novel, The Cat Who Walks Through Walls. The cat is affectionately termed "Schrödinger's Cat" due to his ability to be wherever his favorite person (in the case of the book, the narrator) is. His ability to walk through walls is due to the fact that Pixel does not know that it is impossible.

• The web comic Two Lumps: The Adventures of Ebeneezer and Snooch has an episode (http://twolumps.keenspace.com/d/20040714.html) about Schrödinger's cat. "They're talking about schreddin' cats and puttin' 'em in a box!!!"

• Dan Simmons' novel Endymion begins with hero Raul Endymion trapped in a Schrödinger cat box.

• Steve Martin's 1998 book Pure Drivel includes a piece entitled "Schrödinger's Cat," which presents a summary of the theory, followed by several ficticious, nonsensical theories, including "Wittgenstein's Banana," "Apollo's Non-Apple Non-Strudel," and "Chef Boyardee's Bungee Cord" (which begins, "A bungee cord is hooked at one end to a neutrino, while the other end is hooked to a vibraphone...")

• In the 40th anniversary Doctor Who audio book “Zagreus” produced by Big Finish and released in 2003, the Doctor is locked in a lead lined box that contains cyanide in an effort to explain his situation of being neither dead nor alive. Afterwards, the Doctor does mention he met Schrödinger’s Cat.

• Dirk Gently attempted to use clairvoyance to see inside the box in Dirk Gently's Holistic Detective Agency, by Douglas Adams.

• Saturday by Ian McEwan refers to Schrodinger's Cat.

• Schrödinger's Cat is discussed in "The Summer of Love" by Lisa Mason

Ursula K. Le Guin at an informal bookstore Q&A session, July 2004 Ursula Kroeber Le Guin (born October 21, 1929), is an American author. ... The Compass Rose is a 1982 collection of short stories by Ursula K. Le Guin. ... The Schrödingers Cat trilogy is a trilogy of novels by Robert Anton Wilson, chronicling events and characters in several parallel universes. ... Science fiction is a form of speculative fiction principally dealing with the impact of imagined science and technology, or both, upon society and persons as individuals. ... This proposed logo for a U.S. government agency was dropped due to fears that its Masonic symbolism would provoke conspiracy theories. ... Robert Anton Wilson Robert Anton Wilson or R. A. W. (born January 18, 1932) is a futurologist, libertarian, and novelist. ... Terence David John Pratchett OBE (known to some fans as Pterry – following the convention he used in his book Pyramids where characters were given names such as Ptraci and Pteppic) is an English fantasy author (born April 28, 1948, in Beaconsfield, Bucks), best known for his Discworld series. ... Hellsing manga, volume 1 (English version) Hellsing is an anime and manga series by Kohta Hirano and Studio GONZO. While the anime series is already over, the manga series is still produced in Japan, a new OAV (Coined Hellsing Ultimate) is planned for this series that will cover the original... The roguelikes are usually superficially two-dimensional dungeon crawling computer games, most with simple text or ASCII graphics and many with tiles which replace the rather limited character set with a wider array. ... NetHack is a roguelike computer game. ... Fig. ... Checkerboard Nightmare is a web comic, hosted at Keenspot, created and drawn by Kristofer Straub. ... Web comics are comics that are available on the web. ... Stargate SG-1 (popularly abbreviated as SG1 or SG-1) is a television series based upon the 1994 science fiction movie Stargate. ... The original cast of Sliders. ... Robert A. Heinlein Robert Anson Heinlein (July 7, 1907 – May 8, 1988) was one of the most influential authors in the science fiction genre. ... Book cover The Cat Who Walks Through Walls is a science fiction novel by Robert A. Heinlein published in 1985. ... Web comics are comics that are available on the web. ... Hyperion Hyperion (book) redirects here. ... Steve Martin (right) with Scooter, on The Muppet Show Stephen Glenn Martin (born August 14, 1945) is an American comedian, writer, producer, actor, musician and composer born in Waco, Texas and raised in Orange County, California. ... List of Doctor Who serials Doctor Who audio releases Doctor Who spin-offs - includes a discussion of the many novelisations and original novels based on the series History of Doctor Who The Doctor (Doctor Who) List of supporting characters in Doctor Who, including villains and aliens List of robots in... Big Finish Productions is a British company that produces audio plays based on British cult science fiction properties. ... 2003 is a common year starting on Wednesday of the Gregorian calendar. ... Dirk Gently is a fictional character created by Douglas Adams and featured in the books Dirk Gentlys Holistic Detective Agency and The Long Dark Teatime of the Soul. ... Clairvoyance is defined as a form of extra-sensory perception that it is claimed allows a person to perceive distant objects, persons, or events, including seeing through opaque objects and the detection of types of energy not normally perceptible to humans (i. ... Dirk Gentlys Holistic Detective Agency is a novel by Douglas Adams. ... Douglas Noël Adams in an undated photograph Douglas Noël Adams (March 11, 1952 – May 11, 2001) — also known as Bop Ad or Bob after his illegible signature, or by his initials DNA — was a British comic radio dramatist and author, most notably of The Hitchhikers Guide to the Galaxy... The British hardcover edition, with the Post Office Tower in the background Saturday (2005) is a novel by Ian McEwan about one day in the life of a London neurosurgeon. ... Ian McEwan (born June 21, 1948) is a British novelist, sometimes nicknamed Ian Macabre because of the nature of his work. ...

See also

• Schroedinbug

Schroedinbug is a term used in software programming to describe a computer bug that is not discovered, but shows up after somebody reads the source or uses the application in an unusual way. ...

External links

• Erwin Schrödinger, The Present Situation in Quantum Mechanics (Translation) (http://www.tu-harburg.de/rzt/rzt/it/QM/cat.html)
• A Lazy Layman's Guide to Quantum Physics (http://www.higgo.com/quantum/laymans.htm)
• Poem by Cecil Adams (http://www.straightdope.com/classics/a1_122.html)
• Stephen Notley's Bob the Angry Flower: Schrödinger's Fridge (http://www.angryflower.com/schrod.gif)