Quantum suicide and immortality
In quantum mechanics, quantum suicide is a thought experiment, originally published independently by Hans Moravec in 1987 and Bruno Marchal in 1988, and independently developed further by Max Tegmark in 1998. It attempts to distinguish between the Copenhagen interpretation of quantum mechanics and the Everett many-worlds interpretation by means of a variation of the Schrödinger's cat thought experiment, from the cat's point of view. Quantum immortality refers to the subjective experience of surviving quantum suicide regardless of the odds.
Keith Lynch recalls that Hugh Everett took great delight in paradoxes such as the unexpected hanging. Everett did not mention quantum suicide or quantum immortality in writing, but his work was intended as a solution to the paradoxes of quantum mechanics. Lynch said "Everett firmly believed that his many-worlds theory guaranteed him immortality: His consciousness, he argued, is bound at each branching to follow whatever path does not lead to death", Tegmark explains, however, that life and death situations do not normally hinge upon a sequence of binary quantum events like those in the thought experiment.
Quantum suicide thought experiment
Unlike the Schrödinger's cat thought experiment which used poison gas and a radioactive decay trigger, this version involves a life-terminating device and a device that measures the spin value of protons. Every 10 seconds, the spin value of a fresh proton is measured. Conditioned upon that quantum bit, the weapon is either deployed, killing the experimenter, or it makes an audible "click" and the experimenter survives.
The theories are distinctive from the point of view of the experimenter only; their predictions are otherwise identical.
The probability of surviving the first iteration of the experiment is 50%, under both interpretations, as given by the squared norm of the wave function. At the start of the second iteration, if the Copenhagen interpretation is true, the wave function has already collapsed, so if the experimenter is already dead, there's a 0% chance of survival. However, if the many-worlds interpretation is true, a superposition of the live experimenter necessarily exists, regardless of how many iterations or how improbable the outcome. Barring life after death, it is not possible for the experimenter to experience having been killed, thus the only possible experience is one of having survived every iteration.
Max Tegmark's work
In response to questions about "subjective immortality", Max Tegmark made some brief comments: He acknowledged the argument that "everyone will be immortal" should follow if a survivor outcome is possible for all life-threatening events. The flaw in that argument, he suggests, is that dying is rarely a binary event; it is a progressive process. The quantum suicide thought experiment attempts to isolate all possible outcomes for the duration of the thought experiment. That isolation delays decoherence in such a way that the subjective experience of the superposition is illustrated. It is only within the confines of such an abstract quantum scenario that an observer finds they defy all odds. Another possibility is that although an observer does not die, they nevertheless continue to suffer the effects of aging, bringing to mind the legend of Tithonus.
Quantum suicide themes have been explored in the following works:
- Larry Niven's short story All the Myriad Ways, collected in a collection of the same name (1971)
- Dan Simmons's novel The Hollow Man (1992). Simmons also describes a quantum execution mechanism in his Hyperion Cantos series.
- Greg Egan's novel Quarantine (1992)
- Greg Egan's novel Permutation City (1994), in which one character repeatedly had his mind uploaded and his copy eventually terminated, but found out that he always "ended up" in another world, where his survival was explained by increasingly improbable circumstances.
- Robert Charles Wilson's short story Divided by Infinity (1998)
- Denis Johnson's novel Already Dead (A California Gothic) (1998)
- Jason Shiga's book Meanwhile (2004)
- Greg Bear's short story Schrodinger's Plague found in his book Tangents deals with a doomsday version of this experiment in which instead of a single scientist dying, a deadly virus is released into the populace.
- Michael W. Lucht's short story After Experiment Seven (2012), found in Nature’s Futures section, depicts a series of quantum suicide experiments in a humorous manner.
Quantum immortality themes have been explored in several works:
- The Greg Egan novel Quarantine explores topics related to quantum immortality.
- In the Greg Egan short story The Infinite Assassin, the title character explicitly defines himself this way: "'I' am those who survive, and succeed. The rest are someone else."
- Other science fiction stories exploring these and related ideas include All the Myriad Ways by Larry Niven, and Divided by Infinity by Robert Charles Wilson.
- Terry Pratchett's short story Death and What Comes Next has a philosopher arguing the principle with Death, who has come for him.
- In Alastair Reynolds' short story "The Real Story," a supernova went off less than a light-year from Earth several millennia ago. Nobody noticed because "our" Earth is the quantum survivor -- the only one of all possible Earths to escape unharmed.
- Steven Hall's novel The Raw Shark Texts contains references to Max Tegmark and the Quantum Machine Gun (an alternate name for the quantum suicide thought experiment) suggesting a possible quantum immortality-related reading of the story.
- In Neal Stephenson's 2008 novel Anathem, Fraa Jad has technology that allows him to take advantage of quantum immortality.
- In Dan Simmons' Ilium/Olympos duology a mechanism similar to quantum immortality protects the character of Achilles.
- In Donald Schneider's short story "Pride's Prison,"  the ending of the piece strongly suggests quantum immortality
TV and film
- The episode Perfect Circles in the third season of Six Feet Under contains references and allusions to quantum immortality, as a major character observes several possible outcomes of his life.
- In Fringe, Peter Bishop finds himself transported to an altered timeline which includes the living versions of characters otherwise dead in the original timeline if it weren't for his actions involving a bio-mechanical doomsday device reversing past events in which time is reset.
- In David Lindsay-Abaire's play Rabbit Hole, a grieving mother takes solace in the possibility that her dead son may enjoy quantum immortality. She comes to prefer to believe that this world in which she lives may simply be a "sadder version" of other co-existing, parallel universes. Rabbit Hole won the 2007 Pulitzer Prize for Drama.
- In The Prestige, Robert Angier (Hugh Jackman) repeatedly duplicates himself and kills his previous copy; his continued belief in the survival of his consciousness in the new (living) copy mirrors the principles of quantum immortality without utilizing parallel universes.
- In Source Code, Capt. Colter Stevens (Jake Gyllenhaal) repeatedly experiences "death" as he investigates the bombing of a train. Ultimately, he survives in the universe where the train was not bombed and no one died.
- In the Stargate series, as well as plenty of other science fiction TV shows, the writers regularly brought back "dead" characters for an episode using this mechanic. They also used it to temporarily "kill" characters; in episodes where the timeline is altered and must be fixed, regulars were sometimes killed before the rest of the team finally fixed the timeline, restoring the killed characters in the process.
- In the Misfits series, especially in the "Episode four" of the first season, main characters are killed or end up in terrible situations, but are resurrected as time is rewound.
- In Third Contact, Dr. David Wright learns of the quantum suicide thought experiment through a patient.
- In the Higurashi When They Cry series, Furude Rika is brought back from death and sent to an alternative universe set in the past several times.
- In the video game Alan Wake (Remedy Entertainment, 2010), an in-game TV series called "Night Springs" has a demonstration of quantum immortality, in which a scientist demonstrates that a gun he is holding can't fire. However, the device used to maintain this quantum immortality is accidentally unplugged and the scientist dies.
- BioShock Infinite explores ideas of quantum immortality. In one part of the game, the protagonist enters a space-time tear into a parallel universe where he had already died. Another character, who is discovered to be dead prior to the game's events, periodically makes an appearance throughout the game, suggesting that she has achieved immortality.
- There is a modified SNES emulator called the Many-Worlds Emulator that creates a new video recording each time the user loads from a previous save state (or, equivalently, a branch point). These videos are then flattened into one, depicting many possible outcomes from a set of choices the user makes.
- The webcomic Homestuck has a villain cast called The Felt. One of their members, Clover, states that he has an ability similar to quantum immortality in which he has so much luck that all possible attempts at taking his life fail (for example, that the gun pointed at him will jam if the trigger is pulled).
- In a later part of the same story arc, a character travels between alternate timelines defined by other characters being alive or dead. In each timeline, circumstances have changed (sometimes dramatically) to rationally explain why they are alive or dead.
- "The Many Minds Approach". 25 October 2010. Retrieved 7 December 2010. "This idea was first proposed by Austrian mathematician Hans Moravec in 1987..."
- Moravec, Hans (1988). "The Doomsday Device". Mind Children: The Future of Robot and Human Intelligence. Harvard: Harvard University Press. p. 188. ISBN 978-0-674-57618-6. (If MWI is true, apocalyptic particle accelerators won't function as advertised).
- Marchal, Bruno (1988). "Informatique théorique et philosophie de l'esprit" [Theoretical Computer Science and Philosophy of Mind]. Acte du 3ème colloque international Cognition et Connaissance [Proceedings of the 3rd International Conference Cognition and Knowledge] (Toulouse): 193–227.
- Marchal, Bruno (1991). "Mechanism and personal identity". In De Glas, M.; Gabbay, D. Proceedings of WOCFAI 91 (Paris. Angkor.): 335–345.
- Tegmark, Max The Interpretation of Quantum Mechanics: Many Worlds or Many Words?, 1998
- Tegmark, Max (November 1998). "Quantum immortality". Retrieved 25 October 2010.
- See Eugene Shikhovtsev's Biography of Everett: Keith Lynch remembers 1979–1980