Quantum suicide and immortality

In quantum mechanics, quantum suicide is a thought experiment. It was originally published independently by Hans Moravec in 1987 and Bruno Marchal in 1988 and was further developed 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. In their speculative work on the topic of future science and artificial intelligence, authors Goertzel and Bugaj, describe a very different metaphysical notion as "quantum immortality", one they claim is applicable in all circumstances, for every "intelligent entity", and that serves as a means of "transfer" to other universes. The authors mistakenly portray Frank Tipler's Final anthropic principle and this "quantum immortality" as significant aspects of controversy surrounding Hugh Everett's work.

Keith Lynch recalls that Everett took great delight in paradoxes such as the unexpected hanging. Everett didn't 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 don't normally hinge upon a sequence of binary quantum events like those in the thought experiment.

The quantum suicide thought experiment
Unlike the Schrödinger's cat thought experiment which used poison gas and a radioactive decay trigger, this version involves a lethal weapon and a device that measures the spin value of photons. Every 10 seconds, the spin value of a fresh photon 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 wavefunction. At the start of the second iteration, if the Copenhagen interpretation is true, the wavefunction 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's 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's only within the confines of such an abstract quantum scenario that an observer finds they defy all odds.

In fiction
Authors of science fiction have used themes involving both quantum suicide and quantum immortality. The idea that authors exploit is that a person who dies in one world may survive in another world or parallel universe.