Quantum immortality
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Quantum immortality is the controversial metaphysical speculation deriving from the quantum suicide thought experiment that states the many-worlds interpretation of quantum mechanics implies that conscious beings are immortal.
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[edit] Explanation of the thought experiment
Imagine that a physicist detonates a nuclear bomb beside himself. In almost all parallel universes, the nuclear explosion will vaporize the physicist. However, there should be a small set of alternative universes in which the physicist somehow survives (i.e. the set of universes which support a "miraculous" survival scenario). The idea behind quantum immortality is that the physicist will remain alive in, and thus remain able to experience, at least one of the universes in this set, even though these universes form a tiny subset of all possible universes. Over time the physicist would therefore never perceive his or her own death.
Another example is one provided by quantum suicide, where a physicist sits in front of a gun which is triggered, or not triggered, by radioactive decay. With each run of the experiment there is a fifty-fifty chance that the gun will be triggered and the physicist will die. If the Copenhagen interpretation is correct, then the gun will eventually be triggered and the physicist will die. If the many-worlds interpretation is correct, then at each run of the experiment the physicist will be split into one or more worlds in which he lives and one or more worlds in which he dies. In the worlds where the physicist dies, his consciousness will cease to exist. However, from the point of view of the physicist, the experiment will continue running without his ceasing to exist, because at each branch, he will only be able to observe the result in the world in which he survives, and if many-worlds is correct, the physicist will notice that he never seems to die, therefore "proving" himself to be immortal, at least from his own point of view.
[edit] Required assumptions and controversy
Proponents point out that while it is highly speculative, quantum immortality (QI) violates no known laws of physics assuming some (more or less) controversial assumptions are true:
- The many-worlds interpretation of quantum mechanics is the correct one, as opposed to the Copenhagen interpretation, which does not necessarily indicate the existence of parallel universes.
- All of the possible scenarios in which the proposed physicist (or any entity being argued about in the thought experiment) can die support at least a small subset of survival scenarios.
- Not dying some finite number of times somehow constitutes immortality.
- Consciousness, and the ability to observe, ends at death (not necessarily).
Although quantum immortality is motivated by the quantum suicide thought experiment, Max Tegmark, one of the inventors of this experiment, has stated that he does not believe that quantum immortality is a consequence of his work. He argues that under any sort of normal conditions, before someone dies they undergo a period of diminishment of consciousness, a non-quantum decline (which can be anywhere from seconds to minutes to years), and hence there is no way of establishing a continuous existence from this world to an alternate one in which the person continues to exist.
Also, the philosopher David Lewis, in "How Many Lives Has Schrödinger's Cat?", remarked that in the vast majority of the worlds in which an immortal observer might find himself (i.e. the subset of quantum-possible worlds in which the observer does not die), he will survive, but will be terribly maimed. This is because in each of the scenarios typically given in thought experiments (nuclear bombing, Russian roulette, etc.), for every world in which the observer survives unscathed, there are likely to be far more worlds in which the observer survives terribly disfigured, badly disabled, and so on. It is for this reason, Lewis concludes, that we ought to hope that the many-worlds interpretation is false.
Interestingly, there is another route to quantum immortality that does not require the many-worlds interpretation; see Consciousness causes collapse.
[edit] Fictional depictions
The Greg Egan novel Quarantine explores topics related to quantum immortality.
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.
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.
