Quantum immortality

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Quantum immortality is the controversial speculation that the Everett many-worlds interpretation of quantum mechanics implies that a conscious being cannot cease to be.

Overview

The idea derives from a variant of the quantum suicide thought experiment. Imagine that a physicist detonates a nuclear bomb located beside her. 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 (ie. 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 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 consider herself to be living forever. There are some parallels with this concept in the anthropic principle.

Another example is that 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 50-50 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 a world in which he lives and one in which he dies. In the worlds where the physicist dies, he 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, or at least according to quantum immortality.

Proponents point out that while it is highly speculative, quantum immortality violates no known laws of physics.

Criticism

Detractors regard this idea as nonsense, and argue that this outcome does not fall out naturally from the many-worlds interpretation of quantum mechanics. They say that in the vast majority of universes, the physicist would cease to exist and therefore the most likely experience of a physicist standing next to a nuclear explosion would be the experience (or lack of experience) of ceasing to exist. The counterargument to this is that lack of experience is not itself an experience.

The critics also argue that the continuity of consciousness, and the possibility of it enduring forever, are actually assumptions in this scenario, and ones with no physical basis. They also claim that the logic of the thought experiment would suggest that a conscious observer can never become unconscious, and therefore can never sleep. A counterargument to this is that the theory does not claim that one can never experience worlds where one loses consciousness, but rather that one can never experience the period of unconsciousness itself. The observer will therefore never experience a world where he dies in his sleep, but if he wakes up again he will simply note that there was a gap in his conscious experience.

Another counter argument is that, given an infinite number of situations, at some point a situation would occur where the person could not survive (or remain consious) without breaking at least one law of physics. There will not be a split of universes because the one that wants to split off can't do so without creating a universe where the now broken laws of physics do not exist. Even if assumed that a jump to a more "lenient" universe would happen, as more and more laws would be erased, one would be left with a universe with no laws at all. A universe without physical laws is either impossible or exists as complete chaos because there is nothing to base any form of order on. Any person entering this universe would cease to exist as a person in every sense of the word.

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. His argument is 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.

Fictional depictions

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The Greg Egan novel Permutation City relies heavily on the theory of quantum immortality. In it, a main character miraculously survives several would-be deaths, and eventually organizes and participates in a mass-suicide with dozens of eccentric millionaires in the belief they would find themselves in a self-contained universe of their own design. Egan's first novel, Quarantine, also 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.

See also

External links

et:Kvantsurematus