Quantum suicide and immortality

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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.^[1] 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. The experiment involves looking at the Schrödinger's cat experiment from the point of view of the cat.

Quantum immortality is a metaphysical speculation derived from the quantum suicide thought experiment. It states that the many-worlds interpretation of quantum mechanics implies that conscious beings are immortal. Hugh Everett is reported to have believed in quantum immortality, although he never published on either quantum suicide or quantum immortality.^[2]

Contents 1 The quantum suicide thought experiment 2 Quantum immortality 3 Surviving the quantum thought experiment 4 Required assumptions 5 Arguments against quantum immortality 5.1 Max Tegmark's work 5.2 David Lewis's work 6 Other criticism and controversy 7 In fiction 8 See also 9 References 10 External links

[edit] The quantum suicide thought experiment

Unlike Schrodinger's cat-in-a-box thought experiment which used poison gas and a radioactive decay trigger, this human version involves some sort of lethal weapon and a machine which measures the spin value of a photon. Every 10 seconds, the spin value of a randomly passing photon is measured. Depending on the orientation of the spin, either the weapon is deployed and the man is killed, or it is not and he lives.

With each run of the experiment there is a 50-50 chance that the weapon will be triggered and the experimenter will die. According to the Copenhagen interpretation, the weapon will (in all likelihood) eventually be triggered and the experimenter will die. If the many-worlds interpretation is correct then at each run of the experiment, the experimenter will be split into one world in which he survives and another world in which he dies. In the worlds where the experimenter dies, he will cease to be a conscious entity.

However, from the point of view of the non-dead copies of the experimenter, 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 surviving copies of the experimenter will notice that he never seems to die, therefore "proving" himself to be invulnerable to the gun mechanism in question, from his own point of view.

If the many-worlds interpretation is true, the measure (given in M.W.I. by the squared norm of the wavefunction) of the surviving copies of the experimenter will decrease by 50% with each run of the experiment, but will remain non-zero. So, if the surviving copies become experimenters, those copies will either die during their first attempt, or survive creating duplicates of themselves (copies of copies, that will survive finitely or die).

[edit] Quantum immortality

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The idea behind quantum immortality is that, in running the quantum thought experiment, the experimenter may remain alive 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 experimenter would therefore never perceive his or her own death.^{[citation needed]}

[edit] Surviving the quantum thought experiment

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The small-probability remaining branches are in effect, though unlikely to be experienced by most of the copies of the experimenter that started out. Most of the observer-moments in the universe will not be in such low-measure situations because measure is proportional to the number of copies and therefore the number of that type of observer-moment.

However, the rareness of an observer moment has no relation to presence or absence of experience; if the M.W.I. is true, all non-zero observer moments are experienced, even rare ones. Believers in quantum suicide think it gives a recipe for entering into rare observer moments. The experimenter indeed knows that this type of observer moment is rare, which is why it would be unlikely to occur in interpretations of quantum physics that don't have many worlds.

[edit] Required assumptions

Proponents of the quantum immortality point out that, although it is highly speculative, the theory does not violate any known laws of physics—but only if certain controversial assumptions are made:^{[citation needed]}

1. That the many-worlds interpretation (MWI) is the correct interpretation of quantum mechanics, as opposed to the Copenhagen interpretation, the latter of which does not involve the existence of parallel universes. Note, though, that parallel universes may be possible through other mechanisms in the Copenhagen interpretation.
2. All of the possible scenarios in which the proposed experimenter (or any entity being argued about in the thought experiment) can die support a nonnull subset of survival scenarios.^{[clarification needed]}
3. Not dying some finite number of times (perhaps in parallel universes) constitutes immortality.
4. Permanent cessation of the consciousness, along with the ability to observe, occurs at physical destruction (death).

[edit] Arguments against quantum immortality

Papineau argues against the quantum suicide argument thus: "If one outcome is valuable because it contains my future experiences, surely an alternative outcome which lacks those experiences is of lesser value, simply by comparison with the first outcome. Since expected utility calculations hinge on relative utility values rather than absolute ones, I should be concerned about death as long as the outcome where I die is given less utility than the one where I survive, whatever the absolute value."^[3] Mallah comments on and defends this 'utility' argument against quantum suicide.^[4]

It has been argued by Mallah that quantum suicide cannot give a recipe for "entering into" rare or "low measure" observer moments, because the amount of consciousness or "measure" of these rare observer moments is exactly as much as it would have been without the quantum suicide; in that case quantum suicide merely removes the other observer-moments. This is equivalent, in Mallah's view, to a single-world situation in which one starts off with many copies of the experimenter, and the number of surviving copies is decreased by 50% with each run. Therefore, according to this argument, the quantum nature of the experiment provides no benefit to the experimenter; in terms of his/her subjective life expectancy or rational decision making, or even in terms of his/her trying to decide whether the many-worlds interpretation is correct, the many-worlds interpretation gives results that are the same as that of a single-world interpretation.^[4]

Mallah also gives a "general argument against immortality" which argues that if people are immortal, then it is vanishingly unlikely to find oneself to be of a normal age rather than abnormally old.

It has been countered that in a M.W.I. the amplitude of being the living experimenter can be halved repeatedly without ever reaching zero. However, this point is not disputed by opponents of quantum suicide; rather, they claim that it is not the issue, while Mallah claims that the decrease in measure is the issue.

[edit] Max Tegmark's work

Using logic similar to that of Greg Egan's Dust Theory, Max Tegmark 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 in this world to an alternate one in which the person ceases to exist.^[5] Although quantum immortality is motivated by the quantum suicide thought experiment, Max Tegmark has stated that he does not believe that quantum immortality is a consequence of his work.

[edit] David Lewis's work

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.^[6]

[edit] Other criticism and controversy

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Critics^[who?] contend quantum suicide fails as a thought experiment to achieve its intended purpose. Nonetheless, there are arguments^[specify] involving anthropic considerations among entire universes which do provide evidence^[specify] for the many-worlds interpretation.^[7]

Quantum suicide and quantum immortality remain controversial because a number of thinkers^[who?] disagree on its success or failure and, particularly, its relevance to life expectancy and decision making.

[edit] 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.

[edit] See also

• Final anthropic principle
• Multiverse
• Quantum mysticism

[edit] References

[edit] External links

• "Does the 'many-worlds' interpretation of quantum mechanics imply immortality?" by James Higgo
• The 'Everything' mailing list (and archives), A "discussion of the idea that all possible universes exist".
• How Quantum Suicide Works
• Dying to know