Quantum suicide and immortality
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In quantum mechanics, quantum suicide was a thought experiment. It was independently published in 1987 by Hans Moravec and in 1988 by Bruno Marchal, and 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]
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[edit] Explanation of the thought experiment
For example,
A man sits down before a gun, which is pointed at his head. This is no ordinary gun; it's rigged to a machine that measures the spin of a quantum particle. Each time the trigger is pulled, the spin of the quantum particle -- or quark -- is measured. Depending on the measurement, the gun will either fire, or it won't. If the quantum particle is measured as spinning in a clockwise motion, the gun will fire. If the quark is spinning counterclockwise, the gun won't go off. There'll only be a click.
Nervously, the man takes a breath and pulls the trigger. The gun clicks. He pulls the trigger again. Click. And again: click. The man will continue to pull the trigger again and again with the same result: The gun won't fire. Although it's functioning properly and loaded with bullets, no matter how many times he pulls the trigger, the gun will never fire. He'll continue this process for eternity, becoming immortal.
Go back in time to the beginning of the experiment. The man pulls the trigger for the very first time, and the quark is now measured as spinning clockwise. The gun fires. The man is dead.
But, wait. The man already pulled the trigger the first time -- and an infinite amount of times following that -- and we already know the gun didn't fire. How can the man be dead? The man is unaware, but he's both alive and dead. Each time he pulls the trigger, the universe is split in two. It will continue to split, again and again, each time the trigger is pulled, and becoming quantum immortal.
This thought experiment is called quantum suicide. It was first posed by then-Princeton University theorist Max Tegmark in 1997 (now on faculty at MIT). A thought experiment is an experiment that takes place only in the mind. The quantum level is the smallest level of matter we've detected so far in the universe. Matter at this level is infinitesimal, and it's virtually impossible for scientists to research it in a practical manner using traditional methods of scientific inquiry.
[edit] Repeated runs of the experiment
With each run of the experiment there is a 50-50 chance that the gun will be triggered and the experimenter will die. According to the Copenhagen interpretation, the gun 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 lives and another world in which he dies. After many runs of the experiment, there will be many worlds. In the worlds where the experimenter dies, he will cease to exist.
[edit] The experimenter's point of view
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, at least from his own point of view provided the gun remains unheard to outside observers and the experimenters box remains sealed to prevent quantum measurement and the collapse of the wave function.
[edit] Nuclear bomb
Another example is where an experimenter detonates a nuclear bomb beside himself. In almost all parallel universes, the nuclear explosion will vaporize the experimenter. However, there should be a small set of alternative universes in which the experimenter somehow survives (i.e. the set of universes which support a "miraculous" survival scenario, or some extremely unlikely, but technically possible event occurs saving the experimenter).
[edit] Quantum immortality
The idea behind quantum immortality is that the experimenter 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 experimenter would therefore never perceive his or her own death.[citation needed]
[edit] Required assumptions and controversy
Proponents point out that while it is highly speculative, quantum immortality (QI) violates no known laws of physics as long as certain controversial assumptions are true:[citation needed]
- 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.
- All of the possible scenarios in which the proposed experimenter (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 (perhaps in parallel universes) constitutes immortality.
- Permanent cessation of the consciousness, and the ability to observe, occurs when the gun is fired or bomb is triggered.
[edit] Further explanation
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.
[edit] Rareness of survival
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] Counter-arguments
Papineau argues against the quantum suicide argument thus: that "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 notes that the decrease in measure is the issue.
[edit] Max Tegmark
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.[citation needed] 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
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.[5]
[edit] Quantum suicide could fail
Critics contend quantum suicide fails as a thought experiment to achieve its intended purpose, but there are arguments involving anthropic considerations among entire universes which do provide evidence for the many-worlds interpretation.[6]
[edit] Controversy
Quantum suicide and quantum immortality remain controversial because a number of thinkers disagree on its success or failure and particularly its irrelevance to life expectancy and decision making.
[edit] Quantum suicide and quantum immortality in fiction
Authors of science fiction have used themes involving both quantum suicide and quantum immortality. The basic idea is that a person who dies in one world may survive in another world or parallel universe.
[edit] See also
[edit] References
- ^ Tegmark, Max The Interpretation of Quantum Mechanics: Many Worlds or Many Words?, 1998
- ^ See Keith Lynch's recollections in Eugene Shikhovtsev's Biography of Everett[1]
- ^ Papineau, David “Why you don’t want to get in the box with Schrödinger’s cat” Analysis 63: 51-58. 2003
- ^ a b Mallah, Jacques Many-Worlds Interpretations Can Not Imply 'Quantum Immortality', 2009
- ^ David Lewis. How Many Lives Has Schrödinger's Cat? The Jack Smart Lecture, Canberra, 27 June 2001. Australasian Journal of Philosophy. Vol. 82, No. 1, pp. 3-22; March 2004, pp 21.
- ^ Observational Consequences of Many-Worlds Quantum Theory, 1999.
