Editing Quantum suicide and immortality (section)

=== Analysis by skeptics of the many-worlds interpretation ===

Cosmologist [[Anthony Aguirre]], while personally skeptical of most accounts of the many-worlds interpretation, in his book ''Cosmological Koans'' writes that "[p]erhaps reality actually is this bizarre, and we really do subjectively 'survive' any form of death that is both instantaneous and binary." Aguirre notes, however, that most causes of death do not fulfill these two requirements: "If there are degrees of survival, things are quite different." If loss of consciousness was binary like in the thought experiment, the quantum suicide effect would prevent an observer from subjectively falling asleep or undergoing anesthesia, conditions in which mental activities are greatly diminished but not altogether abolished. Consequently, upon most causes of death, even outwardly sudden, if the quantum suicide effect holds true an observer is more likely to progressively slip into an attenuated state of consciousness, rather than remain fully awake by some very improbable means. Aguirre further states that quantum suicide as a whole might be characterized as a sort of ''[[reductio ad absurdum]]'' against the current understanding of both the many-worlds interpretation and theory of mind. He finally hypothesizes that a different understanding of the relationship between the mind and time should remove the bizarre implications of necessary subjective survival.<ref name=aguirre>{{cite book |last=Aguirre |first=Anthony |year=2019|chapter=What survives|title=Cosmological Koans}}</ref>

Physicist and writer [[Philip Ball]], a critic of the many-worlds interpretation, in his book ''Beyond Weird'', describes the quantum suicide experiment as "cognitively unstable" and exemplificatory of the difficulties of the many-worlds theory with probabilities. While he acknowledges Lev Vaidman's argument that an experimenter should subjectively expect outcomes in proportion of the "measure of existence" of the worlds in which they happen, Ball ultimately rejects this explanation. "What this boils down to is the interpretation of probabilities in the MWI. If all outcomes occur with 100% probability, where does that leave the probabilistic character of quantum mechanics?" Furthermore, Ball explains that such arguments highlight what he recognizes as another major problem of the many-worlds interpretation, connected but independent from the issue of probability: the incompatibility with the notion of selfhood. Ball ascribes most attempts of justifying probabilities in the many-worlds interpretation to "saying that quantum probabilities are just what quantum mechanics look like ''when consciousness is restricted to only one world''" but that "there is in fact no meaningful way to explain or justify such a restriction." Before performing a quantum measurement, an "Alice before" experimenter "can't use quantum mechanics to predict what will happen to her in a way that can be articulated – because there is no logical way to talk about 'her' at any moment except the conscious present (which, in a frantically splitting universe, doesn't exist). Because it is logically impossible to connect the perceptions of Alice Before to Alice After [the experiment], "Alice" has disappeared. [...] [The MWI] eliminates any coherent notion of what we can experience, or have experienced, or are experiencing right now."<ref>{{cite book |last1=Ball |first1=Philip |title=Beyond Weird: Why Everything You Thought You Knew About Quantum Physics Is Different |date=2018 |publisher=University of Chicago Press |isbn=978-0226558387 |chapter=There is no other 'quantum you'}}</ref> 

Philosopher of science Peter J. Lewis, a critic of the many-worlds interpretation, considers the whole thought experiment an example of the difficulty of accommodating [[probability]] within the many-worlds framework: "Standard quantum mechanics yields probabilities for various future occurrences, and these probabilities can be fed into an appropriate decision theory. But if every physically possible consequence of the current state of affairs is certain to occur, on what basis should I decide what to do? For example, if I point a gun at my head and pull the trigger, it looks like Everett's theory entails that I am certain to survive—and that I am certain to die. This is at least worrying, and perhaps rationally disabling."<ref>{{cite web |last1=Lewis|first1=Peter J.|title=Uncertainty and probability for branching selves  |url=http://users.ox.ac.uk/~everett/docs/Lewis%20Uncertainty.pdf |archive-url=https://web.archive.org/web/20161108215751/http://users.ox.ac.uk/%7Eeverett/docs/Lewis%20Uncertainty.pdf |archive-date=2016-11-08 |url-status=live|date=13 November 2001}}</ref> In his book ''Quantum Ontology'', Lewis explains that for the subjective immortality argument to be drawn out of the many-worlds theory, one has to adopt an understanding of probability – the so-called "branch-counting" approach, in which an observer can meaningfully ask "which post-measurement branch will I end up on?" – that is ruled out by experimental, empirical evidence as it would yield probabilities that do not match with the well-confirmed [[Born rule]]. Lewis identifies instead in the Deutsch-Wallace decision-theoretic analysis the most promising (although still, to his judgement, incomplete) way of addressing probabilities in the many-worlds interpretation, in which it is not possible to count branches (and, similarly, the persons that "end up" on each branch). Lewis concludes that {{Avoid wrap|"[t]he}} immortality argument is perhaps best viewed as a dramatic demonstration of the fundamental conflict between branch-counting (or person-counting) intuitions about probability and the decision theoretic approach. The many-worlds theory, to the extent that it is viable, does not entail that you should expect to live forever."<ref>{{cite book |last1=Lewis|first1=Peter J.|title=Quantum Ontology: A Guide to the Metaphysics of Quantum Mechanics |date=2016|publisher=Oxford University Press|isbn=978-0190469818|chapter=Immortality}}</ref>