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This is a somewhat philosophical question. Given that even after person A's death, there's a non-zero chance that a brain fluctuates into existence with exactly the same structure and memories as A's brain, does that imply that A is immortal as given enough time, even if for each fluctuation, it survives for only a short while, A's brain will fluctuate into existence arbitrarily many times and this will enable A to "exist" for an arbitrarily long time.

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This question is either tautological or unanswerable. –  user2963 Mar 30 '12 at 2:17
A brain exists hours after death and A is still dead. The question is not well posed, and touches on the reversibility of death and the meaning of life and therefore belongs to a metaphysical or religious forum –  anna v Mar 30 '12 at 5:09
Who closevoted->off-topic->meta.P.SE? Meta.physics.SE is not the place for metaphysics :/ –  Manishearth Mar 30 '12 at 6:26
1) We don't know if there are any Boltzmann brains in reality, and if there are, we don't know their "demographics". 2) Dying here and now, and then briefly existing again as a copy a googolplex light-years away, is not my notion of "immortality". 3) The Boltzmann brains would include all possible variations on you, in a continuum of identities which start arbitrarily similar to you and end up arbitrarily dissimilar. So which ones are reincarnations of "you" and which ones aren't? –  Mitchell Porter Sep 9 '12 at 4:06
4) Boltzmann brains immediately die like beached whales, only worse. "Immortality via Boltzmann brain" means that, after your earthly life, you regard yourself as being continued by an unfortunate entity randomly assembled in deep space which then immediately dies, and then another such entity elsewhere in space-time which also immediately dies, and then another. If you ever wanted evidence that your thinking about reality, identity, and causality, has taken a wrong turn, you couldn't ask for more than this, that you're seriously considering such a scenario. –  Mitchell Porter Sep 9 '12 at 4:08

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Your question engages many of the same philosophical issues as those raised by so-called quantum immortality (http://en.wikipedia.org/wiki/Quantum_suicide_and_immortality). Discussions of quantum immortality are generally centered around the many worlds interpretation of quantum mechanics. The introduction of Boltzmann brain fluctuations into the discussion is an interesting variation. In any case, this is a question that lends itself more to the tools employed by philosophers than those employed by physicists (although this doesn't stop some physicists from devoting attention to it).

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The difference though is that quantum immortality depends on your interpretation of quantum mechanics and is only applicable to quantum suicide type scenarios. While the Boltzmann Brain idea is independent of all that. –  BBrain Apr 1 '12 at 20:58
@BBrain: not really, you have to make a commitment to a theory of mind which says how consciousness feels its way though a physical universe, and also to a theory of ontology that says that Boltzmann brains are "out there". Both of these are impossible to investigate by logical positivism, so I don't attach meaning to these, but philosophers debate meaningless questions endlessly, so go ask them. –  Ron Maimon Sep 9 '12 at 7:32

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