Psy-Kosh, my argument that Boltzmann brains go poof is a theoretical argument, not an anthropic one. Also, if we want to maximize our correct beliefs in the long run, we should commit to ignore the possibility that we are a brain with beliefs not causally affected by the decision to make that commitment (such as a brain that randomly pops into existence and goes poof). This also is not an anthropic argument.
With regard to longer-lived brains, if you expect there to be enough of them that even the ones with your experience are more common than minds in a real civilization with your experience, then you really should rationally expect to be one (although as a practical matter since there’s nothing much a Boltzmann brain can reasonably expect to do one might as well ignore it*). If you expect there to be more long lived Boltzmann brains than civilization-based minds in general, but not enough for ones with your experience to outnumber civilization-based minds with your experience, then your experience tips the balance in favour of believing you are not a Boltzmann brain after all.
I think your confusion is the result of you not being consistent about whether you accept self-indication, or maybe you being inconsistent about whether you think of the possible space with Boltzmann brains and no civilizations as being additional to or a substitute for space with civilizations. Here’s what different choices of those assumptions imply:
(I assume throughout that that the probability of Boltzmann brains per volume in any space is always lower than the probability of minds in civilizations where they are allowed by physics)*
Assumptions → conclusion
self-indication, additional → our experience is not evidence** for or against the existence of the additional space (or evidence for its existence if we consider the possibility that we may be unusually order-observing entities in that space)
self-indication, substitute → our experience is evidence against the existence of the substitute space
instead of self-indication, assume the probability of being a given observer is inversely proportional to number of observers in possible universe containing that observer (this is the most popular alternative to self-indication) → our experience is evidence against the existence of the additional or substitute space
*unless the Boltzmann brain, at further exponentially reduced probability, also obtained effective means of manipulating its environment...
** basically, define “allowed” to mean (density of minds with our experience in civ) >> (density of Boltzmann brains with our experience), and not allowed to mean the opposite (<<). One would expect the probability of a space with comparable densities to be low enough not to have a significant quantitative or qualitative affect on the conclusions.
*It seems rather unlikely that a space with our current apparent physical laws allows more long-lived B-brains than civilization-based brains. I am too tired to want to think about and write out what would follow if this is not true.
**I am using “evidence” here to mean shifts of probability relative to the outside view prior (conditional on the existence of any observers at all), which means that any experience is evidence for a larger universe (other things being equal) given self-indication, etc.
Psy-Kosh, my argument that Boltzmann brains go poof is a theoretical argument, not an anthropic one. Also, if we want to maximize our correct beliefs in the long run, we should commit to ignore the possibility that we are a brain with beliefs not causally affected by the decision to make that commitment (such as a brain that randomly pops into existence and goes poof). This also is not an anthropic argument.
With regard to longer-lived brains, if you expect there to be enough of them that even the ones with your experience are more common than minds in a real civilization with your experience, then you really should rationally expect to be one (although as a practical matter since there’s nothing much a Boltzmann brain can reasonably expect to do one might as well ignore it*). If you expect there to be more long lived Boltzmann brains than civilization-based minds in general, but not enough for ones with your experience to outnumber civilization-based minds with your experience, then your experience tips the balance in favour of believing you are not a Boltzmann brain after all.
I think your confusion is the result of you not being consistent about whether you accept self-indication, or maybe you being inconsistent about whether you think of the possible space with Boltzmann brains and no civilizations as being additional to or a substitute for space with civilizations. Here’s what different choices of those assumptions imply:
(I assume throughout that that the probability of Boltzmann brains per volume in any space is always lower than the probability of minds in civilizations where they are allowed by physics)*
Assumptions → conclusion
self-indication, additional → our experience is not evidence** for or against the existence of the additional space (or evidence for its existence if we consider the possibility that we may be unusually order-observing entities in that space)
self-indication, substitute → our experience is evidence against the existence of the substitute space
instead of self-indication, assume the probability of being a given observer is inversely proportional to number of observers in possible universe containing that observer (this is the most popular alternative to self-indication) → our experience is evidence against the existence of the additional or substitute space
*unless the Boltzmann brain, at further exponentially reduced probability, also obtained effective means of manipulating its environment...
** basically, define “allowed” to mean (density of minds with our experience in civ) >> (density of Boltzmann brains with our experience), and not allowed to mean the opposite (<<). One would expect the probability of a space with comparable densities to be low enough not to have a significant quantitative or qualitative affect on the conclusions.
*It seems rather unlikely that a space with our current apparent physical laws allows more long-lived B-brains than civilization-based brains. I am too tired to want to think about and write out what would follow if this is not true.
**I am using “evidence” here to mean shifts of probability relative to the outside view prior (conditional on the existence of any observers at all), which means that any experience is evidence for a larger universe (other things being equal) given self-indication, etc.