I noticed an apparently self-defeating aspect of the Boltzmann brain scenario.
Let’s say I do find the Boltzmann brain scenario to be likely (specifically, that I find it likely that I myself am a Boltzmann brain), based on my knowledge of the laws of physics. Then my knowledge of the laws of physics is based on the perceptions and memories that I, as a Boltzmann brain, am arbitrarily hallucinating… in which case there is no reason for me to believe that the real universe (that is, whichever one houses the actual physical substrate of my mind) runs on those laws… the very laws that would provide the only evidence that I am indeed a Boltzmann brain.
So supposing that you are a Boltzmann brain is evidence against the possibility of your being a Boltzmann brain (or at least evidence against all of your evidence for it).
I’m still trying to wrap my own brain (Boltzmann or not) around anthropic reasoning, so I’m not sure if I accept the Boltzmann brain argument in the first place (I don’t think I do), but this may serve as a specific argument against it.
Let me see if I can formalize. This might not be quite what you had in mind, but I think it will be similar:
For clarity we can reduce the possible worlds to two, either there are many many more Boltzman brains than human brains (H1) or there are few if any Boltzman brains (H2).
In H2 aprox. everyone who learns of the Boltzman brain hypothesis (and the evidence in favor) is not a Boltzman brain.
In H1 very very few Boltzman brains will learn of the Boltzman brain hypothesis (and the evidence in favor). A significantly larger percentage of the non-Boltzman brains capable of conceiving the hypothesis will learn of it (and the evidence in favor).
So independent evidence of H1 means (1) H1 is more likely to whatever degree that evidence dictates, (2) if H1 you are more likely than most brains to be non-Boltzman, (3) by the self-indication assumption H2 is more likely because in that world most or all brains are non-Boltzman.
The inference from (2) to (3) seems problematic to me. I’m not sure.
Questions:
How the hell do we evaluate the evidence since any evidence of H1 is also evidence of H2 (if we like the SIA).
What the hell is the proper reference class?
If new evidence came in against H1 would we have to say were more likely to be Boltzman brains?
I noticed an apparently self-defeating aspect of the Boltzmann brain scenario.
Let’s say I do find the Boltzmann brain scenario to be likely (specifically, that I find it likely that I myself am a Boltzmann brain), based on my knowledge of the laws of physics. Then my knowledge of the laws of physics is based on the perceptions and memories that I, as a Boltzmann brain, am arbitrarily hallucinating… in which case there is no reason for me to believe that the real universe (that is, whichever one houses the actual physical substrate of my mind) runs on those laws… the very laws that would provide the only evidence that I am indeed a Boltzmann brain.
So supposing that you are a Boltzmann brain is evidence against the possibility of your being a Boltzmann brain (or at least evidence against all of your evidence for it).
I’m still trying to wrap my own brain (Boltzmann or not) around anthropic reasoning, so I’m not sure if I accept the Boltzmann brain argument in the first place (I don’t think I do), but this may serve as a specific argument against it.
Has this been discussed before?
Let me see if I can formalize. This might not be quite what you had in mind, but I think it will be similar:
For clarity we can reduce the possible worlds to two, either there are many many more Boltzman brains than human brains (H1) or there are few if any Boltzman brains (H2).
In H2 aprox. everyone who learns of the Boltzman brain hypothesis (and the evidence in favor) is not a Boltzman brain.
In H1 very very few Boltzman brains will learn of the Boltzman brain hypothesis (and the evidence in favor). A significantly larger percentage of the non-Boltzman brains capable of conceiving the hypothesis will learn of it (and the evidence in favor).
So independent evidence of H1 means (1) H1 is more likely to whatever degree that evidence dictates, (2) if H1 you are more likely than most brains to be non-Boltzman, (3) by the self-indication assumption H2 is more likely because in that world most or all brains are non-Boltzman.
The inference from (2) to (3) seems problematic to me. I’m not sure.
Questions:
How the hell do we evaluate the evidence since any evidence of H1 is also evidence of H2 (if we like the SIA).
What the hell is the proper reference class?
If new evidence came in against H1 would we have to say were more likely to be Boltzman brains?