As you describe them, an irrational Bob’s beliefs are random, and a rational Bob bases and updates his beliefs on evidence. If he is trying to use a systematic method to determine his degree of rationality, or even trying to devise one, doesn’t that automatically make him rational (even if it’s only just his own definition of ‘rational’)?
Regarding Boltzmann brains:
If I’m not a Boltzmann brain, then my current understanding of the subject of Boltzmann brains correctly tells me that the overwhelmingly vast majority of Boltzmann brains would not have memories and thoughts with the degree of coherence that I do have.
On the other hand, if I am a Boltzmann brain, then I’m either one of the vanishingly rare coherent ones and can trust my thoughts, or I’m so disconnected with reality that I cannot trust my conclusions about the degree of coherence of my thoughts and experiences (like irrational Bob, I suppose).
But if I am an incoherent Boltzmann brain, I am one that can still think of the concept of a Boltzmann brain (and ponder the degree of coherence of my thoughts). I would say that argues against the likelihood of me being an incoherent Boltzmann brain. This leaves the options that I’m either not a Boltzmann brain, or that I’m a relatively coherent one.
As you describe them, an irrational Bob’s beliefs are random, and a rational Bob bases and updates his beliefs on evidence. If he is trying to use a systematic method to determine his degree of rationality, or even trying to devise one, doesn’t that automatically make him rational (even if it’s only just his own definition of ‘rational’)?
Regarding Boltzmann brains:
If I’m not a Boltzmann brain, then my current understanding of the subject of Boltzmann brains correctly tells me that the overwhelmingly vast majority of Boltzmann brains would not have memories and thoughts with the degree of coherence that I do have.
On the other hand, if I am a Boltzmann brain, then I’m either one of the vanishingly rare coherent ones and can trust my thoughts, or I’m so disconnected with reality that I cannot trust my conclusions about the degree of coherence of my thoughts and experiences (like irrational Bob, I suppose).
But if I am an incoherent Boltzmann brain, I am one that can still think of the concept of a Boltzmann brain (and ponder the degree of coherence of my thoughts). I would say that argues against the likelihood of me being an incoherent Boltzmann brain. This leaves the options that I’m either not a Boltzmann brain, or that I’m a relatively coherent one.