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Does the Boltzmann brain scenario also assume that the laws of physics are presented consistently for each individual brain? In other words:

1) Why do we assume that the types of brains fluctuated into existence bear the same relation to the "external world" in order to make sense of that external world? i.e. we assume that the laws of physics are presented consistently to each individual brain.

2) Is it not more feasible that the types of brains fluctuated into existence will be brain states that are doing no more than e.g. making sense of its own brain, rather than simply responding to its environment in the way the orthodox view describes?

It seems perfectly reasonable to imagine brains to be in states in which we perceive the laws of physics to be different to what they actually are.

thanks

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You're correct, a Boltzmann brain would be unlikely to perceive the true laws of physics (presumably their experiences would be as disordered as possible in a way that's consistent with being conscious, based on the assumption that there'd be vastly more possible arrangements of particles corresponding to a brain-like system experiencing a highly disordered world than arrangements corresponding to a brain-like system experiencing a world and past history as ordered and consistent as what we experience). But I haven't seen anyone seriously suggest that we are Boltzmann brains, so this point wouldn't cast doubt on the idea that we do perceive the correct laws of physics.

The usual point of bringing them up is just that we should probably rule out any cosmological scenario which predicts Boltzmann brains would vastly outnumber conscious beings in the earlier low-entropy phase, since if that were the case it'd be unlikely to find yourself in the earlier phase according to the type of anthropic reasoning known as the self-sampling assumption. As physicist Sean Carroll says in this paper, any belief in a cosmological scenario dominated by Boltzmann brains would seem to be "cognitively unstable"--it's intended as a type of reductio ad absurdum argument against such cosmologies.

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