The Boltzmann brain was originally discussed as a sort of thought-experiment or aid to reflection on what might possibly happen in the universe. Its first discussion was in the context of thermal equilibrium. The idea is that there is a non-zero chance that, given enough time, a system such as a gas in thermal equilibrium and with the right constituents might, by very rare random thermal fluctuation, come together in a remarkable configuration such as a brain (with, I suppose, associated oxygen supply, heat removal, etc.)
This notion, sort of wierd and yet sciencey, captures the imagination and hence entered the popular imagination about what physics says or might say. It enables one to pose a question such as, "how can you tell whether you yourself, with all your memories and present experiences, may not be such an entity? All your 'understanding' of cosmic and biological evolution might be just a set of ideas created ready-made in your brain, the whole thing just the result of thermal fluctuation in a gas?"
My question is, has this idea ever approached even approximately to a concept in which people understand what they are talking about sufficiently well that it can support a conclusion that could be falsified or otherwise connect with scientific discussion more generally? It seems to me that attempts to calculate the probability of a Boltzmann brain are simply back-of-the-envelope estimates that are almost certainly wildly off, and as such have practically zero usefulness. A very tiny number $\nu$ which no-one knows how to calculate, even approximately, is combined with a very large number $N$ (some notion of an enormously long future for the universe, for example, or a vast number of different universes) which is also something we know little about, and then their product $N \nu$ is discussed. This $N \nu$ number appears to have some scientific credibility because it is invoked by reputable scientists engaged in discussion about cosmological models and things like that.
I don't want this question to generate just a set of opinions. I am asking whether there is evidence, or some sort of sound basis on which to affirm, that
(1) we understand the relevant probability distributions sufficiently well to trust calculations of this sort (this would require, for example, that one is treating the low-probability wings of the distribution correctly, and accounting for correlated effects correctly)
(2) we know what is physically sufficient to give rise to the sorts of thoughts and experiences enjoyed by humans (e.g. is a brain enough, or does one need a community and the exchange of language, and a stimulating environment, etc.)
It seems to me that the correct answer to both these questions is a simple "no", but if I am mistaken then I would be interested to know it.