> The Boltzmann brain thought experiment suggests that it might be more likely for a single brain to spontaneously form in space, complete with a memory of having existed in our universe, rather than for the entire universe to come about in the manner cosmologists think it actually did.

I don't think that's true though, I think it's more unlikely for a brain to form spontaneously, than a simple (simple compared to the brain) system of rules that then causes galaxies, planets and life with brains to form through interacting processes