In the “Elon Musk” discussion, in the midst of a whole lotta epistemology goin’ on, commenter BruceS referred to the concept of a “Boltzmann Brain” and suggested that Boltzmann didn’t know about evolution. (In fact Boltzmann did know about evolution and thought Darwin’s work was hugely important). The Boltzmann Brain is a thought experiment about a conscious brain arising in a thermodynamic system which is at equilibrium. Such a thing is interesting but vastly improbable.
BruceS explained that he was thinking of a reddit post where the commenter invoked evolution to explain why we don’t need extremely improbable events to explain the existence of our brains (the comment will be found here).
What needs to be added is that all that does not happen in an isolated system at thermodynamic equilibrium, or at least it has a fantastically low probability of happening there. The earth-sun system is not at thermodynamic equilibrium. Energy is flowing outwards from the sun, at high temperature, some is hitting the earth, and some is taken up by plants and then some by animals, at lower temperatures.
It is really the same argument that can be made against Granville Sewell’s nonsensical “Second Law” arguments against evolution. Sewell makes it sound absurd that random evolutionary particles could form buildings and computers. He does this by leaving out the intermediate steps where the particles aggregate into atoms, those into molecules, those into rocks, those into planets, and then energy flow from the sun to those planets enables life to exist. All processes that are far from thermodynamic equilibrium. Life lives by harnessing some of that energy flow. All of this has been understood since … well, since Boltzmann.
Boltzmann Brains are too improbable to worry about, but single-celled organisms do develop sensitivity to their environment, involving waves of excitation that involve electrochemical potentials across their cell membranes. And when multicellular animals developed, some cells specialized in doing that, leading ultimately to Ludwig Boltzmann’s own brain.
Those processes do not simply result from thermodynamic fluctuations in an equilibrium system.