Is an expert defined by how much they know about a subject in an absolute sense? If so, does that information need to be relevant? Can memorizing a book on chemistry from 100 years ago make you an expert?
Or is expertise not about absolutes, like how much you know? Is expertise instead defined by how helpful the expert is in light of some goal? So if the goal is to send people into space, then experts on the geology of Antartica are not very helpful while experts on space travel are.
Finally, who decides who is and isn't an expert? Is it the expert themselves, or some authority, or just anybody? Who decides if a heart surgeon is really an expert? The surgeon, the American Medical Association, or you?
This episode is a sort of meditation on expertise.