I have heard that, in mathematics, there might be several difficulties in changing one's field once one has a tenured position. I am wondering what those difficulties are. Is it possible at all?
Let me mention two difficulties I heard about.
Obviously, one has to learn a new area of math on a professional level, which is not easy.
These days, there is a strong pressure to get grants and, hence, to publish regularly. If one does not yet have a reputation of a serious expert in the new field it will be difficult to get a grant. This pressure is weaker if one has a tenure, but it still exists.