ABSTRACT
I had to make some quite arbitrary decisions as to what I could include and not include, and I could easily imagine someone else very clever or myself in a different mood discussing a rigorously disjoint set of topics. What I chose to do is to talk about three relatively specific, very important problems in physics, astronomy, and to a lesser extent, mathematics and try to generalize from these problems. I chose problems which do have a true interdisciplinary component and, at the same time, are among the most important problems we are currently up against. In each of these, I shall go from the specific to the general, so do not be misled by the headings. They refer to the vague generalities that come at the end.
