We interpret ``fundamental'' to mean that something is fundamental if and only if when it changes a lot of other things change. With this criterion and its variants as the working hypothesis we investigate the following questions: What distinguishes fundamental physics and ``less fundamental'' physics? Which theories of physics are more fundamental? What is the opposite of ``fundamental''? What is progress in fundamental physics? What questions are fundamental? What could be the next big progress in fundamental physics? Among the conclusions we draw are the following. The most fundamental thing in physics is that the universe exists (of course). The opposite of ``fundamental'' is ``irrelevant''. Within the field of fundamental physics there are in fact much research that runs a high chance of being irrelevant. A ``theory of everything'' is not necessarily the most fundamental theory. Knowledge about the some fundamental aspects of nature may be informed by less fundamental theories rather than more fundamental ones. The next big progress in fundamental physics could be the establishment of black hole thermodynamics invoking only quantum theory but not quantum field theory.
Ding Jia