Physics can be defined as the study of matter, energy, and the interaction between them. This is concise and seemingly clear, but physics is a sprawling and dynamic science and this basic definition needs to be amplified to truly reflect what physics is all about. ‘What physics covers and what it doesn’t’ considers the different meanings of matter and energy; and also explains how physics can be defined and described by scale, and how it deals with different aspects of the universe by their size. From quarks to atoms to galaxies, the components of the universe span many orders of magnitude in size. The different sub-divisions of physics are also considered.