We need to use physics to understand the laws that exist deep in nature. This idea cannot be ignored when considering what physics is. The further development of physics not only expands its scope, but also develops from mechanics to light. , heat, electromagnetism, atoms and molecules, and even chemistry have been included in the scope of physics. There is a tendency to reunify all phenomena and integrate all disciplines. We might as well call it unification theory as opposed to differentiation theory. The famous physicist Lu Serford's famous saying: "All science is either physics or stamp collecting." can be regarded as the most concise definition of the general theory of physics.

Such a simple definition is very important for practical work. For scientists doing scientific research, it is convenient and specific. But for the public, it is a bit confusing. This means that when scientists talk about science, when ordinary people talk about science, even researchers in different disciplines (such as: Nature Science and humanities) may have different definitions in mind when talking about science.