Grand challenges in interdisciplinary physics
The dictionary definition of physics is the study of matter, energy, and the interaction between them1. There is no doubt that this definition does describe the core of physics. However, over the last three decades, a shift has occured. Physics has spilled over its boundaries set by the definition quoted, and we now have fields such as econophysics, sociophysics, biological physics, and geological physics. Common for these new fields of physics is that if they are to be defined based on the subjects that are studied, they would not belong to physics. What does make them part of physics is rather the way the subjects are studied. By regarding these new fields as belonging to physics, the dictionary definition of physics no longer holds. One has to revise it. It makes sense to replace the old definition stating that physics is the study of certain quantities by one where physics is defined as a method to approach scientific problems. Physics as a method of approaching scientific problems is different from other sciences. It is hierarchical: more general questions are posed and answered before more specific questions. Here is a concrete example: In the twenties, general quantum mechanics was developed. In the thirties, a general theory of metals was developed. This allowed for studying specific metals, but it also opened up for the search for a class of materials that were between metals and insulators: the semiconductors. In the forties, this resulted in the construction of the first transistor—and the electronics age was born. One may only speculate how long it would have taken to construct