As science progresses, frequently two fields are found to have overlap, where the techniques and areas of study are found to be similar (or identical) to another field of study. Historically speaking, an example of this would be the interface between Physics and Chemistry, at the point where Quantum Mechanics is used to describe things at a chemical level - Quantum Chemistry.
Another such interface is being discovered today as the fields of Physics and Biology work together on a new sort of hybrid of the two. By using the techniques of Physics, applied to the subject material which has been historically Biology, we can make new discoveries by harnessing the combined research methodologies each field can bring to bear.