Cosmology
The series employs physical theories as they are currently known, making it more logical and realistic than several other SF-series. For example, special relativity and its effects are regularly mentioned. (Same goes for geology, biology...) Further "hyperphysical" theories are added to explain the SF-plot. However, they are not contrary, as the authors sometimes use real and fictional physics in unison to explain something.
Read more about this topic: Perry Rhodan