In addition to his major subjects, he also attended lectures in chemistry, zoology, geology, mineralogy and astronomy, as well as logic and metaphysics.

In 1889 he continued his studies at the University of Heidelberg and received a doctoral degree in mathematics in 1892 (at the age of 22).

His thesis is titled Zum Fundamentalsatz über die Existenz von Integralen partieller Differentialgleichungen (On the fundamental theorem on the existence of integrals of partial differential equations) and his supervisor was Leo Königsberger.

During his Greifswald years Mie worked on the computation of scattering of an electromagnetic wave by a homogeneous dielectric sphere, which was published in 1908 under the title of "Contributions to the optics of turbid media, particularly of colloidal metal solutions" in Annalen der Physik.

[2]: 115  His motivation was to explain the 'invisible' electron and relate gravitation to matter; his theory had three core assumptions: 1) electrical and magnetic fields exist inside of electrons, 2) special relativity, and 3) new states of ether would be sufficient to explain all phenomenon of the material world.