Uncertainty principle
The new equations had to be so strange and unusual because Heisenberg was describing a strange world in which some things, such as the orbits of electrons, do not slowly get larger or smaller. The new kinds of changes involve jumps and large gaps between jumps. Electrons can only jump between certain orbits, and the energy gained or lost in changing between orbits is produced when a photon of the right energy is absorbed or a new photon of the right energy is produced. If electrons in hydrogen atoms most frequently jump down (fall) between two particular orbits, then more photons will be emitted at that energy level, and so the light produced at that level will be the most intense.