Although very successful, Planck and Bohr proposals provided somewhat provisional patchwork “scheme” referred to as “the old quantum theory”.
In 1923, physicists looked forward with enormous enthusiasm to detailed solutions to their outstanding problems. They tried to use Bohr’s proposal on the stability of the hydrogen atom and extend it to more general situation as the helium atom. However, within
less than a year, physicists were totally convinced that Bohr’s atomic theory can not be adopted to more complex problems. This meant that a new theory had to be guessed to explain the general model.
Quantum theory as we know it today arouse out of two independent later schemes which were innovated by a pair of young remarkable physicists: a German, Werner Heisenberg, and an Austrian, Erwin Schrödinger.
As a young physicist aged 24 at the time, Werner Heisenberg was particularly interested in general methods for making guesses (matrix mechanics) His work led to the discovery of one of the weirdest principles in the history of science.