En el segundo de sus "papers" de 1926, Schrödinger menciona la teoría de Heisenberg, completada por Born y Jordan, en artículos publicados en 1925. Leo en su "Quantisation and Proper Values - II":

I would not like to proceed without mentioning here that at the present time a research is being prosecuted by Heisenberg, Born, Jordan, and other distinguished workers, to remove the quantum difficulties, which has already yielded such noteworthy success that it cannot be doubted that it contains at least a part oœ the truth. In its tendency, Heisenberg's attempt stands very near the present one, as we have already mentioned. In its method, it is so totally different that I have not yet succeeded in finding the connecting link.

Luego otros, como Carl Eckart, se ocuparían de encontrar la equivalencia de las dos teorías.

I am distinctly hopeful that these two advances will not fight against one another, but on the contrary, just because of the extraordinary difference between the starting-points and between the methods, that they supplement one another and that the one will make progress where the other fails. The strength of Heisenberg's programme lies in the fact that it promises to give the line-intensities,  question that we have not approached as yet.

El tema de atacar el problema de las intensidades de las líneas espectrales era un punto fuerte de la teoría de Heisenberg.