Quantum mechanics of Born, Heisenberg, and Jordan.
From Physics in my Generation (Springer, 1969) by Max Born:
"In Gottingen we also took part in the attempts to distill the unknown mechanics of the atom out of the experimental results ... The art of guessing correct formulas ... was brought to considerable perfection ...
This period was brought to a sudden end by Heisenberg ... He cut the Gordian knot ... he demanded that the theory should be built up by means of quadratic arrays ... one must find a rule ... for the multiplication of such arrays ...
By consideration of known examples discovered by guesswork, Heisenberg found this rule ...
Heisenberg's rule left me no peace, and after a week of intensive thought and trial, I suddenly remembered an algebraic theory that I had learned from my teacher, Rosanes, in Breslau. Such quadratic arrays are quite familiar to mathematicians, and are called matrices ...
[Born writes down the now iconic qp-pq=iħ.]
My excitement over this result was like that of the mariner who, after long voyaging, sees the land from afar..."
