Sigo leyendo el excelente libro de Zeilder, "Quantum field theory, I". Encuentro la cita de un texto de Max Born, incluido en su libro "Physics in my generation". Recuerdo los tiempos de 1925:
In Gottingen we also took part in the attempts to distill the unknown mechanics of the atom out of the experimental results. The logical difficulty became ever more acute. Investigations on scattering and dispersions of light showed that Einstein's conception of transition probability as a measure of the strength of an oscillation was not adequate... The art of guessing correct formulas, which depart from the classical formulas but pass over into them in the sense of Bohr's correspondence principle, was brought to considerable perfection...
Desde 1913 con el trabajo de Bohr, se había avanzado a tientas, adivinando fórmulas para explicar los resultados experimentales.
This period was brought to a sudden end by Heisenberg, who was my assistant at that time. He cut the Gordian knot by a philosophical principle and replaced guesswork by a mathematical rule. The principle asserts that concepts and pictures that do not correspond to physically observable facts should not be used in theoretical description. When Einstein, in setting up his theory of relativity, eliminated his concepts of the absolute velocity of a body and of the absolute simultaneity of two events at different places, he was making use of the same principle. Heisenberg banished the picture of electron orbits with definite radii and periods of rotation, because these quantities are not observable; he demanded that the theory should be built up by means of quadratic arrays. Instead of describing the motion by giving a coordinate as a function of time x = x(t), one ought to determine an array of transition probabilities (xij). To me the decisive part in his work is the requirement that one must find a rule whereby from a given array [matrix]....the array for the square (x2)ij may be found (or, in general, the multiplication law of such arrays).
Ese es el gran avance de Heisenberg: dejó el concepto de posición y velocidad, y expresó las relaciones entre probabilidades. Esas probabilidades de transición desde estado i a estado j se disponían en una matriz. Y Heisenberg consiguió manejar esas matrices como "números", con multiplicación incluida.
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Angel "Java" Lopez