Veamos hoy una dificultad que encontró Dirac al plantear la teoría relativista en cuántica:
How did the further development of quantum theory proceed after this stage? We had a relativistic equation which worked. It gave agreement with experiment to high accuracy for the simple example of the hydrogen atom. It was not long before a new difficulty appeared. Namely, working with this equation, one found that the electron had states of negative energy. For a particle to be in a state of negative energy, of course, is something which appears quite impossible. From an experimental point of view, it is certainly never observed. So it would seem that one had conquered one difficulty only to plunge into another.
Dirac explica que no es infrecuente esta situación en el avance de la ciencia:
It frequently happens with the development of science that, when one gets over one difficulty, one is immediately faced with a newer difficulty an dyou might at first sight think that no real progress has been made. But real progress is made because the new difficulty is more remote thant the previous one .If one looks into things more closely, one usually sees that the new difficulty was really there all the time. It was just hidden previously and swamped by a more crude difficulty and, when the cruder difficulty is explained away, people focus their attention on the new difficulty.
Pero esta vez, la dificultad no era nueva, solo que antes, en teorías no cuánticas, no tenía relevancia:
When this new difficulty of the negative energy states appeared it was an example of a difficulty that was not really new; it was there all the time. In any relativistic theory this difficulty occurs, even in the old classical theory of Lorenz. But it didn't matter under those conditions because an electron could then never jump into one of the states of negative energy. There was continuity which prohibited such jumps. However, with the new Quantum Theory, such jumps could occur and the difficulty could not be ignored in the way in which it had been previously.
En el siguiente post veremos cómo Dirac logra sortear esta dificultad, de una forma muy original.
Angel "Java" Lopez