En la teoría del electrón de Dirac, aparece una partícula con carga eléctrica positiva. Dirac propone una ingeniosa teoría de "agujeros" en un mar de electrones, pero los identifica con los protones y no puede explicar su diferencia de masa. Hermann Weyl sale con la idea de que los "agujeros" deberían tener la misma masa que los electrones, pero sin aportar algo físico, solo basado en matemáticas. Y aparece Oppenheimer:
At this stage in the development of the theory, Oppenheimer made a contribution. Oppenheimer accepted Weyl's conclusion that the holes had to have the same mass as the electrons and faced the physical reality that the holes were not observed in practice. Oppenheimer just said that there was some reason, which we do not understand, why the holes are never observed. He agreed that the holes could not have anything to do with protons, so there had to be some mysterious reason why they did not occur in nature.
Interesante la pregunta de Oppenheimer: ¿dónde están esas partículas? Esa es la pregunta que Weyl no se hizo, y fue algo que le llamó la atención a Dirac.
Well, Oppenheimer was really very close to the mark with this hypothesis. The reason why the holes were not observed was simply that the experimental people had not looked for them in the right place, or if they had looked, they had not recognized what they saw.
Curiosamente, no es que se habían observado, sino que habían aparecido pero nadie las tomó en cuenta. Leamos a Dirac:
I can remember in these early days, even somewhat before this theory of electrons and protons, when talking with people who were working in the Cavendish and were observing tracks of particles in a magnetic field, they said that they sometimes observed an electron going into the source. They treated these occurrences as coincidences. Nobody thought it worthwhile to look more closely into them. The ideas of there being a new particle coming out from the source, instead of an ordinary electron going into the source, was completely foreign to the accepted mode of thought of those days. I do not think anybody had the remotest suspicion of such possibility. They had the evidence before their eyes for these new particles with positive charge and the same mass as the electrons, but they were just unable to appreciate what they saw.
Es notable que existieran estos experimentos, y como nadie esperaba una partícula con carga positiva, no se la reconoció como tal. El Cavendish se perdió la gran oportunidad de descubrir a los positrones.
Angel "Java" Lopez