Angel "Java" Lopez en Blog

14 de Agosto, 2015

Publicado el 14 de Agosto, 2015, 7:14

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Encuentro en estos días el discurso de aceptación de Dirac al premio en memoria de Oppenheimer. Fue el primero en recibirlo, en 1969. Es interesante compartirlo, porque muchas veces me he encontrado con citas parciales del discurso, y ahora tengo la oportunidad de compartirlo completo. Agregaré algunos comentarios cuando pueda. Primero, antes del discurso, transcribo la introducción de Dirac al público presente, por parte de Behram Kursunoglu, profesor y director del Centro de Estudios Teóricos, de la Universidad de Miami. Una foto de Dirac en aquel entonces, con el profesor Kursunoglu:

Decía la presentación:

I consider it a great honor to introduce to you rather briefly Professor Dirac. (I have to do this since all of us here are not physicists.) What I have to tell you is a representative opinion of Professor Dirac by the world of science.

He was born in 1902 in Bristol, England. He graduated from Bristol University and obtained his Ph.D. from Cambridge University, decided to study theoretical physcis at Cambridge and contributed tremendously to the then developing subject of quantum theory. Heisenberg matrix mechanics could hardly be regarded as laws of nature without the fundamental formulation of Dirac. The quantum theory as we know it and apply it today is as formulated by Dirac.

The 1920's were very exciting years for the world of physics. Great discoveries were being made almost overnight. A very rich and rewarding path was opened with the advent of quantum theory. One of the Meccas for the leading physicists of that time was in Gottingen. Young Paul Adrien Maurice Dirac was one of the members of this team - the most versatile one. By the age of 23 he had already written his classic papers which put the concepts of quantum theory on a sound mathematical basis. He reconciled the ideas of relativity with the ideas of quantum theory and invented the well-known relativistic wave equation predicting the existence of a magnetic moment of electron and hence a new fact, the spin.

He further predicted that every elementary particle with a spin 1/2 h has its counterpart with the same mass but opposite electric charge, or that a particle has an antiparticle. It was a prophetic prediction. To the electron, the corresponding system is the positron, which was observed after the prediction in cosmic ray experiments by Anderson in 1932.

Sin embargo, Dirac no predijo el positrón en su primer "paper" del tema. Tardó unos años en proponer una partícula nueva: al principio, pensó que la contrapartida del electrón era el ya conocido protón, aunque no podía explicar la diferencia notable de masa.

Later, electron and positron pairs were actually produced in laboratory experiments. In the same way the proton and neutron should also have their corresponding antiparticles. In view of their mass content being nearly 2000 times that of the electron, experimental observation had to await construction of a large accelerator to produce such particles by collisions of protons with nuclei. This was accomplished in 1955.

Pasaron más de veinte años para conseguir evidencia experimental de antiprotones y antineutrones. Y en este siglo, hemos seguido buscando más partículas en aceleradores: todos podemos recordar la búsqueda del bosón de Higgs, por ejemplo.

His formulation of the statistics of fields and particles, his work on gravitational waves and also his prediction of magnetic monopoles stand as further monuments to his originilaty and deep understanding of natural phenomena.

The impact of Dirac's at the fundamental level has been far reaching, since even now our research in theoretical physics is guided by Dirac's ideas and his formulations. It is often customary, when one has a new idea, to ask if Dirac hasn't done something in this area.

Un caso notable fue el uso del lagrangiano en cuántica por Feynman, que comenzó a usarlo sin conocer el trabajo previo de Dirac. Al conocerlo, lo extendió de manera original.

It turns out that in most instances the subject matter has been dealt with by Dirac in depth, with calarity and originality.

La claridad de Dirac está algo en entredicho. Por un lado, si uno tiene la guía de comentaristas, se encuentra que los artículos de Dirac van al punto y explican el tema. Pero sin esa guía, para muchos físicos contemporáneaos de Dirac, sus artículos eran algo indescifrable y mágico.

His work, besides bringing him the Nobel Prize and coutless other honors and priczes, had been instrumental in many others being awarded the Nobel Prize for the work they have done on his ideas and in the paths opened by Dirac. To cite just a few examples: Willis Lamb, Julian Schwinger, Eugene Wigner, Richard Feyman, S.Tomonaga, C.D.Anderson, E.Segre, O.Chamberlain and many others. (Some of these gentlemen have been guests of the Center.) What he achieved in his early 20's formed the basis on which the Nobel Foundation awarded him the Nobel Prize in 1933 at the age of 31.

Professor Dirac is known as a man, not only in physics but also in ordinary conversations, who dows not make trivial remarks. There is a definite deep and well defined meaning in his every sentence, even though the sentences are not very frequent. He is endowed with all the great virtues of a great man; has no enmities, no dislikes for any human being.

Un ejemplo típico de personalidad de Dirac en Entrevista a Dirac. Ver también Dirac según Gamow.

Professor Dirac is a free man in the true sense of the word. This makes him also very courageous. It is a great honor for us to participate tonight in these modest ceremonies in awarding Professor Dirac the J. Robert Oppenheimer Memorial Prize.

En el próximo post, comenzaremos con el discurso del propio Dirac.

Nos leemos!

Angel "Java" Lopez

Por ajlopez, en: Ciencia