Angel "Java" Lopez en Blog

Publicado el 30 de Abril, 2016, 11:06

Siempre vuelvo a leer el excelente "Quamtum Field Theory I", de Zeidler. Y encuentro hoy una cita de Freeman Dyson, más extensa que la que ya había comentado en Richard Feynman por Freeman Dyson. Se refiere a la época de los treinta del siglo pasado, cuando Feynman se concentra en estudiar por su cuenta la mecánica cuántica de su tiempo:

Dick Feynman (1918-1988) was a profoundly original scientist. He refused to take anybody's word for anything. This meant that he was forced to rediscover or reinvent for himself almost the whole physics. It took him five years of concentrated work to reinvent quantum mechanics. He said that he couldn't understand the official version of quantum mechanics that was taught in the textbooks and so he had to begin afresh from the beginning. This was a heroic enterprise. He worked harder during those years than anybody else I ever knew. At the end he had his version of quantum mechanics that he could understand...

Pero Feynman fue más allá con su versión, logrando resolver problemas más fácilmente:

The calculations that I did for Hans Bethe, using the orthodox method, took me several months of work and several hundred sheets of paper. Dick could get the same answer, calculating on a blackboard, in half an hour...

In orthodox physics, it can be said: Suppose an electron is in this state at a certain time, then you calculate what it will do next by solving the Schrodinger equation introduced by Schrodinger in 1926. Instead of this, Dick simply said:

The electron does whatever it likes.

Feynman había encontrado su camino: sumar todos los caminos posibles del electrón. Y esto lo consiguió meditando y revisando la mecánica cuántica de entoces. Podemos decir que el resultado de Feynman es una extensión del experimento de las dos rendijas: para llegar de A a B, la partícula cuántica pasa por las "infinitas rendijas" del espacio que separa el punto de partida del punto de llegada.

A history of the electron is any possible path in space and time. The behavior of the electron is just the result of adding together all the histories according to some simple rules that Dick worked out. I had the enormous luck to be at Coraell in 1948 when the idea was newborn, and to be for a short time Dick's sounding board...

Feynman basaba sus ideas en conceptos físicos, y los trasladaba a matemáticas:

Dick distrusted my mathematics and I distrusted his intuition. Dick fought against my scepticism, arguing that Einstein had failed  because he stopped thinking in concrete physical images and became a  manipulator of equations. I had to admit that was true. The discoveries of Einstein's earlier years were all based on direct physical intuition.  Einstein's later unified theories failed because they were only sets of equations without physical meaning...

Pero no era fácil entonces entender estas nuevas ideas de Feynman:

Nobody but Dick could use his theory. Without success I tried to  understand him... At the beginning of September after vacations it was time to go back East. I got onto a Greyhound bus and travelled nonstop for three days and nights as far as Chicago. This time I had nobody to talk to. The roads were too bumpy for me to read, and so I sat and looked out of the window and gradually fell into a comfortable stupor. As we were droning across Nebraska on the third day, something suddenly happened. For two weeks I had not thought about physics, and now it came bursting into my consciousness like an explosion. Feynman's pictures and Schwinger's equations began sorting themselves out in my head with a clarity they had never had before. I had no pencil or paper, but everything was so clear I did not need to write it down.

Feynman and Schwinger were just looking at the same set of ideas from two different sides.

Putting their methods together, you would have a theory of quantum electrodynamics that combined the mathematical precision of Schwinger with the practical flexibility of Feynman...

During the rest of the day as we watched the sun go down over the prairie, I was mapping out in my head the shape of the paper I would write when I got to Princeton. The title of the paper would be The radiation theories of Tomonaga, Schwinger, and Feynman.

Es en parte al trabajo de difusión de Dyson que las ideas de Feynman fueron más conocidas, entendidas y aceptadas por la comunidad de físicos. El uso de los diagramas de Feynman facilitó la explicación de esta suma de trayectorias, y es interesante ver la historia de su desarrollo, por ejemplo, ver que los primeros diagramas aparecidos en artículos son diferentes de los que usamos en artículos de divulgación.

Esto es una cita que hace Zeidler de un texto de Dyson, Disturbing the Universe.

Otros posts donde cito el libro de Zeidler:

Teoría de campos y partículas (3)
Una carta de Einstein
John von Neumann y operadores en cuántica

Nos leemos!

Angel "Java" Lopez

Por ajlopez, en: Ciencia