# Hans Bethe Explains

Legendary theoretical physicist Hans Bethe delivered three lectures on quantum theory to his neighbors at the Kendal of Ithaca retirement community (near Cornell University). Given by Professor Bethe at age 93, the lectures are presented here as QuickTime videos synchronized with slides of his talking points and archival material. site

After the war, Bethe brought some of the most outstanding young physicists from Los Alamos to Cornell, in particular, Richard Feynman and Robert Wilson.

Intended for an audience of Professor Bethe's neighbors at Kendal, the lectures hold appeal for experts and non-experts alike. The presentation makes use of limited mathematics while focusing on the personal and historical perspectives of one of the principal architects of quantum theory whose career in physics spans 75 years.

A video introduction and appreciation are provided by Professor Silvan S. Schweber, the physicist and science historian who is Professor Bethe's biographer, and Edwin E. Salpeter, the J. G. White Distinguished Professor of Physical Science Emeritus at Cornell, who was a post-doctoral student of Professor Bethe.

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In the 20's we would say on Monday light is a wave and on Tuesday we say a particle.

The high point for me was 8 minutes into lecture 3 when Bethe shows the uncertainty relation derives from geometric properties of sine waves, in this case the wave function of a free electron, $$\psi = sin ( k x )$$ over distributions of $$\Delta k$$ and $$\Delta t$$.

Bohr, Schrodinger and Heisenberg have done physics a disservice by even the hint that results are uncertain.

Whenever two electrons are interchanged, the wave function changes sign. Pauli principle follows as a special case. Lecture 3, minute 35.

See Brian Cox on Leadership for his one minute explanation of quantum mechanics at the 22 min point into his interview for BBC's Life Scientific.