Walter Kohn's Rabbinical Lesson

I went yesterday to hear Walter Kohn give the fourth lecture in Korea University's Nobel Laureate Lecture Series. He had altered the topic of his talk, switching from the original "Electronic Structure of Matter -- Wave Functions and Density Functionals." The title remained the same, but only the first half of the talk dealt with his Nobel-Prize-winning achievements. In the second half, he presented his views on energy resources for the future.

His brief account of density-functional theory clarified some things that I hadn't understood before (as readers will recall). Schroedinger came first. His 1926 equation enabled scientists to describe the electronic structure of matter, whether atoms, molecules, solids, liquids, or plasmas, but it did not work well with systems of more than 10 to 20 atoms.

Kohn's work improved on this by concentrating on the probability density distribution of electrons in a system in a way that allowed description of far larger systems of up to 500 to 1000 atoms.

How did he do this? I still haven't gotten that far.

But he remarked that his basic idea was rather simple and that it had so surprised him by its accuracy when he first tested it that he was certain that it must be wrong. Further empirical tests convinced him that it was right, and he recalls this confirmation as one of the great exhilirating moments of his scientific career.

Then, he talked about the future, first quoting Niels Bohr, whom he had known personally (or so I understood):

"Prediction is a very tricky thing, especially when it concerns the future."

Nice quote. Not many people caught the humor, but Kohn had anticipated that in a foreign audience and didn't bother to wait for laughter.

Instead, he went on with his talk about the future, choosing a date of about 50 years from now for purposes of illustration, extrapolating population growth, economic development, energy needs, and energy sources. The situation sounded pretty dire, but he believes that if we start now, we can solve the problem of finding renewable energy sources that don't pollute.

His favored solution is solar power.

Now, I've been rather skeptical of solar's potential given that one has to blanket so much land with solar receptors in order to generate enough electricity to meet demand. Kohn, however, did make the crucial, if obvious point that the energy coming from the sun is immense, arrives constantly, and will never run out . . . until the heat death of the universe of something similar.

Then, he gave a rabbinical lesson. About 2000 years ago, there was a young farm worker in the Holy Land who was moving about the land to find work. He passed an old man planting an olive tree.

"Grandfather," he called out, "why are you planting that tree? It won't bear fruit for many years."

"All the more reason to plant now," replied the old man.

And he continued his work. Like Kohn himself.