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Questions left unanswered by the scattering matrix


Conceiving of the scattering matrix from resonating group structure
John Wheeler Scientist
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How I got into that game went back to the London meeting in October of 1934. Two groups describe experiments where helium nuclei collided with other helium nuclei and got biffed off at an angle, how many got scattered on one angle, how many at another, how many at another, and how did this scattering probability depend on energy? That was what the data told. But from it, how could one unravel it and learn something about the nucleus? Well, it was clear that the key point was the temporary formation out of two systems, each of four particles, of the larger formation of eight particles. And that larger system, how did it break up into two systems of four particles? What governed the probability? And it became necessary to find what, in the words of quantum theory, is the probabilities for this, that and the other structure. To describe this point of view, which I found myself forced to adopt, I got a phrase from my friend, Edward Condon, whose place I took at Princeton when he went to become Director of Research at the Westinghouse Electric Company and left his position vacant. Before he left, I told him about these ideas, and he said- you always describe that as resonating group structure. Resonating meaning sometimes it's one way, sometimes it's another way, and group meaning that the particles had come together, formed various clusters, part of the time in one clustering, part of the time in another clustering. So, that way of description had to be translated into mathematics and carried through to get an interpretation of the experiments. I'd love to go back again, in the light of the latest modern day results and see if there are any new conclusions one can form out of it. However, the- struggling with this problem forced me to recognize the similarities between nuclear physics and molecular physics, where you have two molecules come together and interact and come out as new molecules. And how to describe that. Then it turned out the way to do it was to talk of a probability of this wave coming out or that wave coming out. And I condensed this point of view into a description called resonating- not resonating group structure but the scattering matrix. And the scattering matrix is now widely used in an even greater variety of problems, far from the original context of nuclear physics. But this scattering matrix was- and the idea was independently conceived a bit later by Werner Heisenberg - so that I felt happy to have others come into the same road.

John Wheeler, one of the world's most influential physicists, is best known for coining the term 'black holes', for his seminal contributions to the theories of quantum gravity and nuclear fission, as well as for his mind-stretching theories and writings on time, space and gravity.

Listeners: Ken Ford

Ken Ford took his Ph.D. at Princeton in 1953 and worked with Wheeler on a number of research projects, including research for the Hydrogen bomb. He was Professor of Physics at the University of California and Director of the American Institute of Physicists. He collaborated with John Wheeler in the writing of Wheeler's autobiography, 'Geons, Black Holes and Quantum Foam: A Life in Physics' (1998).

Duration: 5 minutes, 10 seconds

Date story recorded: December 1996

Date story went live: 24 January 2008