Saturday, December 08, 2012

A surprising but inevitable discovery

Allan Franklin is a physics historian and philosopher of science from the University of Colorado who specializes in the interdependency of theory and experiment in the advancement of scientific knowledge. It was his paper, "Are the Laws of Physics Inevitable?" (Perspectives in Physics, 2008), that I stumbled upon on my recent return trip from Los Angeles.

The excerpts were more than intriguing:
In 1953 Brice Rustad and Stanley Ruby carried out the most important of these angular correlation experiments on the β decay of He6
Although most of the evidence from β decay was consistent with a doublet VA [vector and axial] interaction, Rustad and Ruby's angular-correlation experiment on He6 provided seemingly conclusive evidence that the β decay was tensor (T).
Sudarshan and Marshak noted that four experiments stood in opposition to the V–A theory, as follows: (1) Rustad and Ruby's electron-neutrino angular-correlation experiments on  He6 ; (2) .... The first two cases were regarded as significant problems, whereas the second two had less evidential weight .... Sudarshan and Marshak suggested that "All of these experiments should be redone...."
Feynman and Gell-Mann went even further in regard to the experimental anomalies. "These theoretical arguments seem to the authors to be strong enough to suggest that the disagreement with the He6 recoil experiment and with some other less accurate experiments indicates that these experiments are wrong [emphasis added by Franklin.
Rustad and Ruby themselves, and [Chien-Shiung] Wu and Arthur Schwarzchild critically reexamined the Rustad-Ruby experiment.
Wu and Schwarzchild then constructed a scale model ten times larger than the Rustad-Ruby apparatus, making the inner walls of the source volume and collimating chimney highly reflecting.
They concluded, finally, that the corrected results "are more in favor of axial vector than tensor contradictory to the original conclusion." Their work thus cast doubt on Rustad and Ruby's original conclusion, and in a postdeadline paper that Rustad and Ruby presented at a meeting of the American Physical Society in January 1958, they agreed with that assessment.*
* There are no abstracts of postdeadline papers. Ruby remembers, however that the tone of their paper was mea culpa; private communication, 1989. 
Wow! I thought I knew a little bit about my father's career in physics but most of this information was coming as a complete surprise. Wu rang a bell. I remembered Stan, or maybe Helga, speaking of a kind of dragon lady Chinese physicist who Stan had worked with. (My earliest memories date to about 1957-8, when we were living in Pittsburgh and Stan was at Westinghouse Labs.) Feynman and Gell-Mann, of course, are both famous names and future Nobelists. Marshak sounded familiar too, but none of those in a way directly connected to Stan.

I was able to login to the UCLA proxy server on the train, and soon downloaded Franklin's paper as a pdf to my iPad. I ravenously read from the 30-page paper, starting with its intriguing opening opening line, "Are the laws of nature discovered or invented?" The introduction goes on to set up the scholarly distinction between social constructionists who believe that theory drives the scientific dialog and rationalists like Franklin to whom experiment is crucial.

To illustrate his argument, Franklin then devotes the rest of the paper recounting the 25-year history of theory and experiment leading to the acceptance of a unified theory of the weak nuclear force, from Enrico Fermi's first theoretical paper on beta decay in 1934 to the successful generalization in 1958 by two independent groups of a Unified Fermi Interaction with V–A coupling that was applicable to meson particle decays as well as beta decays.

Summarizing his argument, Franklin writes:
This history is not one of an unbroken string of successes, but rather one that includes incorrect experimental results, incorrect experiment-theory comparisons, and faulty theoretical analyses. Nevertheless, at the end of the story the proposal of the V–A theory will seem to be an almost inevitable outcome.
A regular comedy of errors, it seems. Then begins a fairly deep dive into nuclear physics as it was understood in the mid-1930s, shortly after the discovery of the neutron and the proposal of a more mysterious particle, the neutrino. I settle back for a challenging read for the next leg of the train trip through Merced, Fresno and Stockton. More in the next post.

No comments:

Post a Comment

Post a comment to the Ruby Family History Project