‚ÄčRoy Chisholm (1926 - 2015)

Texas A&M, Los Alamos, La Jolla and Stanford

For all of us, the transition from Dublin to College Station, Texas, was like time-travel over several centuries. When we asked where we could shop, we were dumbstruck by the answer 'Oh, Piggly-Wiggly is just down the road': it was the first supermarket, and the first American-style name, that we had encountered. Although the USA was seriously troubled by the Vietnam war, it was rich and powerful, and everyday life was very easy and convenient. 'Yu'all are welcome 'were the hospitable words we heard everywhere. What sometimes astonished us was that some these of same people could just as easily come up with 'Just drop an atom bomb on Hanoi'. Texas was very sure of itself, and we only heard a few underground rumblings of suppressed political and social dissent: Berkeley was a long way away.

John Gammel had arranged that I be invited as a Distinguished Visiting Professor.The American salary ensured that we were comfortably off and could travel around in our Country Sedan, which had a playroom in the back. John Gammel was building up a small group of very able staff and students; these included Dr John Nuttall, who was extremely bright. We had regular group discussions on different topics. When Professor Kenneth Watson visited for a few weeks from California, he and John Nuttall gave a series of seminars on many-body dynamics. I contributed to this by studying a paper by Omnes on the three-body problem. These seminars were written up as a book, to which I contributed a chapter (ref 15). Dr Ray Cowan, a mathematician, tried to explain Helgason's book on differential geometry to John Nuttall and me, but we failed to cope with the language and notation. Since that time, I have become more familiar with mathematicians' language; I understand it better now, but I still think that some of their differential geometric notation can be very ambiguous and misleading.

Our travels included three visits to Los Alamos, 800 miles away, in the beautiful state of New Mexico. We enjoyed staying in La Fonda in Santa Fe, and then in the famous 'schoolhouse' in Los Alamos. Dr George Baker Jr, who was John Gammel's partner in bringing the Pade method to the notice of physicists in 1961, had remained at Los Alamos. On my first short visit, I discussed with George a simple model field theory by Peres, suggesting that the Pade method might be applied effectively to it. We showed that this was true, and published a paper suggesting that more serious field theory perturbation expansions, with zero radii of convergence, might give good numerical results through Pade approximants (ref 14). This was really just expanding on John Gammel's original suggestion to me, but our 'tiny model' had considerable effect elsewhere.

Dr Daniel Bessis worked in a group at Saclay, Paris, and was collaborating with Professor Dino Pusterla of Padova on field theory computations. Our tiny model convinced Bessis and Pusterla that the Pade method might work for realistic strong coupling calculations, and over the next few years they, with colleagues Basdevant and Zinn-Justin, carried out several large calculations. Their results, like those of the Gammel group, were mixed. The essential problem was that the only singularities of Pade approximants are poles, so, when a matrix element was evaluated near to a branch cut, the approximants did not have appropriate analytic structure. In their original papers, Baker and Gammel had appreciated the need for adapting the Pade method, by matching the analytic structures of the approximants and the function approximated. Later, this led to a whole new field of research: standard approximants were operated on in various ways to define new approximants with suitable matching analytic structures. George Baker and I said that one could not hope to calculate scattering matrix elements from the perturbation series, because they had to be evaluated on a branch cut: later on, other colleagues and I showed how to do this!

In mid-May, 1966, we left College Station and spent ten days travelling west, visiting the Grand Canyon, Las Vegas (which suffered the loss of 5 dollars at our hands), Death Valley (which was hot), and La Jolla, where we were very well looked after for a week by Professor Norman Kroll and his colleagues. Through Dr Tony Hearn, who was an expert on algebraic computation, I had been invited to join the famous Stanford Theoretical Physics group led by Professor Sid Drell. Most of the time, we rented the delightful home of Bob Moulton, chief administrator of SLAC, just a few yards from 'our' private Olympic swimming pool, which was a delight for our young family. I did not produce any papers there, but I could not help working quite hard in the Drell school. For lunch, the group assembled with enormous sandwiches, and assigned members of staff and students had to report on the progress of their research during the past two weeks - this pressure was the basis of the success of the group, but it still makes me feel quite exhausted. We have happy memories of Stanford, San Francisco, Berkeley, Santa Monica and the Redwoods, from those optimistic days of the mid-sixties.

On leaving from San Francisco airport, we were able to hand over our Country Sedan to Mike and Jaff Newton, who had been in College Station with us. We flew to New York and joined up with our piles of luggage shipped from Texas, and boarded the 'New Amsterdam' for a 5-day crossing of the Atlantic. This was an interesting interlude. The children were happy to spend a lot of time in their activities room while we took part in other activities. Each afternoon, we went to ballroom dancing classes given by the European Professional Champions, and were the only takers: so we each had an excellent partner to dance with. We impressed the family by each becoming the table-tennis champion; the trick was to spin the ball so that it went to one side, just as the roll of the ship took the table in the opposite direction. The ship was stopped just off Cobh, and we had the excitement of seeing our car from Ireland loaded on board from a tender. We just managed to get everyone and all our goods into it at Southampton, and drove off to Canterbury.