## Berni Alder obituary in Nature [and the Metropolis algorithm]

**W**hen reading through the 15 October issue of Nature, I came across an obituary by David Ceperley for Berni Alder (1925-2020). With Thomas Wainwright, Alder invented the technique of molecular dynamics, “silencing criticism that the results were the product of inaccurate computer arithmetic.”

“Berni Alder pioneered computer simulation, in particular of the dynamics of atoms and molecules in condensed matter. To answer fundamental questions, he encouraged the view that computer simulation was a new way of doing science, one that could connect theory with experiment. Alder’s vision transformed the field of statistical mechanics and many other areas of applied science.”

As I was completely unaware of Alder’s contributions to the field, I was most surprised to read the following

“During his PhD, he and the computer scientist Stan Frankel developed an early Monte Carlo algorithm — one in which the spheres are given random displacements — to calculate the properties of the hard-sphere fluid. The advance was scooped by Nicholas Metropolis and his group at the Los Alamos National Laboratory in New Mexico.”

that would imply missing credit is due!, but I could only find the following information on Stan Frankel’s Wikipedia page: Frankel “*worked with PhD candidate Berni Alder in 1949–1950 to develop what is now known as Monte Carlo analysis. They used techniques that Enrico Fermi had pioneered in the 1930s. Due to a lack of local computing resources, Frankel travelled to England in 1950 to run Alder’s project on the Manchester Mark 1 computer. Unfortunately, Alder’s thesis advisor* [John Kirkwood] *was unimpressed, so Alder and Frankel delayed publication of their results until 1955, in the Journal of Chemical Physics. This left the major credit for the technique to a parallel project by a team including Teller and Metropolis who published similar work in the same journal in 1953.”* The (short) paper by Alder, Frankel and Lewinson is however totally silent on a potential precursor to the Metropolis et al. algorithm (included in its references)… It also contains a proposal for a completely uniform filling of a box by particles, provided they do not overlap, but the authors had to stop at 98 particles due to its inefficiency.

December 4, 2020 at 2:08 am

I’m wondering how many more twists Metropolis-Hastings has in its intellectual history! This prompted an idea of a humorous and fictional scene where Laplace is in a cafe drinking with Charles Babbage. (

Hasto be a cafe, not a pub. And pardon the anachronisms.) And Laplace offers Babbage the idea of billiard balls on a table with bumps in the surface, and wanting to find all the troughs. How many times and in what places and in what directions should the balls be tossed? How to measure whether there are troughs or not? Directions of paths, of course, but, then?And Babbage thinks of a discretized table, and wonders how his Engine might master the problem. All along with witty repartee.

And it turns out, I understand from my son, that billiards flow has a meaning beyond the Bayes origin, that these screen-saver-like problems have significance in quantum corrals and such.

December 5, 2020 at 7:31 pm

Looking forward the play… provided it converges to its realisation!