Khagol_114

Scholarly science done in style - A personal perspective of Donald's approach to science T. Padmanabhan The process called violent relaxation is ubiquitous in Nature and is used extensively in astrophysics and cosmology to describe awide variety of cosmic structures. Violent relaxation leads particles, interacting through their mutual gravitational attraction, to reach a (quasi) steady state, similar to that in thermodynamic equilibrium, far more quickly than one would have naively expected. This important physical process could have been discovered by several other major players in statistical mechanics like, e.g., Maxwell, Boltzmann, Gibbs, or James Jeans, just to name a 1 few . It was Donald-Lynden-Bell who realised the importance of this process, worked out its theory and named it as violent relaxation. This is just one of the many, major, creative gems Donald has contributed to science (and is my personal favourite). How come Donald could figure out such a fundamental process occurring in Nature, which escaped the attention of somany others? I believe, the answer, to a great extent, is related to the way Donald approached Science. Most of what he did in Science was driven by his curiosity and the enjoyment he derived from figuring things out. He did not particularly worry whether the problems heworked on had the “approval" of the community. He was fascinated by any interesting problem, and once his curiosity was awakened, he would not mind spending any amount of time tackling it - and incidentally, talking about it with a childlike delight to anyone he could catch! He enjoyed the process of discovery so much that everything else was secondary. Such unshackled creativity is what one needs to make a discovery like violent relaxation. I encountered this aspect of Donald pretty early on during my post-doctoral interaction with him in 1986. Donald once got hold of me during a lunch at Cavendish and described to me a problem he was currently thinking about. The problem was a very practical one and had to do with improving the performance of telescopes. It involvedparaphrasing some of the techniques, used to study the semi-classical limit in quantum mechanics, to understand better the transition from ray-optics to wave- optics. Since the essence of the problem was several decades old, I knew it must have been tackled in some of the classic textbooks like, for example, Born and Wolf; and I mentioned this to him. His reply was very nice and deeply inspirational: "Yes, Paddy; but it is a lotmore fun doing it yourself". No. 114 - April 2018 03 1 In fact, if only Newton had thought about a system with large number of particles moving under their mutual gravitational attraction, and abandoned deterministic evolution for a probabilistic description, he would have discovered statistical mechanics of gravitating systems - and probably violent relaxation - centuries before even the statistical mechanics of normal matterwas developed! Donald's habit of spending time on any question he found interesting transcended conventional physics problems. Once while visiting IoA, Cambridge, I was interested in an age-old problem, viz., what is the minimal number of weighings you need to figure out the odd-ball among N-balls - using just a scale pan without weights and not even knowing whether the odd-ball was lighter or heavier. This problem and its solution, again, are well-known, but I wanted to quantify it from the information-theory perspective. I mentioned this to Donald who immediately got interested in it and had no hesitation spending a large part of the next couple of days thrashing it out. I have seen very few other scientists who are so strongly driven by a desire to figure things out for themselves. Another aspect of Donald is his supreme scholarship, a quality which is fast disappearing among scientists and - muchworse - is no longer respected as something which a scientist should necessarily possess. Donald was a scholar par excellence , even by the Cambridge standards of his times. He knew so much about so many things and had thought so deeply about all the important questions in theoretical astrophysics. I have spent hours - as I am sure have many others - discussing everything from Mach's principle to the correct way of learning elliptic functions. (Yes, there is a correct way. Donald introducedme to an unusual book "Elliptic Functions as they should be" by Albert Eagle which tells you how; needless to say, very few experts in mathematical physics knowabout this book.) He could always bring in a fresh perspective into any problem, whether it dealt with the nine-point circle or the gravitational wave, drawing upon his comprehensive classical education, supplemented by the sharp intellect. These qualities also made Donald fairly immune to peer recognition or its absence. I, for one, believe that Donald's capabilities, and even contributions, have not been given their due recognition by the peers; if it bothered him, I never saw a sign of it. If you enjoy the process of science so much, it is probably natural that you do not care about unimportant side- issues, like peer opinion. He was also unafraid to hold views which ran totally counter to the mainstream science. (Even as late as March 2017, when we last met, he did not believe in the existence of non-baryonic darkmatter!) Once he explained tome in detail the importance of writingwrong papers. The argument went roughly like this: