Other Memorials‎ > ‎

Johan Rønby's Memorial to Hassan Aref

Et rigtigt menneske


Historien om mig og Hassan er smukt indrammet af de grønne bøgeskove, der omgiver Krogerup Højskole nord for København. Her mødte jeg ham for første gang på Fluid.DTU sommerskolen i august 2007. Her mødtes vi for sidste gang på samme sommerskole i august 2011. I de mellemliggende fire år var Hassan min ph.d.-vejleder, min mentor og frem for alt min kære ven. 

Jeg kom til Krogerup i 2007 på udkig efter et ph.d.-projekt. Jeg fattede straks interesse for Hassan og hans forskning, da han på sin drevne facon førte os unge, håbefulde studerende gennem hans på én gang meget simple og meget komplekse univers af strømninger og matematik. Man fornemmede, at her var en herre, der mestrede sit fag til fulde. Efter hans foredrag gik jeg op og introducerede mig for ham, og det blev starten på et mentor-elev forhold, som jeg tror, kun er de færreste forundt. 

I sin forskning havde Hassan kastet sin kærlighed over punkthvirvler - en slags idealiseret udgave af de hvirvler, som man møder alle steder, hvor der er luft eller vand, der bevæger sig. Idealiseringen er af en karakter, så det er svært umiddelbart at finde praktisk anvendelse af disse punkthvirvler. Men det betød ikke så meget for Hassan. Teorien er ren og smuk, og Hassan havde en hang til det, man kunne kalde matematisk æstetik. Det var vigtigere, at de studerede ligninger indeholdt en matematisk skønhed, end om de kunne bruges til praktiske ingeniørberegninger. Han legede sig frem til sine resultater med den mægtige analytiske værktøjskasse, der gemte sig bag hans bare isse. Så skrev han det ned i et ualmindeligt formfuldendt sprog, udgav det i de højest estimerede tidsskrifter, og så måtte folk selv finde ud af, hvad de ville bruge det til. Ikke alle var lige begejstrede for Hassan’s punkhvirvler - især ikke folk med mere hang til det praktisk anvendelige. Ingen betvivlede dog Hassan’s knivskarpe intellekt eller den skyhøje kvalitet i alt hvad han producerede gennem sin mangeårige forskerkarriere. 

I de fire år mellem vores første og sidste møde var Hassan min nærmeste samarbejdspartner. I denne periode var han, næstefter min kone, den person jeg har tilbragt mest tid sammen med. På Krogerup i 2007 havde jeg mere eller mindre bevidst været på udkig efter en slags faglig faderskikkelse. Denne rolle udfyldte Hassan til fulde. Han var nærværende, varm, humoristisk og drillende. Man forlod aldrig Hassan’s kontor uden adskillige anekdoter og gode grin i bagagen. Et ph.d.-forløb fører uvilkårligt ind i lange, golde perioder, hvor det hele driller og motivationen svigter. Her var Hassan altid usvigeligt leveringsdygtig i en peptalk, som kunne give én rygraden og retningen tilbage. Han var et legebarn, og hans legeplads var matematikkens og fysikkens fascinerende univers. Et univers, som han bevægede sig rundt i som en fisk i vandet. Det var uhyre smittende at være i nærheden af. ”Sikke vi tramper”, som musen siger til elefanten. 

Hassan gik ind i sin vejlederrolle med hud og alt det hår, som han ikke havde på hovedet. Under mit ph.d.-forløb har Hassan skiftevis opholdt sig et halvt år på DTU og et halvt år hjemme i USA, hvor han var professor ved Virginia Tech. Adskillige gange har jeg været inviteret hjem at bo hos ham i hans hus ved Virginia Tech og i hans rigtige hjem i Illinois, hvor han boede med sin Susanne. At bo hos Hassan og arbejde med denne næsten uhyggeligt kompetente videnskabsmand alle døgnets vågne timer har været en af de største oplevelser i mit liv. Jeg ser det som den største anerkendelse, at han gad tilbringe så meget tid sammen med mig. Han havde et fantastisk overblik over fysikken og matematikken, i særdeleshed over fluiddynamikken. Ikke blot havde han det faglige overblik, han havde også et stort indblik i sit fags historie. En historie som han allerede i en ung alder selv skrev sig ind i med sin indførelse af begrebet ”kaotisk advektion” til beskrivelse af den overraskende store kompleksitet, som tilsyneladende meget simple strømninger kan udvise. 

Hassan blev den klippe, som jeg byggede min egen spæde forskerkarriere på. Nu er klippen revet væk under mig. Det hele sluttede i fredags, hvor Hassan pludselig døde siddende i sin yndlingslænestol hjemme i huset i Illinois. Han har formentlig siddet med sin MacBook på skødet, hengivet til sin yndlingsbeskæftigelse: At studere dynamikken af de punkthvirvler, som var så gennemgående et tema i hans forskning. 

En af de historier, som Hassan yndede at fortælle, var den om hvordan jeg engang formulerede det noget kluntet, da jeg skulle forklare, at jeg havde talt med nogle mere praktisk orienterede mennesker, og at det havde været interessant og givtigt. Jeg kom til at sige, at det havde været rart at tale med nogle ”rigtige mennesker”. Det fandt Hassan vældig morsomt, og brugte det sidenhen igen og igen imod mig i sine drillerier. 

Kære Hassan. Jeg er fuld af sorg og fortvivlelse og har et stort hul i hjertet, der hvor du sad. Men jeg er også fuld af taknemmelighed over at have været en del af dit liv og virke de sidste fire år. Du var i sandhed et rigtigt menneske.

Johan Rønby, 11. september 2011

Original Danish version appeared: http://www.roenby.com/HA/

A real human being


The history about me and Hassan is beautifully framed by the green beechwood surrounding Krogerup public highschool north of Copenhagen.  Here I met him for the first time at the Fluid.DTU summer school in August 2007.  Here we had our last encounter at the same summer school in August 2011.  In the intervening four years Hassan was my Ph.D. supervisor, my mentor, and above all my dear friend.

I came to the summer school in 2007 in search of a Ph.D. project.  Hassan was one of the last speakers, and I immediately found him and his research interesting, as he introduced us in his own steady and stringent way to his fascinating universe of flows and mathematics.  It was simple and complex at the same time. And it was clear that here was a scientist who mastered his field to perfection.  After his lecture, I went and introduced myself to him.  This was the beginning of a mentor-pupil relationship, which, I believe, only very few have the good fortune to experience. 

In his research Hassan had become enamored with point vortices – an idealized model of the vortices one encounters everywhere in the motion of air or water.  The nature of this idealization does not make the practical applications of these model vortices immediately clear.  This did not worry Hassan too much. The theory behind point vortex dynamics is pure and beautiful, and Hassan had an inclination for what one could call mathematical aesthetics. To Hassan it was more important that the equations under consideration contained a mathematical beauty, rather than their potential as a practical engineering tool. He played with his results, applying the immense analytical toolbox hidden under his balding dome. He then wrote up his results in his elegant and flawless style and published it in the most prestigious scientific journals. After that it was up to his fellow scientists to decide what they wanted to do with it. Not everyone was as enthusiastic as Hassan about his point vortices. But no one ever doubted Hassan’s razor sharp intellect or the uncompromising quality of everything he produced during his long scientific career. 

In the four years between our first and last meeting Hassan was my closest collaborator. During this period he was, apart from my wife, the person that I spent the most time with. At Krogerup back in 2007, I was, more or less consciously, looking for a kind of intellectual father figure. Hassan more than fulfilled this need. He was warm, caring, humorous, and always joking. Our meetings were always filled with laughter and amusing anecdotes. A Ph.D. project will inevitably contain long, hard periods where nothing works out as it should and ones motivation fails.  Hassan could deliver a pep-talk on demand to strengthen ones nerve and get one back on track. Hassan was a child in a playground, a fascinating universe of mathematics and physics. In this universe he moved around freely like a fish in the sea. It was extremely contagious to experience. “Oh, how we are trampling”, as the mouse said to the elephant.

Hassan put his whole person into his role as a mentor. During my graduate studies, Hassan took turns working half a year at the Technical University of Denmark (DTU) and half a year at home in the States, where he was a professor at Virginia Tech.  Several times I was invited to stay at his house at Virginia Tech and in his real home in Illinois, where he lived with his Susanne.  To live under the same roof as Hassan, and work with this, almost frighteningly, competent scientist, has been one of the greatest experiences of my life.  I feel it as a great acknowledgement that Hassan chose to spend so many hours in my company.  He had an incredible overview of physics and mathematics, in particular the field of fluid dynamics.  He did not only master this subjects; he also had a great insight in its historic evolution.  A history which he himself became a part of at a young age, when he introduced the notion of “chaotic advection” to describe the surprisingly rich complexity emerging from seemingly simple fluid flows. 

Hassan was the rock on which I founded my budding scientific career. Now that foundation is wiped away from under my feet. It all ended this Friday, when Hassan suddenly died, sitting in his favorite armchair at his home in Illinois. He was probably sitting with his MacBook on his lap devoted to his favorite occupation: To study the dynamics of those point vortices that until the very end were the underlying focus of his research.

One of the stories that Hassan liked to tell was about a clumsy phrase I once used: I was telling him about a conversation with some more practically oriented people, and that the conversation had been interesting and rewarding. By accident I said that it had been nice to talk to some “real human beings” for a change. Hassan found this extremely amusing, and teased me with these “real human beings” over and over again.

Dear Hassan. I am full of sorrow and despair, and there is a big hole in my heart where you used to sit. But I am also overwhelmingly grateful for having been part of your life and work for the past four years. You were truly a real human being.

Johan Rønby, September 11, 2011

Comments