## Tuesday, May 28, 2013

### Smoluchowski, Milanković: birthdays

Two Slavic, Austrian-Hungarian physicists were introduced to the sunlight on May 28th.

Marian Smoluchowski was born as a Pole in Austria in 1872; Milutin Milanković was born as a Serb in (then) Croatia, Kingdom of Hungary, in 1879. Smoluchowski was a statistical physicist; Milanković was a climatologist, astronomer, geophysicist – and also a construction engineer.

Marian Smoluchowski was born to an upper-class family near Vienna. He studied physics in Vienna; Exner and Stefan were among his teachers. His research followed the tradition of Ludwig Boltzmann from the beginning. When he was 40, he moved to Krakow to teach experimental physics. He was a keen mountain-climber and skier in the Alps and the Tatra Mountains. His being a resilient athlete didn't prevent him from death at the age of 45 – dysentery epidemics.

His important work was all about statistical physics. In 1904, he noticed that there were density fluctuations in gases and he also managed to correctly explain critical opalescence as a consequence of these fluctuations. In 1906, independently of Einstein's 1905 work, he expained the Brownian motion using the collisions between molecules and the pollen particles.

Note that these insights clarified not only power laws but also some relationships between coefficients. Both Einstein and Smoluchowski discovered the Einstein relation $$D=\mu k_B T$$ between the diffusion constant, mobility, and temperature. And both of them realized why the average traveled distance scales like $$\Delta x\sim \sqrt{t}$$. To find this scaling, it's useful to study how $$(\Delta x(t))^2$$ is statistically distributed.

I still sort of remember the times when I was a kid and these widespread insights based on the second power (or the square root, when inverted) looked surprising, unexplained to me. After some time, one understands that the second power is the most right function to measure the magnitude of things if the sign doesn't matter.

In 1916, Smoluchowski wrote his convection-diffusion equation sometimes bearing his name.

Now, Milutin Milanković was born to a "locally higher-class" family in a village in Eastern Croatia, near the Serbian border. I still don't understand how these Southern brothers of ours assign nationality to them. He is born in Croatia (both according to the old maps as well as current maps); he speaks the Serbo-Croatian language which is really the same for both nations; and he is still considered Serbian, not Croatian. What does it even mean? ;-)

Aside from the Serbs' being orthodox Christians (a criterion that can't reliably work today when the religious diversity is higher and atheists exist everywhere, too), the only explanation I can think of is that the Serbians sometimes like to use Cyrillic (which is also a bad criterion; last time I visited Belgrade, it was full of the Latin alphabet, too). Milutin Milanković's name is spelled Милутин Миланковић in Serbian Cyrillic; I have never appreciated that the last letter was an hbar (Planck's constant). ;-)

We just said that Smoluchowski was a mountain-climber and skier and died when he was 45. On the other hand, Milanković had frail health from the beginning (which forced his brother to educate him at home) and his three brothers died of tuberculosis soon. However, Milanković himself died of stroke when he was 79. A message of these two lives is that sport is a speedy way to the grave while non-lethal illnesses and disorders are what keeps you alive. ;-)

When he was 17, he went to Vienna to study civil engineering, and when he was 26, in 1905 (yes, he was just 2 months younger than Einstein), he already began to build dams, bridges, viaducts, aqueducts, and other structures in reinforced concrete across Austria-Hungary. This successful career makes it kind of incredible that he also became the guy who revealed the causes behind the most important among the large yet constantly repeating climate changes, the glaciation cycles: the Milanković cycles.

To make these important discoveries on the interface of astronomy, geophysics, and climatology, he first had to realize that atmospheric science was an inferior scientific discipline. In his words formulated in 1912:
Most of meteorology is nothing but a collection off innumerable empirical findings, mainly numerical data, with traces of physics used to explain some of them... Mathematics was even less applied, nothing more than elementary calculus... Advanced mathematics had no role in that science...
Despite this realistic appraisal, Milanković was actually a key person who did lots of insights to transform this inferior scientific discipline into an exact science. He suddenly started to introduce integrals and many other things into meteorology and climatology, something that most of the low-brow folks in the discipline had not known, in order to explain the terrestrial climate and the climate of other planets in the Solar System.

Most famously, he discovered the Milanković cycles in the 1920s. The alternation of ice ages and interglacials at the timescale of tens of thousands or hundreds of thousands of years is caused by variations of various orbital parameters – obliquity (axial tilt), eccentricity, and longitude of perihelion – which make the ice accumulate or melt at the most important "driving" place of the globe near the Arctic Circle.

The theory was believed and abandoned at various moments but the 2006 paper by Gerard Roe (building on realizations by Nigel Calder in the 1970s and probably others) eliminated all the doubts that a vast majority of the variation in the glaciation cycles has been caused by the Milanković (astronomical) cycles. The detailed agreement between all the wiggles of the theoretically calculated (astronomical, orbital) cyan curve and the empirical, reconstructed white curve is stunning and eliminates all the doubts that these astronomical cycles are what drives the variations by up to nearly 10 °C at the timescale of tens of thousands of years.

Recall that he was also a construction engineer. Aside from that job and the astronomical climatology, he also became an achieved historian of science, a popularizer of science, a reformer of the Julian calendar (who affected how some orthodox churches measure time), geologist often debating Alfred Wegener, and a scientific bureaucrat in Yugoslavia after the war.

On May 28th, 1987, Matthias Rust, a German (then) teenager, landed on the Red Square in Moscow. He did it to build a bridge between the communist and capitalist worlds, he says above. He was released after 14 months instead of the planned 4 years. Now he works as an analyst for an investment bank and plans to teach yoga.

1. Smoluchowski work is very important in Physical Chemistry. His framework provides a very useful approach to study the rate of chemical reactions, mostly very fast one in the sub-nanosecond timescale in which classical diffusion is important. Very worth remembering him!

2. No one really gets the Croat vs Serb thing but boy do we make a big fuss out of it! ;)

3. "...the 2006 paper by Gerard Roe (building on realizations by Nigel Calder in the 1970s and probably others)..."
No scientist works in isolation, but I wonder whether Roe was aware of Calder's
earlier paper. He certainly didn't cite it

4. Thanks for this nicely entertaining article Lumo

Милутин Миланковић should read Милутин Миланкови in proper units ... :-P!

"Marian Smoluchowski was a keen mountain-climber and skier in the Alps and the Tatra Mountains.... "

... at least he was no surfer or (Italian) biker dude, or he would probably not have been able to do nice statistical physics :-D

Cheers

5. Hi Lubos, Back in 1974 new scientific contributions (as opposed to news, reviews, editorial etc) published in Nature were classified either as 'Articles' (mostly about 4 pages) or as 'Letters' (1 or 2 pages). In the 15 November edition there were 3 articles and about 35 letters. One of the letters is the item by Nigel Calder about Milankovic cycles entitled 'Arithmetic of ice ages'. I think many people would refer to letters to Nature as 'papers'. However with perhaps 1500 letters to Nature published every year one can see that a single letter could easily get forgotten or missed.

6. Thanks. Well, as your comment shows, the letter didn't "get" forgotten. Only someone may have forgotten it and it's his or her personal error, not something that should get objectivized by verbs like "get".