Sunday, December 22, 2013

More on the Habitable Zone and on understanding complexity

Diagram from Kasting and Harman showing how close
Earth is to boundary of Habitable Zone.
Having been in China for so long has made it difficult to blog on some of the fascinating scientific papers. But here are a couple that have caught my eye.

"Increased insolation threshold for runaway greenhouse processes on Earth-like planets" by Jérémy Leconte et al. in Nature shows that if the earth were 5% closer to the Sun then we'd be subject to runaway greenhouse processes and all the water would evaporate. This isn't exactly a fine-tuning argument but what it does show is that "Habitable Earth-Like Planets" are appreciably rarer than conventionally thought.  I suspect that it will turn out that the tolerance between habitability and the Earth's present characteristics will be about +5% in each direction - and here we find a -5% constraint.  (Kasting and Harman is the News and Views paper in Nature that comments on Leconte at al.)

Fig 3 of Brockmann and Hebling shows how, by plotting the
arrival of an epidemic and looking at the Effective Distance
of these arrivals, the correct source can be identified.
On a completely different subject, but one also close to my heart, there is "The Hidden Geometry of Complex, Network-Driven Contagion Phenomena" by Dirk Brockmann and Dirk Helbing in Science. This develops an "effective distance" measure on complex networks such as the air passenger transport network and uses it to model the spread of epidemics.

This is a completely beautiful paper, which not only allows an approximate de-coupling of the geometry and the epidemic characteristics but enables the source of an epidemic to be identified. There is a very good "Perspective" on this by Angela MacLean.

There is also a review of a fascinating book called Complexity and the Arrow of Time with a chapter by Simon Conway Morris ("Once there were bacteria, now there is New York") and a moving obit of my son's PhD Supervisor Michael Neuberger in Science. May he rest in peace and rise in glory.

No comments: