# The fox knows many things, but the hedgehog knows one big thing

The title is a (translated of course) quote from Archilochus, a Greek poet from the 7th century BC. Somewhat randomly, this quote from a long dead Greek poet is very popular in the fields of data science and prediction. Nate Silver’s fivethirtyeight.com site has a stylised fox as logo in reference to this quote, although I don’t think he was the first to start using it. The quote is used to classify people, in particular those making predictions, into two groups: the hedgehogs and the foxes.

# Beautiful numbers

A lot, maybe most, of the fun behaviour that occurs in physics is controlled by dimensionless numbers, i.e., quantities that don’t have units such as metres or seconds. These dimensionless numbers are typically ratios between two quantities. Each of the two quantities has the same dimensions (units) and so these units cancel, making the ratio dimensionless. There are many of them in physics, but perhaps the only one in common use is the Mach number — named after the German physicist Ernst Mach. The Mach number is the ratio between two speeds, the speed of an object, often an aircraft as above, and the speed of sound. When the Mach number is greater than one, the plane is supersonic, and when it is less than one the plane is subsonic.

# Dragon-kings, black swans and an anti-HIV drug

Next week, I am off to Paris for a workshop, so I am writing my talk. Above is a plot of French cities. The x-axis is the log of the rank of the city, where the ranking of the city is by size, i.e., the first point (shown in pink) is for France’s largest city, Paris, at an a x value of log(1)=0, while the second point is France’s second largest city, Marseille, at a value log(2)=0.30, the third is Lyon at log(3)=0.48, etc. The y axis is the population of the city, raised to the power c = 0.18. This value is a fitting parameter, the value of 0.18 is the one that makes the data closest to a straight line — as you can see for this value of c the data falls on a pretty decent straight line.

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# The Marangoni effect

Liquids form approximately spherical droplets because of surface tension. Surface tension is a force acting at the surfaces of liquids that tends to contract the area of these surfaces, and a sphere has the minimum surface area for a given volume. This is cute. But even cuter is that any time the surface tension of a liquid is not the same everywhere ,then the areas of the surface at lower surface tension tend to expand while those areas at higher surface tension contract – this is called the Marangoni effect and is illustrated in the YouTube clip above.

# Learning from my old boss

Twenty plus years I ago I was a fresh-faced PhD student, and my then PhD supervisor, George Jackson was selling the science his group, including me, did. I remember that he was a fan of triangles like the one shown above. His group was doing both computer simulations and theory at the time, and he wanted to make the point that they complement each other, and help to understand and predict experiment.

# Evaporation!

A few weeks ago, our new boss, Vice Chancellor Professor Max Lu, visited the physics department. He started last year and is touring the departments in his new domain. I think it went well, it was good to both tell him what we do, and listen to what he had to say. In a UK academic environment that often looks dominated by league tables and competition, it was good to hear him stress the importance of our teaching students great stuff, stuff that they will use and that will make them better people.

# More and less snow on the roof of Europe

Earlier this week I was at scientific meeting on how water freezes, a key problem in understanding how the  cold clouds and snow form. The very last talk I caught before I had to leave to catch my train, showed some striking data. We know that ice and snow in the atmosphere almost always start to form not just from water on its own, but from water in contact with a tiny particle in the atmosphere. So the number of these particles and their surface properties greatly influence how clouds and snow form. If, for whatever reason, there are many of these particles in the air, we may get more snow.

# People in this country have had enough of experts

The title is a quote of Michael Gove — to be fair on him I think he was referring to economists – a profession whose track record of consistently making inaccurate predictions is notorious. But still, as a PhD educated scientist, the quote does rankle a bit. Although that may be just my natural reaction to Michael Gove – he could read the phone book and I’d still get grumpy.

# Making spines in two steps

This is a sea urchin, sea urchins can’t move fast so rely on these spines and the fact that they have a hard shell, to protect them from predators. Both the spines and the shell are made from crystalline calcium carbonate in the form of a mineral called calcite. Scientists have long been fascinated by how animals such as sea urchins grow these calcite crystals to form these striking spines. Continue reading