On the face of it you might think that this precious sphere of life we call Earth is a complex world surrounded by the plain and uncomplicated vacuum of space. However, appearances can be deceptive as Professor Sandra Chapman, a plasma astrophysicist from Warwick University, revealed in her talk to the Society.
The title of the talk, "Complexity in Space", points to the turbulence that can be observed beyond our planet providing you have the right kind of ruler to measure it. One of the yardsticks is the Cluster mission; a quartet of spacecraft that swing in and out of Earth's magnetic field. Sometimes, they will be inside the Earth's magnetic shield and sometimes they will be outside, fully exposed to the supersonic solar wind. Like the Red Arrows of space, they travel in formation in the shape of a pyramid following highly elongated, polar orbits, which take them between 19,000 and 119,000 km from Earth. Using data from Cluster and other spacecraft, Professor Chapman's main aim is to try and understand the behaviour of plasma.
The study of plasma began in 1879, when William Crookes, an English physicist, identified this 4th state of matter where a material's constituent atoms or molecules have been ionized. Plasmas have unique properties compared to those of the other solids, liquids or gases and can be found in fluorescent light bulbs, the air around a lightning strike or in the beautiful spectacle of the Northern Lights. It is an astounding fact that plasma is the most common form of matter making up around 99% of the visible universe. Our Earth is an island of what we term 'ordinary' matter travelling through a sea of plasma.
In trying to gain some sort of understanding of the complicated world of plasma, Prof Chapman has had to borrow heavily from studies in mathematical complexity. This has led to setting up experiments using piles of rice or damp sand and recording how and why the particles build up and then avalanche. This seemingly trivial exercise has a direct analogy to the size of auroral areas over the Earth's poles. For both physical systems there is no favourite size for an event. The avalanches range from tiny spills to tumbling masses, and similarly the auroral areas can vary from tiny regions to vast sections of the poles. The only time that a huge aurora can be predicted reliably is when the Sun gives off a huge solar flare that heads in our direction. In relation to the pile of sand, this would be the same as dumping a whole bucket-load of sand on the top of the pile all at once.
The occurrence of avalanches at all size scales is a hallmark of self-organized criticality (SOC). In physics, a critical point is a point at which a system changes radically its behavior or structure, for instance, from solid to liquid. Numerous natural events show this SOC behaviour, whether it be the occurrence of earthquakes, forest fires or even rainfall. Somehow, by a process that is not yet fully understood, the feedback in a SOC system ensures that there is no way to predict what size of event will be generated by a disturbance only a probability of how likely it is. The most well known analogy to this is how a butterfly flapping its wings over the other side of the world can generate a hurricane.
So, the next time you complain that the weather forecast is way off mark, don't blame the forecasters - remember it's that pesky butterfly exercising its wings!