Free Radicals - Michael Brooks [91]
Through a series of laboratory experiments, polar expeditions and mathematical calculations, Birkeland had worked out that the aurora borealis – the northern lights – were the result of an interaction between the Earth’s magnetic field and space-borne electric currents. ‘It seems to be a natural consequence of our points of view to assume that the whole of space is filled with electrons and flying electric ions of all kinds,’ he wrote in 1913. ‘It does not seem unreasonable therefore to think that the greater part of the material masses in the universe is found, not in the solar systems or nebulae, but in “empty” space.’
Those electrons and flying electric ions, Birkeland surmised, must come from the Sun, but his theory could be tested only by making measurements in space. At a time when the aeroplane was just a decade old, that was far beyond science’s capabilities, and it was not until 1963 that Birkeland was proved right. And that is partly because, in the intervening years, Sydney Chapman seized the throne of space physics. Birkeland’s expeditions had established that aurorae occur as a result of electrons flowing down through the atmosphere along the lines of the Earth’s magnetic field. Chapman, though, had other ideas. He had developed a theory in which electrons moved only through the ionosphere, one of the outer layers of the Earth’s atmosphere.
In Chapman’s scheme there was no downward movement, so it made no headway in explaining why the aurorae are visible from the Earth’s surface. However, his mathematics was beautifully constructed and reproducible by anyone with a basic skill in maths. This was the root of his appeal: his approach to space physics was to simplify the situation until solvable equations emerged. Mathematically challenged space physicists loved it and took it on board. And that is why, when Hannes Alfvén offered a complex but rigorous mathematical support for Birkeland’s idea of currents that travelled down towards the Earth’s surface from the ionosphere, it was rejected out of hand. The editors at Terrestrial Magnetism and Atmospheric Electricity, the leading American journal of space physics, were at least candid about the reason for rejection. Alfvén’s calculations, they said, could not be right because they did not agree with Chapman’s calculations. That Chapman might have been wrong did not occur to them. Or if it did, that wasn’t a road they were prepared to go down.
Chapman’s influence was astonishingly far-reaching. ‘I have no trouble publishing in Soviet astrophysical journals, but my work is unacceptable to the American astrophysical journals,’ Alfvén once said. In the end, he managed to publish what is now the foundation of our modern understanding of what goes on above our heads in a Swedish-language journal called Kungliga Svenska Vetenskapsakademiens Handlingar. It’s unlikely that you – or most physicists, for that matter – have ever heard of it. And yet it contains the original paper on what might go wrong when an angry Sun spits a well-aimed flare towards the Earth.
In January 2009, the US National Academy of Sciences issued a research report on the dangers posed by the Sun. To be precise, the report was issued by the Committee on the Societal and Economic Impacts of Severe Space Weather Events. But this was no minority interest issue: the research was carried out by some senior figures at US universities, and funded by NASA. The committee concluded that there was a chance that, in the next few years, the United States could be brought to its knees by solar activity. If the Sun flings out one fortuitously aimed gob of material, it could cause a geomagnetic storm powerful enough to leave half a continent without electrical power.
In our modern, technological society, electricity supply is vital. When particles spat out by the Sun in a violent ‘coronal mass ejection’ interact with the Earth’s magnetic field, the result can be chaos. The interaction can induce enormous currents capable of melting wires in transformers in power transmission