The pioneers who tamed electricity had an exciting ride, and the picture became much more enticing once the intimate relationship of electricity with magnetism came out of the closet. Halfway through the 18th century, Benjamin Franklin was magnetising and demagnetising iron bars by subjecting them to an electrical current. 70 years later, the accidental arrangement of a compass needle and an electrically charged wire at an evening lecture by Danish physics professor Hans Orsted provided the first experimental evidence of the dynamic relationship between the two phenomena. By subsequent investigation Orsted was able to show a principle of profound importance to our understanding of the universe, and indeed, to the dazzling acceleration of man’s advance into an era of high technology. He observed that a freely suspended magnet tended to curl around an electrical conductor, in other words, that an interaction between electric current and a magnetic field produced rotation. It wanted to spin! Quite by chance, Orsted had stumbled upon the principle of the electric motor. And then came Faraday.
English chemist and physicist Michael Faraday was one of the most luminous scientific thinkers of the 19th century, and amongst many other achievements, became famous as a founding father of electromagnetism. He had endured a deprived childhood as the son of an itinerant Geordie blacksmith, and received only the rudiments of education. At 14, he was apprenticed to a London bookbinder. This, for Faraday, was an opportunity to read, and read he did. An early edition of the Encyclopaedia Britannica taught him the basics of electrical theory, and before long Faraday was building electrical apparatus at home. The die was cast; this was the foundation of a life-long dedication to the experimental method in science.
Using the deductions of French physicist André Ampère that Orsted’s magnetic field formed what amounted to a cylinder around the electric wire, Faraday built the world’s first rudimentary electric motor. By surrounding a conductor with an enveloping magnetic field, he got the conductor to rotate. It was revealed to be a universal principle: An electron stream wrapped in a magnetic field equals spin. In 1831, by a stroke of genius, he reversed the process. By rotating a copper disk in a magnetic field, he produced a continuous electrical current, a phenomenon known as the dynamo effect. Michael Faraday had thus demonstrated also the operation of the first electric generator. This was the second great principle: Spin a conducting material in a magnetic field and you get a stream of electrons—an electric current. His experiments clearly showed the dynamic symbiosis between electricity and magnetism, and revealed to the world how that interaction could get things spinning or conversely, how spin produced the electrical response.
Electromagnets, created by winding an electric wire around an iron bar, had been produced since the 1820’s, and they demonstrated tangibly that a circulating electrical current—a helix—would produce a magnetic field. We will learn shortly how Kristian Birkeland demonstrated in his laboratory that a magnetic field could create a visible, functioning helix in plasma. Not even the superluminal vision of Michael Faraday could have foreseen how profoundly those two principles would change our world and, ultimately, the way that we understand the cosmos. James Clerk Maxwell bound these elements of natural law together in a mathematical formalism, thereby giving the world the electromagnetic theory of light, and the equations with which technology could drive us into the space age. In a few words I have described an intellectual adventure of immense and enduring importance to mankind, one that gave to the world what are arguably amongst the most useful and resilient principles in the history of science.
The picture is this: We have a web of magnetic force fields criss-crossing the deep sky, and into it surge endless clouds of electrically charged plasma. Electricity meets magnetism. What do you think happens next? That’s right, the plasma rotates. It twists and turns and rolls, and organises itself into fantastic electromagnetic tendrils called filaments. Plasma dominates the observable universe. Most of what we can see in the cosmos is plasma, concentrated in the stars and spread throughout gaping interstellar voids. The Sun is covered in an ocean of plasma, part of our atmosphere known as the ionosphere is plasma, and so are the aforementioned auroras and even everyday bolts of lightning. There is plasma in fluorescent lighting tubes and the structure of metallic crystals. The Solar System is suffused with plasma in the form of solar winds. It is all around us, and must therefore surely be the richest and most fertile field of investigation for any physicist. It is certainly one of the most accessible. What is plasma, and why is it so special? Let’s backtrack a bit.
Nobel laureate Irving Langmuir coined the name “plasma” for the phenomenon that he studied in General Electric’s laboratories. To Langmuir, the dynamic behaviour of ionised hydrogen gas when exposed to electrical and magnetic fields was enthrallingly lifelike, particularly in its ability to organise into working subsystems. All of these plasma pioneers found a common underlying principle of immense importance to the extrapolation of our plasma knowledge to the cosmos—it is scale invariant. That is, plasma behaviour in the laboratory is the same as plasma behaviour in galaxies and beyond, for as far as we can see. If we see consistent shapes in partial vacuums in the laboratory, and the same intricate shapes again repeated endlessly in the partial vacuum of space, then we would be foolish—or impossibly stubborn—not to make the connection. We cannot exaggerate how potentially useful that makes plasma science to astronomers. Now all we’ve got to do is get them to use it!
It was Alvén’s predecessor, the visionary Norwegian experimentalist Kristian Birkeland who first looked at the cosmos with electric eyes. The great strength of both Birkeland’s and Alfvén’s work lay in the experimental foundation of their theories. Birkeland was able to deduce the operating principles of the auroras from lab work he had done with cathode rays in partial vacuums. He noticed a correlation between sunspots and auroral excitement. From that he deduced (correctly) that the rays causing the auroras were emanating from the Sun, and that they consisted of streams of electrons. Further, he reasoned, the preference for polar regions shown by auroras suggested that the shimmering charged particles were somehow linked to the Earth’s magnetic field. Birkeland is today most famous for noticing that electric currents in plasma spiral into twisted, corkscrew shaped streams that now bear the name Birkeland currents, and which are seen in every corner of the sky.
There is structure and form in plasma, and sometimes it is striking. Because plasma has been studied so carefully, both inside the laboratory and out, we know and recognise plasma structures everywhere. Understanding those structures and their functions is crucial to any extrapolation we make from a terrestrial environment to the cosmos at large. A key formation is called a double layer. When a voltage potential exists across plasma, it causes freed electrons to flow through it in the form of an electric current. Now here’s the interesting part: In lab experiments, the current in a plasma-filled glass tube forms a barrier roughly half way along. It is a concentration of the strongest electrical fields, and acts as a natural capacitor—storing electrical force for later discharge. Double layers are now recognised ubiquitously in space plasmas, and we shall see shortly how they affect the behaviour of stars.
Double layers are associated with exceptionally strong z-pinches. The converging streams at that scale are easily powerful enough to compress matter lying between them to densities high enough to form cohesive planetary structures and even stars. In fact, this is probably the way that galaxies evolve, and if we get a more accurate picture of what galaxies actually consist of, it makes a lot more sense. Far from being tightly packed conglomerations of stars, galaxies are in reality very sparsely populated by anything solid. On his website, Professor Don Scott provides a much more realistic definition. A galaxy is, in the words of Dr Scott, “A vast formation of plasma clouds that contain electrical currents and occasional, widely distributed tiny lumped points of matter called nebulae, stars, and planets.” Apart from being a steadfast empirical scientist and professor in the field of electrical engineering, Don Scott is also a very enthusiastic amateur astronomer. You know, the type of person who actually looks at what he talks about. My kind of man.
1. Alfvén, H 1981Cosmic Plasma Dordrecht, D Reidel Publishing Company.
2. Alfvén, H and Arrhenius, G 1976 Evolution of the Solar System Honolulu, University Press of the Pacific.
3. Lerner, E 1992 The Big Bang Never Happened New York, Vintage Books.
4. Ratcliffe, H 2008 The Virtue of Heresy—Confessions of a Dissident Astronomer Raleigh, BookSurge.
5. Scott, D 2006 The Electric Sky Portland, Mikamar Publishing.
 Later it would be found that both protons and electrons stream from the Sun.
 Donald E. Scott in www.electric-cosmos.org.