The Electromagnetic Force




The plasma physicist Hannes Alfvén drew an analogy between the human body and and large bodies in space. Before the invention of the microscope1, it was absurd to think that a strong, healthy man could be weakened by something millions of times smaller than he2,3. Surely, most ancient peoples thought, the warding off of large and powerful spirits was necessary to prevent sickness and death.

So too, before the discovery of the pervasive plasma state in space by satellites, planetary probes, radiotelescopes, and other instruments used to measure electromagnetic radiation outside the visible, it seemed unthinkable that large bodies such as stars and the nebulae (galaxies) could be interacting in any other way than through gravitational forces. Indeed, the whole history of astronomy before the radiotelescope was founded on the enormous success Johannes Kepler had in predicting the motion of the planets through Newton's gravitation. This clock-like precision changed with the discovery that space was filled with flickering sources producing intense continuous, flickering and chaotic electromagnetic radiation [the pioneering papers on radio astronomy were all published in electrical engineering journals; astronomers of the era could see no rational reason why radiowaves might emanate from space nor that they could be harbingers of current-conducting space plasma].

While there is no doubt that planetary systems interact gravitationally with their host star, matter in the solid, liquid, and even non-ionized gaseous state is not known for certain to exist anywhere other than in the crustal region of planets, meteorites, and comets. For example, all space above the earth is plasma, and the core of the earth is magnetohydrodynamic magma (magnetized plasma).But even the crustal regions consist of the atoms of matter that are made up of the two longest-lived fundamental particles, electrons and protons, that are the constituent members of plasma4.

Gravity can hold sway, for example in our planetary system, only when forces much stronger than gravity are canceled out; electromagnetism, for instance, which is the binding force for virtually all ordinary biological and chemical phenomena or Earth, is intrinsically 10^39 times stronger than gravity. If the dominant form of matter were subject to the electromagnetic force as well as to the force of gravity, gravity would be swamped by the more compelling pulls and tugs of electromagnetism.

An indication of the dominance of the magnetic force is given by a ball bearing on a table. All of the Earth's mountains, seas, core, sand, rivers, and lifeforms exert a gravitational pull on the bearing preventing it from flying off into space. Yet the smallest horseshoe magnet easily snatches it away.

But perhaps the most important characteristic of electromagnetism is that it obeys the longest-range force law in the universe. When two or more non-plasma bodies interact gravitationally, their force law varies inversely as the square of the distance between them; 1/4 the pull if they are 2 arbitrary measurement units apart, 1/9 the pull for a distance of 3 units apart, 1/16 the pull for 4 units apart, and so on. When plasmas, say streams of charged particles, interact electromagnetically, their force law varies inversely as the distance between them, 1/2 the pull if they are 2 arbitrary measurement units apart, 1/3 the pull for a distance of 3 units apart, 1/4 the pull for 4 units apart, and so on. So at 4 arbitrary distance units apart, the electromagnetic force is 4 times greater than that of gravitation, relatively speaking, and at 100 units, apart, the electromagnetic force is 100 times that of gravitation. Moreover, the electromagnetic force can be repulsive if the streams in interaction are flowing in opposite directions. Thus immense plasma streams measured in megaparsecs, carrying galaxies and stars, can appear to be falling towards nothing when they are actually repelling.

The electromagnetic forces between two Birkeland currents, which are electric currents aligned along magnetic-field lines. These currents have parallel components that exert a long-range attractive force and circular components that provide short-range repulsion.

Left: The geometry used in computer simulations. If the electrons are moving near the speed of light they emit synchrotron radiation beamed along their magnetic-field line, so the emission nearly mirrors the magnetic field pattern.

Right: How the forces due to the Birkeland current components vary with separation, along with the behavior of the combined (net) force.


1. An electron microscope is able to view particles down to 0.2 nanometer (one nanometer is a billionth of a meter) or less in size, or more than a thousand times smaller than a microscope. With high-voltage electron microscopes, image resolution on the atomic level can be reached.

2. Bacteria are measured in microns, or 0.00004 inches and viruses are about 3,000 angstroms in size, or 1/100,000 inch.

3. The oldest sign of life is a fossilized bacterial cell discovered in a rock in Africa and estimated at about 3.5 billion years old.

4. The proton may well have a lifetime longer than 10^18 billion years, a period perhaps comparable with Joseph Bohm's age for the plasma era of an evolving universe.