The fascinating work of the Swedish physicist Hannes Alfven lighted the tortuous path to the answer. In the 1950’s he discovered a kind of energy which nobody even thought existed, which he labeled “magnetohydrodynamic” energy. Abbreviated, it’s called mhd. Actually, it’s a combination of magnetic, electrical, and physical forces.

It can be described best with what I call a “kitchen example”. Suppose you took a glass cylinder containing mercury at room temperature – and everyone knows it’s “molten” or liquid under those conditions. It’s so dense that you can float a glass mirror on top of it. So let’s do just that, and make some scratches on the mirror. If you shine a light down on the mirror, the light beam will reflect on the ceiling and show images of the scratches in the mirror on the ceiling.

Now let’s put an agitator – like a miniature version of a washing machine agitator – in the bottom of the cylinder of mercury, with a shaft or axle going through the bottom of the cylinder, and fastened to the agitator. Let’s put a handle on the end of the shaft sticking out of the bottom of the cylinder. We can twirl the agitator back and forth with the handle (slowly only, because the mercury is so dense and heavy) and agitate the mercury in the glass cylinder.

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When we agitate the mercury in this fashion we find that the slipperiness of the mercury, atom to atom, is so great that all of the motion of the agitator is absorbed by the mercury before it ever reaches the top surface where the mirror is. The mirror won’t budge.

If we wind a wire around the glass cylinder and connect it to a battery, we will have an electromagnet – following the same principles used in the doorbell of your home. There is an electrical current flowing around the cylinder, and a magnetic field going through the cylinder, end-to-end.

Now we find that things have changed. When we rotate the agitator back and forth, the mercury acts as if it were a plastic, or near-solid. The mirror makes all of the moves that the agitator does, showing that the mercury has lost its internal slipperiness, and is moving integrally as if it were almost solid.

Alfven tried a refined version of this experiment in his laboratory, and this is how the phenomenon was discovered. It was first reasoned that tiny electrical charges, called “eddy currents”, were being generated in the mercury, which in turn were generating tiny local opposing magnetic fields, and this was causing the solidifying effect. He reasoned that if this were true, the larger the diameter he made the glass cylinder, the bigger the electrical current and the stronger the magnetic field would have to be to maintain the same physical force link between the agitator and mirror.

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