Gravity & Magnetism

A challenging item in the unfinished business of science is to find some connection between magnetism and gravitation. The universe is shot through & through with electromagnetism; gravitation is everywhere too. Physicists have long been convinced that the two must be related somehow, but try as they would (and the most talented have tried), they could establish no basic connecting law.

Last fortnight Britain's famed, curly-haired Professor Patrick Maynard Stuart Blackett of Manchester University told the Royal Society how the problem might be (perhaps has been) solved.

As everyone knows, said Blackett, the earth has a magnetic field, but no one has figured out why. The magnetism does not come from iron deep underground, because the earth's core is far too hot to be "ferro-magnetic." As early as 1891, physicists guessed that the magnetism might be due to some inherent property of revolving bodies. They could not prove it.

A new bit of evidence came in when the strength of the sun's magnetic field was measured. It turned out to be closely proportionate to the earth's, allowing for the sun's greater mass and slower turning. But two observations are not enough to base a general law on; they might be mere coincidence.

Guiding Star. Last year some new evidence turned up. Dr. H. W. Babcock of Mt. Wilson Observatory, Calif, performed the unlikely feat of measuring (by spectrum analysis) the magnetic field of the star called 78 Virginis. When Professor Blackett heard about it, he grabbed pencil & paper. The star's size, mass and speed of revolution could be estimated fairly accurately. Nothing more was needed. The magnetic field of remote 78 Virginis just about proved what theorizing had already predicted: it was closely proportionate to the magnetic fields of the earth and sun.

Three matching bits of evidence in a row were more than coincidence. While the Fellows of the Royal Society watched intently, Blackett wrote down an equation* which may become as famous as Einstein's law, E--mc^2. It looked like the physical hybrid which science had been searching for so eagerly. On one side of the equation was magnetism, an electrical effect; on the other were basic gravitational quantities.

Said Professor Blackett modestly: "It is suggested tentatively that . . . the above equation represents some new and fundamental property of rotating matter. Perhaps this relation will provide the long-sought connection between electromagnetic and gravitational phenomena."

The new law can be checked by observing the spectra of stars, especially the dense "white dwarfs," which ought to have intense magnetic fields around their close-packed matter. It might even be proved in earthly laboratories, by spinning large masses of nonmagnetic material, such as bronze, and seeing whether they generate their own magnetic fields. Here was a fascinating assignment for a skillful (and well-financed) lab man.

*P=ss (G 1/2/2c) U, where P is the strength of the magnetic field; ss is a constant near unity; G is the gravitational constant (6.670 X 10^-8); c is the speed of light; U is the angular momentum (spin) of a revolving body.

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