Proving Einstein Right

"The chief attraction of the theory lies in its logical completeness," wrote Albert Einstein after publishing his general theory of relativity in 1915. "If a single one of the conclusions drawn from it proves to be wrong, it must be given up; to modify it without destroying the whole structure seems to be impossible."

Scientists have been rising to the challenge ever since. Not that they have been motivated by a desire to destroy Einstein's remarkable intellectual achievement--which explains gravity and the large-scale behavior of the universe on the basis of relative motion. Their ingenious tests have been devised largely to satisfy themselves that the theory is indeed sound.

Venusian Distance. Harvard physicists, for example, have measured the minute frequency change that takes place in gamma rays projected vertically for as little as 70 ft. in the earth's gravitational field. Their results upheld the gravity-caused shifts in frequency predicted by Einstein. An M.I.T. scientist plans to bounce high-frequency radar pulses off Venus as it begins to swing behind the sun. If Einstein's theory holds, the radar waves will be slowed down slightly as they pass through the strongest part of the solar gravitational field--enough to cause a 40-mile error in radar measurement of the distance of Venus from the earth.

Still another effort, which is perhaps the most delicate and sophisticated relativity check yet designed, will even involve NASA's growing capability in space. Within the next few years, if all goes well, a satellite will be launched into a 500-mile-high polar orbit. It will carry a virtually perfect gyroscope--one that is almost completely free from friction, gravitational pull or magnetic fields. If the general relativity theory is correct, according to calculations made by Stanford University Physicist Leonard Schiff, the gyroscope should precess--change the direction of its axis of rotation--about 1/500th of a degree each year that it is in orbit. This gradual and almost imperceptible change would be caused by the continuous passage of the gyroscope through Einsteinian space, which is "warped" by the earth's gravitational field.

Mercurial Change. To build so perfect a gyroscope, Stanford Physicists William Fairbank and Francis Everitt will use a sphere of quartz coated with niobium, a metal that becomes a superconductor and shows no resistance to electric current when cooled to extremely low temperatures. The sphere will be placed inside an evacuated quartz shell, also coated with niobium, and suspended in an electrostatic field. Suspending it in this manner will allow it to spin in a near-perfect vacuum without touching anything; it will be free from all friction. The gyroscope container will be kept in a bath of liquid helium at a temperature of--452DEGF. to make the niobium coating superconducting. In this supercooled state it will shield the gyroscope from the effects of any external magnetic field. Once in orbit, the free-spinning gyroscope will also be weightless and almost completely free of gravitational pull.

Measurement of any precession should be a tip-off to the effects of general relativity and will involve equally complex technology. In the satellite, a telescope attached to the framework around the gyroscope will read the direction of a fixed star. Because the spinning quartz sphere in the gyroscope is coated with a superconductor, it will produce a magnetic field oriented in the same direction as its spin axis. This field will induce currents in metallic superconducting loops surrounding the gyro and permit detection of any change in the direction of the axis with respect to the position of the star. The system is being designed to permit determination of changes of less than one one-hundred-thousandth of a degree.

The Stanford experiment is based on a test of general relativity proposed by Einstein himself. Equations based on his theory, he suggested, would accurately predict the orientation of the orbit of Mercury, which changes about one-eightieth of a degree more per century than Newtonian physics can account for. Though it was found that general relativity did indeed account for the additional amount of Mercurial change, some scientists still insist that the observed results are not necessarily conclusive, that the discrepancy might be partially caused by the shape of the sun. The orbiting gyroscope will leave little room for such uncertainties.

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