Measuring the Universe

Where lies the land to which the ship would go?

Far, far, ahead is all her seamen know.

--Arthur Hugh Clough

Astronauts heading for some distant planet may not be quite as ignorant as Clough's seamen. But if a spaceshipload of them were to blast off tomorrow, they could not predict their landing point within thousands of miles. Such uncertainty could be disastrous, and Physicist F. E. Lowther of General Electric Co. hopes to do something about it. He is starting his campaign with an effort to correct that old reliable constant of physics: the speed of light (now calculated at 186,282 m.p.h.).

The best way now available for measuring the distance of an object far out in space is to bounce a radio signal off it and measure the time it takes for the reflected pulse of radio energy to return. This time interval, multiplied by the speed of light (which is the same as the speed of radio waves), gives the round-trip distance. But the speed of light, complains Dr. Lowther, is known only with the inaccuracy of three parts per million.

This minor-sounding inaccuracy means that the nearby moon on earth's very doorstep follows an orbit that cannot be measured closer than 3/4 mile.

The speed of light is measured by reflecting a beam back and forth between carefully placed mirrors and clocking the time it takes the light to cover that measured distance. Dr. Lowther proposes to improve this experiment by using the pure brilliance of newly developed lasers (TIME, April 20) and new electronic techniques. He hopes to pinpoint the speed of light to three parts per 100 million, which will give the distance to the moon within 72 ft.

Measuring the distance to Mars or other such far-out planets is far trickier; they are well beyond the useful range of available radar. Astronomers calculate the interplanetary distance by observing the time it takes for Mars to complete one orbit around the sun and comparing that time with the earth's own time on its orbit. Since the distances of the planets from the sun are in proportion to their periods of revolution, the radius of the Martian orbit can thus be measured in terms of the basic "astronomical unit": the average distance of the earth from the sun.

Artificial Planet. Trouble is, that the astronomical unit is known with even greater inaccuracy than the speed of light. As Mars curves around its orbit, its measured distance from the earth may be as much as 2,000 miles in error. Dr. Lowther hopes to clear up this unhappy situation by lofting a small satellite into an orbit around the sun. Lowther's satellite would carry extremely sensitive radio equipment to amplify signals from earth and send them back again on a slightly different wave length. This sophisticated radar system would make no use of the speed of light in its measurements. The distance from the earth to the satellite would be calculated in actual wave lengths of radio energy with an error of only 6 ft.

After Dr. Lowther's noisy little artificial planet has been tracked through several trips around the sun, its orbit will be known with much greater accuracy than that of any natural planet. And from its carefully plotted position astronomers will be able to measure correctly the earth's distance from the sun. Then it will also be possible to plot accurate orbits for all the other planets.

Changed Concept? Besides drawing a precision map of the solar system, Dr. Lowther's artificial planet may get a crack at even more interesting jobs. Since its orbit will be slightly but measurably disturbed by the gravitational attraction of all the other passing planets, its waverings can be used to check the mass of individual planets. It may also detect large meteors that chance to streak close by. It may point to far-out, undiscovered planets, or even to dark, invisible stars. Its most radical use, Dr. Lowther figures, will be to check the inverse-square law, which says that the strength of light and gravitation diminishes inversely with the square of the distance from their source. This law is regarded as one of the fundamentals of physics, but Dr. Lowther is eying it closely. If the returning radio signals from his artificial planet are either too strong or too weak to fit the theory, it may mean that they and light (and perhaps gravitation too) diminish not with the square but with the 1.999 power of the distance. Such a result would call for an entirely new conception of the universe.

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