# Take off the weight of the earth

## health : Suddenly the earth becomes eight trillion tons lighter

The earth has become eight trillion tons lighter overnight. Given their mass, that's not much, but at least it's remarkable. And she's not the only one who lost weight. Each of us can feel a little relieved these days, even if a traditional scale won't tell the difference. The weight loss is tiny. Jens Gundlach's pendulum scales alone register such subtle differences.

The American researcher from the University of Washington determined Newton's gravitational constant with unprecedented precision. She is very small. Its value is 0.000 000 000 066 7390. And the measurement is only subject to an uncertainty of 0.0014 percent.

The tiny constant plays the main role in Newton's law of gravitation. This says that two massive bodies attract each other. However, the attraction is very weak, otherwise all people would stick together all the time. In the case of the stars, however, the attraction is clearly noticeable. The gravity of the sun is so strong that the earth and other planets are always kept close to them and do not disappear into cold space.

When Henry Cavendish determined the gravitational constant in 1798, he used two heavy spheres to do this. Between them he hung a pair of lighter balls on a thin wire. He brought the heavy balls very close to the light balls, which were thereby pulled a little out of their equilibrium position. From the oscillation of the balls and the twisting of the wire, Cavendish calculated the gravitational constant with astonishing accuracy.

Gundlach and his colleague Stephen Merkowitz have now made decisive improvements to Cavendish's 200-year-old experiment. They used four stainless steel balls weighing 8.14 kilograms. While the wire in Cavendish's experiment twisted due to the gravitational force of the balls, the American researchers switched off this torsion: They precisely adjusted the rotational speed of the laboratory table to the gravitational force with the help of a computer.

At a congress of the American Physical Society in Long Beach, California, the researchers presented their measurement results to the public. According to you, the value of the gravitational constant is known 100 times more precisely than before. This is of great importance for research, because Newton's gravitational constant, together with the speed of light and Planck's quantum of action, is one of the most important natural constants.

With their help and new laser measurements from the "Lageos" satellites, the scientists determined, among other things, the earth's mass. It is "only" 5.97223 trillion tons and thus almost eight trillion tons less than previous calculations had shown. The sun, on the other hand, is much heavier with a recalculated 1,988,430 trillion tons.