Planet Earth has a gravitational field that is not so large by cosmic standards, but it is certainly greater than the analogous field of any object on its surface. Because of this, it becomes meaningless to compare in laboratory conditions the gravitational effect of two arbitrary objects on each other – it will not manifest itself in any way, since it will be leveled by the gravitational attraction of the planet. However, researchers from the University of Vienna and the Austrian Academy of Sciences have found a way around this obstacle.
Strictly speaking, European scientists only scaled the experience of their great predecessor, Henry Cavendish. He built a torsion pendulum by hanging a rod on a thin wire, at both ends of which were fixed small and light balls. This made it possible to balance the gravitational attraction of the planet relative to them, but preserve the freedom of movement in the horizontal plane. Cavendish brought large and heavy balls to small balls so that their mutual gravitational attraction would make the pendulum turn a little.
In an experiment at the end of the 18th century, a wooden beam 1.8 m long was used, which was replaced by a glass rod only 40 mm long. Instead of 160-kilogram lead balls, hollow gold spheres weighing 90 mg were suspended, which is comparable to the weight of a ladybug. Knowing the parameters of the wire and using a laser to accurately measure the vibrations, the scientists obtained a deviation of a few millionths of a mm, which was the smallest gravitational force measured in laboratory conditions.
The experiment served as a demonstration of Einstein’s correctness that mass is capable of bending space-time and exerting a gravitational effect, no matter how small it is. Now scientists are planning to conduct a new experiment with a thousand times less masses – at this level, they will have to face quantum effects.