The gravitational constant G determines the strength of gravity—the force that makes apples fall to the ground or pulls the Earth in its orbit around the sun. It is part of Isaac Newton’s law of universal gravitation, which he first formulated more than 300 years ago. The constant cannot be derived mathematically; it has to be determined through experiment.
Over the centuries, scientists have conducted numerous experiments to determine the value of G, but the scientific community isn’t satisfied with the current figure. It is still less precise than the values of all the other fundamental natural constants—for example, the speed of light in a vacuum.
One reason gravity is extremely difficult to quantify is that it is a very weak force and cannot be isolated: when you measure the gravity between two bodies, you also measure the effect of all other bodies in the world.
“The only option for resolving this situation is to measure the gravitational constant with as many different methods as possible,” explains Jürg Dual, a professor in the Department of Mechanical and Process Engineering at ETH Zurich. He and his colleagues conducted a new experiment to redetermine the gravitational constant and have now presented their work in the scientific journal Nature Physics.
To rule out sources of interference as far as possible, Dual’s team set up their measuring equipment in what used to be the Furggels fortress, located near Pfäfers above Bad Ragaz, Switzerland. The experimental setup consists of two beams suspended in vacuum chambers. After the researchers set one vibrating, gravitational coupling caused the second beam to also exhibit minimal movement (in the picometre range – i.e., one trillionth of a metre). Using laser devices, the team measured the motion of the two beams, and the measurement of this dynamic effect allowed them to infer the magnitude of the gravitational constant.
The value the researchers arrived at using this method is 2.2 percent higher than the current official value given by the Committee on Data for Science and Technology. However, Dual acknowledges that the new value is subject to a great deal of uncertainty: “To obtain a reliable value, we still need to reduce this uncertainty by a considerable amount. We’re already in the process of taking measurements with a slightly modified experimental setup so that we can determine the constant G with even greater precision.” Initial results are available but haven’t yet been published. Still, Dual confirms that “we’re on the right track.” (https://www.nature.com/articles/s41567-022-01642-8)
AR Issue #73
Defying Gravity
by Len Kasten
