New method proposed for observing the time variation of the universal gravitational constant G

The universal gravity formula, where G is the universal gravitational constant. New research is dedicated to exploring the range of variation of this constant over the long history of the universe.

Scientists have introduced a series of physical constants with constant values to explain the universe we live in, such as the universal gravitational constant G, which is one of the constants used to quantify the gravitational force between two massive objects (or any two objects).

Some scientists suspect that these constants may have changed over the long history of the universe. Some alternative theories of gravity speculate that the universal gravitational constant, G, appears to change over time.

Researchers at the Tata Institute of Fundamental Research, an Indian public research institute, recently proposed a method to speculate on the extent to which the universal gravitational constant has floated over the long history of the universe.

Principal investigator Parameswaran Ajith said, “Our study shows that gravitational waves emitted from the merger event of two neutron stars can measure the range of the fluctuation of the universal gravitational constant G.”

They measured the overall value of GM/c² from the gravitational wave signals, where M is the mass of the merging neutron star and c is the speed of light. Although it is not possible to measure the mass of each neutron star independently, the researchers know the mass range of neutron stars: if a neutron star is too large, it will collapse under its own gravity; if it is too small, it will not be able to retain its own matter.

Thus, this study suggests that the range of masses of neutron stars can be used to deduce the range of the universal gravitational constant G at the time of their merger.

Previously, researchers have only been able to detect the gravitational constant G in the very early universe – for example, a few minutes after the Big Bang – or in the “near future” – about 100 million years ago. With this new method, researchers will be able to see what the gravitational constant G was like in other universes.

And, as scientists detect gravitational wave devices with increasing sensitivity, they will be able to detect more of these merger events in the future, and will be able to understand how the constant G has changed at more points in time in the universe.

“Gravitational-wave detectors like LIGO in the United States and Virgo in Italy are continuing to improve their sensitivity, and new detectors are being built in Japan and India.” Agis said, “In the next decade, we will be able to detect hundreds of pairs of gravitational waves from neutron star merger events, and the next generation of detectors will be able to detect millions of pairs. Each observation will provide a range of values for the constant G at that point in time in the universe. In this way, we should be able to build an atlas of the range of values of the universal gravitational constant G over the tens of billions of years before and after the Universe.”

The study was published April 8 in Physical Review Letters.