Sometimes, I read journal articles and press releases and think, “That is madness. It works, but it is madness.” But as the Cheshire cat once said, “We’re all mad here.”

In a new paper in Physical Review Letters, Diego Blas and Alexander C. Jenkins propose using the Moon to detect the small changes in the structure of space that occur when a gravitational wave passes through our part of the universe.

Gravitational waves are created when masses merge, explode, or otherwise radically change their combined mass and energy. They can be generated by orbiting high mass objects like neutron star pairs, and theory says they also reverberated through the early universe. Just like different radio electronics are needed to detect AM, FM, and shortwave radio, different setups are needed to detect gravitational waves generated by different sources. Currently, Earth-based detectors, including LIGO and Virgo, can detect waves from merging neutron stars to small and intermediate-mass black holes.

Researchers would also like to be able to detect gravitational waves generated in the early universe that are still traveling through space. Up until about 400,000 years after the universe formed, space was opaque to light. We’ll never be able to see with a telescope what happened in those early millennia. Gravitational waves, however, may be out there carrying information from that time. And, if they were on the radio dial, they’d require tuning into the microhertz part of the dial.

And if those gravitational waves wash over the Earth-Moon system, they just might change the distance to the Moon enough that we’re able to detect it and detect the subtle changes to the Moon’s orbit. We may also get further information by observing other well-understood systems of two objects.

According to Blas: This coverage is vital to obtaining a precise image of the evolution of the universe, as well as its composition. Covering the microhertz frequency range is a challenge, which now may be feasible without the need of building new detectors, and only observing the orbits of systems we already know. This connection between fundamental aspects of the universe and more mundane objects is particularly fascinating and can eventually lead to the detection of the earliest signals we have ever seen, and thus change what we know about the cosmos.

To make this a reality, regular laser ranging of the Moon and monitoring of its orbit will be required. We have the ability. We just need the time, money, and expanded facilities.

More Information

Universitat Autònoma de Barcelona press release

“Bridging the μHz Gap in the Gravitational-Wave Landscape with Binary Resonances,” Diego Blas and Alexander C. Jenkins, 2022 March 11, Physical Review Letters