Did you know that the distance between the Earth and the moon is constantly changing? The space between them can change as much as 1,000 kilometers (620 miles) in six hours and the average distance between them is growing each year.

An international team of researchers was able to learn much more from the moon’s movement. By precisely measuring the variation of distance from the Earth to the moon, scientists can detect gravitational waves to a frequency that even the most high-tech man-made machines cannot.

What are gravitational waves?

Gravitational waves are energy-carrying waves, also known as “ripples” in spacetime. Their origin is from some of the most energetic and violent processes that have happened in the universe, such as the collision of two black holes or a star exploding.

Albert Einstein was the first to predict this natural phenomenon in the early 20th century and it was finally able to be recorded in 2015. Gravitational waves are measured in frequency by detectors, but current equipment humans are just not sensitive enough to pick up the most highly energetic types. Making the waves invisible to even the most advanced technology in this field. This is where the relationship between Earth and the moon comes into play.

How can the moon help measure gravitational waves?

The reason for the distance between the Earth and the moon is minuscule changes in gravitational waves. These energetic ripples constantly hit the moon’s orbit path, therefore altering its course. What makes the moon the perfect candidate is how highly precise we can measure its distance from us.

Lasers from multiple observatories around the world have been positioned to hit mirrors placed on the surface of the moon by the Apollo space mission, and are reflected back to Earth. This system allows for accurate measurement of the moon’s distance down to the centimeter, translating to an error of one billionth.

This idea of a natural-detector, published in Physical Review Letters, is an extremely innovative way of creating a highly precise detection of gravitational waves. Removing the need to spend money and time producing complicated detectors that could take decades to create.

Why are researchers interested in measuring gravitational waves?

It is believed that some of these very high-frequency gravitational waves were birthed at the dawn of time. Being able to track their activity allows the study of the early phases of the universe. Understanding this time period is essential for answering a multitude of questions about the laws of nature and everything that exists. Furthering our knowledge about gravitational waves, in general, could forward a number of technological innovations on Earth in the future.

Source study: Physical Review Letters – Bridging the μHz Gap in the Gravitational-Wave Landscape with Binary Resonancesgravitational waves