Laser gyroscopes measure small changes in daytime length on Earth

Recently, scientists used laser gyroscopes to measure that the change in Earth's rotational speed is less than one millionth. This technology can help scientists understand the complex flow of water and air, which can cause the smallest adjustments to the Earth's rotation.

The Earth's rotation is not completely stable. Planets accelerate or slow down as they rotate, slightly shortening or prolonging a day by a few milliseconds. Many of these changes are well-known. For example, one of the changes is caused by tidal forces, which are generated by the gravitational pull of the moon and sun, causing the Earth to deform. Scientists know how to predict these effects on Earth's rotation. However, other changes caused by fluctuations in the Earth's atmosphere and water bodies are more difficult to estimate.

The gyroscope, known as the "G", is located at the Wetzl Geodetic Observatory in Germany and aims to measure these small impacts. This is the so-called ring laser gyroscope. In it, the laser beam propagates around a square ring of 4 meters on each side. One bundle rotates clockwise, while the other bundle rotates counterclockwise. The wavelength of a beam of light that is aligned with the direction of Earth's rotation will be elongated, while a beam of light that propagates against the direction of Earth's rotation will contract. When combined, two beams of light with slightly different wavelengths will generate a "beat" signal, similar to two slightly out of tune notes.

Researchers reported in the September 18th issue of the journal Nature Photonics that this rhythm reveals the speed of Earth's rotation, allowing G to measure the length of a day with an accuracy of over one millisecond.

Other methods of measuring the Earth's rotational speed rely on external references. For example, telescopes can use the position of distant quasars (bright cores of active galaxies) to determine the degree of Earth's rotation. But these technologies provide the average results within a day. G measures the rotation rate every few hours. Its measurements were conducted in an underground laboratory.

Physicist Ulrich Schreiber of the Technical University of Munich stated that there is no need to understand the external world, "because gyroscopes measure absolute rotation." This means that the rotation it measures is not relative to other references, but rather the rotation itself.

Scientists have previously measured the Earth's rotation and tilt using other laser gyroscopes (SN: 7/17/20). But they have not yet measured the length of a day to the high accuracy achieved by G. The gyroscope is also stable enough to operate continuously for several months, allowing researchers to sort out changes that occur over a long time scale.

The function of G is unique: "This measurement is considered impossible for other detectors," said physicist Angela Di Virgilio of the National Institute of Nuclear Physics in Pisa, Italy, who was not involved in the new study. Therefore, they obtained some results from this impressive instrument, which is a good thing.

These measurements can help scientists improve their models of Earth's air circulation and ocean currents. In the future, scientists hope to measure more elusive effects through improved ring laser gyroscopes. According to Albert Einstein's general theory of relativity, rotating planets drag spacetime. A ring laser gyroscope may one day perceive the twists and turns of time and space.

Source: Laser Network