Researchers in Italy are hoping to measure Earth’s rotation using a laser gyroscope installed deep underground, with enough experimental precision to reveal measurable effects of Einstein’s Gneral Theory of Relativity.
The ring laser gyroscope (RLG) technology enabling these Earth-based measurements provide, unlike those made by referencing celestial objects, inertial rotation information, revealing fluctuations in the rotation rate from the grounded reference frame.
A group from the Italian National Institute for Nuclear Physics’ Laboratori Nazionali del Gran Sasso (LNGS) are researching the measurement of the gyroscopic precession Earth undergoes due to a relativistic effect called the Lense-Thirring effect.
This research program, called Gyroscopes in General Relativity (GINGER), would eventually use an array of such highly sensitive RLGs. For now, the team say they have successfully demonstrated its prototype, called “GINGERino”, and acquired many additional seismic measurements necessary to help achieve their aims.
The work has just been published in Review of Scientific Instruments, in which the group reports their successful installation of the single-axis GINGERino instrument inside the INFN’s subterranean laboratory LNGS, and its ability to detect local ground rotational motion. Ultimately, GINGER aims to measure Earth’s rotation rate vector with a relative accuracy of better than one part per billion to observe the miniscule Lense-Thirring effects.
“The effect is detectable as a small difference between the Earth’s rotation rate value measured by a ground based observatory, and the value measured in an inertial reference frame,” said Jacopo Belfi, lead author and a researcher working for the Pisa section of INFN. “This small difference is generated by the Earth’s mass and angular momentum and has been foreseen by Einstein’s General Theory of Relativity. From the experimental point of view, one needs to measure the Earth rotation rate vector with a relative accuracy better than one part per billion, corresponding to an absolute rotation rate resolution of 10-14 radians per second.”
The remote, underground location of these systems is essential for making these types of sensitive measurements – to remove the equipment from external disturbances such as from hydrology, temperature or barometric pressure changes.