This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: Newton's theory of gravity has described the tides accurately for centuries. But could a tiny trace of Einstein's general relativity also be hidden in them?
In a new study, a mathematician at Freie Universität Berlin has outlined how a targeted approach could be used to search for effects of this nature. The paper, titled "Frame Degeneracy and Sine-Quadrature Residuals in Lunar Tidal Modeling," was recently published in The Astrophysical Journal. The moon and the sun pull on the oceans and on the solid Earth, and both deform in response.
These movements can be recorded with high-precision instruments and calculated very accurately with Newtonian gravity. However, a fuller description of gravity is provided by Einstein's general theory of relativity, according to which mass and energy alter spacetime, and changes in spacetime can travel as gravitational waves. The new study brings these two perspectives together in one mathematical model.
It extends the classical model of lunar tides by an additional term that is based on the cross polarization of a gravitational wave, which is one of the characteristic ways in which gravitational waves can deform spacetime. "We are not claiming to have discovered a new gravitational effect. What we show is how one could look for it in a targeted way," says Muhittin Eser, a mathematician in the Department of Mathematics and Computer Science at Freie Universität Berlin and the author of the study.
"The Earth–moon system is particularly interesting for this because we can already describe and measure its tidal effects very precisely." One difficulty is distinguishing possible additional signals from known uncertainties. Deviations from the predicted tidal signals can come from the choice of reference frame, from uncertainties in computing the positions of the Earth and moon or from systematic measurement errors. The study therefore shows which influences would have to be controlled before a remaining signal could be examined as a possible additional physical effect.
The study offers a quantitative basis for future searches for very small deviations from the classical description. Such searches could draw on high-precision measurements of gravity and tides, on geodetic observations and on lunar laser ranging. In lunar laser ranging, laser pulses are sent to reflectors on the moon to measure the Earth–moon distance very precisely.
Extract — continue reading at the source.
