General Relativity Wins an Old Debate

General Relativity Wins an Old Debate

Isaac Newton’s most highly regarded scientific publication is his three-volume work Principia. In it, he powerfully demonstrated that the motions of the heavens operated according to the same natural laws that governed motion on Earth. Specifically, he formulated the universal law of gravitation, which describes the attractive force between any objects with mass.

Despite its successes, Newton’s description of gravity did not match certain astronomical measurements. The most prominent discrepancy concerned the orbit of Mercury around the Sun. Each of the planets revolves around the Sun in an elliptical manner with the Sun at one focus. Perihelion is the location on a planet’s orbit closest to the Sun. According to Newton’s theory, assuming that only one planet and the Sun exist, the perihelion is fixed. Under more realistic scenarios (for example, more planets in the system), the perihelion location moves around the Sun. Astronomers measured this “perihelion advance” for Mercury. The measured value did not match the predicted value from Newtonian gravity.

In his general theory of relativity (first published in 1916) Albert Einstein outlined a test that showed how his theory properly accounted for the perihelion advance of Mercury. However, he was not alone in developing models to explain this observation. Another model, the Brans-Dicke theory of gravitation, also explained Mercury’s behavior with one requirement—the Sun must demonstrate an oblateness (flattening) caused by a rapidly rotating core. In other words, a rapidly spinning core causes the Sun’s equator to bulge much the same way squeezing a rubber ball on opposite sides does. Earlier measurements seemed to confirm the required solar oblateness although there was no way to determine the rotation of the Sun’s core.

Recent work by a team of U.S. scientistsconfirm the solar oblateness detected by previous measurements. However, the oblateness arises from magnetic features on the Sun—not from a rapidly spinning core. Thus, it seems that general relativity provided the correct description of solar system dynamics all along.

Coupled with numerous other tests, general relativity ranks as one of the most examined—and most successful—theories known. Such results demonstrate that RTB’s creation model, which incorporates general relativity, rests on firm scientific footing.