Newton's Law of Universal Gravitation, formulated by Sir Isaac Newton in the 17th century, was a groundbreaking achievement that successfully described the motion of celestial bodies and other objects under the influence of gravity. However, as scientific knowledge advanced, certain limitations and discrepancies with observational evidence became apparent. Einstein's theory of relativity, particularly his theory of general relativity, addressed these shortcomings and provided a more comprehensive and accurate description of gravity. Here are some of the key issues with Newton's law and how general relativity resolved them:
Instantaneous Action at a Distance: According to Newton's law, gravitational forces act instantaneously across any distance, irrespective of the distance between objects. This idea seemed contradictory to the notion of information propagation limited by the speed of light in special relativity. General relativity eliminated this issue by describing gravity as the curvature of spacetime caused by mass and energy. The curvature of spacetime propagates at the speed of light, ensuring that the effects of gravity travel at a finite speed and are consistent with the principles of relativity.
Gravitational Time Dilation: Newton's law did not account for the phenomenon of time dilation caused by gravity. However, general relativity predicts that time runs slower in the presence of a gravitational field. This has been verified through precise experiments, such as the Pound-Rebka experiment and the gravitational time dilation experienced by clocks in satellites.
Explaining the Orbit of Mercury: One of the significant discrepancies between Newton's law and observations was the precession of the perihelion (closest point to the Sun) of Mercury's orbit. Newton's law predicted a fixed elliptical orbit, while measurements indicated a slow rotation of the orbit's orientation. General relativity correctly accounted for this precession as a result of the curvature of spacetime near the massive Sun.
Light Bending: Newtonian gravity did not predict the bending of light by gravitational fields, whereas general relativity successfully explained this effect. During a solar eclipse in 1919, Arthur Eddington's observations confirmed that starlight passing close to the Sun is deflected by the Sun's gravitational field, validating Einstein's predictions.
Overall, Einstein's theory of general relativity resolved these issues by providing a more comprehensive and accurate description of gravity, incorporating the curvature of spacetime and accounting for the observations that Newton's law could not fully explain. General relativity has since become the foundation of our understanding of gravity, passing rigorous experimental tests and providing accurate predictions in various astrophysical and cosmological scenarios.