Newton’s law of gravity is used with great success in most everyday situations, and indeed, in planning planetary space missions such as the Rosetta probe.
However, Einstein’s theory of general relativity and a theory of quantum gravity are needed to describe the observed effects of gravitational interaction under different circumstances.
Write a short account, explaining the circumstances where general relativity and quantum gravity depart from Newton’s theory, giving one example of an effect or prediction for each of these alternative theories
Newton's law of gravity, though highly accurate in many everyday situations and for planning planetary space missions, does have its limitations when it comes to certain circumstances. This is where Einstein's theory of general relativity and a theory of quantum gravity come into play.
General relativity, developed by Albert Einstein, provides a more accurate description of gravity in extreme situations where strong gravitational fields or high velocities are involved. One example of when general relativity departs from Newton's theory is the prediction of gravitational time dilation. According to general relativity, time runs slower in regions with stronger gravitational fields. This effect has been experimentally confirmed through precision measurements and GPS technology, which must account for the difference in time experienced between satellites in orbit and Earth's surface.
On the other hand, quantum gravity, which attempts to unify general relativity with quantum mechanics, becomes crucial at an even larger scale. When considering the extremely high energy and small distances associated with black holes or the initial moments of the universe, quantum gravity becomes necessary to describe the gravitational interaction. However, a fully developed theory of quantum gravity is still a subject of active research and remains a challenge.
One example of an effect/prediction in the realm of quantum gravity is the concept of the "quantum foam" or "spacetime foam." According to this idea, spacetime itself fluctuates at extremely small scales, leading to a frothy and dynamic "foam-like" structure. This would result in the uncertainty of properties such as position and energy, challenging our classical understanding of spacetime as a smooth and continuous fabric.
In summary, general relativity departs from Newton's theory in circumstances involving strong gravitational fields and high velocities, while quantum gravity is required on an even grander scale such as black holes or the early universe. Gravitational time dilation serves as an example of a prediction from general relativity, while the concept of the "quantum foam" represents an effect/prediction in the realm of quantum gravity.