Gravitation
Gravitation, or gravity, is a natural phenomenon by which physical bodies attract each other with a force proportional to their masses.
General description
Gravitation is most familiar as the agent that gives weight to objects with mass and causes them to fall to the ground when dropped. Gravitation causes dispersed matter to coalesce, and coalesced matter to remain intact, thus accounting for the existence of the Earth, the Sun, and most of the macroscopic objects in the universe.
Gravitation is responsible for keeping the Earth and the other planets in their orbits around the Sun; for keeping the Moon in its orbit around the Earth; for the formation of tides; for natural convection, by which fluid flow occurs under the influence of a density gradient and gravity; for heating the interiors of forming stars and planets to very high temperatures; and for various other phenomena observed on Earth.
Gravitation is one of the four fundamental interactions of nature, along with electromagnetism, and the nuclear strong force and weak force. Modern physics describes gravitation using the general theory of relativity by Einstein, in which it is a consequence of the curvature of spacetime governing the motion of inertial objects. The simpler Newton's law of universal gravitation provides an accurate approximation for most physical situations.
Mme. Blavatsky of Gravitation
Helena Petrovna Blavatsky challenged the concept of gravity as the cause of attraction between bodies. She wrote:
Astronomers who see in gravitation an easy-going solution for many things, and an universal force which allows them to calculate thereby planetary motions, care little about the Cause of Attraction. They call Gravity a law, a cause in itself. We call the forces acting under that name effects, and very secondary effects, too. One day it will be found that the scientific hypothesis does not answer after all. . .[1]
Scientific Theories
Newton's theory of gravitation
Isaac Newton formulated the inverse-square law of universal gravitation. Although gravity was frequently regarded as a property of matter, Newton himself did not think so. Actually, he only described the action of gravity but not the cause for it. In a letter to an acquaintance of him, Richard Bentley:
It is inconceivable that inanimate brute matter should (without the mediation of something else which is not material) operate upon and affect other matter without mutual contact; as it must if gravitation in the sense of Epicurus be essential and inherent in it. And this is one reason why I desired you would not ascribe innate gravity to me. That gravity should be innate, inherent, and essential to matter so that one body may act upon another at a distance through a vacuum without the mediation of any thing else by and through which their action or force may be conveyed from one to another is to me so great an absurdity that I believe that no man who has in philosophical matters any competent faculty of thinking can ever fall into it. Gravity must be caused by an agent acting constantly according to certain laws, but whether this agent be material or immaterial is a question.[2]
Although Newton's law was useful in general applications, there were some problems that it could not solve. Newton's theory was finally superseded in 1915 when Albert Einstein developed the theory of general relativity, and was able to solved such problems.
Einstein's theory or relativity
According to the general relativity, gravity is not an attractive force. It's the curvature of the spacetime fabric by matter, which causes bodies to follow certain orbits and free-falling objects move along locally straight paths called geodesics. Einstein's theory is so precise that, as Einstein predicted, even light follows the spacetime curvature. However, the general relativity model cannot account for the sub-atomic level of reality.
Gravity and quantum mechanics
General relativity is incompatible with quantum mechanics. The latter describes gravity in itw own way, treating it like the other fundamental forces--it postulates that the attractive force of gravity arises due to exchange of still undiscovered gravitons. However, this approach has failures that require a more complete theory of quantum gravity, or a new approach to quantum mechanics.
Online resources
Articles
- Is Gravitation a Law? by H. P. Blavatsky