For all these reasons, Einstein in 1915 developed a new theory of gravity called General Relativity. Today GR is accepted as the standard description of classical gravitational phenomena. (Alternative theories of gravitation exist but are more complicated than GR.) GR is consistent with all currently available measurements. For weak gravitational fields and bodies moving at slow speeds at small distances, Einstein's GR gives the same answers as Newton's law of gravitation. Crucial experiments that justified the adoption of GR over Newtonian gravity were the gravitational redshift, the deflection of light rays by the Sun, and the precession of the orbit of Mercury. More recent experimental confirmations were gravitational waves from orbiting binary stars and existence of black holes. |

For the first two of these reasons, Einstein in 1915 developed a new theory of gravity called General Relativity. Today GR is accepted as the standard description of classical gravitational phenomena. (Alternative theories of gravitation exist but are more complicated than GR.) GR is consistent with all currently available measurements. For weak gravitational fields and bodies moving at slow speeds at small distances, Einstein's GR gives almost exactly the same predictions as Newton's law of gravitation. Crucial experiments that justified the adoption of GR over Newtonian gravity were the gravitational redshift, the deflection of light rays by the Sun, and the precession of the orbit of Mercury. More recent experimental confirmations of GR were gravitational waves from orbiting binary stars and existence of neutron stars and black holes. |

Gravity is the only one of the four fundamental forces of nature that stubbornly refuses to be quantised (the other three being Electromagnetism, the Strong Force, and the Weak Force). What quantisation means, is that the force is measured in discrete steps that cannot be reduced in size, no matter what; alternatively, that gravitation is trasmitted by particle called gravitons. Scientists have theorized about the graviton for years, but have been frustrated in their attempts to find a consistent quantum theory for it. Many believe that [String Theory]? holds a great deal of promise to unify general relativity and quantum mechanics, but this promise has yet to be realized. |

Gravity is the only one of the four fundamental forces of nature that stubbornly refuses to be quantised (the other three being Electromagnetism, the Strong Force, and the Weak Force). What quantisation means, is that the force is measured in discrete steps that cannot be reduced in size, no matter what; alternatively, that gravitational interaction is trasmitted by particles called gravitons. Scientists have theorized about the graviton for years, but have been frustrated in their attempts to find a consistent quantum theory for it. Many believe that string theory holds a great deal of promise to unify general relativity and quantum mechanics, but this promise has yet to be realized. |