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In both Newtonian mechanics and special relativity, space and then spacetime are assumed to be flat, and we can construct a global Cartesian coordinate system. In general relativity, these restrictions on the shape of spacetime and on the coordinate system to be used are lost. Therefore, a different definition of inertial motion is required.
Before Newton's law of gravity, there were many theories explaining gravity. Philoshophers made observations about things falling down − and developed theories why they do – as early as Aristotle who thought that rocks fall to the ground because seeking the ground was an essential part of their nature.
In string theory, believed by some to be a consistent theory of quantum gravity, the graviton is a massless state of a fundamental string. If it exists, the graviton is expected to be massless because the gravitational force has a very long range, and appears to propagate at the speed of light.
In Einstein's theory and related theories of gravitation, curvature at every point in spacetime is also caused by whatever matter is present. Here, too, mass is a key property in determining the gravitational influence of matter. But in a relativistic theory of gravity, mass cannot be the only source of gravity.
Depending on which features of general relativity and quantum theory are accepted unchanged, and on what level changes are introduced, [204] there are numerous other attempts to arrive at a viable theory of quantum gravity, some examples being the lattice theory of gravity based on the Feynman Path Integral approach and Regge calculus, [191 ...
A theory of gravity is a "metric theory" if and only if it can be given a mathematical representation in which two conditions hold: Condition 1 : There exists a symmetric metric tensor g μ ν {\displaystyle g_{\mu \nu }\,} of signature (−, +, +, +), which governs proper-length and proper-time measurements in the usual manner of special and ...
If we remove the hundred pound weight, and put on a scruple of gold, it will not swim, but will sink to the bottom of its own accord. Hence, it is undeniable that the gravity of a substance depends not on the amount of its weight, but on its nature. [30] [31] (translated from the original Latin by W. Newton)
In physics, the special theory of relativity, or special relativity for short, is a scientific theory of the relationship between space and time. In Albert Einstein 's 1905 paper, On the Electrodynamics of Moving Bodies , the theory is presented as being based on just two postulates : [ p 1 ] [ 1 ] [ 2 ]