General relativity is a theory of space and time.
The theory was published by Albert Einstein in 1915.
The main idea of general relativity is that space and time are two different parts of spacetime. In general relativity, gravity doesn't work the same way that Sir Isaac Newton said was how gravity worked. According to Einstein, gravity changes not only space, but also time. (Time dilation)
An important idea in general relativity is the "principle of equivalence". An example is that two people, one in an elevator on the surface of the Earth, and the other in an elevator in outer space but accelerating upwards at 9.8 m/s2 will each observe the same behavior of an object they drop from their hands. The object will accelerate to the floor at 9.8 m/s2 in either case.
This makes it impossible for either to distinguish whether or not they are at rest in a gravitational field. Other versions of this type of "thought experiment" were used to show that light would curve in an accelerating frame of reference.
The force pulling the Earth towards the Sun is about the same as a second force. This second force is called the centrifugal force. The centrifugal force exists because the Earth moves sideways. This sideways motion makes the distance between the Earth and Sun increase. Since the Earth is being pulled towards the sun and moving away at the same time, it stays at about the same distance. This is also how the Moon orbits the earth. In this second case, Earth is the ball and the Moon is the object.
The Sun and other objects with mass curve four dimensional spacetime fabric.
General relativity has predicted many things which were later seen. These include:
This article uses material from the Wikipedia Simple English article General relativity, which is released under the Creative Commons Attribution-ShareAlike 3.0 license ("CC BY-SA 3.0"); additional terms may apply (view authors). Content is available under CC BY-SA 4.0 unless otherwise noted. Images, videos and audio are available under their respective licenses.
®Wikipedia is a registered trademark of the Wiki Foundation, Inc. Wiki Simple English (DUHOCTRUNGQUOC.VN) is an independent company and has no affiliation with Wiki Foundation.