Related topics: black holes

NASA's WFIRST will help uncover the universe's fate

Scientists have discovered that a mysterious pressure dubbed "dark energy" makes up about 68% of the total energy content of the cosmos, but so far we don't know much more about it. Exploring the nature of dark energy is ...

Skating droplets move in orbits

They look like planets: Two droplets move in orbits on an ice cold fluid surface. They attract each other, and by almost frictionless movement on their own vapour, they skate around each other. It is a fascinating mechanism ...

Providing a solution to the worst-ever prediction in physics

The cosmological constant, introduced a century ago by Albert Einstein in his theory of general relativity, is a thorn in the side of physicists. The difference between the theoretical prediction of this parameter and its ...

General relativity

General relativity or the general theory of relativity is the geometric theory of gravitation published by Albert Einstein in 1916. It is the current description of gravitation in modern physics. It unifies special relativity and Newton's law of universal gravitation, and describes gravity as a geometric property of space and time, or spacetime. In particular, the curvature of spacetime is directly related to the four-momentum (mass-energy and linear momentum) of whatever matter and radiation are present. The relation is specified by the Einstein field equations, a system of partial differential equations.

Many predictions of general relativity differ significantly from those of classical physics, especially concerning the passage of time, the geometry of space, the motion of bodies in free fall, and the propagation of light. Examples of such differences include gravitational time dilation, the gravitational redshift of light, and the gravitational time delay. General relativity's predictions have been confirmed in all observations and experiments to date. Although general relativity is not the only relativistic theory of gravity, it is the simplest theory that is consistent with experimental data. However, unanswered questions remain, the most fundamental being how general relativity can be reconciled with the laws of quantum physics to produce a complete and self-consistent theory of quantum gravity.

Einstein's theory has important astrophysical implications. It points towards the existence of black holes—regions of space in which space and time are distorted in such a way that nothing, not even light, can escape—as an end-state for massive stars. There is evidence that such stellar black holes as well as more massive varieties of black hole are responsible for the intense radiation emitted by certain types of astronomical objects such as active galactic nuclei or microquasars. The bending of light by gravity can lead to the phenomenon of gravitational lensing, where multiple images of the same distant astronomical object are visible in the sky. General relativity also predicts the existence of gravitational waves, which have since been measured indirectly; a direct measurement is the aim of projects such as LIGO. In addition, general relativity is the basis of current cosmological models of a consistently expanding universe.

This text uses material from Wikipedia, licensed under CC BY-SA