Selected aspects of cosmology are described in the category Cosmology of our Spotlights on relativity.The first direct observation of gravitational waves in 2015 has led to an increased public interest in topics of general relativity (GR) and astronomy. The basic features of the big bang models are reviewed in the chapter Cosmology of Elementary Einstein. Further information about these two meanings and why it is important to distinguish between them can be found in the spotlight text A tale of two big bangs. In a more general sense, the term is applied to the earliest cosmic eras, in which the universe was exceedingly hot and dense. In a strict sense, the big bang is a spacetime singularity, a state of infinite density - the initial state the big bang models predict for our universe. The word "big bang" has two different meanings. They make precise predictions about nucleosynthesis in the early universe, the existence and properties of the cosmic background radiation, and the distribution of distant galaxies in the cosmos, which have been confirmed by astronomical observation. Firmly grounded in Einstein's theory of general relativity, they describe a universe that began in a very hot initial state and has expanded (and cooled down) ever since. big bang The big bang models are the foundation of modern cosmology. However, for astrophysical black holes (that typically have more or even much more than one solar mass), that radiation would be undetectable, even if we could transport today's most sensitive sensors into the immediate vicinity of the black hole. Once quantum theory is taken into account, this assumption no longer holds - on the contrary, it seems as if black holes should emit so-called Hawking radiation. In Einstein's theory, black holes are truly black, due to the fact that no radiation or light can ever escape them. Selected aspects of the physics of black holes and neutron stars are described in the category Black holes & Co. black holes (black hole) Region in space where a sufficient amount of mass is concentrated so that it forms a gravitational prison - a region into which matter or light can enter from the outside, but from which nothing that has once entered can ever leave.īasic information on this key phenomenon of Einstein's general theory of relativity can be found in the chapter Black holes & Co. Further information about many different aspects of general relativity and its applications can be found in our section Spotlights on relativity. general relativity (general theory of relativity) Albert Einstein's theory of gravity a generalization of his special theory of relativity.įor information about the concepts and applications of this theory, we recommend the chapter general relativity of our introductory section Elementary Einstein. More information about the nature of gravity in general relativity can be found in the spotlight text Gravity: From weightlessness to curvature. In Einstein's general theory of relativity: The fact that matter that possesses mass, energy, pressure or similar properties distorts spacetime, and that this distortion in turn influences whatever matter might be present.Īn introduction to the basic ideas of general relativity is provided by the section General relativity of Elementary Einstein. gravity (gravitation) In classical physics: An action-at-a-distance force by which all bodies that possess mass attract each other (see Newtonian theory of gravity), synonym: gravitational force. Selected aspects of gravitational wave physics are described in the category Gravitational waves of our Spotlights on relativity. gravity See gravitation gravitational waves Distortions of space geometry that propagate through space with the speed of light, analogous to ripples on the surface of a pond propagating as water waves.įor more informations about gravitational waves, please consult the chapter Gravitational waves of Elementary Einstein. Simple examples are water-waves - wave crests and troughs travelling over a water surface, and a Mexican wave in a football stadium, with fans alternately standing up and sitting down - the pattern moves throught the stadium, not the fans themselves.Īn especially simple form for a wave is a sinus wave, a regular pattern of wave crests and troughs. In a general sense: any travelling pattern, whether or not it involves matter being transported as well.
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