|
Inhomogeneous Cosmology
An inhomogeneous cosmology is a physical cosmological theory (an astronomical model of the physical universe's origin and evolution) which, unlike the dominant cosmological concordance model, postulates that inhomogeneities in the distribution of matter across the universe affect local gravitational forces (i.e., at the galactic level) enough to skew our view of the Universe. When the universe began, matter was distributed homogeneously, but over billions of years, galaxies, clusters of galaxies, and superclusters coalesced. Einstein's theory of general relativity states that they warp the space-time around them. While the concordance model acknowledges this fact, it assumes that such inhomogeneities are not sufficient to affect large-scale averages of gravity observations. Two studies claimed in 1998-1999 that high redshift supernovae were further away than the distance predicted by calculations. It was suggested that the expansion of the universe was accelerating, and d ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Cosmological Principle
In modern physical cosmology, the cosmological principle is the notion that the spatial distribution of matter in the universe is uniformly isotropic and homogeneous when viewed on a large enough scale, since the forces are expected to act equally throughout the universe on a large scale, and should, therefore, produce no observable inequalities in the large-scale structuring over the course of evolution of the matter field that was initially laid down by the Big Bang. Definition Astronomer William Keel explains: The cosmological principle is usually stated formally as 'Viewed on a sufficiently large scale, the properties of the universe are the same for all observers.' This amounts to the strongly philosophical statement that the part of the universe which we can see is a fair sample, and that the same physical laws apply throughout. In essence, this in a sense says that the universe is knowable and is playing fair with scientists. As Andrew Liddle puts it, "the cosmologic ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Cosmological Constant
In cosmology, the cosmological constant (usually denoted by the Greek capital letter lambda: ), alternatively called Einstein's cosmological constant, is a coefficient that Albert Einstein initially added to his field equations of general relativity. He later removed it; however, much later it was revived to express the energy density of space, or vacuum energy, that arises in quantum mechanics. It is closely associated with the concept of dark energy. Einstein introduced the constant in 1917. to counterbalance the effect of gravity and achieve a static universe, which was then assumed. Einstein's cosmological constant was abandoned after Edwin Hubble confirmed that the universe was expanding. From the 1930s until the late 1990s, most physicists agreed with Einstein's choice of setting the cosmological constant to zero. That changed with the discovery in 1998 that the expansion of the universe is accelerating, implying that the cosmological constant may have a positive valu ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Static Universe
In cosmology, a static universe (also referred to as stationary, infinite, static infinite or static eternal) is a cosmological model in which the universe is both spatially and temporally infinite, and space is neither expanding nor contracting. Such a universe does not have so-called spatial curvature; that is to say that it is 'flat' or Euclidean. A static infinite universe was first proposed by English astronomer Thomas Digges (1546–1595). In contrast to this model, Albert Einstein proposed a temporally infinite but spatially finite model - ''static eternal universe'' - as his preferred cosmology during 1917, in his paper ''Cosmological Considerations in the General Theory of Relativity''. After the discovery of the redshift-distance relationship (deduced by the inverse correlation of galactic brightness to redshift) by American astronomers Vesto Slipher and Edwin Hubble, the Belgian astrophysicist and priest Georges Lemaître interpreted the redshift as evidence of ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Sphere
A sphere (from Ancient Greek, Greek , ) is a surface (mathematics), surface analogous to the circle, a curve. In solid geometry, a sphere is the Locus (mathematics), set of points that are all at the same distance from a given point in three-dimensional space.. That given point is the center (geometry), ''center'' of the sphere, and the distance is the sphere's ''radius''. The earliest known mentions of spheres appear in the work of the Greek mathematics, ancient Greek mathematicians. The sphere is a fundamental surface in many fields of mathematics. Spheres and nearly-spherical shapes also appear in nature and industry. Bubble (physics), Bubbles such as soap bubbles take a spherical shape in equilibrium. The Earth is spherical Earth, often approximated as a sphere in geography, and the celestial sphere is an important concept in astronomy. Manufactured items including pressure vessels and most curved mirrors and lenses are based on spheres. Spheres rolling, roll smoothly in ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Four-dimensional Space
Four-dimensional space (4D) is the mathematical extension of the concept of three-dimensional space (3D). Three-dimensional space is the simplest possible abstraction of the observation that one needs only three numbers, called ''dimensions'', to describe the sizes or locations of objects in the everyday world. This concept of ordinary space is called Euclidean space because it corresponds to EuclidEuclidean geometry, 's geometry, which was originally abstracted from the spatial experiences of everyday life. Single locations in Euclidean 4D space can be given as Vector space, vectors or ''n-tuples, 4-tuples'', i.e., as ordered lists of numbers such as . For example, the volume of a rectangular box is found by measuring and multiplying its length, width, and height (often labeled , , and ). It is only when such locations are linked together into more complicated shapes that the full richness and geometric complexity of 4D spaces emerge. A hint of that complexity can be seen in ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Shape Of The Universe
In physical cosmology, the shape of the universe refers to both its local and global geometry. Local geometry is defined primarily by its curvature, while the global geometry is characterised by its topology (which itself is constrained by curvature). General relativity explains how spatial curvature (local geometry) is constrained by gravity. The global topology of the universe cannot be deduced from measurements of curvature inferred from observations within the family of homogeneous general relativistic models alone, due to the existence of locally indistinguishable spaces with varying global topological characteristics. For example; a multiply connected space like a 3 torus has everywhere zero curvature but is finite in extent, whereas a flat simply connected space is infinite in extent (such as Euclidean space). Current observational evidence ( WMAP, BOOMERanG, and Planck for example) imply that the observable universe is spatially flat to within a 0.4% margin of error o ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
End Of Universe
End, END, Ending, or ENDS may refer to: End Mathematics *End (category theory) *End (topology) *End (graph theory) * End (group theory) (a subcase of the previous) * End (endomorphism) Sports and games *End (gridiron football) *End, a division of play in the sports of curling, target archery and pétanque * End (dominoes), one of the halves of the face of a domino Entertainment * End (band) an American hardcore punk supergroup *End key on a modern computer keyboard * End Poem, a narrative written by Julian Gough for ''Minecraft'' * End Records, a record label *"End", a song by The Cure from ''Wish'' * "Ends" (song) a 1998 song by Everlast, off the album ''Whitey Ford Sings the Blues'' * ''End'' (album), by Explosions in the Sky * "Ends" (''Spaced''), a television episode Other uses *End, in weaving, a single thread of the warp *''Ends (short story collection)'' (1988 book) anthology of Gordon R. Dickson stories END * European Nuclear Disarmament * Endoglin, a glycoprotein * ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Isotropy
In physics and geometry, isotropy () is uniformity in all orientations. Precise definitions depend on the subject area. Exceptions, or inequalities, are frequently indicated by the prefix ' or ', hence ''anisotropy''. ''Anisotropy'' is also used to describe situations where properties vary systematically, dependent on direction. Isotropic radiation has the same intensity regardless of the direction of measurement, and an isotropic field exerts the same action regardless of how the test particle is oriented. Mathematics Within mathematics, ''isotropy'' has a few different meanings: ; Isotropic manifolds: A manifold is isotropic if the geometry on the manifold is the same regardless of direction. A similar concept is homogeneity. ; Isotropic quadratic form: A quadratic form ''q'' is said to be isotropic if there is a non-zero vector ''v'' such that ; such a ''v'' is an isotropic vector or null vector. In complex geometry, a line through the origin in the direction of an is ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Curvature Of Space Time
In physics, curved spacetime is the mathematical model in which, with Einstein's theory of general relativity, gravity naturally arises, as opposed to being described as a fundamental force in Isaac Newton, Newton's static Euclidean reference frame. Objects move along Geodesics in general relativity, geodesics—curved paths determined by the local geometry of spacetime—rather than being influenced directly by distant bodies. This framework led to two fundamental principles: coordinate independence, which asserts that the laws of physics are the same regardless of the coordinate system used, and the equivalence principle, which states that the effects of gravity are indistinguishable from those of acceleration in sufficiently small regions of space. These principles laid the groundwork for a deeper understanding of gravity through the geometry of spacetime, as formalized in Einstein's field equations. Introduction Newton's theories assumed that motion takes place against the bac ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
John Wheeler (physicist)
John Archibald Wheeler (July 9, 1911April 13, 2008) was an American theoretical physicist. He was largely responsible for reviving interest in general relativity in the United States after World War II. Wheeler also worked with Niels Bohr to explain the basic principles of nuclear fission. Together with Gregory Breit, Wheeler developed the concept of the Breit–Wheeler process. He is best known for popularizing the term "black hole" for objects with gravitational collapse already predicted during the early 20th century, for inventing the terms "quantum foam", "neutron moderator", "wormhole" and "it from bit", and for hypothesizing the "one-electron universe". Stephen Hawking called Wheeler the "hero of the black hole story". At 21, Wheeler earned his doctorate at Johns Hopkins University under the supervision of Karl Herzfeld. He studied under Breit and Bohr on a National Research Council fellowship. In 1939 he collaborated with Bohr on a series of papers using the liquid d ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Void (astronomy)
Cosmic voids (also known as dark space) are vast spaces between Galaxy filament, filaments (the largest-scale structures in the universe), which contain void galaxy, very few or no Galaxy, galaxies. In spite of their size, most galaxies are not located in voids. This is because most galaxies are gravitationally bound together, creating huge cosmic structures known as galaxy filaments. The cosmological evolution of the void regions differs drastically from the evolution of the universe as a whole: there is a long stage when Shape_of_the_universe#Curvature_of_the_universe, the curvature term dominates, which prevents the formation of galaxy clusters and massive galaxies. Hence, although even the emptiest regions of voids contain more than ~15% of the average matter density of the universe, the voids look almost empty to an observer. Voids typically have a diameter of 10 to 100 Parsec#Megaparsecs and gigaparsecs, megaparsecs (30 to 300 million light-years); particularly large void ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
