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According to the Big Bang theory, the universe originated in an infinitely dense and physically paradoxical singularity. Space has expanded with the passage of time, objects being moved farther away from each other.
In cosmology, the Big Bang theory is the prevailing scientific theory about the early development and shape of the universe. The central idea is that the observation that galaxies appear to be receding from each other can be combined with the theory of general relativity to extrapolate the conditions of the universe back in time. This leads to the conclusion that as one goes back in time, the universe becomes increasingly hot and dense.
There are a number of consequences to this view. One consequence is that the universe now is very different than the universe in the past or in the future. The Big Bang theory predicts that at some point, the matter in the universe was hot and dense enough to prevent light from flowing freely in space. That this period of the universe would be observable in the form of cosmic background radiation (CBR) was first predicted in the 1940s, and the discovery of such radiation in the 1960s swung most scientific opinion against the Big Bang theory's chief rival, the steady state theoryFor alternative meanings see steady state (disambiguation). The steady state theory is a model developed in 1949 by Fred Hoyle, Thomas Gold and others as an alternative to the Big Bang theory. Although the model had a large number of supporters among cosm.
Using current physical theories to extrapolate the Hubble expansion of the universe backwards leads to a gravitational singularityA gravitational singularity occurs when an astrophysical model, typically based on general relativity, predicts a point of infinite curvature. The term is closely related to the mathematical meaning of "singularity": a gravitational singularity occurs whe, at which all distances become zero and temperatures and pressures become infinite. What this means is unclear, and most physicists believe that this is because of our limited understanding of the laws of physicsThe following are some of the unsolved problems in physics . This is an incomplete list of outstanding problems in physics. Some of these problems are theoretical, meaning that existing theories seem incapable of explaining some observed phenomenon or exp with regard to this type of situation, and in particular, the lack of a theory of quantum gravityQuantum gravity is the field of theoretical physics attempting to unify the theory of quantum mechanics, which describes three of the fundamental forces of nature, with general relativity, the theory of the fourth fundamental force: gravity. The ultimate.
There are actually many theories about the Big Bang. Some theories purport to explain the cause of the Big Bang itself, and as such have been criticized as being modern creation myths. Some people believe that the Big Bang theory lends support to traditional views of creation, for example as given in GenesisThis article is about Genesis the first book of the Hebrew Bible. See Genesis (disambiguation) for other usages of the word. Genesis ( Greek: , having the meanings of "birth", "creation", "cause", "beginning", "source" and "origin"; translated from Hebrew, while others believe that all Big Bang theories are inconsistent with such views. The relationship between religion and the Big Bang theory is discussed below.
Based on measurements of the expansion of the universe using type I supernovae, measurements of the lumpiness of the cosmic microwave background, and measurements of the correlation function of galaxies, it is currently believed that the universe has an age of 13.7 ± 0.2 billion years. The fact that these three separate measurements of completely different things are all consistent with each other is considered strong evidence for the model.
The universe as we know it was initially almost uniformly filled with energy and extremely hot. As the distances in the universe rapidly grew, the temperature dropped, leading to the creation of the known forces of physics, elementary particles, and eventually hydrogen and helium atoms in a process called Big bang nucleosynthesis.
Over time, the slightly denser regions of the almost, but not quite, uniformly distributed matter were pulled together by gravity into clumps, forming gas clouds, stars, galaxies, and the other astronomical structures seen today. The details of how the process of galaxy formation occurred depends on the type of matter in the universe, and the three competing pictures of how this occurred are based on the properties of three types of matter known as cold dark matter, hot dark matter, and baryonic matter. These three models have been tested through computer simulations and observations of galactic correlation functions. The best measurements available (from WMAP) show that the dominant form of matter in the universe is in the form of cold dark matter. The other two types of matter make up less than 20% of the matter in the universe.
It is at present unknown whether the singularity of spacetime described above is a physical reality or just a mathematical extrapolation of general relativity beyond its limits of applicability. The resolution of this depends on a theory of quantum gravity, which is not currently available. Nevertheless, there has been intense theoretical work on trying to figure out what happened before the Big Bang. Some of these efforts involve the ekpyrotic universe, and there has also been interest in the anthropic principle.
In general relativity, one usually talks about spacetime and cannot cleanly separate space from time. In the Big Bang theory, this difficulty does not arise; Weyl's postulate is assumed and time can be unambiguously measured at any point as the "time since the Big Bang". Measurements in this system rely on so-called conformal distances and times which removes the expansion of the universe from consideration of spacetime measurements.
The Big Bang was not an explosion of matter moving outward to fill an empty universe; it is space itself that is expanding. So, bizarre as it may seem, the distance between any two fixed points in our universe is increasing. Intuitively this seems impossible: if the distance between two things increases then it seems that by definition one or both must be moving. But this is not so, as becomes clear if one considers the simplistic but logically equivalent model of a universe of constant size (whether finite or infinite), in which everything is shrinking. The people who live in this universe are shrinking too, as are all their scientific instruments. When these people measure the distance between two points that are sufficiently far apart, the distance will seem to be increasing, because the yardsticks they use to measure with are shrinking along with everything else. The fundamental assumption in this idea is that spacetime on the largest scales is unaffected by locality; objects that are bound together do not expand with spacetime's expansion because local forces keep them together. The expansion of the universe on local scales is so small that the difference of any local forces is unmeasurable by current techniques.
Because it is space itself that is expanding, and not a case of objects flying apart through space, the distance (in the sense of comoving distance) between far removed galaxies can increase faster than the speed of light without violating the laws of special relativity.
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