The Universe is everything that physically exists: the entirety of space and time, all forms of matter, energy and momentum, and the physical laws and physical constants that govern them. In a well-defined, mathematical sense, the universe can even be said to contain that which does not exist; according to the path-integral formulation of quantum mechanics, even unrealized possibilities contribute to the probability amplitudes of events in the universe. The universe is sometimes denoted as the cosmos or Nature, as in "cosmology" or "natural philosophy".
Scientific experiments have yielded several general facts about the observable universe. The age of the universe is estimated to be 13.7±0.2 billion years. The universe is very large, possibly infinite, being at least 93 billion light years across, and consisting mainly of matter, rather than antimatter. Only 4% of the matter and energy in the universe is luminous, that is, directly observable from its emitted electromagnetic radiation ("light" in its most general sense); the remainder consists of dark energy (73%) and dark matter (23%). The nature and composition of dark energy and dark matter are unknown. The luminous matter within the universe is sparse and consists principally of galaxies, which are distributed uniformly when averaged over length-scales longer than 300 million light years; on smaller length scales, galaxies tend to clump into clusters, superclusters and even larger structures. The light arriving from distant galaxies is detectably redshifted, with the redshift increasing with the galaxy's distance from Earth. The universe is bathed in a microwave radiation that is highly isotropic (uniform across different directions), and corresponds to a blackbody spectrum of roughly 2.7 Kelvin. The relative percentages of the lighter chemical elements — especially hydrogen, deuterium and helium — is apparently the same throughout the universe. The universe is expanding, in the sense that the distance between widely separated objects is increasing with time. The universe has at least three spatial dimensions and one temporal (time) dimension, although extremely small additional dimensions cannot be ruled out experimentally; spacetime appears to be smoothly and simply connected, with very small curvature, so that Euclidean geometry is accurate on the average throughout the universe. The universe appears to be governed by the same physical laws and constants throughout its extent and history.
Throughout their recorded history, humans have proposed several cosmologies and cosmogonies to account for their observations of the universe. The earliest quantitative models were developed by the ancient Greeks, who proposed that the universe possessed infinite space and had existed eternally, but contained a single set of concentric spheres of finite size (corresponding to the fixed stars, the Sun and various planets) rotating about a spherical but unmoving Earth. Over the centuries, more careful astronomical observations and improved theories of gravity led to Copernicus' heliocentric model and, eventually, to the present Lambda-CDM model of the Big Bang, which accounts for all the available data. According to such Big Bang theories, everything in the universe — all forms of matter and energy, and even spacetime itself — came into being at a single event, a gravitational singularity; as space expanded with time, the matter and energy cooled sufficiently to allow the stable condensation of elementary particles into the primordial nuclei and atoms. Once atoms formed, matter became transparent to most wavelengths of electromagnetic radiation; the ambient microwave radiation observed today is the residual radiation that decoupled from the matter.
According to the prevailing scientific models, the Universe is governed by the Standard Model of physics (which governs various forms of matter and fields), as well as special and general relativity (which govern spacetime and its interaction with matter and fields). On cosmological length scales, the dominant interaction in the universe is gravitation. Hence, the theory of general relativity (the most accurate description of gravity presently available) offers the best predictions for the overall development of the universe, including its origin, expansion (which mainly accounts for the observed redshift), large-scale structure and ultimate fate. However, components of the Standard Model — particularly those relating to nucleosynthesis, atomic spectra, and CP violation — are needed to account for other experimental observations, such as the distribution of chemical elements and microwave radiation throughout the universe, as well as the matter-antimatter asymmetry.
sum wierd guy posted all this in a thread i made, if that blew your mind your not the only one
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