dark matter..?
Dark matter's existence is inferred from gravitational effects on visible matter and gravitational lensing of background radiation, and was originally hypothesized to account for discrepancies between calculations of the mass of galaxies, clusters of galaxies and the entire universe made through dynamical and general relativistic means, and calculations based on the mass of the visible "luminous" matter these objects contain: stars and the gas and dust of the interstellar and intergalactic medium.[1] The most widely accepted explanation for these phenomena is that dark matter exists and that it is most likely[3] composed of heavy particles that interact only through gravity and possibly the weak force;
however, alternate explanations have been proposed, and there is not
yet sufficient experimental evidence to determine which is correct. Many
experiments to detect proposed dark matter particles through
non-gravitational means are underway.[5]
According to observations of structures larger than solar systems, as well as Big Bang cosmology interpreted under the Friedmann equations and the FLRW metric, dark matter accounts for 23% of the mass-energy content of the observable universe. In comparison, ordinary matter accounts for only 4.6% of the mass-energy content of the observable universe, with the remainder being attributable to dark energy.[6] From these figures, dark matter constitutes 83%, (23/(23+4.6)), of the matter in the universe, whereas ordinary matter makes up only 17%.
As important as dark matter is thought to be in the cosmos, direct evidence of its existence and a concrete understanding of its nature have remained elusive. Though the theory of dark matter remains the most widely accepted theory to explain the anomalies in observed galactic rotation, some alternative theoretical approaches have been developed which broadly fall into the categories of modified gravitational laws and quantum gravitational laws.[8]
According to observations of structures larger than solar systems, as well as Big Bang cosmology interpreted under the Friedmann equations and the FLRW metric, dark matter accounts for 23% of the mass-energy content of the observable universe. In comparison, ordinary matter accounts for only 4.6% of the mass-energy content of the observable universe, with the remainder being attributable to dark energy.[6] From these figures, dark matter constitutes 83%, (23/(23+4.6)), of the matter in the universe, whereas ordinary matter makes up only 17%.
As important as dark matter is thought to be in the cosmos, direct evidence of its existence and a concrete understanding of its nature have remained elusive. Though the theory of dark matter remains the most widely accepted theory to explain the anomalies in observed galactic rotation, some alternative theoretical approaches have been developed which broadly fall into the categories of modified gravitational laws and quantum gravitational laws.[8]
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