No evidence of quintessence is yet available, but it has not been ruled out either. Ninety-five percent of the energy in the universe is of unknown origin, and is classified as either "dark energy" or "dark … [20] and in Perlmutter et al.,[21] and the Lambda-CDM model then became the leading model. This image shows the distribution of dark matter, galaxies, and hot gas in the core of the merging galaxy cluster Abell 520. It turns out that roughly 68% of the universe is dark energy. The large difference between these two supports a smooth component of dark energy making up the difference. Two proposed forms of dark energy are the cosmological constant,[11][12] representing a constant energy density filling space homogeneously, and scalar fields such as quintessence or moduli, dynamic quantities having energy densities that can vary in time and space. Eventually theorists came up with three sorts of explanations. Thus, it provides a direct estimate of the Hubble parameter. [31] Some people argue that the only indications for the existence of dark energy are observations of distance measurements and their associated redshifts. Cosmologists believe about 70 percent of the universe consists of dark energy, 25 percent is dark matter, and only four percent normal matter (the stuff that stars, planets and people are made of). The evidence for dark energy is heavily dependent on the theory of general relativity. For a cosmological constant, or any other model that predicts that the acceleration will continue indefinitely, the ultimate result will be that galaxies outside the Local Group will have a line-of-sight velocity that continually increases with time, eventually far exceeding the speed of light. For radiation, the decrease in energy density is greater, because an increase in spatial distance also causes a redshift.[26]. See also big bang. Specifically, when the volume of the universe doubles, the density of dark matter is halved, but the density of dark energy is nearly unchanged (it is exactly constant in the case of a cosmological constant). [76] A laboratory direct detection attempt failed to detect any force associated with dark energy.[46]. Measurements of the cosmic microwave background suggest the universe began in a hot Big Bang, from which general relativity explains its evolution and the subsequent large scale motion. The standard model of cosmology indicates that the total mass - energy of the universe contains 4.9% ordinary matter, 26.8% dark matter and 68.3% dark energy Thus, dark matter constitutes 84.5% of total mass, while dark energy plus dark matter constitute 95.1% of total mass–energy content. The significant focus of The 4 Percent Universe is on the developments of astronomical science in the 20th century, including the formation of the … Come to think of it, maybe it shouldn't be called "normal" matter at all, since it is such a small fraction of the universe. Dark energy. Well, if we knew exactly we would have a nobel prize – we know that they exist though. Type Ia supernovae are the best-known standard candles across cosmological distances because of their extreme and consistent luminosity. Using baryon acoustic oscillations, it is possible to investigate the effect of dark energy in the history of the Universe, and constrain parameters of the equation of state of dark energy. The remaining portion of the universe consists of ordinary matter and dark matter . This can be understood intuitively: for an ordinary particle in a cube-shaped box, doubling the length of an edge of the box decreases the density (and hence energy density) by a factor of eight (23). In the Friedmann–Lemaître–Robertson–Walker metric, it can be shown that a strong constant negative pressure in all the universe causes an acceleration in the expansion if the universe is already expanding, or a deceleration in contraction if the universe is already contracting. In order for it not to clump and form structure like matter, the field must be very light so that it has a large Compton wavelength. Here are a few possible explanations physicists are currently looking into for this strange form of matter. Dark matter and dark energy Ordinary matter makes up just 5 percent of the contents of the universe; the remaining 95 percent is made of dark matter and dark energy. So the expansion of the universe has not been slowing due to gravity, as everyone thought, it has been accelerating. Has not been observed, but it has not been slowing due to,. 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