Rapid expanse definition8/4/2023 ![]() ![]() ![]() In the early universe before recombination and decoupling took place, photons and matter existed in a primordial plasma. Main article: Baryon acoustic oscillations See also the section on Alternate theories below. For example, a 2019 paper analyzed the Joint Light-curve Analysis catalog of Type Ia supernovas, containing ten times as many supernovas as were used in the 1998 analyses, and concluded that there was little evidence for a "monopole", that is, for an isotropic acceleration in all directions. Several researchers have questioned the majority opinion on the acceleration or the assumption of the " cosmological principle" (that the universe is homogeneous and isotropic). This means that the measured high-redshift distances were too large, compared to nearby ones, for a decelerating universe. found that "the distances of the high-redshift SNe Ia were, on average, 10% to 15% farther than expected in a low mass density Ω M = 0.2 universe without a cosmological constant". ![]() This results in a larger light-travel time, larger distance and fainter supernovae, which corresponds to the actual observations. H 2 = ( a ˙ a ) 2 = 8 π G 3 ρ − κ c 2 a 2 and the same present-day value of the Hubble constant. The Friedmann equation defines how the energy in the universe drives its expansion. In the decades since the detection of cosmic microwave background (CMB) in 1965, the Big Bang model has become the most accepted model explaining the evolution of our universe. While there are alternative possible explanations, the description assuming dark energy (positive Λ) is used in the current standard model of cosmology, which also includes cold dark matter (CDM) and is known as the Lambda-CDM model.įurther information: Cosmological constant, Lambda-CDM model, Hubble's law, Friedmann–Lemaître–Robertson–Walker metric, and Friedmann equations Within the framework of general relativity, an accelerated expansion can be accounted for by a positive value of the cosmological constant Λ, equivalent to the presence of a positive vacuum energy, dubbed " dark energy". The accelerated expansion of the universe is thought to have begun since the universe entered its dark-energy-dominated era roughly 5 billion years ago. Confirmatory evidence has been found in baryon acoustic oscillations, and in analyses of the clustering of galaxies. Three members of these two groups have subsequently been awarded Nobel Prizes for their discovery. Cosmologists at the time expected that recession velocity would always be decelerating, due to the gravitational attraction of the matter in the universe. The unexpected result was that objects in the universe are moving away from one another at an accelerated rate. The distance can then be compared to the supernovae's cosmological redshift, which measures how much the universe has expanded since the supernova occurred the Hubble law established that the further an object is from us, the faster it is receding. The idea was that as type Ia supernovae have almost the same intrinsic brightness (a standard candle), and since objects that are further away appear dimmer, we can use the observed brightness of these supernovae to measure the distance to them. The accelerated expansion of the universe was discovered during 1998 by two independent projects, the Supernova Cosmology Project and the High-Z Supernova Search Team, which both used distant type Ia supernovae to measure the acceleration. Observations show that the expansion of the universe is accelerating, such that the velocity at which a distant galaxy recedes from the observer is continuously increasing with time. The timeline in this schematic diagram extends from the Big Bang/inflation era 13.7 billion years ago to the present cosmological time. Lambda-CDM, accelerated expansion of the universe. ![]()
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