Unbound worlds apart map5/15/2023 Swedish astronomer Knut Lundmark was the first person to find observational evidence for expansion in 1924. In 1922, Alexander Friedmann used Einstein field equations to provide theoretical evidence that the universe is expanding. In 1912, Vesto Slipher discovered that light from remote galaxies was redshifted, which was later interpreted as galaxies receding from the Earth. In June 2016, NASA and ESA scientists reported that the universe was found to be expanding 5% to 9% faster than thought earlier, based on studies using the Hubble Space Telescope. According to the simplest extrapolation of the currently favored cosmological model, the Lambda-CDM model, this acceleration becomes more dominant into the future. Physicists have postulated the existence of dark energy, appearing as a cosmological constant in the simplest gravitational models, as a way to explain this late-time acceleration. A much slower and gradual expansion of space continued after this, until at around 9.8 billion years after the Big Bang (4 billion years ago) it began to gradually expand more quickly, and is still doing so. This would be equivalent to expanding an object 1 nanometer (10 −9 m, about half the width of a molecule of DNA) in length to one approximately 10.6 light years (about 10 17 m or 62 trillion miles) long. As such, the only galaxies receding from one another as a result of metric expansion are those separated by cosmologically relevant scales larger than the length scales associated with the gravitational collapse that are possible in the age of the universe given the matter density and average expansion rate.Īccording to inflation theory, during the inflationary epoch about 10 −32 of a second after the Big Bang, the universe suddenly expanded, and its volume increased by a factor of at least 10 78 (an expansion of distance by a factor of at least 10 26 in each of the three dimensions). However, the model is valid only on large scales (roughly the scale of galaxy clusters and above), because gravity binds matter together strongly enough that metric expansion cannot be observed on a smaller scale at this time. Metric expansion is a key feature of Big Bang cosmology, is modeled mathematically with the Friedmann–Lemaître–Robertson–Walker metric and is a generic property of the universe we inhabit. Therefore, unlike other expansions and explosions, it cannot be observed from "outside" of it it is believed that there is no "outside" to observe from. It is a property of the universe as a whole and occurs throughout the universe, rather than happening just to one part of the universe. Objects that recede beyond the cosmic event horizon will eventually become unobservable, as no new light from them will be capable of overcoming the universe's expansion, limiting the size of our observable universe.Īs an effect of general relativity, the expansion of the universe is different from the expansions and explosions seen in daily life. While objects within space cannot travel faster than light, this limitation does not apply to the effects of changes in the metric itself. ![]() To any observer in the universe, it appears that all of space is expanding, and that all but the nearest galaxies (which are bound by gravity) recede at speeds that are proportional to their distance from the observer. ![]() As the spatial part of the universe's spacetime metric increases in scale, objects become more distant from one another at ever-increasing speeds. This expansion involves neither space nor objects in space "moving" in a traditional sense, but rather it is the metric (which governs the size and geometry of spacetime itself) that changes in scale. The universe does not expand "into" anything and does not require space to exist "outside" it. It is an intrinsic expansion whereby the scale of space itself changes. The expansion of the universe is the increase in distance between any two given gravitationally unbound parts of the observable universe with time.
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