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A space for the unbound physical11/10/2023 ![]() ![]() According to Ian Steer of the NASA/IPAC Extragalactic Database of Galaxy Distances, "Lundmark's extragalactic distance estimates were far more accurate than Hubble's, consistent with an expansion rate (Hubble constant) that was within 1% of the best measurements today." ![]() 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. Slipher discovered that light from remote galaxies was redshifted, which was later interpreted as galaxies receding from the Earth. 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. Cosmic expansion subsequently decelerated down to much slower rates, 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. 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). Although cosmic expansion is often framed as a consequence of general relativity, it is also predicted by Newtonian gravity. Contrary to common misconception, it is equally valid to adopt a description in which space does not expand and objects simply move apart under the influence of their mutual gravity. However, this is not a generally covariant description but rather only a choice of coordinates. ![]() Within this framework, stationary objects separate over time because space is expanding. It can be modeled mathematically with the Friedmann–Lemaître–Robertson–Walker metric, where it corresponds to an increase in the scale of the spatial part of the universe's spacetime metric (which governs the size and geometry of spacetime). While objects cannot move faster than light, this limitation only applies with respect to local reference frames and does not limit the recession rates of cosmologically distant objects.Ĭosmic expansion is a key feature of Big Bang cosmology. To any observer in the universe, it appears that all but the nearest galaxies (which are bound by gravity) recede at speeds that are proportional to their distance from the observer, on average. It is an intrinsic expansion the universe does not expand "into" anything and does not require space to exist "outside" it. The expansion of the universe is the increase in distance between gravitationally unbound parts of the observable universe with time. ![]()
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