Langsung ke konten utama


The expansion of the universe is the increase of the distance between two distant parts of the universe with time.[1] It is an intrinsic expansion whereby the scale of space itself changes. The universe does not expand "into" anything and does not require space to exist "outside" it. Technically, neither space nor objects in space move. Instead it is the metric governing the size and geometry of spacetime itself that changes in scale. Although light and objects within spacetime cannot travel faster than the speed of light, this limitation does not restrict the metric itself. To an observer it appears that space is expanding and all but the nearest galaxies are receding into the distance.

 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 1078 (an expansion of distance by a factor of at least 1026 in each of the three dimensions), 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 1017 m or 62 trillion miles) long. 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 today.

 The metric expansion of space is a completely different kind of expansion than the expansions and explosions seen in daily life. It also seems to be a property of the universe as a whole rather than a phenomenon that applies just to one part of the universe or can be observed from "outside" it.

 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. However, the model is valid only on large scales (roughly the scale of galaxy clusters and above), because gravitational attraction binds matter together strongly enough that metric expansion cannot be observed at this time, on a smaller scale. 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.

 Physicists have postulated the existence of dark energy, appearing as a cosmological constant in the simplest gravitational models as a way to explain the acceleration. According to the simplest extrapolation of the currently-favored cosmological model, the Lambda-CDM model, this acceleration becomes more dominant into the future. 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.[2]

 While special relativity prohibits objects from moving faster than light with respect to a local reference frame where spacetime can be treated as flat and unchanging, it does not apply to situations where spacetime curvature or evolution in time become important. These situations are described by general relativity, which allows the separation between two distant objects to increase faster than the speed of light, although the definition of "separation" is different from that used in an inertial frame. This can be seen when observing distant galaxies more than the Hubble radius away from us (approximately 4.5 gigaparsecs or 14.7 billion light-years); these galaxies have a recession speed that is faster than the speed of light. Light that is emitted today from galaxies beyond the cosmological event horizon, about 5 gigaparsecs or 16 billion light-years, will never reach us, although we can still see the light that these galaxies emitted in the past. Because of the high rate of expansion, it is also possible for a distance between two objects to be greater than the value calculated by multiplying the speed of light by the age of the universe. These details are a frequent source of confusion among amateurs and even professional physicists.[3] Due to the non-intuitive nature of the subject and what has been described by some as "careless" choices of wording, certain descriptions of the metric expansion of space and the misconceptions to which such descriptions can lead are an ongoing subject of discussion within education and communication of scientific concepts.

 Source: Wikipedia

Komentar

Posting Komentar

Postingan populer dari blog ini

Study suggests Mars hosted life-sustaining habitat for millions of years

In a new study announced on Monday and available in the current volume of Earth and Planetary Science Letters, an international team led by scientists from Brown University in the United States said the planet Mars once had the right water and temperatures to host simple life forms — just not on its surface. Mars's rocky, subterranean layer once, for some hundreds of millions of years, had enough water and reductants to support some of the same kinds of microbial communities seen on Earth. "We showed, based on basic physics and chemistry calculations, that the ancient Martian subsurface likely had enough dissolved hydrogen to power a global subsurface biosphere," reported lead author and current Brown graduate student Jesse Tarnas. The paper does not claim life on Mars did exist but rather that conditions suitable for life are very likely to have lasted for an extended time. This habitable zone, located beneath Mars's then-frozen surface, would have reached
1 komentar
Baca selengkapnya

Was a giant planet ejected from our solar system?

A fifth giant planet was kicked out of the early solar system, according to computer simulations by a US-based planetary scientist. The sacrifice of this gas giant paved the way for the stable configuration of planets seen today, says David Nesvorný, who believes that the expulsion prevented Jupiter from migrating inwards and scattering the Earth and its fellow inner planets. The Nice model (named after the city in France where it was devised) is currently the best explanation of why the solar system looks the way it does today. It describes how early gravitational interactions between the large outer planets and planetesimals – smaller bodies that are the building blocks of planets – would have scattered the latter throughout the solar system. This accounts for the period known as the “late heavy bombardment”, the scars of which bodies such as the Moon still bear today. It also helps explain the structure of the asteroid and Kuiper belts. However, for the model to work, the plane
Posting Komentar
Baca selengkapnya

Extraterrestrial life, Alien?

Extraterrestrial life,[n 1] also called alien life (or, if it is a sentient or relatively complex individual, an "extraterrestrial" or "alien"), is life that occurs outside of Earth and that probably did not originate from Earth. These hypothetical life forms may range from simple prokaryotes to beings with civilizations far more advanced than humanity.[1][2] The Drake equation speculates about the existence of intelligent life elsewhere in the universe. The science of extraterrestrial life in all its forms is known as exobiology. Since the mid-20th century, there has been an ongoing search for signs of extraterrestrial life. This encompasses a search for current and historic extraterrestrial life, and a narrower search for extraterrestrial intelligent life. Depending on the category of search, methods range from the analysis of telescope and specimen data[3] to radios used to detect and send communication signals. The concept of extraterrestrial life, and p
Posting Komentar
Baca selengkapnya