Expansion of the Universe

With the assumption, and it is a big assumption, that the rate of expansion of the Universe has been constant, then the time of expansion so far is given by ... 

The expansion of the Universe is governed by the field equations of General Relativity for isotropic expansion or contraction ... 

Observations of distant supemovae indicate expansion of the Universe accelerating. 

Today we would hesitate to comment on the energy or entropy of the universe, because we have no way to measure these quantities, and we would refer only to the surroundings that are observed to interact with the system. Some cosmological theorists have suggested that the increase in entropy posmlated by the second law is a result of the expansion of the universe [6]. One recent set of astronomical measurements leads to a prediction that the universe will continue to expand, and another predicts that expansion will reach a maximum and reverse [7]. 

Physics is also concerned with the very large think about cosmology and astrophysics. Issues include the beginning of the universe, known as the Big Bang, which occurred some 13.7 billion years ago, the expansion of the universe, formation and evolution of stars and galaxies, and properties of black holes. Here too there are connections between physics and chemistry the origin of the atoms in nuclear reactions within stars and the nature of molecules found in interstellar space, for example. 

As is well known, the expansion of the Universe was revealed through the redshifting of light from distant galaxies. The fate of such a dynamic universe then became one of the main questions to be addressed by cosmology. 

The expansion of the Universe is accelerating The news is too recent to accept without reserve. It must be checked again and again, in the most critical spirit, and yet with open mind, for it is of the utmost importance. 

This world cannot be motionless. It must move if it is not to collapse. The planets revolve around the stars, whilst the stars whirl around the centre of the Galaxy. Galaxies themselves form moving swarms called clusters, and these clusters move away from one another, swept along by the expansion of the Universe. If they did not, they would simply hurl themselves together under the effect of gravity. The Universe is expanding, and it is this that saves it from collapse. Everywhere and on every scale, motions clearly oppose fall. 

Apart from rotating about their axes, the galaxies display systematic motions relative to one another. In fact, they are moving apart at speeds proportional to the distance between them. The recession speed amounts to some 100 km s for every 3 million light-years of separation. This overall motion is the clearest evidence we have for the expansion of the Universe. 

How did the galaxies and protogalaxies form How did matter gather up in this way, despite the expansion of the Universe which tends rather to dilute it ... 

As the weak interaction is the slowest of all, it was the first to find itself unable to keep up with the rapid expansion of the Universe. The neutrinos it produces, which serve as an indicator of the weak interaction, were the first to experience decoupling, the particle equivalent of social exclusion. By the first second, expansion-cooled neutrinos ceased to interact with other matter in the form of protons and neutrons. This left the latter free to organise themselves into nuclei. Indeed, fertile reactions soon got under way between protons and neutrons. However, the instability of species with atomic masses between 5 and 8 quickly put paid to this first attempt at nuclear architecture. The two species of nucleon, protons and neutrons, were distributed over a narrow range of nuclei from hydrogen to lithium-7, but in a quite unequal way. 

Perlmutter, Riess, Smith Acceleration of the expansion of the Universe... 

Because of the expansion of the universe, the stars and other celestial bodies are all moving away from each other. This phenomenon is known as... 

Ya.B. s love for and unrelenting interest in the theory of elementary particles have maintained his interest in the problem of the earliest stages of expansion of the Universe, in the search for the reasons for the creation of our world, and in the nature of the first metric and density fluctuations which later led to the formation of the observed structure of the Universe. 

In the theory of formation of the large-scale structure of the Universe which Ya.B. constructed the expansion of the Universe and mutual attraction of particles are also taken into account, but the qualitative results are close to the results of the model problem. 

Therefore, the fact that more distant stars are more redshifted (the Hubble effect) does not prove that they are moving away from us, only that they are moving at higher velocities than those stars that are closer by. Such a situation appear quite natural. Stars might move in a random way, but move faster the farther away they are. Perhaps because they are just like water molecules in a turbulent river, or perhaps even simpler, because they rotate in relation to a larger universe. In either case there would be a redshift that increases with distance. Thus, the expansion of the universe and the big bang are not directly proved by a redshift of distant stars. 

It is apparent that the numbers and masses of the flavor and quark-lepton transforming gauge bosons are larger than those of the SU(5) minimal model. This means that the value of a is lower, and assuming that the duration of the inflationary period is fixed, the scale for the expansion of the universe is reduced. This means that there is the enhanced prospect for deviations from flatness. So one may presume that the universe started as a small 3-sphere with a large curvature, where the inflationary period flattened out the universe, but maybe not completely. This leaves open the prospect that if before inflation that if the universe were open or closed, k = 1, that the universe today still contains this structure on a sufficiently large scale. The closer to flatness the universe is, the tighter are the constraints on the masses of particles in the early universe. 

On a cosmic scale, the second law is in agreement with the currently accepted theory of the expansion of the universe from an initial, highly located Big Bang. ... 

The expansion of the Universe in encoded into the time dependence of the scale factor ad ). The quantity t corresponds to the cosmic time. One can easily show that observers situated at xl = Const follow geodesics, therefore cosmic time corresponds to the proper time of such observers. It is assumed that any matter element is at rest or almost at rest with respect to the spatial part of the coordinate system. For this reason, the xl are called comoving coordinates, and any distance measured using line element ijdx dx3 is called comoving distance. 

The Cosmic Microwave Background (as discussed, for example, in Ned Wright s contribution to this volume), is, along with the expansion of the Universe and the abundance of the light elements, one of the three so-called pil-... 

Although these are the equations that we would right down from first principles in a Newtonian analysis, they are also the small-scale and small-velocity limit of General Relativity. To account for the expansion of the Universe, we change to comoving coordinates, r and peculiar velocity, u, defined from physical coordinates, x, and velocities, v as... 

In a Universe dominated instead by curvature or an accelerating component such as a cosmological constant, the expansion of the universe is more rapid than in a matter dominated universe. In both of these cases, there is no longer a growing mode neither solution to Equation 10.10 grows with time. 

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