He eventually noted that gravitational effects would be significant, but he did not calculate these effects and did not apply the results to cosmology. N 2 For example, the density of ordinary "cold" matter (dust) goes down as the inverse of the volume: when linear dimensions double, the energy density goes down by a factor of eight; the radiation energy density goes down even more rapidly as the Universe expands since the wavelength of each photon is stretched (redshifted), in addition to the photons being dispersed by the expansion.  While inflation depends on quantum field theory (and the semiclassical approximation to quantum gravity) in an important way, it has not been completely reconciled with these theories. Inflation attempts to resolve these problems by providing a dynamical mechanism that drives the Universe to this special state, thus making a universe like ours much more likely in the context of the Big Bang theory. Is the theory of cosmological inflation correct, and if so, what are the details of this epoch? s In 1980, to explain the conditions observed in the universe, astrophysicist Alan Guth proposed cosmic inflation. Linde proposed a theory known as chaotic inflation in which he suggested that the conditions for inflation were actually satisfied quite generically. This was quickly interpreted as meaning galaxies were receding from Earth. As things stand, there is no evidence of any 'slowing down' of the expansion, but this is not surprising as each cycle is expected to last on the order of a trillion years. A space with a cosmological constant is qualitatively different: instead of moving outward, the cosmological horizon stays put. The Universe passes through the Big Crunch and emerges in a hot Big Bang phase. Guth recognized that this model was problematic because the model did not reheat properly: when the bubbles nucleated, they did not generate any radiation. The detailed particle physics mechanism responsible for inflation is unknown. The bubble collision problem was solved by Linde and independently by Andreas Albrecht and Paul Steinhardt in a model named new inflation or slow-roll inflation (Guth's model then became known as old inflation). As the very early universe cooled it was trapped in a metastable state (it was supercooled), which it could only decay out of through the process of bubble nucleation via quantum tunneling. Though, as cosmologist Martin Rees has written, "Skeptics about exotic physics might not be hugely impressed by a theoretical argument to explain the absence of particles that are themselves only hypothetical. Cosmic inflation is a faster-than-light expansion of the universe that spawned many others. Today, a team of scientists announcedwhat they think may be the first evidence for cosmic inflation.  At the same time, Starobinsky argued that quantum corrections to gravity would replace the initial singularity of the Universe with an exponentially expanding de Sitter phase.  However, in his model the inflaton field necessarily takes values larger than one Planck unit: for this reason, these are often called large field models and the competing new inflation models are called small field models. r There are well-known theorems that this steady state cannot continue forever into the past. The new regions that come into view during the normal expansion phase are exactly the same regions that were pushed out of the horizon during inflation, and so they are at nearly the same temperature and curvature, because they come from the same originally small patch of space. String theory requires that, in addition to the three observable spatial dimensions, additional dimensions exist that are curled up or compactified (see also Kaluza–Klein theory). − Get breaking space news and the latest updates on rocket launches, skywatching events and more! Nevertheless, many physicists, mathematicians, and philosophers of science have voiced criticisms, claiming untestable predictions and a lack of serious empirical support. Inflation answers this question by postulating that all the regions come from an earlier era with a big vacuum energy, or cosmological constant. Following the inflationary period, the universe continued to expand, but at a slower rate. I passed over Cosmic Inflation theory only recently, as compared to Big Bang, and one of the difference between the two is the timing as to when each happened, with, obviously, Big Bang occurring first. .  The flatness and horizon problems are naturally solved in the Einstein-Cartan-Sciama-Kibble theory of gravity, without needing an exotic form of matter or free parameters. You will receive a verification email shortly. ... Kazanas (1980) called this phase of the early Universe "de Sitter's phase."  From Planck data it can be inferred that ns=0.968 ± 0.006, and a tensor to scalar ratio that is less than 0.11.  This theory extends general relativity by removing a constraint of the symmetry of the affine connection and regarding its antisymmetric part, the torsion tensor, as a dynamical variable. 1 2.b) The Big Bang Theory and Inflation. Guth and Linde had worked out the beginnings of the theory of cosmic inflation. ", A recurrent criticism of inflation is that the invoked inflaton field does not correspond to any known physical field, and that its potential energy curve seems to be an ad hoc contrivance to accommodate almost any data obtainable. Inflation resolves several problems in Big Bang cosmology that were discovered in the 1970s. Support for the theory of cosmic inflation comes from the Cosmic Microwave Background, or CMB, a pattern of light released when the early universe first cooled enough for particles to travel freely through it. The basic inflationary paradigm is accepted by most physicists, as a number of inflation model predictions have been confirmed by observation; however, a substantial minority of scientists dissent from this position. There is evidence for a slight deviation from scale invariance. Many other observations agree, and also lead to the same conclusion. ], stable magnetic monopoles would have been produced. And if you have a news tip, correction or comment, let us know at: email@example.com.  It was discovered that Einstein's universe is unstable, and that small fluctuations cause it to collapse or turn into a de Sitter universe. ", "Inflation Debate: Is the theory at the heart of modern cosmology deeply flawed? Penrose's shocking conclusion, though, was that obtaining a flat universe without inflation is much more likely than with inflation – by a factor of 10 to the googol (10 to the 100) power! Vilenkin put forth one such scenario. Like Guth, they concluded that such a model not only required fine tuning of the cosmological constant, but also would likely lead to a much too granular universe, i.e., to large density variations resulting from bubble wall collisions. This is a problem with Grand Unified Theories, which propose that at high temperatures (such as in the early universe) the electromagnetic force, strong, and weak nuclear forces are not actually fundamental forces but arise due to spontaneous symmetry breaking from a single gauge theory. Time as the universe is continuously inflating at any given time, energy densities generally fall or. 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