In Alan Guth realized that false vacuum decay in the early universe would solve the problem, leading him to propose a scalar-driven inflation. Early inflationary models Guth proposed inflation in January to explain the nonexistence of magnetic monopoles;   it was Guth who coined the term "inflation". 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. The physical size of the Hubble radius solid line as a function of the linear expansion scale factor of the universe.
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In Alan Guth realized that false vacuum decay in the early universe would solve the problem, leading him to propose a scalar-driven inflation. Early inflationary models Guth proposed inflation in January to explain the nonexistence of magnetic monopoles;   it was Guth who coined the term "inflation". 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.
The physical size of the Hubble radius solid line as a function of the linear expansion scale factor of the universe.
During cosmological inflation, the Hubble radius is constant. The physical wavelength of a perturbation mode dashed line is also shown. The plot illustrates how the perturbation mode grows larger than the horizon during cosmological inflation before coming back inside the horizon, which grows rapidly during radiation domination.
If cosmological inflation had never happened, and radiation domination continued back until a gravitational singularity , then the mode would never have been inside the horizon in the very early universe, and no causal mechanism could have ensured that the universe was homogeneous on the scale of the perturbation mode.
Guth proposed that as the early universe cooled, it was trapped in a false vacuum with a high energy density, which is much like a cosmological constant.
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. Bubbles of true vacuum spontaneously form in the sea of false vacuum and rapidly begin expanding at the speed of light.
Guth recognized that this model was problematic because the model did not reheat properly: when the bubbles nucleated, they did not generate any radiation.
Radiation could only be generated in collisions between bubble walls. But if inflation lasted long enough to solve the initial conditions problems, collisions between bubbles became exceedingly rare.
In any one causal patch it is likely that only one bubble would nucleate. Guth himself did not refer to work of Kazanas until he published a book on the subject under the title "The inflationary universe: the quest for a new theory of cosmic origin" , where he apologizes for not having referenced the work of Kazanas and of others, related to inflation. In this model, instead of tunneling out of a false vacuum state, inflation occurred by a scalar field rolling down a potential energy hill.
When the field rolls very slowly compared to the expansion of the Universe, inflation occurs. However, when the hill becomes steeper, inflation ends and reheating can occur. Effects of asymmetries Main article: Primordial fluctuations Eventually, it was shown that new inflation does not produce a perfectly symmetric universe, but that quantum fluctuations in the inflaton are created.
These fluctuations form the primordial seeds for all structure created in the later universe. In addition, it accounts for the observed flatness and absence of magnetic monopoles.
Inflation predicts that the structures visible in the Universe today formed through the gravitational collapse of perturbations that were formed as quantum mechanical fluctuations in the inflationary epoch.
The detailed form of the spectrum of perturbations, called a nearly-scale-invariant Gaussian random field is very specific and has only two free parameters. One is the amplitude of the spectrum and the spectral index , which measures the slight deviation from scale invariance predicted by inflation perfect scale invariance corresponds to the idealized de Sitter universe. The simplest inflation models, those without fine-tuning , predict a tensor to scalar ratio near 0.
This structure for the perturbations has been confirmed by the Planck spacecraft , WMAP spacecraft and other cosmic microwave background CMB experiments, and galaxy surveys , especially the ongoing Sloan Digital Sky Survey. There is evidence for a slight deviation from scale invariance. The simplest inflation models predict that ns is between 0. These are considered an important confirmation of the theory of inflation.
Except in contrived models, this is true regardless of how inflation is realized in particle physics. Occasionally, effects are observed that appear to contradict the simplest models of inflation. The first-year WMAP data suggested that the spectrum might not be nearly scale-invariant, but might instead have a slight curvature. Some have claimed that this is a signature of non-Gaussianity and thus contradicts the simplest models of inflation. Others have suggested that the effect may be due to other new physics, foreground contamination, or even publication bias.
In particular, high precision measurements of the so-called "B-modes" of the polarization of the background radiation could provide evidence of the gravitational radiation produced by inflation, and could also show whether the energy scale of inflation predicted by the simplest models — GeV is correct. The team announced the tensor-to-scalar power ratio r was between 0. What is the hypothetical inflaton field giving rise to inflation? Other models of inflation relied on the properties of Grand Unified Theories.
At present, while inflation is understood principally by its detailed predictions of the initial conditions for the hot early universe, the particle physics is largely ad hoc modelling. As such, although predictions of inflation have been consistent with the results of observational tests, many open questions remain.
Fine-tuning problem One of the most severe challenges for inflation arises from the need for fine tuning. In new inflation, the slow-roll conditions must be satisfied for inflation to occur. The slow-roll conditions say that the inflaton potential must be flat compared to the large vacuum energy and that the inflaton particles must have a small mass.
THE INFLATIONARY UNIVERSE
His early childhood was unremarkable, although he showed a strong aptitude for mathematics. After attending several public schools, he skipped his senior year to enrol in a five-year program at the Massachusetts Institute of Technology MIT , partly because he was concerned about being drafted for the Vietnam War, of which he strongly disapproved. In , he married his high school sweetheart, Susan Tisch, and they were to have two children: Lawrence and Jennifer However, after graduating, Guth had a hard time finding a permanent job, partly because of the intense competition for university professor positions due to the baby boom, and he spent nine years traveling across the country pursuing temporary post-doctorate jobs related to physics, including time spent at Princeton to , Columbia to , Cornell to and at the Linear Accelerator Center at Stanford to His early focus at Princeton was on particle physics, particularly the study of quarks , the elementary particles that make up protons and neutrons.
The shortcoming that inflation is intended to fill in is the basic fact that although the Big Bang theory is called the Big Bang theory it is, in fact, not really a theory of a bang at all; it never was. I agree with what Paul said at the end of his talk about comparing these two models; it is yet to be seen which one works. But there are two grounds for comparing them. One is that in both cases the theory needs to be better developed. This is more true for the cyclic model, where one has the issue of what happens when branes collide. The cyclic theory could die when that problem finally gets solved definitively.