The Inflationary Universe is a popular science book by theoretical physicist Alan Guth , first published in The book explores the theory of inflation , which was first presented by the author in In April , physicist and Nobel laureate Steven Weinberg included The Inflationary Universe in a personal list of "the 13 best science books for the general reader". From Wikipedia, the free encyclopedia. The Inflationary Universe Softcover edition. Dewey Decimal.

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The Inflation Theory proposes a period of extremely rapid exponential expansion of the universe during its first few moments. It was developed around to explain several puzzles with the standard Big Bang theory, in which the universe expands relatively gradually throughout its history. While the Big Bang theory successfully explains the "blackbody spectrum" of the cosmic microwave background radiation and the origin of the light elements , it has three significant problems:.

It proposes a period of extremely rapid exponential expansion of the universe prior to the more gradual Big Bang expansion, during which time the energy density of the universe was dominated by a cosmological constant -type of vacuum energy that later decayed to produce the matter and radiation that fill the universe today. Inflation was both rapid, and strong. Inflation is now considered an extension of the Big Bang theory since it explains the above puzzles so well, while retaining the basic paradigm of a homogeneous expanding universe.

Moreover, Inflation Theory links important ideas in modern physics, such as symmetry breaking and phase transitions, to cosmology. As a bonus, Inflation also explains the origin of structure in the universe.

Prior to inflation, the portion of the universe we can observe today was microscopic, and quantum fluctuation in the density of matter on these microscopic scales expanded to astronomical scales during Inflation.

Over the next several hundred million years, the higher density regions condensed into stars, galaxies, and clusters of galaxies. Wilkinson Microwave Anisotropy Probe. What is the Inflation Theory? Limitations of the Big Bang Theory While the Big Bang theory successfully explains the "blackbody spectrum" of the cosmic microwave background radiation and the origin of the light elements , it has three significant problems: The Flatness Problem: WMAP has determined the geometry of the universe to be nearly flat.

However, under Big Bang cosmology, curvature grows with time. A universe as flat as we see it today would require an extreme fine-tuning of conditions in the past, which would be an unbelievable coincidence.

The Horizon Problem: Distant regions of space in opposite directions of the sky are so far apart that, assuming standard Big Bang expansion, they could never have been in causal contact with each other. This is because the light travel time between them exceeds the age of the universe.

Yet the uniformity of the cosmic microwave background temperature tells us that these regions must have been in contact with each other in the past. The Monopole Problem: Big Bang cosmology predicts that a very large number of heavy, stable "magnetic monopoles" should have been produced in the early universe.

However, magnetic monopoles have never been observed, so if they exist at all, they are much more rare than the Big Bang theory predicts. How Does Inflation Solve these Problems? The Flatness Problem: Imagine living on the surface of a soccer ball a 2-dimensional world. It might be obvious to you that this surface was curved and that you were living in a closed universe. However, if that ball expanded to the size of the Earth, it would appear flat to you, even though it is still a sphere on larger scales.

Now imagine increasing the size of that ball to astronomical scales. To you, it would appear to be flat as far as you could see, even though it might have been very curved to start with. Inflation stretches any initial curvature of the 3-dimensional universe to near flatness. The Horizon Problem: Since Inflation supposes a burst of exponential expansion in the early universe, it follows that distant regions were actually much closer together prior to Inflation than they would have been with only standard Big Bang expansion.

Thus, such regions could have been in causal contact prior to Inflation and could have attained a uniform temperature. The Monopole Problem: Inflation allows for magnetic monopoles to exist as long as they were produced prior to the period of inflation.

During inflation, the density of monopoles drops exponentially, so their abundance drops to undetectable levels. Further Reading: Alan H.

Alan H. Edward J. Wollack Page Updated: Friday,

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## What is the Inflation Theory?

He imagined a mind-bogglingly brief event, at the very beginning of the big bang, during which the entire universe expanded exponentially, going from microscopic to cosmic size. That night was the birth of the concept of cosmic inflation. Such an explosive growth, supposedly fueled by a mysterious repulsive force, could solve in one stroke several of the problems that had plagued the young theory of the big bang. In fact, as he himself narrates in his highly recommendable book, The Inflationary Universe , at the time Guth was a particle physicist on a stint at the Stanford Linear Accelerator Center, and struggling to find a permanent job and his idea came to him while he was trying to solve the monopole problem.

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## 10 Questions for Alan Guth, Pioneer of the Inflationary Model of the Universe

The standard model of hot big-bang cosmology requires initial conditions which are problematic in two ways: 1 The early universe is assumed to be highly homogeneous, in spite of the fact that separated regions were causally disconnected horizon problem ; and 2 the initial value of the Hubble constant must be fine tuned to extraordinary accuracy to produce a universe as flat i. These problems would disappear if, in its early history, the universe supercooled to temperatures 28 or more orders of magnitude below the critical temperature for some phase transition. A huge expansion factor would then result from a period of exponential growth, and the entropy of the universe would be multiplied by a huge factor when the latent heat is released. Such a scenario is completely natural in the context of grand unified models of elementary-particle interactions. In such models, the supercooling is also relevant to the problem of monopole suppression. Unfortunately, the scenario seems to lead to some unacceptable consequences, so modifications must be sought. The editors of the Physical Review journals have curated a collection of landmark papers on General Relativity to celebrate its centennial.