Cosmology - Inflationary Epoch

• There are an essentialy infinite number of Big Bang universes that are either open or closed. These are determined by the particular density of the universe. The density determines the overall geometry or curvature of the Universe. There is only one density, called the critical density, in which the the Universe is neither open or closed and in which the curvature is flat. Such a Universe has a present density of one (in relative Units). For an open or closed Universe, the present day density could be anything (although there is an important anthropic principle at work here in that only a small number of possible Universes live long enough or have enough density to produce stars, planets and intelligence). The observations suggest that the present day density is in the range 0.01-1 --> the fact that it is this close means that the value for mean density immediately after big bang was to very high degree the critical value in order for it to be only slighty different, if at all, after 10-20 billion years.
• This enigmatic result is known as flatness problem

Homogeneity Problem

• The angular size of the Universe at the time of recombination was 2 degrees. Thus each 2 degree region of the sky represents a causally disconnected region of space-time. Despite this, the Microwave Background radiation coming from different directions of the sky is the same. For standard big bang cosmology, this means that the initial conditions of the Universe had to be homogeneous - a very improbable state. So the question of why is the Universe so homogenous is an unpalatable answer.

  Inflationary Epoch

  • Early 1980s, Alan Guth suggested new epoch should be added, known as inflationary epoch, lasting between 10^-35 and 10^-24 seconds
  • Characteristics of inflationary epoch
    • Extremely small portion of Universe ballooned outward in all directions at speeds much greater than speed of light
    • Becomes many billions of times its original size to become visible Universe of today
    • Inflated portion pushed much of material that was originally near our location far beyond its boundaries
    • Because inflated portion so small, its properties, such as temperature, extremely homogeneous accounting for homogeneity of observable Universe
    • Because observable Universe is tiny fraction of entire Universe, it appears very flat, just as a football field can appear quite flat while actually being part of curved surface of Earth

  Grand Unified Theory (GUT)

  • During very early period in Universe, another series of events possibly took place which were predicted in early 1970s
  • Suspected that all four forces in nature - gravity, electromagnetic, and strong and weak forces - were unified into a single force at time of big bang
    • Gravity became separate force at 10E(-43) seconds after big bang, when temperature 10E(32) K
    • Strong force became separate force at 10E(-35) seconds, or beginning of inflationary epoch, when temperature 10E(27) K
    • Electromagnetic and weak force broke apart at 10E(-12) seconds, when temperature was 10E(15) K

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