Theoretical cosmology has been strongly influenced by a new conception of the very early universe advanced by MIT physicist Alan Guth (1947-) in 1982. A remarkable characteristic of the cosmic background radiation is its uniformity—points on the sky 180 degrees apart possess the same temperature to an accuracy of 1 part in 100,000. These temperatures correspond to parts of the universe that can have had no contact since the initial bang that created the world. Using general relativity, thermodynamics, and particle physics, Guth devised a theory known as inflation to explain this fact. According to this conception, at the very beginning of its history the universe underwent a phase transition resulting in a period of exponential expansion lasting only a tiny fraction of a second—in an instant the universe inflated, creating the homogeneity and isotropy we observe today in the cosmic background radiation. The rapid expansion also resulted in the disappearance of objects known as a magnetic monopoles, hypothetical particles not encountered in nature but predicted to exist in abundance by conventional big bang models.

Inflation requires the universe to be much more massive than it apparently is. A large percentage of the universe must consist of some form of nonbary-onic mass or energy. An inflationary universe is also a flat universe, one which is perfectly Euclidean and which will expand forever. The exponential expansion in the first instants of the big bang resulted in this flat geometry, in the same way that a balloon inflated to a very large size produces a surface that locally is very close to being flat.

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