What is the Inflation Theory?

The Inflation Theory proposes a period of extremely rapid (exponential) expansion of the universe shortly after the Big Bang.

Limitations of the Big Bang Theory

While the Big Bang theory successfully explains the shape of the cosmic microwave background spectrum and the origin of the light elements, it leaves open a number of important questions:

• Why is the universe so uniform on the largest length scales?
• Why is the physical scale of the universe so much larger than the fundamental scale of gravity, the Planck length, which is one billionth of one trillionth of the size of an atomic nucleus?
• Why are there so many photons in the universe?
• What physical process produced the initial fluctuations in the density of matter?

The Inflation Theory

The Inflation Theory, developed by Alan Guth, Andrei Linde, and Paul Steinhardt, offers answers to these questions and several other open questions in cosmology. It proposes a period of extremely rapid (exponential) expansion of the universe shortly after the Big Bang, during which time the energy density of the universe was dominated by a cosmological constant term that later decayed to produce the matter and radiation that fill the universe today. The Inflation Theory links important ideas in modern physics, such as symmetry breaking and phase transitions, to cosmology.

Predictions of the Inflation Theory

In its simplest form, the Inflation Theory makes a number of important predictions:

• That the density of the universe is close to the critical density, and thus the geometry of the universe is flat.
• That the fluctuations in the primordial density in the early universe had the same amplitude on all physical scales.
• That there should be, on average, equal numbers of hot and cold spots in the fluctuations of the cosmic microwave background temperature.

MAP will be able to test these predictions.

Further Reading:

• Guth, A.L. & Steinhardt, P.J., "The Inflationary Universe", Scientific American, May 1984.

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Last updated: Friday, 05-21-1999