What does inflation have to do with the early Universe?

When most of us hear the word “inflation” we think of the rising cost of living or maybe blowing up a balloon. For cosmologists, inflation is a key concept in understanding how the Universe came to be the way it is.

Big Bang cosmology has been remarkably successful in explaining many aspects of the Universe, including the expansion that is seen and the abundances of some elements. The simplest model of the Big Bang leaves some puzzles, however. One of these is that on the very largest scale the Universe is extremely uniform. The microwave background seen by COBE (COsmic Background Explorer) and WMAP (Wilkinson Microwave Anisotropy Probe) is almost the same in all directions. The Universe is so large, however, that light could not travel across it in the 13,700,000,000 years since the Big Bang. So how do the different parts of the Universe “know” about each other? At the same time, the Universe is not too uniform. It does have stars and galaxies that are concentrations of matter. How did these irregularities come out of something that was so smooth?

A solution to these and other issues with the simple Big Bang model is the idea of inflation: in the first fraction of a second that the Universe existed, it expanded at a tremendous rate, vastly more rapid than the expansion that is now seen. In this sense, it is like blowing up a balloon, only what was expanding was space itself. This brief period of inflation produced the uniformity that is now seen. It also meant that tiny quantum fluctuations in the Universe during this time could grow large enough to become the “seeds” of stars and galaxies that are seen today.

The idea of inflation has developed into a number of theories about the details of how this process works. Recently, analysis of three years of observations with WMAP has started to address some of the predictions made by inflation theories. Most importantly, the WMAP results support the basic idea of inflation. In the first trillionth of a second, the Universe really did appear to grow by many orders of magnitude. Thanks to the detailed study of the polarization of the WMAP data, the WMAP team could also check which models of inflation seem most promising. They find that the simplest models are most consistent. The WMAP program is ongoing. It will continue to collect information about the amazing start of our Universe.

The press release from the WMAP team can be seen at http://map.gsfc.nasa.gov/m_or/PressRelease_03_06.html

A nice visualization of the current ideas about the history of the Universe also comes from the WMAP team (see http://map.gsfc.nasa.gov/m_mm.html)

This week's question comes from Dr. Dave Thompson. Dr. Thompson is an astrophysicist who studies gamma rays in the Exploration of the Universe Division. He helped build, test, and analyze data from EGRET on the Compton Gamma Ray Observatory, and he is now helping build part of the Gamma Ray Large Area Space Telescope (GLAST), scheduled for launch in 2007. His particular scientific interest is gamma-ray pulsars.