A picture of our universe from the first moments of its existence helps explain why it looks the way it does.

by Jo Locke

Photo courtesy of NASA/WMAP Science Team The new picture of the early universe shows tiny temperature fluctuations in CMB, where red and blue colours indicate warmer and cooler spots. The white lines show the direction of polarisation of the oldest light.

For centuries, people have looked up at the stars and wondered why they are scattered the way they are in the night sky. Scientists still haven't completely solved this, but in March 2006 some researchers came a whole lot closer to understanding how our universe came to look the way it does. Using data from a NASA satellite, they were able to capture in the greatest detail yet a picture of the light from our universe dating back to instants after the Big Bang when it was first created. It's a breakthrough in cosmological research since it has allowed scientists to gaze back to the first trillionth of a second of our universe and distinguish between different versions of what happened in those crucial instants after the Big Bang.

The light that scientists are observing is cosmic microwave background radiation (CMB), or the afterglow of light that still remains from the Big Bang 13.7 billion years ago. The Wilkinson Microwave Anisotropy Probe (WMAP) satellite, launched in 2001 and now a million miles from Earth in the direction opposite the sun, has been measuring minute temperature fluctuations in the afterglow for three years. In 2003, the temperature fluctuations it had recorded had produced a very detailed picture of the early universe and allowed scientists to get answers to questions about the age of the universe, its composition and how it developed. Since then, the satellite has been looking at polarisation, or the pattern of the residual afterglow, a signal less than a hundred times weaker that the previous temperature maps. This data has added detail to the picture obtained in 2003 and has determined that the first stars were formed 400 million years after the Big Bang. "This is brand new territory," said Princeton University physicist Lyman Page, a WMAP team member. "We are quantifying the cosmos in a different way to open up a new window for understanding the universe in its earliest times."

Photo courtesy of NASA/WMAP Science Team Artist's rendition of the WMAP spacecraft.

This recent data is groundbreaking since it is the first evidence to support the theory of inflation, first proposed 25 years ago. The theory states that in the instants after the Big Bang, the universe expanded at an incredible rate. This rapid expansion, which is thought to have caused the volume of the universe to expand from just a few centimetres to about 18 billion light years in a fleeting moment, left its mark as rips or tears, called quantum fluctuations, in the very early universe. These were thought to have been amplified in the CMB radiation, and in the images from the WMAP satellite, scientists were able to see evidence of this as variations in brightness.

In addition to supporting the inflation theory, the new WMAP data also supports theories of what happened to matter and energy in the 13.7 billion years since the Big Bang. Fluctuations in density seen in the images are considered to be a sort of template for star and galaxy formation and life. They reveal that only 4% of our universe is made up of atoms, whereas 74% is a mysterious dark energy and 22% is unidentified dark matter. Dark energy is thought to be what is causing our universe to continue to expand, albeit much more slowly than during the moments of inflation.

Photo courtesy of NASA/WMAP Science Team Universe Timeline: This image shows that the expansion of the universe has been quite gradual after the initial period of inflation.

Obtaining data that supports cosmological theories is a big step forward in truly understanding the universe. Since the accidental discovery of CMB radiation in 1978, researchers have been slowly filling in the picture of how the universe was formed. As WMAP scientist David Spergel says: "When I started in this field we had lots of competing ideas about what was going on, we didn't know what the shape of the universe was, we didn't understand where galaxies come from, and now all the pieces seem to fit, and we seem to have a coherent model that ties with what we see in the early universe".

For more info, visit:

WMAP Press Release
http://wmap.gsfc.nasa.gov/m_or/PressRelease_03_06.html

WMAP reveals infant universe
http://www.astronomy.com/asy/default.aspx?c=a&id=4051