Imagine the Universe!

Satellite Showcase

The Wilkinson Microwave Anisotropy Probe (WMAP)

A Universe Before Stars: Unraveling the Mysteries of the Earliest Moments in Time

Can you imagine a Universe without stars? You'll need to go way back in time.

The Universe is now about 15 billion years old. During the Universe's preschool years -- the first billion years or so -- there were no twinkling jewels to see in the night sky; no galaxies swirling about like pinwheels nor comets streaking across the heavens.

In fact, for the first 400,000 years after the Big Bang, the entire Universe was one great fog of protons, electrons, and radiation. You couldn't see anything.

Sound boring? On one level, the scene does seem to be like an astronomer's worst nightmare: no stars, no visibility. Yet nothing could be further from the truth. This fog is actually one of the hottest topics in science, for hidden within the fog are clues to the most pressing questions of our existence:

  • What is the shape of the Universe?
  • What kind of strange matter is in the Universe?
  • How did the Universe grow from a fireball to the vast structure of galaxies and galaxy clusters we see today?
  • Does a mysterious force acting like anti-gravity dominate the Universe?

For the "big" questions, the fog is where it's at. But how does one go about studying a fog that existed billions of years ago?

About 400,000 years after the Big Bang, the fog lifted and light broke through. This light -- essentially the afterglow of the Big Bang, the very first light to shine in the Universe -- carries the history of what went on during those first years. As fate would have it, this fossil light is still shining today in the form of microwaves. The entire Universe is bathed in the stuff.

History of the Universe
A schematic of the history of the universe,
showing the difference before and after the lifting of the "fog".
(Click on image to enlarge it)

On June 30, 2001, NASA launched the Wilkenson Microwave Anisotropy Probe (WMAP) to survey this ancient radiation in unprecedented detail. Just as we can study dinosaur bones and reconstruct their lives from millions of years ago, we can probe this ancient light and reconstruct the Universe as it was about 15 billions years ago. WMAP is looking at a cosmic glow far older than anything that the Hubble Space Telescope or Chandra X-ray Observatory can see. WMAP will "map" slight temperature fluctuations within the microwave background that vary by only 0.00001 C across a chilly light that now averages 2.73 C above absolute zero. The temperature differences today point back to density differences in the fiery baby universe, in which there was a little more matter here and a little less matter there. Areas of slightly enhanced density had stronger gravity than low-density areas. The high-density areas "pulled back" on the background radiation, making it appear slightly cooler in those directions. The slight difference in density led to our current structure of galaxies, galaxy clusters, and voids of seemingly empty space.

So WMAP is a cosmologist's dream come true, supplying the long-sought data needed to test the crazy theories we have of how it all began and how we got from there to here. By comparing the earliest structure of the universe to what we see today, WMAP will help determine how and when the first galaxies formed. WMAP will also address the more trippy questions: Is the universe's geometry flat or curved around in some funky way? Is the stuff we're made of really an anomaly in a universe dominated by dark matter and dark energy? Is inflation correct, the theory that the universe expanded from the atomic scale to the cosmic scale in a fraction of a second, far faster than light?

Join us on this special exhibit, as we explore the questions that WMAP will seek to answer:

Our thanks to Lindsay Clark and Dr. David Spergel of the WMAP project for their assistance with this Special Exhibit. Images used in this exhibit are courtesy of the WMAP project.

Additional Links

starWMAP Home Page (

star Introduction to the Cosmic Microwave Background (

Imagine the Universe is a service of the High Energy Astrophysics Science Archive Research Center (HEASARC), Dr. Alan Smale (Director), within the Astrophysics Science Division (ASD) at NASA's Goddard Space Flight Center.

The Imagine Team
Acting Project Leader: Dr. Barbara Mattson
All material on this site has been created and updated between 1997-2012.

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