Mapping Big Bang's Shadow


Gazing at the night sky, it's easy to become overwhelmed by the immensity of the universe. What's out there? What does it all mean? NASA scientists have not undertaken to answer the riddles of the meaning of life, but they hope a satellite they launched recently will give clues to the earliest events in the universe.

The satellite, called MAP for Microwave Anisotropy Probe, will examine the afterglow of the formation of the universe. Scientists hope the examination will help answer questions about what the universe is made of and how quickly it is expanding.

In particular, they think the MAP project may be able to determine once and for all whether exotic "dark matter" and "dark energy" exist, how much of the universe they make up, and just what their nature might be.

MAP, launched June 30, will examine what astronomers call the cosmic background radiation--the leftover glow from the Big Bang that physicists hypothesize was the dawn of the universe. The light is a "fossil relic of ancient times," says Dr. Chuck Bennett, an astrophysicist at NASA's Goddard Space Flight Center and principal investigator for the mission.

The radiation has its origin only 300,000 years after the beginning of the universe, and the images produced by MAP will provide a detailed picture of the universe as it existed then. In the intervening billions of years, when the light has traveled trillions of kilometers, the radiation has cooled to just a few degrees above absolute zero (-460 degrees). But even in this much cooler state, the radiation preserves the pattern of the universe in its infancy.

According to prevailing physics theories, which have been strongly supported by experimental evidence, the universe suddenly came to be from nothing and has been growing ever since. The theories hold that, in the microseconds after it began, the universe underwent an unimaginably rapid and sudden expansion, growing by billions of times in size in a fraction of a second.

Expansion of the universe was remarkably uniform, resulting in an almost-even distribution across the entire universe. But had the distribution been totally smooth, there would be no galaxies or planets or people, just an evenly spread sea of stuff.

Instead, when we look to the heavens we see "a clumpy-looking sky"--clumps made of stars, of galaxies, of clusters of galaxies, explains Bennett. These clumps probably grew from "seeds," or tiny spots in the earliest universe where matter was more concentrated than at other spots.

Those spots, in turn, are mirrored in the background radiation as tiny fluctuations in the temperature of the remaining glow.

Those temperature differences are so tiny--only millionths of a degree--that the hunt for their existence went on for 27 years. In 1992, a satellite called COBE (Cosmic Background Explorer) brought back the first hard evidence of the variations.

Now, researchers hope MAP will provide detailed images of the fluctuations across the universe. Having a detailed map of the temperature variations should help scientists develop a picture of what the infant universe looked like. Scientists also hope the MAP data will help them figure out the puzzle of the so-called dark matter that they believe makes up the vast majority of the contents of the universe.

All the ordinary matter in the universe--the stuff that makes up everything we can see, from dust to stars--does not add up to enough to generate the gravitational force that holds the universe together. To account for the gap--to explain why the universe has not simply flown apart over billions of years--scientists have hypothesized the existence of what has been called "dark matter"--because it does not interact with light and thus cannot be seen--as well as an even more elusive dark energy.

By studying the cosmic radiation, the MAP team hopes to learn about dark matter by seeing how it interacted with the cosmic radiation.

The tiny size of the temperature differentials within the radiation--billions of times smaller than the contaminating light from the sun, Earth and moon--pose the greatest challenge for MAP's designers. The key, as the real estate saying goes, is location, location, location.

In this case, the ideal location is a place called L2--an orbital position about four times farther from the Earth than the moon is, heading away from the sun. Satellites studying the sun are often parked in the opposite direction, known as L1; MAP will be the first satellite to orbit at L2.

One advantage of L2 is that the distance from the sun makes it somewhat easier to detect the tiny fluctuations in temperature within the background radiation.

In addition, MAP will be able to gather data from 100% of the sky. Other ground and balloon-borne efforts have given high-resolution data, but for only 1% to 2% of the sky.

"Imagine yourself out in your backyard," suggests Bennett. "When you look up, you see all of the sky that is not obscured by the Earth. MAP will solve this problem by getting out away from the Earth, revealing the whole sky."

Finally, once it arrives, MAP will need very little energy to maintain its orbit. For all those reasons, L2 is "a great place to be," says Bennett.

Right now, MAP is looping between the Earth and the moon, passing the time until the moon reaches a place from which its gravitational field can be used like a slingshot to propel MAP out to L2. MAP is expected to reach its destination in late September.

Because the temperature differentials within the cosmic radiation are so small, MAP will make differential, rather than absolute, measurements. Bennett likens the task to weighing two cups of sand and detecting a difference of a couple of grains.

MAP will accomplish the task by comparing temperatures of two points in space over and over.

Stability is crucial to the endeavor. Any changes in the temperature of the satellite would have a big impact on the accuracy of the data. In designing MAP, scientists had to create an unchanging environment, a "very unusual requirement for a spacecraft," says Bennett.

MAP will work incredibly fast, scanning 30% of the sky every hour. This will help to ensure that no changes occur in the equipment between measurements. MAP's findings will achieve high accuracy by keeping the errors small, says UCLA scientist and MAP team member Ned Wright. The downside is that the the billions of temperature comparisons made by MAP will take months to analyze, adding up to a "monumental data-processing task" for Wright.

MAP will collect data for about two years, with the first results projected to come in 18 months. Bennett admits that he wants watching MAP in action to be "about as exciting as watching grass grow." The absence of any drama during data collection will help to guarantee the accuracy of the findings. This, Bennett says, is "the recipe for a fantastic end result."


Universal Afterglow

A recently launched satellite will study the afterglow of the universe's formation. Scientists hope the project will help them learn more about what the universe is made of and how it formed.


Detecting Matter

The afterglow of the creation of the universe--now cooled to nearly absolute zero (minus 460 degrees F)--pervades all space and is extremely uniform across the sky. Tiny temperature variations in this background radiation hint at the universe's structure at the earliest moments in time. Cooler, denser regions mark places where matter was concentrated. The MAP team will study these signals to provide answers about the birth of the universe and its makeup, including exotic dark matter and dark energy.

COBE: NASA's Cosmic Background Explorer satellite in 1992 provided the first map of the tiny temperature variations seen in the background microwave radiation. Shading variations reflect temperature differences at the level of a few parts per million.

MAP: The MAP project will provide much more detailed information about the small temperature fluctuations. The map shown is a simulation of what scientists expect to see.

Sources: NASA; Times staff reports

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