Mapping the Baby Universe
by Christopher Wanjek
NASA's MAP mission will map the cosmic microwave background in unprecedented detail.
And in the beginning there was fog. This was the universe for the first 300,000 or so years after the Big Bang: a dense, white fog of free electrons and protons. Light could not travel a trillionth of a millimeter without bumping into an electron. Visibility was nil.
But then something happened. The universe cooled to a mere 2700?C, cold enough to allow electrons to cling to protons. Particles combined to form hydrogen atoms. Light, at long last, broke free and shone across the universe to reveal the structure inside. As luck would have it, this first light is still with us today; the expansion of the universe has "stretched" (redshifted) it into the microwave band. And oh, what stories it has to tell.
This cosmic microwave background is essentially the afterglow of the Big Bang. It comes from an era one billion years or so before anything Hubble or Chandra can see. In human terms, the universe was only 12 hours old; stars wouldn't turn on until the universe was ready to enter grade school.
In June, NASA plans to launch the Microwave Anisotropy Probe (MAP) to survey the ancient radiation in unprecedented detail. MAP will "map" slight temperature fluctuations within the microwave background that vary by only 0.00001?C across a chilly radiation 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. "It's the old story of the rich get richer," says MAP science team member Alan Kogut of NASA's Goddard Space Flight Center. "Regions of denser matter pulled in more matter, making them even denser and able to pull in more matter."
The cosmic microwave background itself was discovered by accident in 1964 by Arno Penzias and Robert Wilson of Bell Laboratories. They were trying to eliminate static interfering with radio experiments. They tuned out local radio stations and even built pigeon traps to rid themselves of birds nesting in and around their radio receiver, because the pigeon droppings were a strong source of static.
Despite their best efforts, Penzias and Wilson couldn't eliminate a constant low-level noise. They came to realize (after a good deal of discussion with Princeton cosmologists) that this noise has been lingering for 10 billion to 15 billion years, as predicted by the Big Bang theory. They snagged the 1978 Nobel Prize for their discovery.
COBE was the first satellite to study the cosmic microwave fossil. In 1992, COBE found that there were indeed fluctuations in the temperature, a discovery that got everyone's creative juices flowing as to what could have caused the fluctuations. COBE had a resolution of about 7?, just enough to provide a fuzzy picture. MAP will "...study the microwave background at the smallest angular scales," says Princeton University cosmologist David Wilkinson. "That's where most of the information is about cosmology."
So MAP 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, MAP will help determine how and when the first galaxies formed. MAP 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?
Three recent balloon-borne experiments, BOOMERANG, MAXIMA, and TopHat, studied the microwave background at high angular resolution, although they could only survey a tiny patch of sky during their brief flights. BOOMERANG found hot and cold spots around 1? in width, in accordance with the predictions of inflationary theory. This supports the notion that we live in a flat, Euclidean universe that will expand forever.
MAP will survey the cosmic microwave background for two years from an L2 orbit, which places it four times farther than the Moon in the direction opposite of the Sun, trailing Earth in her orbit. MAP's thoroughness will essentially smooth out the slight discrepancies among data from the many recent non-satellite experiments, as well as winnow the chaff of cosmological theories.
MAP may very well be one of the most important space-science mission of our time, but don't expect a steady stream of pretty Hubble-type images. MAP is a one-shot deal, ultimately yielding a single two-year image of the baby universe. But whereas a Hubble picture says a thousand words, the MAP survey will speak of 15 billion years of glorious static.
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