Somewhere between 12 billion and 15 billion years ago, scientists say, the universe was little more than a searing-hot bowl of primordial soup, filled with atomic particles floating freely through space.
Later, as the plasma soup cooled, molecules of the simple elements like hydrogen and helium - the building blocks of all matter in the cosmos - coalesced, eventually forming stars, planets, and galaxies. But the exact recipe brewed by the "big bang" tens of billions of years ago remains a mystery.
Tomorrow, NASA is scheduled to launch a satellite that could give scientists their most detailed look at this elusive recipe. For at least the next three years, a solar-paneled craft outfitted with four coordinated telescopes will peer into the heavens to study these simple elements - remnants of the big bang. From the probe's data, scientists hope to better understand forces that caused the creation of the universe as well as processes that continue to shape it.
"What we are really trying to confirm here is that we understand what happened in the big bang and that it is consistent with what we understand about how galaxies evolve - and how the chemical elements that make up all normal materials come into being and change over time," says Kenneth Sembach, a research scientist at Johns Hopkins University and the chief science coordinator for the mission.
What makes the Far Ultraviolet Spectroscopic Explorer (FUSE) unique is its telescope, which is designed to capture light from a largely unexplored part of the ultraviolet spectrum. This region, called the far ultraviolet region, is visible to neither human eyes nor to the current crop of high-tech telescopes.
But in this region reside crucial spectral signatures from the early universe for helium, hydrogen, and deuterium - elements with only one or two protons and scant electrons and neutrons. These signatures will tell scientists a great deal about the density and characteristics of these elements. In addition, they will allow scientists to measure how much deuterium, hydrogen, and helium are present in gas clouds around the sun, on the outskirts of the Milky Way, and in areas between nearby galaxies where stars form.
But foremost in researchers' minds is detecting amounts of deuterium, a type of hydrogen that has an additional neutron in its nucleus.
"Deuterium is the most important," says Dr. Sembach. "The amount of it that was created in the big bang is a sensitive indicator of what the temperature and the density and the conditions were like just minutes after the big bang."
Indeed, deuterium could give insight into how the universe has evolved during the past 12 to 15 billion years.
"Deuterium will provide us a way to track how the amount of the various elements in the universe has changed with time because deuterium was only made in the big bang," says George Sonnenborn, chief scientist for NASA on the mission. "The amount of deuterium produced in the big bang is related to the total amount of normal matter that exists in the universe."
Knowing the total amount of matter - and the ratio of elements - that exists in the universe will allow astronomers to answer crucial questions such as whether the universe will continue expanding infinitely or eventually collapse on itself.
Indirectly, the calculations from FUSE will also offer scientists clues about the distribution of mysterious dark matter. No one is quite sure what dark matter is, but calculations of the mass of the universe, as well as the as-yet unexplained actions of some heavenly objects, indicate that some sort of other matter exists, and is far more abundant than ordinary matter.
For FUSE to get exact measurements, however, is not as simple as pointing the mirrors in the right direction. FUSE is not effective at capturing light from more distant objects. Its outer limit of observation is approximately 3 billion light years, far short of light from the time of the big bang.
Furthermore, the chemical composition of the universe has changed since the big bang as unstable deuterium has been destroyed in the cores of stars.
"We are looking at that abundance now. We are not looking at it 14 billion years ago," says Sembach. "Over the course of time, the quantity of deuterium has changed. It has decreased. Stars destroy it and convert it to different things."
To find deuterium, scientists will study hundreds of places of varying ages and in varying parts of the nearby universe, where celestial phenomena are better understood and more easily observed.
From this information they hope to extrapolate the initial recipe for the primordial soup and plot the different points of the history of the universe. One result of this process, scientists say, will be better information on how galaxies evolve and what the mechanics of star formation are.
"We are pushing the horizons here, and you know there are going to be interesting things," says Sembach. "I think it would be great fun if we ... saw different values for the deuterium abundance everywhere we looked. It would mean that things are much more complicated than we now think and that we really have a lot of work left to do."