BOOMERanG keeps coming back.
The strange acronym is the name of the airborne telescope, Balloon Observations of Millimetric Extragalactic Radiation and Geophysics, which helped physicists determine the shape of the universe a year ago. That groundbreaking announcement, first published last May in Nature, proved to be merely the beginning of the experiment’s usefulness. UCSB physicist John Ruhl and his team of graduate students reported they have cleaned up the data from the initial experiment near Antarctica at an American Physical Society press conference last week in Washington, D.C.
Last year, the telescope was lofted around Antarctica on a giant balloon. Once airborne, several pieces of the telescope’s equipment failed. These were intended to track the location and direction of the telescope. Ruhl’s team has spent the last year reconstructing the lost positioning data from the malfunctioning telescope. They also cleaned up interference from cosmic rays in the experimental data and developed better methods for analyzing existing results. The improved data will continue to help astronomers analyze the definite shape and origin of the universe.
This is the theory astronomers have come up with to date: The universe began with an enormous and rapid expansion of space. They believe at one point, very near its beginning, the universe was roughly the size of a proton. A billionth of a billionth of a billionth of a second later, it was the size of Earth. The fundamental particles and building blocks of the universe were forming during this time, theorists say.
Today, most of the energy in the universe is actually in the form of ordinary matter. At that time, however, most of the energy in the universe was in the form of radiation, or light. In the midst of this soup of radiation energy that made up the early universe, it was impossible for the small building blocks of matter, like electrons or protons, to form into the atoms and molecules we think of as ordinary matter. Instead, they existed in a state of matter known as plasma. Today, plasma can be found inside of stars, riding the outside of lightning bolts or in very expensive laboratories.
As exotic as plasma may seem, it does not worry physicists very much. They have convenient equations to describe it. That is because it is made up of normal, identifiable particles called baryons. Physicists file it under “stuff we know.” The only problem is 90 percent of the universe is made up of something else. This something is called “dark matter,” and physicists know almost nothing about it – only that it must exist because the visible structure of the universe would not make sense without it.
“It’s not possible to make it [to the modern universe] with only baryons and no dark matter, given what we see in the sky,” Ruhl said.
It remains for physicists to figure out exactly what the universe is made of.
The reason the stuff is called “dark matter” is because it does not respond to light. If it did, astronomers would be able to see it with their telescopes, and a lot of particle physicists would be out of work. The only nice thing about this is since dark matter does not respond to light, it began to clump together long before the baryons ceased to be plasma.
This means the plasma began to respond to the gravitational effects of dark matter. The plasma would fall in toward the dark matter clumps, compressing itself as it fell. When it became compressed, it would heat up and expand outward again, cool off and fall back inward.
This cycle continued, creating waves in the plasma as it went along. These waves were regions of high and low density, like traffic jams and open spaces on the freeway. The dense regions were the most compressed and took the longest to cool off. Some parts of the plasma that made up the universe cooled and turned into normal matter before others.
“As the universe formed,” Ruhl said, “the plasma turned into transparent hydrogen gas.” When it did so, it released the light that had been trapped inside the plasma. This light has been traveling through space ever since that time. The waves that make it up have been stretched by the expansion of space.
The light from the oldest structures in the universe has had the most time to be stretched out. Today, the original shape of the universe appears as a pattern of light in the sky. The light cannot be seen because it is made up of microwaves, but astronomers can measure it. The oldest portions are the most stretched, while the newest, densest portions are the least stretched. The gravitational pull of these denser sections pulled surrounding matter together to become what we see as galaxies today.
The BOOMERanG telescope is the device that gathered the most precise information to date on these patterns of light in the sky. When it flew around Antarctica two years ago, some pieces of equipment on board the balloon-borne experiment failed during its initial flight, making it difficult for astronomers to determine exactly what portion of the sky they were observing. However, Ruhl and his team of grad students were able to piece together enough preliminary results from the experiment last year to determine the basic shape of the universe.
As it turns out the universe is flat. This does not mean it looks like a tabletop. What it means, Ruhl said, is that if you were to shoot two parallel laser beams out into space, they would remain parallel forever, instead of curving toward or away from one another like longitude lines on the earth.
Ruhl and his team recently finished sorting out and examining the rest of the data from the experiment – 14 times the original amount. This additional data could greatly improve astronomers’ understanding of the basic shape and nature of the universe.