| Searching for B-Mode Polarization
In particular, the team is advancing technologies for large arrays of super-sensitive detectors and other components needed to build an instrument, called CMBPol, to detect a particular type of polarization signal — B-mode, in the parlance of cosmologists. “If we detect this pattern of polarization in the cosmic background radiation, it will give us the ‘smoking gun’ evidence that inflation did indeed occur,” said Dave Chuss, one of the co-investigators on the team.
While WMAP offered tantalizing evidence supporting the inflation theory, definitive proof still remains elusive without a new instrument, he added.
WMAP, the follow-on mission to COBE whose results earned Principal Investigator John Mather a Nobel Prize last year, studied the afterglow radiation in greater detail and provided more precise measurements of the tiny temperature differences in the background light. These differences varied by about a millionth of a degree and pointed to density differences that eventually gave rise to the stars and galaxies seen today.
It also measured E-mode polarization of the microwave background radiation, which pointed to the time when the light from the first stars ionized hydrogen atoms and liberated electrons from protons. At this point, the first stars — the predecessors to all subsequent generations of stars — were fully formed. WMAP, with its measurements of E-mode polarization patterns and its detailed temperature map, concluded that the first stars formed about 400 million years after the big bang.
While WMAP detected E-mode polarization patterns, the other type of polarization — B-mode — remains below its sensitivity threshold. This remaining piece to the inflation puzzle is what CMBPol would be designed to find. With this measurement, scientists could investigate the very first instants of the history of the universe and obtain the energy scale of inflation.
Technology Within Reach
Although Moseley says the technology is within reach, the detectors present a challenge. The polarization signal is at least 100 times fainter than the temperature signal picked up by COBE and WMAP. Therefore, the detectors must be sensitive enough to find the signal. “If we find the pattern, it will rule out all the other viable models” on how the universe behaved the first trillionth of a second after its birth, he said.
“We actually know a huge amount about the overall structure of the universe,” Moseley said. “What we’re trying to get at are the physics, the big-bang measurements so that we can limit the number of models. This is very good science.”
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This graphic shows the timeline of the universe. Although the universe has expanded gradually over most of its history, scientists believe that it expanded from subatomic scales to the astronomical in a fraction of a second after its birth. Goddard hopes to build an instrument that would search for signs of this cosmic inflation.
Members of the CMBPol instrument team include (from left to right) Dave Chuss, Wen-Ting Hsieh, Thomas Stevenson, George Voellmer, Harvey Moseley, Ed Wollack, Kongpop U-Yen, Nga Cao, and Elmer Sharp.
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