FEATURE
Did Inflation Happen? Goddard Scientist Builds Instrument to Prove Cosmology Theory
In 2012, Goddard scientist Al Kogut will loft a balloon-borne instrument to an altitude of 120,000 feet — where the atmosphere thins into the vacuum of space — to search for definitive proof that the infant universe expanded from subatomic scales to the galactic in a fraction of a second after its birth.
To find the evidence, Kogut is building the Primordial Inflation Polarization Explorer (PIPER). It will measure the faint signal of primordial gravity waves imprinted in the polarization of the cosmic background radiation, the remnant light from the first moment of the universe’s creation that bathes the sky in all directions. The instrument is slated to fly four times as a balloon payload, gathering 96 hours of data.
“It’s What Put the ‘Big’ in the Big Bang”
“If we see this signal, we will have proved that inflation happened. We will have shown that the inflation theory is right and the others are wrong,” Kogut said. “If inflation did occur, we’ll also learn at what energy this occurred. This number is important for understanding the physics. It’s what put the ‘big’ in the big bang.”
Considered a staggering idea just two decades ago, the inflation theory postulates that the universe expanded far faster than the speed of light and grew exponentially almost instantaneously. Scientific results from the Goddard-developed Cosmic Background Explorer (COBE) revealed tantalizing clues that inflation did, in fact, occur. It found tiny temperature differences in the cosmic background radiation. These differences varied by only a few millionths of a degree and pointed to density differences that eventually gave rise to the stars and galaxies seen today.
COBE’s successor, the Wilkinson Microwave Anisotropy Probe (WMAP), studied the afterglow radiation in more detail and also showed that the geometry of the universe was flat — a physical dimension also attributable to inflation, Kogut said.
However, other theories also explain these dynamics, Kogut said. What the science community needs is definitive proof of the primordial gravity waves — phenomena that the other theories can’t explain.
R&D Funds Critical
Building the instrument that could provide that proof, however, is challenging. PIPER must carry four very large detector arrays — each containing 1,280 pixels — to collect as many photons as possible. To prevent the faint signal from being overwhelmed by instrument-generated heat, Kogut’s team must place the instrument inside a dewar and cool it to just 1.5 degrees above absolute
zero — even colder than the cosmic microwave background radiation where the gravity waves could lie hidden. The detectors needed to sense the signal will be maintained at an even colder temperature of 0.1 Kelvin.
With her technique, the pixels are constructed on a single silicon wafer bonded onto a read-out circuit. This reduces the amount of handwork, making it easier for technologists to increase the size of the array. Despite the breakthrough, Kogut said it still would take three years to build the detectors. “They’re so complicated,” he said. |
Al Kogut, the principal investigator of the balloon-borne Primordial Inflation Polarization Explorer, will search for clues of cosmological inflation. He is pictured here (third from the left) with students who are helping him build the instrument (left to right): Samelys Rodriguez, Andrew Ziegelstein, Erin Wilson (now a NASA employee), and James Hinderks.
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With R&D funds, Kogut also developed the dewar to keep the instrument cold. That dewar flew on the Absolute Radiometer for Cosmology, Astrophysics, and Diffuse Emission experiment, another balloon payload that he flew in 2006 to detect heat from the first generation of stars (see story below). PIPER will use the same dewar.
“This is why Goddard is so successful,” Kogut added. “We build on technologies that work.”
In addition to solving a longstanding cosmological question, PIPER could set the stage for Goddard winning a follow-on mission — CMBPol — that NASA hopes to fly within a decade. “PIPER is a pathfinder to demonstrate new technologies and determine whether CMBPol has something to measure,” Kogut said. If he and his team see the signal, CMBPol would carry out identical science, except the mission would spend years, not hours, gathering the faint gravity-wave signal. “PIPER will be able to detect the signal, it just won’t be as precise as CMBPol,” he said. “It’s similar to what COBE did. COBE found the temperature differences in the cosmic background radiation and WMAP came along to provide the details.”
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