Cosmic Seeker
When she was growing up in Milan, Italy, science was something of a family business for Elena Pierpaoli. Her mother and aunt were physicists, her sister a mathematician and her father an economist.
So it seems fitting that she would end up in cosmology. After all, math and physics are the lingua franca of the field. But much of her work seeks to discover the long-hidden shape of the universe and the nature of its component parts.
While Pierpaoli was initially attracted to particle physics as an undergraduate, she soon discovered her calling in cosmology.
“The early universe offered more theoretical projects along a less trodden path,” said Pierpaoli, associate professor of physics and astronomy in USC College. “Also, the undergraduate classes I took in extragalactic astronomy and cosmology proposed many problems with a variety of explanations that still had no consolidated answers.”
Reconciling theories about the nature of the universe with actual observations is the theme that ties together her research. She wants to know how the universe began, how fast it’s expanding now and what that can tell us about its future — Will it expand forever or hit some critical point and begin to contract?
But she also investigates the basic constituents of the universe — from trying to characterize mysterious, invisible dark matter and dark energy to understanding the properties of more ordinary matter. She seeks to understand the geography of galaxies, what scientists call the large scale structure of the universe, and how large clumps of galaxies, called galaxy clusters, have evolved over time. All this information can be used to understand how it all started during the Big Bang.
“I want to know what gave rise to galaxies, to clusters of galaxies, and to the structures in the universe,” Pierpaoli said. “But I also want to answer more fundamental questions, about the early universe and particle physics.”
In studying this array of topics, she has made contributions to many different areas of extragalactic astronomy, cosmology and astrophysics.
After postdoctoral work at the University of British Columbia and prestigious research fellowships at Princeton and Caltech, Pierpaoli joined the College as its sole cosmologist in 2006. Coincidentally, that was the same year that the Nobel Prize in Physics went to scientists who studied light from the early universe — cosmic microwave background (CMB) radiation.
The Earth is constantly bombarded with low levels of CMB radiation from space. It’s harmless to us and invisible to the naked eye, but it’s also a message from the deepest past: Scientists think the CMB radiation reaching us today began its journey about 380,000 years after the Big Bang, and has spent billions of years traveling through space.
Later this year, the Planck satellite is scheduled to launch, carrying aloft a package of telescope and instruments that will afford researchers like Pierpaoli the best view to-date of CMB radiation.
Pierpaoli has been a member of the Planck mission science team for well over a decade now — ever since she was a graduate student in her native Italy. As part of the team, she has helped conceptualize what kinds of data the mission should collect in order to answer the big questions of cosmology.
That includes figuring out exactly what Planck, which will be sent out 1.5 million kilometers from Earth, should focus on as its telescope sweeps the entire sky, twice. Critically, it also involves figuring out the best ways to analyze and interpret the data once they start coming in. The first full-sky map will be available six months after launch.
Working with data collected by one of Planck’s predecessors, the COBE satellite, as well as other ground-based and balloon-borne experiments, Pierpaoli helped to reveal more about the shape and structure of the universe itself. Calculating the universe’s geometry has long been a divisive issue for astrophysicists, a debate in which the arguments relied solely on theoretical conjectures and models.
Specifically, she revealed that space seems very nearly flat — in other words, the geometry of the universe obeys the same rules as on a sheet of paper.
Pierpaoli and her collaborators developed a new analytical technique that allowed them to combine data from a number of groups working on different CMB experiments. Their paper, published in 2000, produced the “first real data showing that the universe is mostly flat,” she said, adding, “The merit of that finding was mostly technical.”
USC College’s Clifford Johnson, a colleague in the physics and astronomy department who is familiar with her work, called this statement “unjustified modesty. This was absolutely a piece of research that changed people’s minds.”
In addition to determining the universe’s geometry, by analyzing CMB data Pierpaoli hopes to understand what exactly it’s made of. “Despite great improvements in understanding the matter content of the universe, we are not quite yet done!” she said. “The nature of dark matter is still a heavily debated topic, since we are still looking for the model that fits with all of the data. The nature of dark energy is completely unknown.”
Planck’s more-accurate measurements of the CMB will tell us more about the universe’s age and constituents, as well as when the first stars shone and more about how the universe’s expansion has recently accelerated. But Pierpaoli is also excited about the other data that Planck will collect.
“There’s much more science contained in the Planck measurements than just the CMB data,” she said. “By observing the entire sky at nine different frequencies, ranging from the radio to the infrared, we’ll be able to learn more about distant galaxies, other galaxy clusters and our own galaxy.
“One day, many of the big questions will be answered, thanks in part to the precise measurement of the CMB spectrum that Planck will provide,” she continued. “The goal now is to be sure we are prepared to interpret the data as soon as they become available.”