From IWU Magazine, Spring 2010
A Universe Filled with Questions
Story by TIM OBERMILLER
“Dark energy” may sound like a phrase from a Star Wars film. But for cosmologists such as Assistant Professor of Physics Thushara Perera,
the search to verify and understand this bizarre form of energy may be key in grasping
the fundamental nature and destiny of our universe.
“Everything we know about the universe is probably 5 percent of what is really out
there,” Perera says. “My research has been completely based on finding the missing
elements of the universe. Dark energy is one of those elements.”
Perera develops technologies to trace how the universe formed. Behind him, junior
physics major Jesse Schaar prepares a liquid-helium container used to cool devices
that detect light from early galaxies.
(Photo by Marc Featherly)
Perera’s quest to understand the true nature of the universe began as a teenager growing
up in Sri Lanka. His parents were doctors, “and my father was always interested in
learning more about different topics in astronomy, such as black holes. But without
the necessary background in mathematics, he felt his understanding would always be
superficial. I think it was my father’s drive to have a deeper understanding of the
universe that also inspired me.”
As a college student at Ohio Wesleyan University, Perera majored in math and physics.
“If you want to have a deeper understanding of the universe, you always go to physics,”
he says, describing his chosen field of cosmology as “a sub-branch of physics.”
“Just as in any branch of physics, there are two kinds of cosmologists,” he continues.
“There are theoretical cosmologists, who use mathematical models to create theories
about the evolution and composition of the universe. And there are experimentalists
who devise ways to gather data that confirm or falsify these theorists’ predictions
and occasionally find something totally unexpected. I am an experimentalist.”
Among the biggest questions cosmologists are now attempting to answer is: “Will the
universe go on forever or not?”
According the Big Bang model, the universe began about 13.7 billion years ago when
all the energy and matter of space was condensed into one extremely hot, dense point.
It has since been expanding and changing into the vast cosmos we live in today. While
cosmologists generally accept this model, theories differ about what the eventual
fate of the universe will be.
Recent theories have suggested that the universe will simply stop expanding at some
point and reach a plateau of equilibrium that holds it in a steady state. Another
theory supports the idea of a “big crunch” that will occur as the expanding universe
slows down enough that it will begin to collapse under gravitational forces.
But what if something is making the expansion speed up instead of slow down? That
was the startling conclusion based on measurements of supernovae published by two
international teams of astronomers in 1998, which called into doubt the established
expectation of a universe that was expanding at ever-slower rates.
Because gravity pulls things together and never pushes them apart, gravity exerted
by the known matter in the universe should create a drag that slows down the universe
as it expands. However, the supernovae study — later verified by many other cosmological
observations — suggested that some mysterious, repulsive force, a “dark energy,” must
exist to explain the model of an accelerating universe.
It is now believed that dark energy currently accounts for about 70 percent of the
total mass-energy of the universe, says Perera — the rest being dark matter (about
25 percent) and ordinary matter (5 percent). That’s a radical shift in thinking from
just decades ago, when scientists thought that the universe was comprised almost entirely
of ordinary matter — the protons, neutrons and electrons that make up everything from
distant stars to human beings.
The chart above depicts three possible futures for the universe, depending on the
behavior of dark energy. First verified by astronomical measurements in 1998, dark
energy is believed to account for 70 percent of the total mass-energy of the universe.
Scientists first postulated the existence of a non-visible form of matter, called
“dark matter,” in the 1930s to explain certain gravitational effects observed in the
motion of galaxies. Experiments are continuing to directly detect dark matter, but
physicists suspect it is composed of sub-atomic particles, called WIMPS, that interact
very weakly with ordinary matter, making them extremely difficult to detect.
Perera participated in dark-matter detection experiments as a graduate student at
Case Western Reserve University. Using an array of semiconductor detectors cooled
to extremely low temperatures, Perera and his collaborators hoped to detect any rare
WIMP-scattering events among a vast number of more common particle interactions.
“Dark matter has still not been detected directly,” Perera says, “but we must be getting
closer because recent experiments have become exquisitely sensitive.”
While dark matter’s existence may soon be confirmed, the search to understand dark
energy is just beginning. When Perera became a postdoctoral research fellow at the
University of Chicago’s Enrico Fermi Institute in 2002, he couldn’t resist the challenge
of joining that search.
“They gave me the freedom to just roam around, sit in at various group meetings and
decide which group I wanted to join,” Perera recalls. “The group I chose was working
on an experiment that would have potential for revealing the nature of dark energy.
And the detectors they were developing had technology similar to those used in dark-matter
experiments. So it was a good match.”
In 2005, as a research associate at the University of Massachusetts, Amherst, Perera
continued to develop superconducting detectors and semiconducting technologies for
use in the Astronomical Thermal Emission Camera (AzTEC). Mounted on telescopes in
extremely high and dry places, the camera is sensitive enough to examine light wavelengths
from early in the universe, all the way back to 300,000 years after the Big Bang.
“The aging process of the universe stretches ancient light, and you have to go through
a lot of trouble to see it,” says Perera. “But that light is critical to answering
fundamental questions about early galaxies and how they formed.” With this and other
experimental data, cosmologists hope to determine the expansion history of the universe
— and what role dark energy may play in that expansion.
Joining Illinois Wesleyan’s faculty in 2008, Perera continues his work with AzTEC
by analyzing data the camera collects, and by building and designing hardware for
future cameras. This coming fall, he plans to have IWU physics students help him in
Dark-energy investigations are currently centered at big research universities. “If
my students and I are able to make a piece of hardware that is useful for instruments
being built at several large institutions, that would be an example of a small university
making an important contribution to this field,” says Perera. It would also help keep
alive his goal of helping answer some of the most intriguing questions posed by careful
observations of our universe.
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