Distinguished Professor: Leonard Parker
A pioneer in the study of the early universe, he established the field of curved-space quantum field theory.
To celebrate his 60th birthday in 2002, the eminent theoretical physicist Stephen Hawking convened a meeting of elite thinkers in cosmology, the study of the origin, structure and evolution of the universe. Among this select gathering at Cambridge University in England was UWM physics Professor Leonard Parker. Indeed, Hawking's celebrated work on radiating black holes was made possible by Parker's prior research.
"I was the first to show that the expansion of the universe and strong gravitational fields can produce elementary particles out of a vacuum," Parker explains. "That's a process that's important because it amplifies fluctuations in the very early universe, in what we call the inflationary stage of the universe where it's expanding very rapidly early on. Those fluctuations are now observable in the cosmic background radiation that we see."
Parker's early discoveries established the field of curved-space quantum field theory, which, according to UWM Physics Professor Bruce Allen, has "played a central role in the development of modern physical theories and now underlies some of the most promising models for the development and evolution of the early universe."
Hawking's theoretical work on particle creation by black holes—objects with gravitational fields so strong that not even light can escape from them—relied on concepts and methods first developed by Parker.
Perhaps the best indicator of the importance of Parker's research is his funding record: he has received continuous funding from the National Science Foundation since 1969.
Of all his accomplishments, Parker is most proud of his establishment of what is now the Center For Gravitation And Cosmology at UWM, a widely recognized research group that Parker considers "one of the best in the world." Consisting of six faculty, several postdoctoral fellows, and a number of graduate students, members of the group consistently attract a total of more than $1 million in research funding annually.
Currently, Parker and his collaborators are among many trying to explain the apparent acceleration of the expansion of the universe. One possibility he's exploring is vacuum energy, a form of energy permeating all of space and possessing negative pressure, which results in a repulsive gravitational force. "So far it agrees with the observations," Parker says. "As we get more observations, it could be disproved. We're getting close to knowing."