Mark Trodden, chair of the Department of Physics and Astronomy in Penn’s School of Arts & Sciences, has devoted his career to studying the intersection of what he calls the physics of the tiny, or quantum mechanics, and the physics of the very large, or general relativity. His goal is to reach a fuller understanding of the universe.

He grew up in the northwest of England, near Manchester and Liverpool, and was the first member of his family to go to college. Although he was good at many things in school, he says mathematics is the first thing he really loved.

“I found it beautiful and challenging,” he says. “I liked the abstraction of it. I found it sort of magical in that things that are quite opaque and seemingly intractable, you can find a solution by expressing the problem in mathematical form.”

He went to Cambridge to study math, and over time became interested in mathematics as it was applied to physical systems, which led him towards theoretical physics

He stayed at Cambridge to complete a master’s degree, focusing on theoretical physics. In 1992, his studies took him to the U.S., where he completed his Ph.D. at Brown University in 1995. He went on to become a postdoctoral fellow in the Center for Theoretical Physics at the Massachusetts Institute of Technology, and at Case Western Reserve University in their Particle Astrophysics group. He then became a tenure-track assistant professor at Syracuse University.

After rising through the ranks at Syracuse, eventually receiving an endowed chair as a full professor, Trodden made the move to Penn in 2009, where he became the Fay R. and Eugene L. Langberg Professor of Physics and co-director of the newly minted Center for Particle Cosmology. He’s been at Penn ever since.

He explains that being at Penn allows him to be part of a broad and interesting group of people working in particle physics and cosmology that doesn’t exist at most other places.

“We are one of the premier places for putting together everything from the very theoretical side to the very observational side of a number of issues in cosmology,” he says.

As department chair of Physics and Astronomy, Trodden is also responsible for putting together a coherent plan to make sure that Penn stays at the “bleeding edge” of all areas in which they do research.

Trodden’s own interests span a number of different areas of fundamental physics, ranging from high energy physics to gravity and cosmology. His best-known work focuses on the accelerating expansion of the universe.

Trodden explains that this acceleration goes against one’s intuition about how gravity works.

“One way to think about it is that yes, everything’s moving away from us and the further away things are moving away faster, but of course they’re still attracted to us as they are to everything else: through gravity,” Trodden explains. “So you would think that they would be slowing down, because after all gravity is an attractive force.”

Twenty years after its discovery, the theoretical explanation for this acceleration is still unknown. One possibility is that it’s due to what Einstein called the cosmological constant. Another is that there’s a new type of mass and energy that is exerting a strange new force on matter in the universe, which people call dark energy.

“There’s a more radical possibility that there is no new stuff out there pushing things around, but that the set of rules that tells us how the existing stuff of the universe pushes things around is not the same as we thought it was,” Trodden says. “That’s a clumsy way of saying maybe Einstein’s Theory of General Relativity is not exactly right at large distances. Maybe gravity is modified.”

Trodden has been working on this idea since before he came to Penn, and wrote a well-known paper on it in 2003, which appeared in the journal Physical Review D.

One of the myths Trodden would like to dispel about science is that it’s an isolated, lonely existence—when, in fact, it’s extremely social and collaborative. He says his favorite moments involve standing at a blackboard with other people, “hammering out ideas and trying to find a common track through a problem to make a breakthrough.”

He added that on the whole, science is a slow and incremental process.

“A lot of it is going down wrong alleys and dead ends,” he says. “Most of the time you’re not finding out something huge and new, you’re finding out something small and new. Or you have an idea that seems to hang together beautifully and nature just refuses to agree with you and data rules out your theory.”

All of these things, he says, are exciting in their own way, and it’s a privilege to be involved in the process.

“It’s kind of a ridiculous thing that someone pays me to sit at a desk and think about how the universe works,” Trodden says. “I’m very lucky to be able to do that.”