Building Toward Discovery
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Building Toward Discovery

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A Drexel Professor’s Role in Finding Gravitational Waves

When talking about his contributions to science, Isaac Newton said, “If I have seen farther, it is by standing on the shoulders of giants.” The quote refers to the process that makes up the backbone of scientific study: The steady building of research that eventually leads to game-changing discoveries.

With the February 2016 discovery of gravitational waves by the LIGO Scientific Collaboration, the group’s scientists confirmed one of the predictions made by Albert Einstein decades ago when he set out his theory of relativity. But while LIGO certainly stands on Einstein’s shoulders, there’s another scientist whose shoulders helped the group “see farther”: Stephen McMillan, PhD

McMillan, professor and department head of physics at Drexel University, published a paper in The Astrophysical Journal back in 2000, when LIGO was first constructing its antennae to search for the waves. In the paper, co-authored by Simon F. Portegies Zwart, then of Boston University, a procedure was laid out for calculating how many black hole binaries could be created in star clusters. That number could then be scaled up to determine the number in galaxies and the universe.

“Back in 2000, the gravity wave community was pretty desperate for something they’d be able to observe. We wrote this paper when the LIGO people were grasping at straws,” McMillan recalls. “We looked at neutron star mergers and black hole mergers, which are most likely to occur in star clusters. We developed the procedure to make estimates for scale. We put together the methodology that a lot of other papers used.”

When they began their work, McMillan says he wasn’t sure if there would even be anything measurable, even by LIGO. But they set out to just “improve our understanding” of the science of black hole binaries.

As it turned out, their work gave the LIGO group an idea of what signals they could look for to record the existence of the waves, and the 2000 paper was cited in LIGO’s 2016 paper confirming their discovery.

The discovery of gravitational waves is exciting to everyone in physics, McMillan says, and he’s happy to have been a part of the process that began with Einstein.

“This is a whole different type of radiation,” McMillan said. “This is an alternate way of viewing the universe. Any time you have a new type of medium, it’s remarkable how much information can be extracted.”

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