Jewish cosmologist is a star at CMU
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Science & ReligionScientific superstar bridges two universes

Jewish cosmologist is a star at CMU

"You're looking to the why - what are the physical laws that make our universe look like this? Everything else is secondary."

Rachel Mandelbaum. (Photo courtesy of Rachel Mandelbaum)
Rachel Mandelbaum. (Photo courtesy of Rachel Mandelbaum)

Rachel Mandelbaum has always asked why.

“From when I was a pretty young child, I was interested in learning how stuff worked,” she said. In elementary school, she read reams of books about science and the scientific method.

Today, the Princeton University alum, mother of three and Orthodox Jew is a professor at Carnegie Mellon University, living the science she once explored as a child.

“I’m an observational cosmologist,” she explained. “We use information from telescopes to learn the history of the universe for the last eight, nine billion years.”

For Mandelbaum, it’s more about the physics of the equation than the history that’s been captured, the science learned over time.

“You’re looking to the why — what are the physical laws that make our universe look like this? Everything else is secondary to that,” Mandelbaum said. Her cosmology teachings — the work of explaining an expanding universe — are mostly for graduate students seeking PhDs.

Mandelbaum said her explorations of science and faith “are totally compatible things.”

“Learning the physics of the universe, researching to learn more about it is entirely in the spirit of being a practicing Jew,” she said. “The sets of questions don’t overlap but that sense of asking ‘Why?’ is something I tend to do in many aspects of my life.”

Mandelbaum moved to Pittsburgh about eight years ago from New Jersey, where she served as a research professor at her alma mater. (Her eldest daughter, who is 19, attends Princeton as well, though she’s leaning toward computer sciences instead of physics.)

Speaking to Mandelbaum, you’d think she was just another college professor in a city ripe with them. That’s just not the case, her colleagues said.

“She’s one of the reasons I came here,” said Scott Dodelson, the head of the physics department at Carnegie Mellon University, who came to Pittsburgh from Chicago about three years ago. “She’s kind of world-renowned. She’s the best at what she does … and she’s incredibly thoughtful, on a different scale than the rest of us.”

To illustrate, Dodelson pointed to the LSST Dark Energy Science Collaboration, a group of roughly 1,000 thinkers and academics Mandelbaum helps lead. About five years ago, before Mandelbaum was leading the group, federal policies appeared to restrict colleagues from certain countries — Iran and Syria, to name two — taking part in the work.

Mandelbaum wasn’t going forward excluding anybody based on their nationality.

“Rachel basically said, ‘We’re not doing this — we can’t let this meeting discriminate against our colleagues,’” Dodelson said. “She works in a field [where] she’s one of the world leaders. I’m a little in awe of her work.”

Mandelbaum’s work is a little heavy for a layperson to digest, though she approaches it voraciously.

“Weak gravitational lensing, the deflection of light by mass, is one of the best tools to constrain the growth of cosmic structure with time and reveal the nature of dark energy,” she wrote in a paper published in 2018 by Annual Reviews of Astronomy and Astrophysics. “I discuss the sources of systematic uncertainty in weak lensing measurements and their theoretical interpretation, including our current understanding and other options for future improvement.”

“I’m sorry to say that the intro is a bit less accessible than I remembered,” she quipped, when sending the Chronicle the research paper.

Fred Gilman, a professor of theoretical physics who served as dean of CMU’s Mellon College of Science from 2007 to 2016, is glowing when he speaks about Mandelbaum.

“She is a scientific superstar,” Gilman said.

“A great teacher, advisor and mentor for students at all levels,” he added. “A wonderful person and colleague.”

Dodelson said the fact that Mandelbaum is identifiably Jewish, keeping kosher at school events or wearing a head covering, is a big part of how she’s seen. And her act of being Jewish in the university setting sends a powerful message.

“Academics have reservations about religion, in general,” Dodelson said. “The fact that she’s so open is impressive — it tells people, ‘You can be what you want to be.’” PJC

Justin Vellucci is a freelance writer living in Pittsburgh.

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