Jonathan Pober

Assistant Professor of Physics
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Jonathan Pober
Assistant Professor of Physics
It is the ultimate research effort: trying to understand the origin of everything. Jonathan Pober examines the 14-billion-year history of the universe as we know it in the wavelength of hydrogen.

Jonathan Pober looks back to the beginning of time for a living. It’s amazing that astronomers have developed this capability, and at a pivotal point in his life, Pober was amazed to learn he could contribute to the effort.

He was a pre-med undergraduate at Haverford College when he took the half-credit, every-other-week freshman seminar in astrophysics that future doctors could take to study physics in a way that might engage them more than sliding blocks on ramps, he said.

“My interest in this field almost took me by surprise,” he said “It was honestly for me a ‘People can actually study this?’ moment. It wasn’t just for Stephen Hawking and Albert Einstein. I sort of ran away with it from there.”

He not only ended up making physics and astronomy two of his majors (he triple majored in philosophy), but also he joined a research lab studying the earliest structure of the universe based on data about the “Cosmic Microwave Background” (CMB). This is a pervasive emanation of electromagnetic radiation that gave astronomers their first picture of how matter was distributed around the cosmos only about 385,000 years after the Big Bang about 14 billion years ago.

The CMB surrounds us but is slightly stronger from some directions than others — some call it “lumpy” or “anisotropic.” That’s important because even faintly apparent clumps of matter back then could serve as centers of gravitational attraction that eventually would coalesce into clusters of galaxies and stars.

“They are sort of the seeds of structure in the universe,” Pober said.

Pober got right to work on helping develop ways to find more and finer detail of these variances in the CMB signal. The smaller the details astronomers seek, the better they must become at filtering out all the other signals in the foreground that might interfere and blur the picture.

After graduation in 2007, Pober went to the University of Cambridge for a year to continue his studies and to earn a master’s degree in physics. From there he went to the University of California–Berkeley, where he earned a second masters and his Ph.D. in astronomy.

At Berkeley, Pober found the wavelength he’s been tuned to ever since: the signature radio wave emitted by plain old, neutral hydrogen, the most abundant and simplest element. While the CMB reveals a single moment in time, tracking hydrogen’s radiation allows astronomers to look at a range of times in the history of the universe. The wavelength emitted by hydrogen is 21 centimeters, but because the universe has been expanding since the Big Bang, that wavelength appears to us to be proportionally shifted longer and longer the farther away and therefore older the hydrogen is. So if Pober wants to see what the distribution of hydrogen looked like, say, 500 million years after the Big Bang, he can look for hydrogen whose wavelength has been shifted to about two meters. Tuning to a different wavelength would give him a glimpse at hydrogen of a different vintage.

So while the CMB provides a snapshot, 21 cm hydrogen provides more of a movie of the universe’s evolution since.

“Understanding how we get the diversity of galaxies and structure we see in the universe today is something we are looking to do,” he said.

The trick remains, however, developing the instrumentation and analytical methods to filter out all the noise and interference in the foreground that could intervene.

Pober’s teaching interests are more down to Earth. At Berkeley he delighted in designing and co-teaching a class with a social scientist and philosopher called “Sense & Sensibility & Science.” The general education class taught the students, who hailed from a diversity of academic interests, about how science can fit into societal decision making. He said he enjoyed teaching a mix of students with a mix of methods. It’s a mistake to just try the same thing over and over if it isn’t working.

“Different people learn in different ways,” he said. “It’s too easy to make the assumption that ‘this is how I learned it, this is how other people will learn it. If they didn’t get it the first time, I’ll just repeat myself.’”

Since finishing at Berkeley in 2013, Pober has been at the University of Washington. Coming to Brown, as Pober will do in January 2016, provides him the chance to strike a happy balance between his research and teaching interests.

“I’m really excited to be at a place where undergraduates are spending time with professors,” he said.

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