Cover Story

The Physicist with a Music Degree

The New IAS Director Andrew Cohen Has an Intriguing History

Before joining IAS, Prof Andrew Cohen has been Professor of Physics at Boston University. He has also served as Chairman of the Board of the Aspen Center for Physics since 2015.
\\   I owe my parents a tremendous debt, allowing me to be reckless while finding my own way.  \\

Prof Andrew Cohen, the new Director of lAS, Lam Woo Foundation Professor and Chair Professor of Physics at HKUST, is not your typical scientist. In fact, nobody, himself included, would have guessed he would one day become a physicist. His father received a college degree relying on the Gl Bill for returning World War II veterans, but having a real academic in the family was not something that his parents had ever considered. As a child, Cohen hated school and his parents let him drop out when he was just 13 years old.

He loved museums, though, and there was an abundance of them in his hometown of Washington DC. He could often be found roaming around the museums and learning on his own. But DC wasn't the ideal place for him. “Unlike the vibrant capitalcity of today, it was a bit of a sleepy area back then, especially the suburb I grew up in. In retrospect it was a great place to grow up, but at the time I desperately wanted to get away,” he said.

A 14-year-old Cohen thus left his childhood home and enrolled at the University of Delaware. A year and a half later he moved to California to join Stanford University. “In addition to pride, I guess my parents were mostly gripped by fear as I was on my own at such a young age,” he joked. “But I owe them a tremendous debt, allowing me to be reckless while finding my own way.”

Stanford was an eye opener to the young Cohen, who was amazed by the variety of new things to learn. While at Stanford he changed his major almost constantly, taking courses in everything from computers to psychology. He eventually settled on specializing in physics and music, earning degrees in both areas.

Other than music and physics, he was a lover of foreign literature. His first taste of Chinese literature was the Dream of the Red Chamber (紅樓夢), a novel he read after being told that the book was one of the greatest masterpieces in the Chinese language. Yet he found the novel in translation underwhelming. To find out if the book was truly as good as people claimed, Cohen decided to study Chinese with the hope of reading the novel in its original language. “Even though my Chinese is quite limited, after a second read, I fell in love with it,” he recalled fondly.

In 1979, a delegation of prominent US scientists, including the soon-to-be Physics Nobelist Prof Arthur Schawlow, visited China. Cohen, just finishing his final year as an undergraduate, was working in Schawlow's laboratory. After returning from the trip and learning about Cohen's interest in Chinese, Schawlow told the young Cohen that he knew the President of the East China Normal University who might be able to arrange a trip to China for him. It was through this connection that Cohen was among the first group of Americans to visit China when the nation reopened its gates to the world in the late 1970s.​

An Unlikely Physicist

When his sojourn in China concluded, Cohen returned to the US where he was asked by Schawlow to enroll as a non-matriculated graduate student and work in his laboratory. On a whim, he applied to the Harvard graduate school, with little understanding of what research in physics was like. “I thought it would be the same as undergraduate studies in which professors lecture students in classrooms, and we spend our time mastering the profound accomplishments of the past. It was a complete novelty to me that graduate schools are about students making their own discoveries,” he said.

As a person of many interests, Cohen found physics particularly appealing: “It is a broad discipline that engages with the way the world works across a huge variety of phenomena. For example, quantum physics allows understanding of atomic and subatomic systems, where probability and statistics enter in a deep way; econophysics uses the area of physics known as statistical mechanics to solve economics problems; the renormalization group—a technique developed to understand how the behavior of systems on the large scale can arise from the interactions of its components on small scales—has been applied to machine learning in computer science.”

Driven by his newfound passion for research, Cohen went on to earn a PhD in Physics at Harvard University. There he spent one year as a postdoctoral fellow and then joined the Harvard Society of Fellows, where he relished the intellectual exchange with peers from across a wide variety of disciplines.

Cohen studies how nature operates at extremely short distances in a field known as high energy physics. It is so named because probes with very high energy are needed to explore the principles that govern the behavior of physical systems at short distances. Particles are first accelerated to high energies and subsequently allowed to interact or “collide”, and the products of these interactions are then examined. The large complexes used to accelerate the particles, collide them, and observe the outcome are called colliders. The highest energy collider currently in operation is the Large Hadron Collider located at the CERN laboratory near Geneva, Switzerland.

One piece of work that Cohen has a particular fondness for arose from another experiment at CERN. In 2011, scientists on the OPERA experiment reported on subatomic particles called neutrinos appearing to travel faster than light, in apparent violation of the principle of special relativity. Cohen was in Boston when he heard the news. “It was a bombshell. It would be one of the most important discoveries of the century if proven true,” he recalled.

Nobel Laureate Arthur Schawlow, featured in this photo taken at his Stanford laboratory, saw the potential in the young Collen and encouraged him to pursue a graduate degree in Physics.

He was obsessed with the news and poked at the results as scientists do. Then a thought struck him: it was well-known that electrons traveling faster than light lose energy through a phenomenon known as Cerenkov radiation. Cohen knew that faster-than-light neutrinos do not produce Cerenkov radiation since neutrinos are not electrically charged. But he realized that such neutrinos would emit a peculiar relative of Cerenkov radiation, which has since become known as Cohen-Glashow radiation.

Over the next two days, he worked out the details to conclude that if the neutrinos were traveling as fast as reported by the OPERA experiment, these neutrinos would have lost all their energy to Cohen-Glashow radiation. Hence the observation of high energy neutrinos in the OPERA experiment was incompatible with faster-than-light travel. On the third day, he finished the paper with a collaborator, Sheldon Glashow, and the paper was published a few weeks later.

“It was the fastest paper I have ever written and one of my fondest memories in research so far,” he said. After a year of painstaking work by the OPERA scientists, a flaw was found in the original apparatus. Once the flaw was corrected, the neutrino speed was found to be compatible with the speed of light. Cohen's work still provides the best limit on the maximum speed of neutrinos.

\\  Cohen's work still provides the best limit on the maximum speed of neutrinos.  \\

Research and Education

The Large Hadron Collider, the world's biggest and most powerful particle accelerator, at the CERN lab in Geneva consists of a 27-km ring of superconducting magnets. Cohen has been working closely with scientists there to test predictions of different theories.

Basic research advances our fundamental knowledge about the world. It is not uncommon for people outside the scientific community, including politicians, businessmen, and other laypeople, to question the practicality of this kind of research. Cohen believes that research need not always be in the service of specific applications or technologies. Scientific research, like other creative activity, has intrinsic value in discovering how our world works and finding our place in the universe.

“That said, scientific discoveries have led to, and will continue to lead to, profound changes in our lives. But at the time the research is conducted, we often cannot tell how these developments may lead to important applications. If we limit ourselves to applied research, we would miss opportunities for potential applications in the future,” he added. Indeed, were it not for basic research in science and mathematics a century ago, little of today's technology would exist. It is unlikely that scientists of previous generations would have predicted the profound effect on our civilization that their work has had.

Cohen tries to imbue the spirit of discovery in everything he does. At Boston University, he has taught a course for undergraduates not specializing in the sciences. “All undergraduates are required to take a set of so-called general education courses, designed to introduce students to a variety of fields outside their own specialization. Such general education courses often function as surveys of subjects, and rarely introduce students to material that they might find useful in later life. For example, students are often expected to memorize Newton's Laws in a physics general education course. But being able to recite these laws is not particularly useful to these students.What is more important is to provide students with the tools to observe the world around them and extract meaning from what they see,” he said.

He often used movies to inspire students to make discoveries on their own: “Movies function like a shared laboratory. Each film has its own physical rules and tends to stick to those rules. By observing the movie we can try to determine these rules in a process of discovery that is very much like determining the laws of nature.”

To Cohen, the hero of Crouching Tiger, Hidden Dragon is Yuen Woo-ping, the martial arts choreographer, who weaves together physics and character development.
\\  If we limit ourselves to applied research, we would miss opportunities for potential applications in the future.  \\

One of his favorite movies for the course was Crouching Tiger, Hidden Dragon (臥虎藏龍). He would ask students to observe the character movements, especially during fight scenes, and attempt to deduce when real rules of nature, such as the conservation of momentum, were being obeyed, and when they were being violated. For this particular movie, the students would learn that character arcs played a role in whether the rules of nature were being obeyed or not. The action scenes were often choreographed to illuminate the character of the protagonists, and students were able to quantitatively understand this through their own observation. Cohen's unorthodox approach to teaching has earned him awards and a reputation as an excellent lecturer.

Coming to HKUST

Having called Boston his home for almost 30 years, Cohen's decision to move to Hong Kong was not made lightly. Impressed by his time at the Harvard Society of Fellows, he hopes to create an environment at HKUST where researchers can pursue their ideas unfettered by administrative constraints and surrounded by peers from other disciplines. lAS presents the perfect opportunity to pursue this passion of his.

Cohen has joined several programs and conferences hosted by IAS in the past, including the High Energy Physics program and the Gordon Research Conference​. He thinks very highly of HKUST: “It is an amazing institution and vastly more accomplished than a 25-year-old organization has any right to be. HKUST is comparable to other great universities and the institution and its faculty deserve more recognition.”

Institutions in the US and Europe are facing increasing challenges in financing and conducting scientific research. The strong drive at HKUST for doing high quality research and the support the University administration provides is clearly one reason the University has been so successful. “Hong Kong is not well known in the US and Europe as a research powerhouse, but it should be. And perhaps even the Hong Kong people themselves are not fully aware of the amazing activities that take place here. The conditions are great at HKUST and with the proper support we can build upon the successful center of research and higher learning that is already here,” he said.

Prof Cohen enjoys bringing people together to engage in intellectual discussions and creative activities.