Graduate Student Reflections: An Interview with Mike Hepler

This semester, in our spring series, PCURs will interview a graduate student. In Graduate Student Reflections: Life in Academia, interviews with graduate students shed light on the variety of paths one can take to get to graduate school and beyond, and the many insights gained along the way from research projects and mentors. Here, Nicholas shares his interview with Mike Hepler, a fourth-year Ph.D. candidate in the Department of Mechanical and Aerospace Engineering.


Mike Hepler is a graduate student in the Department of Mechanical and Aerospace Engineering



Was it difficult transitioning back to school?

Getting back into the mindset of classes was a struggle.  Knowing that you are going back into the world of coursework, exams and generals was a bit daunting and off-putting.  However, I came into the classes not with a mindset of performance and grades, but of gathering skillsets, building professional relationships, and learning as much as possible from each classroom experience.  For classes that are often described as “drinking from the firehose,” it was this flexible and resilient attitude toward learning that helped me keep a healthy outlook toward graduate school.

On top of this, there was a lot of excitement around getting into lab, into research, and even teaching courses. It made the transition more of a juggling act, but also exciting.  There were new friends to meet, new relationships to manage, and a system of unspoken responsibilities and expectations to navigate.  Academia is certainly a strange place to work, but the flexibility can be exciting and empowering.

What is your research about?

Currently, the US and Russia have an agreement under the new Strategic Arms Reduction Treaty (START) which limits the number of deployed nuclear weapons each country may have at any time.  In order to enforce this treaty, each country uses national technical means like satellites and a limited number of inspections to monitor the number of deployed bombers, Intercontinental Ballistic Missiles (ICBM), and Submarine-Launched Ballistic Missiles (SLBM).  Under this regime, the things that are being verified are not warheads themselves, but the number of “delivery vehicles,” which serve as a convenient analog to the total number of weapons a nation might have.  Delivery vehicles are generally big and easier to spot. Delivery vehicles can be measured and observed without giving away highly classified design information about the weapons they carry.

However, one can imagine more ambitious treaties in which limitations and reductions not only apply to deployed weapons, but also to the thousands of stockpiled warheads each nation has produced.  Under such a treaty, it may be necessary to verify more than just the delivery vehicles, and instead require verifying the authenticity of individual item claimed to be nuclear warheads.  But how do you make measurements of an object whose design is secret?

If you were an inspector, what measurements do you make to verify that an item counted in the treaty is a real weapon?  If a host nation is supposed to dismantle hundreds or thousands of weapons, how can you be sure that the thing being dismantled is a real weapon, and not an imitation?  On the other hand, if you are a host nation, and someone from another country tells you that they want to make measurements of your highly-engineered and highly-classified weapon, what would you permit to be measured?  Who does the measuring?  How can you be sure that information will not be leaked?

My research attempts to provide a way of measuring an object in such a way that you can be certain of the item’s authenticity, without revealing information about the object itself.  Our group has developed a physical implementation of what’s known as a “zero-knowledge proof.”  Used for many years in information and computer security, these “interactive” proofs allow one to verify a mathematical statement, while learning nothing about why the statement is true.

In our experiments, we use a beam of neutrons to image an inspected item.  Following what is known as the template method, we essentially add the inverse image of a “golden warhead” that has previously been verified, to the image of an inspected item.  Similar to a photograph, if the items are the same, we should see the positive and negative images cancel leaving a flat image.  All of the bright spots have cancelled out with all of the dark spots, and vice versa.  If the items are the same, this image conveys no information other than the fact that the items are equivalent.  If the host nation tries to cheat by presenting an inspected item that is not the same as the template, the “negative” and “positive” images will not completely cancel out, revealing the dishonest item.

How did you end up deciding to go to graduate school?

I started graduate school for a mix of reasons.  First of all, I was searching for an intellectually stimulating work environment and one that would allow me to work on a subject that I personally found interesting.   I had always excelled in school, and it seemed to be a good extension of my interests, my classroom engagement, and the enjoyable research opportunities that I pursued during my undergraduate career.

Family and personal reasons played another key role for pursuing graduate studies.  While I had some initial doubts about applying, many in my family had always expressed interest in pursuing STEM and advanced degrees, but for various reasons did not or could not.  In some ways, it was this family narrative that pushed me initially to study physics and to follow through.  Because I did well in my undergraduate studies, I felt compelled to pursue the academic route through the Ph.D.

Finally, I would say that I was not totally sure that a Ph.D. was for me, and I don’t think many people are certain of their desire when they enter a graduate program.  However, when I was applying and received acceptance letters, I was excited to take the chance and learn how I liked it through the experience.

How do you try to separate School and Life?

For me, academia is a component of my life, and not my only interest.  It is easy for research and the academic world to creep into your schedule, demanding late nights, and throwing unpredictable deadlines at you.  To maintain my other interests, communities, and personal sanity, I, firstly, have lived off of the campus for my entire graduate career.  The physical separation of work and personal space is something that I enjoy and that has given me the mental and physical space to separate the two.  By living off of the campus, I have made many friends and connections outside of the university, and it allows me to feel more rooted in a wider community.

Next, and most importantly, I have tried to set up what I refer to as “sacred” times and spaces that work does not enter under normal conditions.  There are times for sports, reflection, reading, and hobbies that are the bedrock of my schedule.  They are priorities that don’t get shifted around lightly, and are really a source of my energy and balance.  In the moment, it can be difficult to stop working to go to a French conversation group when there is an upcoming deadline or I’m “in the zone” working on research.  But setting these times and spaces aside and making them a priority help me do the work I want and need to do in my graduate career.

What was the most unexpected part of graduate school?

I have to say that an unexpected aspect of graduate school was how quickly you can get pulled into the world of research.  First year at Princeton really gets people engaged across departments and within their departmental cohort.  Shared assignments, apartment complexes, and social scenes bring people together from every discipline.  However, after general exams finish and people get deep into their research, it takes real investment to keep the community together.  For me, personally, this has been a big task because friendships and a social community has been a foundation for facing all the challenges and opportunities academia entails.

What is the best part of graduate school?

The best part of the graduate experience has been, hands down, the community of fellow quirky, engaged, and kind people that you meet in graduate school.  While it’s easy to get sucked into your own world and research, there are passionate people everywhere on campus and in every discipline.  The cross-disciplinary relationships and opportunities have been enormously satisfying and have expanded the way I think about the world in ways I never anticipated.

I can do research with engineering Ph.D.’s from around the world in the morning and have lunch with WWS masters students who have served in the US Foreign Service.  I can go bouldering with experts in sociology and near-eastern studies and have dinner with friends from comparative literature. During my graduate career, investing in community has been one of my most cherished experiences.


I was really glad that I had the chance to talk to Mike and hear about his experiences in graduate school. Mike’s research work is particularly interesting given its combination of science and policy, and for more information about his work and the Science and Global Security Program, please look here. He’s been a great mentor and friend to me in the time I’ve known him. We’ve worked together on both policy issues in the Wilson school and also on issues outside the classroom through the Princeton Citizen Scientists, and I’m grateful for the diverse experiences that he and the other graduate students can bring to Princeton’s campus life.

Nicholas Wu, Social Sciences Correspondent