Samantha O’Sullivan

Theoretical Physicist

Hi, I’m Sam! I’m a PhD student in theoretical physics at the University of Oxford. I use mathematical models to predict and understand biological evolution (which is how living things change over time). I’m currently applying our theories to model the development and evolution of seal teeth!

My story

I was born and raised in Washington DC, USA, as an American British dual citizen. My mom is African American, my dad is English, and my parents met in a book club, so it’s no surprise I grew up loving to read! As a kid, I loved to learn about everything: history, chemistry, languages, drama, physics- you name it. I grew up with two brothers and played lots of sports, but I also loved to sing and act in musicals as well. As I grew up, I was passionate about my African American heritage and culture, and I researched my family tree going back to 1830, where I found the names of my enslaved ancestors in South Carolina and their deep Christian faith, which is the foundation of my own faith today.

In school, I began to gravitate (no pun intended) towards math and physics. Solving math problems was a fun challenge, and I was blessed with great math and physics teachers who encouraged my skills and challenged me. But my love for other subjects never went away, and I always looked out for ways to blend my love of learning many topics together.

Growing up in Washington DC, I adored the Smithsonian museums. My favorite museum was the National Air and Space Museum, because of the cool physics exhibits! Fast forward ten years, and in high school I got a job working there, leading public science demonstrations to museum visitors and many kids just like my younger self! Working at the Smithsonian was a most rewarding experience, as I got to blend my love for learning, science, communication, and meeting new people, all in one job!

For university I was accepted to attend Harvard, a top University in the States, and excitedly enrolled! In my first year, I explored lots of subjects that interested me: philosophy, history, English, physics, and math. I eventually decided to study both Physics and African American Studies. I believe I was the first student at Harvard to earn a degree in both topics! I absolutely loved it. I got to merge my interests in a unique way and wrote my senior thesis on ‘Gullah Physics: Challenging English Language Hegemony in Science’. My thesis explored the history of Gullah, an African American creole language spoken by my family in South Carolina, and I taught the physics of buoyancy in Gullah to a class of schoolchildren in Charleston, South Carolina. I advocated for the translation and teaching of science into many non-English languages. This shows how you can combine different subject matters that interest you to become your final area of expertise!

With the encouragement of wonderful professors and mentors, I began to conduct physics research in high school and throughout university. I tried out lots of types of physics research: including astrophysics, where I studied pulsars, experimental condensed matter physics, where I studied superconductors, and plasma physics, where I studied tokamak reactors. I loved research! I found it so exciting to work together in a team, brainstorm new ideas, and develop new knowledge. I decided I wanted to earn a PhD and continue research after university.

My parents encouraged me to apply, and in 2021 I was blessed with a Rhodes Scholarship to study at University of Oxford! In 2022 I began my PhD in Condensed Matter Physics, continuing research of superconducting materials. Once arriving in Oxford, I loved the vibrant Oxford university life! I became involved in tons of activities: I joined the Magdalen College rowing team, led the Rhodes Christian Fellowship, and I found a wonderful church community.

While researching superconductors, I began to explore other areas of physics research and discovered the Louis group, which, among other topics, applies mathematical theories to understand biological evolution. I was so fascinated by the research and its interdisciplinary applications. I joined the group and am now studying for a PhD in theoretical physics with Prof. Ard Louis!

My research

A big question in evolutionary biology is how nature’s preferences and patterns (called biases) affect how living things develop and evolve. Certain patterns in genes can affect how traits look and function, and scientists in my field, including biologists, physicists, and mathematicians, make models to predict these patterns. Some models suggest that, in general, evolution favors simple and symmetric shapes in nature over complex ones. So far, this pattern has been observed in molecules like DNA- the substance that carries a living thing’s genes, which pass traits, or features, from one generation to the next. But mostly I am interested in understanding if this pattern also holds for larger biological traits like teeth.

In my research, I’m currently testing this idea by looking at the teeth of the seal Phoca hispida ladogensis. I use a computer model called ToothMaker to simulate how teeth form in these seals. By introducing small changes in the tooth parameters, I then look at how the mutant teeth develop. I’ve found that, when I randomly mutate a tooth parameter, simpler mutant tooth shapes appear more often than more complex mutant shapes, supporting the idea of a bias towards simplicity. But there are still many more simulations for us to run, and new systems to test our exciting theory on!

Most of my day is spent on my computer coding, reading papers on theories, or meeting with my team members to discuss results. I love how my research merges so many fields of study: I get to use my skills as a physicist to blend ideas from biology, math, and computer science! I also love meeting new people from different areas of expertise and learning from them. Recently, I got to travel to Barcelona to present my research at a conference, the Collaboratorium Annual Symposium: Modelling Biology Across Scales. It was so exciting to ask questions and receive feedback and new ideas from experts in a range of fields.

Outside of work, I live in Oxford with my miniature goldendoodle dog, Nala! Every morning, I take Nala to South Park, which has a beautiful view of the city, while I walk, pray, and Nala runs around: a great start our day. I’m having a great time in my PhD and love the work I get to do!