*“DDay is gone.” Those words reverberated in my mind, as I hurriedly walked the path back to my dorm. *

I made this same walk every day on my way back from the engineering school, but today was different. Instead of thinking about the future — my upcoming exams, a party the next weekend, or my summer job — I was fixated on the past. I remembered DDay’s face, the stories he told us about cycling and dancing, his punishment of ten push-ups for misbehaving in class, and his method for performing integration by parts. I felt a fullness in my face as I sped up the road trying to hold in my tears for fear of bumping into someone I knew.

As I entered my dorm, I pulled out my phone to call my best friend, Janosz. In high school, we had both taken precalculus and calculus from Dr. Colin Day, a.k.a. “DDay”, and then we followed in his footsteps by attending his alma mater, Vassar College. But now Janosz and I were separated across time zones for our junior years abroad, and my phone call went to his answering machine. At a loss, I pulled up DDay’s Facebook page and saw the outpouring of comments on his timeline. Many of the comments were from students like me, people who had benefited from the high standard he held us to in his AP Calculus class.

On the first day of our calculus class during my senior year of high school, DDay said, “Most of you will get 5s on the AP test if you follow along,” as if it were an established fact. But he held his promise with lectures and exercises that were perfectly tuned to drill into us the rules of calculus and an overall intuition about how functions, differentials, and integrals operate. DDay had earned a Ph.D. in mathematics, and he brought his deep understanding of the subject to the classroom. I vividly remember the day he pulled out his Ph.D. thesis on the mathematics of knots to show our class. It was the first time I had ever seen a dissertation, and I was enamored of the byzantine symbols and illustrations that lined the pages. It seemed so different from the textbooks with which I was familiar. This was an original piece of work that had pushed the boundaries of human knowledge. I was suddenly cognizant of how little of mathematics I really understood, but I was also excited about the prospect of going ever deeper into a subject and ultimately constructing new knowledge.

I wanted to tell him how his calculus class set the trajectory of the rest of my life and how I had found my lifelong passion thanks to him. But now he was gone.

With an appetite to learn more about mathematics, Janosz and I started at Vassar College the next fall, although we didn’t choose Vassar because of its math program. DDay had told us about his undergraduate years there and in particular about his participation in the dance program. The idea that someone could be a mathematical genius and a world-class ballet dancer was astonishing to us. Every stereotype we had seen of mathematicians and scientists suggested that they could not possess the grace and balance of a dancer. DDay also led our school’s cycling team and yoga class and was in such good shape that he looked ten years younger than he really was. He exemplified Aristotelian virtue, so Vassar seemed like a place where we too could flourish in areas other than just science and math.

When I arrived on campus, I quickly found my way into philosophy classes, into the campus Islamic society, and even into the college’s unofficial stand-up comedy group. But nothing pulled me in more than the world of physics, astronomy, and mathematics. With DDay’s calculus training under my belt, physics suddenly made so much more sense to me than it had when I had taken it as a high-school freshman. For the first time ever, I felt like I was not just wandering through a course. The laws and equations of physics spoke to me in a language I understood: calculus. After a couple of physics classes, I declared my major in physics and also decided to spend my junior year “abroad” at Dartmouth College to take engineering courses that weren’t available at Vassar. And that’s when I heard about DDay’s passing.

I had not spoken to DDay since he was diagnosed with cancer; the regret of not telling him how he had impacted me began to set in as I tried to call more of my high school friends from my dorm room. My love for physics had grown to the point that I knew I wanted to pursue a Ph.D., but I never had the chance to tell DDay. I wanted to tell him how his calculus class set the trajectory of the rest of my life and how I had found my lifelong passion thanks to him. But now he was gone.

Four years later, I began my Ph.D. research on gravitational waves at UChicago, as Janosz pursued his on astrophysical fluids at Cambridge. We had remained best friends through the years and somehow had ended up in adjacent sub-fields of study. Finally, we were actually creating new knowledge, just like we had seen in DDay’s dissertation. The research group I had joined was part of the LIGO Collaboration, a world-wide group of astronomers and physicists looking for gravitational waves, the elusive “ripples in spacetime” that Einstein had predicted a century earlier but had yet to be detected. A few months after starting my first Ph.D. research project, LIGO detected the first gravitational wave ever, which was produced in the collision of two black holes roughly a billion light-years away.

Once the gravitational wave was thoroughly analyzed, the LIGO Collaboration (along with the Virgo Collaboration) told the world about this groundbreaking discovery, and the day was filled with press conferences, interviews, and celebration. But I couldn't help but remember DDay. We had added further credibility to Einstein’s theory of gravity, a theory written in the language of calculus. The discovery of gravitational waves would never have been possible without the calculus teachers who instilled in us the skills and excitement needed to pursue research in physics and astronomy. Without DDay, I would never have been able to understand black holes, the expansion of the universe, and the nature of space-time. I would never have become “Dr. Doctor.”

Without DDay, I would never have been able to understand black holes, the expansion of the universe, and the nature of space-time. I would never have become “Dr. Doctor.”

I use calculus daily, and every derivative, integral, and Taylor series is a reminder of DDay. But now as a Ph.D. myself, I am learning something new from him beyond mathematics. With his Ph.D., DDay went on to teach us calculus and help us ace the AP exam. He had pushed the bounds of mathematics but ultimately decided to put that aside to teach us how to take limits and perform integration by parts. I have been able to produce original research in astrophysics because DDay spent his days showing me the basics instead of having his head in his own research. Reflecting on that has given me insight on where to take my own doctorate. The academic rat race applies constant pressure to maximize my own citations and move up the academic ladder or to exit the field and become a quant or chief engineer, always looking to increase prestige or salary. But thinking about DDay, I realize I don’t need to do any of those things to have a lasting positive impact on the people around me. I just need to share the beauty of science and mathematics with students, ride my bike, and dance.