Before I made any photographs of Paul Alivisatos, we sat and talked. It was a hot afternoon in the spring of 2026 at his longtime home in the Berkeley Hills, with sharp light and still air. He was visiting from Chicago, where he had become president of the University of Chicago in 2021. At home, he was easy company. We soon found ourselves talking about Leica cameras.

Paul was interested in how a lens directs attention, how making a photograph begins with noticing something worth a closer look. I had come curious about his science and found someone curious about my work too.

His research offers a startling reason to look closely. Take a semiconductor and make crystals of it only a few nanometers across, each a tiny fraction of the width of a human hair. At that scale, changing the size of a crystal can change the color of light it emits. Smaller crystals can glow toward the blue end of the spectrum; larger ones toward the red. The chemistry can stay the same.

These particles are called quantum dots. Inside them, electrons are confined to so little space that their available energies depend on the crystal’s dimensions. Size becomes a way to tune the material.

Paul helped develop methods for making these crystals with precise control over their size and shape. That painstaking chemistry gave researchers a reliable way to explore their unusual behavior and put it to use. His group helped establish quantum dots as fluorescent labels for biological imaging. Particles of different sizes could light up different structures within cells, producing distinct colors under the same illumination.

I find something wonderful in that: a change too small for us to see alters the light that allows us to see something else.

Our conversation also turned to what quantum mechanics leaves unresolved. We can predict the behavior of matter with astonishing success. How much does that tell us about what is really happening? Paul seemed at ease with the question. Decades of research had given him plenty of answers and plenty still to wonder about.

Before Chicago, he had directed Lawrence Berkeley National Laboratory and served as Berkeley’s executive vice chancellor and provost. But he told me he still worked with students, including undergraduates, a couple of times a week. Amid the demands of leading a university, he kept a place for the direct pleasure of research.

Nearly every day in Chicago, he said, brought a conversation or event where he learned something new. I could believe it. He seemed to enjoy hearing about my work as much as explaining his own.

After the photographs, Paul walked with me up the long flight of stairs from the house, all the way to my car. I had come to learn about a world measured in billionths of a meter. What stayed with me was the generosity of the afternoon.