Goodbye.

One beautiful Fall day seventeen years ago I wandered into an office and my life profoundly changed. I was an undergraduate at Princeton, and was looking for a thesis advisor. Jadwin Hall was an intimidating place. Plenty of names familiar from my textbooks. Nobel laureates scattered about. And we were expected to just barge into their offices, and ask to work with them. One office door was always open. As you walked by you could peek in, and see its occupant hard at work. Hunched over his notebook, scribbling away. Or standing by his bookcase, deep in thought. Most often at the blackboard, chalk in hand. This was John Archibald Wheeler, one of the legends of modern physics. He did foundational work on quantum mechanics, collaborating with Niels Bohr on some of the earliest work in nuclear fission. He invented the S-matrix. He played important roles in both the Manhattan project (atomic bomb) and the Matterhorn project (Hydrogen bomb). He made major contributions to general relativity, co-authoring with Charlie Misner and Kip Thorne the bible of the field. He was legendary for his way with words, coining such terms as wormholes, quantum foam, black holes, and the wave function of the Universe (the Wheeler-DeWitt equation). He trained generations of students; one of his first was Richard Feynman. Fortunately, being a relatively clueless 20-year old, I was only dimly aware of these things. I was interested in gravity and cosmology, and I had heard Wheeler knew a thing or two about such topics. So I waltzed in, and asked if he had any projects I could work on. I staggered out of his office four hours later, laden with books, a clearly defined project in my hands. For the ensuing two years I spent essentially every weekday with Wheeler. Each morning I would rush over to his office, always to be greeted the same way: "What's new?" I would have been up late the night before, desperately trying to find something interesting with which to answer that question. We would then spend hours working together, going over my results, scrutinizing my calculations, poring through the literature, brainstorming new ideas. Wheeler gave me a direct and personal introduction to the joys of research. We would break for lunch, and walk up to the faculty club. I often had trouble keeping up with him. He would always take the stairs ("No time to wait for an elevator!"). He would hook his arm into the banisters, and swing around, practically leaping from one flight to the next. This was 1990; Wheeler was 79 years old. We would often work all afternoon (with the occasional interruption, the nuisance of having to leave for my class lectures). Every evening I would walk with him from Jadwin up across the full length of campus, to catch his bus. We would pass the corner of Ivy lane and Washington road, where he had scratched 137 into the concrete when they were pouring the sidewalk. We would pass Jones Hall, where he used to discuss relativity with Einstein. We would continue on through campus, crossing in front of Nassau Hall. Wheeler would insist we walk diagonally to the far gate, instead of exiting through the more convenient FitzRandolph Gate. An Undergraduate was not meant to exit FitzRandolph Gate until graduation, and Wheeler didn't want to be responsible for what might occur were I to break tradition. For two years I sat at the feet of the master, and I absorbed as much as I could. I learned about science, and about life. Wheeler had broad interests. We would often discuss biology, or history, or poetry. Over the ensuing years we kept in touch. We collaborated together on Wheeler's last published paper. Yesterday I spent a couple of hours at Wheeler's bedside. I tried to say thank you. But it was impossible to convey how much he means to me, and how grateful I am to him. In that moment when I crossed the threshold to his office, I was embarking on a new path. I am still on that path, and every day I am grateful to him for showing me the way. John Wheeler died this morning.