It is beyond belief that not only am I again writing a post about the premature death of a colleague whom I have known for decades, but that I am doing it about two of them.

Over the past weekend, two of the world’s most influential and brilliant theoretical high-energy physicists — Steve Gubser of Princeton University and Ann Nelson of the University of Washington — fell to their deaths in separate mountain accidents, one in the Alps and one in the Cascades.

Theoretical high energy physics is a small community, and within the United States itself the community is tiny. Ann and Steve were both justifiably famous and highly respected as exceptionally bright lights in their areas of research. Even for those who had not met them personally, this is a stunning and irreplaceable loss of talent and of knowledge.

But most of us did know them personally. For me, and for others with a personal connection to them, the news is devastating and tragic. I encountered Steve when he was a student and I was a postdoc in the Princeton area, and later helped bring him into a social group where he met his future wife (a great scientist in her own right, and a friend of mine going back decades). As for Ann, she was one of my teachers at Stanford in graduate school, then my senior colleague on four long scientific papers, and then my colleague (along with her husband David B. Kaplan) for five years at the University of Washington, where she had the office next to mine. I cannot express what a privilege it always was to work with her, learn from her, and laugh with her.

I don’t have the heart or energy right now to write more about this, but I will try to do so at a later time. Right now I join their spouses and families, and my colleagues, in mourning.