I first encountered Michael Cohen when, as a freshman newly arrived at MIT, he walked into my office unannounced to ask if I had any open problems for him to solve. My first reaction was bemused annoyance: who does this punk think he is? he’s ready to do theory, but doesn’t even know enough to make an appointment first? also, why doesn’t he shave?

And then, five minutes later, I was practically begging him to do research with me. “OK, so you didn’t like that problem? Wait, I’ve got another one! Hey, where are you going…”

Within those five minutes, it had become obvious that this was a freshman who I could—must—talk to like an advanced grad student or professor. Sadly for quantum computing, Michael ultimately decided to go into classical parts of theoretical computer science, such as low-rank approximation and fast algorithms for geometry and linear-algebra problems. But that didn’t stop him from later taking my graduate course on quantum complexity theory, where he sat in the front and loudly interrupted me every minute, stream-of-consciousness style, so that my “lectures” often turned into dialogues with him. Totally unforgivable—all the more so because his musings were always on point, constantly catching me in errors or unjustified claims (one of which I blogged about previously).

Not once did I ever suspect he did it to show off: he was simply so overtaken by his urge to understand the point at hand, as to be oblivious to all niceties. Yet somehow, that social obliviousness didn’t stop him from accumulating a huge circle of friends. (Well, it was MIT.)

Michael stayed on at MIT as a grad student, racking up an incredible publication list by age 25. This semester, he went to visit the Simons Institute for Theory of Computing in Berkeley.

Three days ago, Michael was found dead in his apartment in Berkeley, after having cancelled a scheduled talk because he was feeling unwell. No cause has been given.

The horrible news came just as I was arriving in Germany for the Heidelberg Laureate Forum, to speak about quantum supremacy. So I barely had time to process the tragedy—yet it was always in the background, especially as I learned that in his brief life, Michael had also touched many of the other computer scientists who I spoke with in Heidelberg, such as Dan Spielman, whose approach to Ramanujan graphs (with Marcus and Srivastava) Michael had made constructive in one of his most celebrated works. Only now is the full weight of what happened bearing down on me.

I understand that memorial events are being planned at both MIT and Berkeley. Feel free to share memories of Michael in the comments; see also Luca’s post and Lance’s post.

This is an unfathomable loss for Michael’s family, for his many friends and colleagues, and for a field that’s been robbed of decades of breakthroughs.