Michael Rabin Passed Away on April 14, 2026, at the age of 94

Michael Rabin passed away on April 14, 2026 at the age of 94. (Scott Aaronson has also blogged about his passing, see here.) I had many points to make about him; however, the first one got so long that I will just do that one for today's blog post.Rabin is an extremely well rounded \(\ldots\) computer scientist? Computer scientist seems too narrow, and the point of this point is that he is well rounded. So I will start this thought again.The following is an extremely important question that permeates computer science, mathematics, and I am sure other fields:Given a problem, how hard it is?Note that this is a rather broad problem since the terms problem and hard are very broad. And by hard I mean upper bounds and lower bounds.Rabin has worked on this problem in many different domains. I list them in roughly the order of hardness, starting from the hardest.1) Recursive Algebra: Mathematicians had proven that every field has an algebraic closure. In 1960 Rabin asked and answered…