Michael Hartl

Welcome to Michael Hartl’s home on the Web! I’m a theoretical physicist with a background as a technology entrepreneur. You might know me as founder of Tau Day and author of The Tau Manifesto, as cofounder and principal author at Learn Enough, or as the creator of the Ruby on Rails Tutorial.

I’m the author of over a dozen books, including Learn Enough Python to Be Dangerous and the Ruby on Rails Tutorial, published jointly by Learn Enough (online courses) and Pearson Education (print editions, ebooks, and video bundles). Since the acquisition of Learn Enough in 2022 and the completion of my final Learn Enough tutorial, I have been focusing on reconnecting with my physics roots, beginning with a systematic course of study in mathematics. Check out Michael Hartl’s Substack posts and follow me on Twitter for more. I am also active as an investor and advisor to several startups; see my /now page for more on what I’m up to now.

I’m an alumnus of Harvard (A.B. in Physics), Caltech (Ph.D. in Physics), and Y Combinator (with a company that is long, long defunct). As a graduate student and postdoc at Caltech, I studied black hole dynamics and was an instructor in theoretical and computational physics, receiving the Lifetime Achievement Award for Excellence in Teaching. At the request of Kip Thorne, I also served as Caltech’s editor for an update to The Feynman Lectures on Physics. (You can read more about this remarkable project here.)

Other interests include old books, languages, nutrition, physical fitness, singing, and martial arts (including Krav Maga Level 5, a “black belt in self-defense”).