Fermi Physics Estimations
Physicist Enrico Fermi was so renowned for his ability to make remarkably accurate estimates that solved seemingly intractable problems using little-to-no data that an entire class of estimation exercises now bears his name: “Fermi problems”. While the “How many piano tuners are there in Chicago?” question is commonly presented as an example of a Fermi problem in public discourse, Fermi is known within the physics community for estimating the strength of the Trinity atomic bomb when it was tested in New Mexico by dropping small pieces of paper and estimating their displacement. He concluded that the blast corresponded to exploding about 10 kton of TNT; the actual equivalence was about 21 kton*.
In Fermi Physics Estimations (Fall 2026) we will learn specific techniques for mastering the art of solving Fermi problems, and we will apply them to problems from across the field of physics. By the end of this ten week class, you will be a Fermi estimate master - assuming, of course, that you do the work! Mastering this skill will serve you both in and out of physics: if you pursue physics theory, it will help you quickly estimate the reasonableness of an idea; if you pursue physics experiment, it will help you manage experimental decisions and evaluate experimental results in real time; and if you leave physics behind forever, it will be a prized skill in many jobs (as it is especially useful for quickly auditing LLM assertions as either reasonable or unreasonable).
Knowledge of calculus and prior physics work are NOT required for this class, making it unique in our Curie Circle course offerings! This class does involve a heavy amount of mental math, so your physics learning gains will be the greatest if you are already comfortable estimating multiplications, divisions, exponents, and logarithms in your head. However, if you are not yet comfortable with mental math, you will undoubtedly improve that skill by applying yourself in this course. As for the physics, I only need your enthusiasm and curiosity as I will teach you the concepts and equations relevant to the physics discipline and associated Fermi problems we are exploring each week.
This class will meet virtually via Zoom on Wednesdays from 4:30 to 6:00 PM San Francisco time and Thursdays from 4:30 to 6:30 PM San Francisco time from September 23 to December 3.
Applications for Fall 2026 are due July 19. After that, we will continue to accept applications on a rolling basis while spots remain. Click here to apply!
“About 40 seconds after the explosion, the air blast reached me. I tried to estimate its strength by dropping from about six feet small pieces of paper before, during, and after the passage of the blast wave. Since, at the time, there was no wind I could observe very distinctly and actually measure the displacement of the pieces of paper that were in the process of falling while the blast was passing. The shift was about 2½ meters, which, at the time, I estimated to correspond to the blast that would be produced by ten thousand tons of T.N.T.”
*The personal, societal, and environmental impacts from the Trinity test and the bombings of Hiroshima and Nagasaki are still felt today, and discourse among historians about whether or not the bomb was needed to initiate the end of World War II continues. For a brief overview of this discourse, please see the Atomic Heritage Foundation’s Debate over the Bomb webpage, which includes a video recording of a 2013 discussion among historians at an NSF-funded workshop. Note that this course is not about this history, but Fermi’s accurate estimate of the explosion strength during the Trinity test remains an excellent example of combining physics knowledge and estimation prowess to quickly assess a physical situation.