Po-Shen Loh: Carnegie Mellon mathematics professor and national coach of the USA International Math Olympiad team. Founder of the education platform Expii and the privacy-first contact-tracing app NOVID.
What this episode covers
Po-Shen Loh joins Lex Fridman to discuss the beauty of mathematics, the art of teaching invention rather than memorization, and the Math Olympiad. A large part of the conversation covers his NOVID app, which reframes contact tracing around network distance and self-interested incentives so people protect themselves rather than being forced into quarantine. They dig into combinatorics, voting trees, distributed algorithms, P vs NP, and how aligning individual incentives can solve coordination problems. Loh closes on a personal metric of meaning: maximizing the person-years of impact that outlast his own life.
The guest's own work
NOVID
Po-Shen Loh
“by the way what is the app called oh it's called novid covered with an ad very nice”— Po-Shen Loh
Expii
Po-Shen Loh
“founder of xp that does online education of basic math and science he's also the founder of novid an app”— Lex Fridman
Also referenced (named, not recommended)
The Lord of the Rings
J.R.R. Tolkien
“like for example like the lord of the rings that's the content right but yes the thing that always inspired me”— Po-Shen Loh
Arrival
Denis Villeneuve
“stephen wolfram and his son help with the movie arrival like the developing an alien language like how would aliens communicate”— Lex Fridman
Big reveals from this episode
- Loh and his team 'accidentally discovered a new way to control diseases' while building NOVID with network theory and smartphones.
- The core insight: measure distance to a disease not in feet or seconds but in how many close physical relationships separate you from it.
- Counterintuitive claim that the deadlier and more transmissible a disease, the stronger people's incentive to adopt the app.
- Standard contact-tracing apps barely lower YOUR own chance of getting sick, which is why they fail; NOVID flips the incentive to self-protection.
- Loh's exams are 90% of the grade and 100% invention, with zero overlap with anything he taught or previously asked.
- As head coach he told the Math Olympiad leadership he'd accept worse results, aiming instead to maximize students he'd read about in the New York Times in 20 years.
- His personal meaning metric: maximize person-years of impact that matter after he is gone, even if not attributed to him.
Worth remembering
- Loh's high-school games drew every pixel and letter from scratch in Pascal, using assembly code copied from a book to plot a single pixel.
- With only ~8 billion people and linear-time algorithms, NOVID can recompute everyone's disease distance hourly on a small cloud machine.
- Real social networks are sparse; tracking a person's top ~100 connections captures most of the signal.
- At the IMO you have 4.5 hours for 3 problems per day; solving even one of the six earns an honorable mention.
- Loh reads math textbooks by checking the proof's length, closing the book, and re-proving it himself, since length is roughly linear in number of insights.
- Among 1024 candidates there's always one who beats at least 512 others, provable via a simple expected-value double-counting argument.
- His simple new method for solving quadratic equations may make it into textbooks, raising his 'impact score'.
- Loh notes Scott Aaronson puts the probability that P does not equal NP at only about three percent.