Andrew H. Jaffe

Cosmologist & writer

How we know what we know.

I study the universe’s oldest light for a living, and write about the models and probabilities we use to make sense of it.

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Imperial College LondonPlanck Co-InvestigatorAuthor, The Random Universe

The book

What probability can teach us about the cosmos

The Random Universe explores how physicists use probability to draw conclusions about the universe from limited, uncertain data — and what that reveals about how science works. Out now from Yale University Press.

Probably the best book I’ve ever read on what the scientific method really is.
— Brian Clegg

About the book →

Watch a short talk about the book, or find recent and upcoming appearances.

Recent writing

Aug 2026

Around the world in 383 days

Two years ago, we were at the start of our sabbatical year, starting in Indonesia but with extended stays in Japan, New York, and the Netherlands. We’ve been back almost a year but I still think about our time abroad every day.

Jul 2026

What My Thirty-Year-Old Algorithm Taught an AI

On using Claude to revisit decades-old code, debug a stubborn cosmology sampler, and why the hands-on work still matters.

Oct 2025

The Trump Administration’s Contempt for Science

On what it costs a country to stop taking science seriously. Yale University Press blog.

About

I am a cosmologist and astrophysicist, in the Department of Physics at Imperial College London, where I am also the Director of the Imperial Centre for Inference and Cosmology. I am especially interested in the interpretation and analysis of cosmological data using principled Bayesian statistical techniques.

I also occasionally express my opinions on music, politics, parenthood, or technology.