Thermodynamics

Notes on why Andy Weir’s astrophage (from Project Hail Mary*) violates the second law of thermodynamics, prompted by watching Veritasium’s “The Most Misunderstood Concept in Physics”.*

The claim

In the book, astrophage feeds by absorbing heat directly — infrared/thermal energy from its surroundings (a star’s corona, or the dense atmosphere of Rocky’s homeworld Erid) — and stores that energy in a compact, fully recoverable form (described as mass added to held neutrinos). Critically, it does this without radiating anything back out during absorption. It behaves as a perfect heat sink: energy goes in, nothing thermal comes out, and the energy can later be released as clean, usable energy (propulsion).