In 1918, Arthur Stanley Eddington stood before a British military tribunal as a Quaker conscientious objector, risking imprisonment for refusing to fight. At the same time, he was championing a revolutionary theory smuggled out of enemy Germany through Dutch physicist Willem de Sitter. This episode follows the Cambridge astronomer, Plumian Professor and observatory director, who was one of the few people on Earth able to read the tensor calculus of general relativity, and the intervention by Astronomer Royal Frank Watson Dyson that turned an eclipse expedition into a matter of national prestige.

The hosts explain the physics at stake: Newtonian math predicted starlight bending by about 0.83 arc seconds near the Sun, while Einstein’s 1915 theory predicted 1.75, roughly the width of a human hair seen from a mile away. They cover the rain-ruined 1912 and war-interrupted 1914 attempts that saved Einstein from his own flawed 1911 calculation, the clockmaker Edwin Turner Cottingham who kept the telescopes tracking, the storm on Principe on May 29, 1919, the 16 plates that mostly failed, and the small four-inch backup telescope at Sobral that delivered the clearest images.

• Why Einstein’s 1915 papers had to be routed through a neutral party to reach British scientists during wartime
• How Dyson persuaded a military tribunal to grant a 12-month draft extension for a scientific expedition
• Why the Hyades star cluster made the 1919 eclipse the perfect celestial laboratory
• How Philipp Lenard’s German physics movement tried to discredit relativity with plagiarism claims tied to an 1801 calculation
• Why Karl Popper used the Eddington experiment as the foundation for his concept of falsifiability