Measuring a change in length smaller than one ten-thousandth of a proton across four kilometers sounds like a cruel thought experiment, yet that is exactly what the Laser Interferometer Gravitational-Wave Observatory does. This episode covers the century-long road from Einstein’s 1916 prediction, and his doubts that the waves could ever be detected, through the work of Soviet theorists, Joseph Weber’s resonant mass antennas, and the laser interferometry prototypes of Rainer Weiss and Kip Thorne. It also digs into the messy 1980s and early 1990s, when a forced MIT-Caltech partnership, frozen NSF funding, and organizational chaos nearly killed the project until Barry Barish took over in 1994.

The hosts explain Barish’s evolutionary pitch, an initial LIGO that would likely detect nothing followed by an Advanced LIGO upgrade, which secured roughly 395 million dollars, the largest NSF award at the time. They walk through the L-shaped vacuum arms in Livingston and Hanford, beam splitters, destructive interference, Fabry-Perot cavities that bounce light 280 times, and the noise-fighting campaign against trucks, ocean storms, lunar tides, Barkhausen noise and thirsty ravens pecking frost off nitrogen pipes. The episode culminates in the September 14, 2015 detection of two merging black holes 1.3 billion light years away, the 2017 Nobel Prize, neutron star mergers seen in both gravity and light, and the LIGO Voyager plan for cryogenic silicon mirrors.

• Why the Hulse-Taylor binary pulsar convinced funders the waves were real
• How a laser interferometer turns a stretched arm into a flicker of light
• The 3,000 kilometer separation that rules out local noise and allows triangulation
• The raven anomaly, repaved roads and other bizarre interference stories
• What neutron star collisions revealed about the origin of gold and heavy elements