Art Bell welcomes Sean Carroll, senior research associate in physics at the California Institute of Technology, for a conversation about cosmology timed with the landmark discovery of Earth-like exoplanet Gliese 581c. Art opens with extensive coverage of this newly found world just 20.5 light years away, describing its Earth-like temperatures, potential for liquid water, and the possibility it could harbor life far older than our own given its ancient host star.

Carroll explains how astronomers detected the planet through tiny Doppler shifts in starlight caused by the gravitational tug of orbiting planets. He notes that finding such a world among only the hundred closest stars suggests there could be a billion similar planets in our galaxy alone. The discussion covers what conditions would truly make a planet habitable, including atmosphere composition, tidal locking, and the effects of doubled surface gravity on human survival.

The conversation expands into broader cosmological territory as Carroll discusses dark matter, dark energy, the expansion of the universe, and modifications to Einstein general relativity. Art and Carroll debate the likelihood of extraterrestrial life, the challenges of interstellar travel, and Seth Shostak revelation that the president would be notified first if SETI ever confirmed an alien signal.