Hour Four starts with a bang-the big bang in which everything began. "Origins: Back to the Beginning" explores how the colossal, mind-boggling forces of the early universe made it possible for habitable worlds to emerge. The clues begin with a race among scientists to capture lingering echoes of the big bang's ferocious energy in a microwave "whisper" from deep space. The race pits underdog astronomer Tony Readhead and his improvised detector in the high Andes against NASA scientists and their state-of-the-art satellite probe. Tyson shares his excitement with viewers as computer animation of the big bang's echo emerges on the screen. It's as close as we can get to a "photograph" of the primordial universe. Here we glimpse the seeds from which all the galaxies, stars, and planets eventually grew.