Glass, Cold, Sound, Clean, Time and Light. Just a random collection of items in the physical world, right? Not in the hands of science journalist Steven Johnson, who weaves a revelatory tale of technological wonders in his new book and PBS series, "How We Got to Now: Six Innovations That Made the Modern World." Join Julie and Robert for an interview with the man behind the book and series.
What about darkness is so unsettling? Find out about the most extreme instances of an absence of light and how it works on our bodies.