In “Into the Unknown,” an astronomer explores the mysteries of the cosmos and the limits of what science can test.What is time? If the universe is expanding, what is it expanding into? What happened just before the Big Bang?Some of the most head-scratching ideas in physics strain the limits of what science can test. In her book Into the Unknown: The Quest to Understand the Mysteries of the Cosmos, astronomer Dr. Kelsey Johnson describes some of those concepts, and sketches out ways to try to wrap your brain around them. Johnson joins Host Ira Flatow to talk about the limits of scientific inquiry, and what mysteries lie at the limits of science.Transcripts for each segment will be available after the show airs on sciencefriday.com.  Subscribe to this podcast. Plus, to stay updated on all things science, sign up for Science Friday's newsletters.