When John and Ken began shopping around their idea for a philosophy-on-the-radio show nearly 20 years ago, many believed it would never work, let alone stay on the air. Nearly two decades later, the program that questions everything (except your intelligence) has hit 500 episodes—just in time for current co-hosts Josh and Ray to spend our annual summer reading special thinking about time and books about time.

• Physicist Carlo Rovelli, author of The Order of Time
• Political scientist Elizabeth Cohen, author of The Political Value of Time
• Poet and essayist Jane Hirshfield, author of Ledger
• Philosopher Jorah Dannenberg on Ted Chiang's Story of Your Life.