The earliest time measurements were observations of cycles of the natural world, using patterns of changes from day to night and season to season to build calendars. More precise time-keeping eventually came along to put time in more convenient boxes. But what exactly are we measuring? Andrew Zimmerman Jones contemplates whether time is something that physically exists or is just in our heads.
America's favorite astrophysicist Neil degrasse Tyson takes a look at the somewhat-questionable science behind 3 Movies, ie Gravity, The Martian and The Matrix.
