James Cameron’s “Avatar: The Way of Water” has been smashing box office records this month. Do you remember the substance “unobtanium” at the center of the original film’s plot? According to a recent headline from Smithsonian Magazine, it is actually a real thing… sort of. Dr. Matthew Shindell, curator of Planetary Science and Exploration at the National Air and Space Museum, joined “Something Offbeat” this week to explore the history of “unobtanium” and take us on a trip to the line between science and science fiction.