Based on the novel by Isaac Asimov, published by Doubleday in 1950.
Originally broadcast on NBC, June 17, 1951.
(A story by Isaac Asimov, "The Portable Star," appears in Thrilling Wonder Stories, Volume 1, its first-ever publication in a book.)
Yes, based on the novel. We saw with "Mr. Costello, Hero," how a novelette lost some of its power in being cut to fit the radio timeslot. I have to wonder what made the producers of Dimension X even attempt to adapt an entire novel into a 24-minute radio episode. In the actual event, though, it turned out pretty well.
An amusing result of boiling down the plot to its absolute essentials is that the main character of the novel went by the wayside. That character was a 62-year-old retired tailor from the 20th century whom a nuclear laboratory accident sends into the far future. Needless to say, his presence makes "the Sixty" more of a pressing issue than it is in the radio version.
Pebble in the Sky started out as a short novel called "Grow Old with Me!" which was rejected by Thrilling Wonder Stories' sister magazine Startling Stories. This version was rediscovered in Asimov's papers in the 1980's, and was finally published as part of The Alternate Asimovs. I haven't read it, but I'm guessing that the tailor's story is even more important there. In Pebble, it starts out as the central element, only to be pushed further and further to the sidelines... to the point that, when I read it, I wondered what the point had been of starting with the tailor at all. Whatever the reason for that is, Dimension X essentially did the job that Asimov's editor at Doubleday should have had him do.
Incidentally, another major change in the radio version is the ending. I don't want to give anything away, so I'll just say that the title doesn't get a chance to gain that meaning at the end of the novel.
I wonder what the origin is of this particular recording. There's a laugh at the beginning, a sneeze part way through, and a small coughing fit near the end, all far too clear compared to the main audio to have been part of it. It sounds like someone with a cold recorded it off the radio with a microphone.