The protagonist, Professor Hugo Pinero, builds a machine that will predict how long a person will live. It does this by sending a signal along the world line of a person and detecting the echo from the far end. Professor Pinero's invention has a powerful impact on the life insurance industry, as well as on his own life.
Pinero is mentioned in passing in the novels Time Enough for Love and Methuselah's Children when the practically immortal Lazarus Long mentions having been examined and being sent away because the machine is "broken".
Heinlein was motivated to write the story by an editorial in Thrilling Wonder Stories magazine, in which Hugo Gernsback wrote that he wanted to foster new talent in the field, and that "We shall endeavor to present one amateur writer's story in each forthcoming issue [...] until further notice." Thrilling Wonder Stories's rate at the time was 0.5¢ per word. After Heinlein had written the 7,000-word story, he submitted it first to a rival magazine, Astounding, which paid 1¢ per word. Astounding bought the story, and at their higher rate, Heinlein was paid $70 (equivalent to $1,460 in 2022).
According to Virginia Heinlein's introductory biography of her husband in Grumbles from the Grave, upon receiving the check for the story Heinlein reportedly said, "How long has this racket been going on?" Later, Heinlein's authorized biography included a version of the story in which Thrilling Wonder Stories had advertised a $50 contest. The first known version of this story appeared in a 1985 interview published in Xignals, a science fiction newsletter.
There has grown in the minds of certain groups in this country the idea that just because a man or corporation has made a profit out of the public for a number of years, the government and the courts are charged with guaranteeing such a profit in the future, even in the face of changing circumstances and contrary to public interest. This strange doctrine is supported by neither statute or common law. Neither corporations or individuals have the right to come into court and ask that the clock of history be stopped, or turned back.
In the realm of science another passage has come to be quoted:
There are but two ways of forming an opinion in science. One is the scientific method; the other, the scholastic. One can judge from experiment, or one can blindly accept authority. To the scientific mind, experimental proof is all important and theory is merely a convenience in description, to be junked when it no longer fits. To the academic mind, authority is everything and facts are junked when they do not fit theory laid down by authority.
A television web series loosely based on the short story began in 2017.
- Gifford, J. Daniel (2000). Robert A. Heinlein: A Reader's Companion. Nitrosyncretic Press. pp. 110–111. ISBN 0967987415.
- Patterson, William H. Jr. (2010). Robert A. Heinlein: In Dialogue with His Century, Volume 1: Learning Curve, 1907–1948. Tor. pp. 215–216. ISBN 978-0-7653-1962-3.
- Heinlein, Robert A. (2010). The Nonfiction of Robert Heinlein: Volume II. Vol. 38 (Virginia ed.). Virginia Edition Publishing Company. ISBN 9781897350430.
- Cesarini, Lisa McHugh; Cesarini, Paul (2008). "From Jefferson to Metallica to your Campus: Copyright Issues in Student Peer-to-Peer File Sharing". Journal of Technology Studies. 34 (1). ISSN 1541-9258. Retrieved 2016-11-24.
- McClure, Ian (2007). "Be Careful What You Wish For: Copyright's Campaign for Property Rights and an Eminent Consequence of Intellectual Monopoly" (PDF). Chapman Law Review. 10 (3). Retrieved 2012-05-04.
- "Life-Line" title listing at the Internet Speculative Fiction Database
- "Life-Line" on the Internet Archive