The End of Eternity
Isaac Asimov
 The Eternity of the title is an organization and a place which exists outside time. It is staffed by male humans called Eternals who are recruited from different eras of human history commencing with the twenty-seventh century. The Eternals are capable of traveling “upwhen” and “downwhen” within Eternity and entering the conventional temporal world at almost any point of their choice, apart from a section of the far future which they cannot enter. Collectively they form a corps of Platonic guardians who carry out carefully calculated and planned strategic minimum actions, called Reality Changes, within the temporal world in order to minimize human suffering as integrated over the whole of (future) human history. As the plot unfolds, however, it is increasingly evident that Eternity itself suffers from serious maladjustments. The Eternals feel an unspoken collective guilt which causes them to scapegoat the "Technicians", the experts who actually execute Reality Changes by doing something that will alter the flow of events. The Eternals are also troubled that beyond a certain point in the future they are blocked by unknown means from entering Time. These are the "Hidden Centuries". Beyond the Hidden Centuries they can emerge, but find the earth devoid of human life. A key plot element which emerges quickly as the story unfolds is the relatively static nature of the human societies in the various future centuries, and the repeated failure of space travel in all accessible centuries. We later learn that Laban Twissell (Harlan’s superior and the leading figure on the governing Council) is from "a Century in the 30,000s", yet nothing much is different in that time. The protagonist is a Technician named Andrew Harlan, who finds himself involved in an ontological paradox orchestrated by his superiors. He is to secure the creation of Eternity by sending a young Eternal back in time with the mathematical knowledge to make it possible. To facilitate this Harlan's superiors in Eternity allow him to pursue his study of "prehistory", which is history prior to the Eternity's creation that, because Eternity had not yet been created then, cannot be traveled to nor changed. This intellectual pursuit is largely frowned upon by the Eternals, especially Harlan's superiors, but it becomes apparent his expert knowledge on the subject will be vital to Eternity's creation. Harlan himself is in trouble with the leaders of Eternity. He has been entrapped by one of them into entering into a relationship with a non-Eternal woman, Noÿs Lambent. This was intended merely to prove a point about the effect of Eternity on the individuals from real time who learn of it, but it has the unintended consequence of making Harlan besotted with the woman, so much so that he smuggles her into Eternity, since he has discovered that she will cease to exist in real time when the Eternals make their next Reality Change. Harlan’s whole scheme comes apart when it is revealed the leaders are fully aware of his activities. Normally the Eternals traverse from century to century within Eternity in a kind of temporal elevator called a kettle. A special version of the kettle has been built, however, for Harlan to dispatch a young Eternal, one Brinsley Sheridan Cooper, back to the 24th century, which lies “beyond the downwhen terminus” accessible via Eternity and its kettle system. Cooper is carefully instructed that he is to teach the principles and technology of time travel to its historic inventor, Vikkor Mallansohn, but unbeknownst to Cooper or Harlan, he will actually become Mallansohn himself. However Harlan, filled with malice after (erroneously) concluding that Twissell has trapped him and will deprive him of Noÿs, scrambles the time settings just as the special kettle departs. Cooper is trapped in the wrong time, so Eternity cannot be created. Unless something is done to change the past, Harlan’s reality, and Eternity, will be erased from existence. Twissell reveals that he too had once improperly loved a woman in Time, and manages to persuade Harlan that he sympathizes. Calming down, Harlan tries to think of a way that Cooper, also adept in the concept of Reality Change, could send him a message to return and retrieve him. Harlan believes that the apparently random target setting he chose on the kettle was the 20th century, and it occurs to him that Cooper was interested in his collection of artifacts from that time, particularly magazines. Perhaps the trapped Cooper would have found a way of leaving his SOS message in one of them. This is where Asimov’s mistaken “mushroom cloud” appears in the novel. Harlan comes upon an ad for stock tips—All the Talk Of the Market, concealing the acrostic A-T-O-M, accompanying a drawing of a mushroom cloud. The year on the masthead of the preserved publication is 1932. Since this predates the first atomic explosion, it must be a coded message from someone from the future—a reality change caused by Cooper. Before he reveals this discovery to the other Eternals, Harlan exacts a price, his lover is to be returned to him and both will go back to rescue Cooper. Once the couple arrive in 1932, Harlan reveals his last surprise. He has deduced that the woman, Noÿs Lambent, is herself an agent of Reality Change. She is from those centuries the Eternals cannot enter. She does not deny it. Instead she tells Harlan that her people, who prefer to watch past time rather than travel in it or change it, discovered that Eternity was, in choosing safety for humanity, suppressing creativity. In the end this has the effect of denying humanity's access to the stars, as alien species advance technologically and confine humanity to Earth. Eventually humanity will die out, millions of years in the future, leaving an empty Earth. However, if Eternity could be prevented from being created, humans would leave Earth and colonize the stars. Thus they cut themselves off from Eternity and began to plot its demise. It was not any specific Change but the very existence of any such organization as Eternity which had the deleterious effect, since when given the choice humanity would always choose safety. Noÿs Lambent reveals that in order to make Eternity improbable, Harlan needs only to decide to leave Cooper stranded in 1932. She also intends to send a carefully worded letter to Italy, causing a man (presumably Enrico Fermi) to "begin experimenting with the neutronic bombardment of uranium". This will start a chain of events which will lead to the first atom bomb in 1945. In the reality known up to that point, atomic power was discovered somewhat later (it is not explained when, but the 24th century had nuclear reactors, and no nuclear bombs were detonated until the 30th century). Acquiring the technology sooner, humanity will be diverted to focus more on the science of nucleonics and therefore develop interstellar space travel instead of time travel technology, and leading to a Galactic Empire instead of Eternity. Harlan at first intends to kill Noÿs and carry out his mission, but in comparing her story to that of the freakish and occasionally inhuman Eternals he has encountered, Harlan confirms his lingering suspicions that Eternity has been wrong for humanity. At the very moment he decides to help her, a Reality Change occurs and the 'kettle' linking them with Eternity vanishes into thin air.