The spear, the bow, the gun, and finally the guided missile had given him weapons of infinite range and all but infinite power. Without those weapons, often though he had used them against himself, Man would never have conquered his world. Into them he had put his heart and soul, and for ages they had served him well. But now, as long as they existed, he was living on borrowed time.
This passage appears at the end of Part One of 2001, as the narrator concludes his story of the evolution of man to his present state. Foremost, it is the first mention of one of the major themes of the book—the destructive potential of nuclear weapons. Inasmuch as the central story line does not explicitly mention nuclear weapons, this mention is one of the critical passages that alert us to the author's concern with weapons of mass destruction. This passage is also interesting in illustrating the unclear phenomenon in an evolutionary context. Nuclear weapons are conceived, not as an independent invention, or in relation to the study of physics that produced them, but rather as an advanced weapon that comes as part of a long chain of human tools and weapons developed over millennia. By placing nuclear weapons in this context, the author acknowledges that such weapons were not made in order to be destructive and, further, that man generally had good reasons for making weapons. The potential negative side effect of nuclear weapons, however, was too great to be ignored.
Even now, he could not fully accept the idea that Frank had been deliberately killed—it was so utterly irrational. It was beyond all reason that Hal, who had performed flawlessly for so long, should suddenly turn assassin.
Here, Bowman first seriously faces the possibility that Hal could have become a murderer. The notion is so foreign to him, because Hal has been programmed to behave in a certain way and he had been functioning properly. Bowman is legitimately shocked to discover that the technology aboard the ship does not fully function, and that Hal's inner workings had not been fully understood, and he could malfunction. Bowman thinks that it is crazy that this computer program should develop a mind of its own and plot to commit actions unthinkable to its creators.
The stars were thinning out; the glare of the Milky Way was dimming into a pale ghost of the glory he had known—and, when he was ready, would know again. He was back, precisely where he wished to be, in the space that men called real.
This passage comes at the end of Bowman's transformation to a Star-Child. He is made immortal and led back to the part of the universe he had originally inhabited, to face the world from an entirely different perspective. The end of this passage emphasizes the breadth of the universe as compared to man's knowledge of it. Bowman has been brought back to "the space that men called real," not the space that is real, since as he and the reader know, Bowman has been through far more than men know of or could acknowledge exists.