Bowman anxiously waited as Discovery moved closer to the Star Gate. It had still not changed at all—Bowman saw no way in. As he passed over it, it began to appear as if receding. The last sentence he communicated to mission control was "The thing's hollow—it goes on forever—and—oh my God!—it's full of stars!" The Star Gate opened and closed and disappeared from Japetus.
In Chapter 31, Bowman is reflecting on the political reasons for which the real purpose of the Discovery mission was kept secret. "From his present viewpoint," the narrator tells us, "looking back on Earth as a dim star almost lost in the Sun, such considerations now seemed ludicrously parochial." Bowman's universe has expanded tremendously. With the knowledge that extra-terrestrial intelligence once existed, he comes to see the squabbles of humans as less significant. Once humans are no longer unique in being intelligent beings, human interactions can no longer be viewed with the same cosmic significance. The discovery of intelligent life, and especially intelligent life that precedes humans could be expected to have effects much like the Copernican Revolution. Man's view of his own importance declined when he discovered that he was not at the center of the Universe, that the physical world had not been created around him. In much the same way, the discovery that other intelligent life preceded man would upset humanity's conception of itself as special, in being the most intelligent living thing in the Universe. Man would become just another of the intelligent civilizations that once existed—stripped of the distinction of interacting with the universe in a special way that no others had.
As Bowman approaches Japetus, he realizes that he has no hope of surviving the mission and he will never return to Earth. Rather than bemoan his fate, however, Bowman is excited about the exploration that lies in front of him. His perspective on the entire world has been radically shifted by his knowledge of extra-terrestrial intelligence. Much as matters of the Earth seem insignificant, even his own life is not that important. A true explorer, his curiosity about this unknown civilization is enough to sustain him. He is genuinely excited to explore the Star Gate, even though he believes that he will soon die.