 What does the viewport allow Rikud to realize?
Every day for a week now, Rikud had come to the viewport to watch the great changeless sweep of space. But ever since the engines somewhere in the rear of the world had changed their tone, from the steady whining Rikud had heard all twenty-five years of his life, to the sullen roar that came to his ears now, the feelings had grown. The stars—it was a meaningless concept to Rikud, but that was what everyone called the bright pinpoints of light on the black backdrop in the viewport—were not apparent in the speckled profusion Rikud had always known. Rikud knew that something which he could not explain had entered the elder man's head for a moment, but it had departed almost before Chuls knew of its existence. Rikud, for his part, wanted to get back to the viewport and watch the one new bright star. But if he wasn't reading himself, Rikud usually went to sleep. You can find several of them under 'astronomy,' with a cross-reference under 'stars.' "You know," Rikud said, sitting up now, "the stars in the viewport are changing." The view had changed, and the strangeness of it made Rikud's pulses leap with excitement. All the stars were paler now than before, and where Rikud had seen the one bright central star, he now saw a globe of light, white with a tinge of blue in it, and so bright that it hurt his eyes to look.
 There is more to the world outside of the ship they are on.
 There is more to the world outside of the ship they are on.  The viewport is not a flat space, and objects can pass through it.  The stars are indeed changing.  The garden outside is moving.