 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. 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 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. But how could a star change into a blinking blue-white globe—if, indeed, that was the star Rikud had seen earlier? Rikud couldn't remember, and he suddenly wished he could read Crifer's book on astronomy, which meant the same as stars. Presently Rikud became aware that his eyes were not tearing any longer, and he turned to look at the viewport. Rikud turned again to the port, where he could see nothing but an obscuring cloud of white vapor, murky, swirling, more confusing than ever.
 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.