 What is not a theme explored in this story?
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. But something soft had cushioned the impact—something which had come into being just for the moment and then abruptly passed into non-being again, something which was as impalpable as air. True, this was the only case of its kind, the exception to the rule, but it proved the world was not perfect. Now if the world had walked from—somewhere, through the vast star-speckled darkness and to the great garden outside, this also was purposeful.
 Equality must be realized.
 Change is necessary and inevitable for survival.  Fear is a powerful motivator.  Perception can often be all-encompassing.  Equality must be realized.