The Witling

"An excellent SF adventure. Our heroes are captured on a medieval planet where it turns out the locals have telekinetic powers. Lacking such powers, our heroes are regarded as inferior "witlings". Vinge, as usual, writes well and has thought things through in interesting ways. Conservation of momentum causes interesting limits (and also interesting capabilities) for telekinesis. For example, it is cheap to move between points at the same longitude and opposite latitude. So the Summer kingdom has a single Imperial palace split between the hemispheres, and the Winter kingdom has annual migrations from North pole to South pole."