The Black Alarm by George O. Smith — Read

Steve's return with the clean-up squad was made without mishap. It had been lonely work, for the half-dozen vortex-fighters swept the skies singly, roaming back and forth along the millions of miles across which the explosion had taken place. Sometimes they dropped into the realm below the speed of light to wipe out a bit of wispy cloud that looked as though it might be trouble brewing in the more firm structure of universal space. But mostly they raced back and forth at speeds that multiplied the velocity of light by many times. Nothing they saw reacted with their damping beams; nothing splashed against the nullifying bombs -- and then, these, too, had to be destroyed lest they start a counter-vortex of their own.

Steve had been too busy during the mop-up operations to pay attention to his own feelings. On the way home he had taken time to think, and then came that first recoiling in abject fear. Utter emptiness, absolute nothing, sheer black space closed down upon him with an inherent fear as strong as the inherent fear of falling. Man had a million of years of evolution on earth, with a constant of one gravity pulling him down onto something that his senses told him was flat, hard substantial, and everlasting. Of all that man could count upon, the earth was the one thing that he could consider unchanging.