Vernor Vinge Department of Mathematical Sciences San Diego State University (c) 1993 by Vernor Vinge (This article may be reproduced for noncommercial purposes if it is copied in its entirety, including this notice.) The original version of this article was presented at the VISION-21 Symposium sponsored by NASA Lewis Research Center and the Ohio Aerospace Institute, March 30-31, 1993. A slightly changed version appeared in the Winter 1993 issue of Whole Earth Review. Abstract Within thirty years...