While the Sears Tower is arguably the greatest achievement in skyscraper engineering so far.it's unlikely that architects and engineers have a bandoned the question is : Just the world's tallest building.The question is.Just how high can a building go? Structural engineer William LeMessurier has designed a skyscraper nearly one-half mile high,twice as tall as the Sears Tower. And architect Robert Sobel claims that existing technology could produce a 500-story building.From Ron Bachman."Reaching for sky."Dial(May1990): 15.