Ever since Stephen Hawking wrote his world-wide best-seller A Brief History of Time , publishers have been searching for a physicist who could repeat that success. Now Brian Greene, a 36-year-old theoretical physicist from Columbia University in New York, appears to have pulled off the trick with a book on string theory. Published in the US in February, the first printing of The Elegant Universe sold out within a week, and by mid-March the book was on its fourth "healthy" print-run.