I am reading Brian Greene's book The Elegant Universe. In chapter 2 he writes about Special Relativity and gives an explanation of why and how time slows down as an object travels in space at a significant fraction of the speed of light. While I have known of this happening for some time, this is the first time that I have read a non-mathematical explanation that I was finally able to understand. I highly recommend this book to anyone interested in physics. Although the book is about String Theory the opening chapters give an excellent background for the lay reader such as myself.