When I was a child, after bedtime I would often get out of my bed in my pajamas, go to the window and stare at the stars. I had so many questions. How far away were those tiny points of light? Did space go on forever and ever, or was there some end to space,some giant edge? And if so, what lay beyond the edge? Another of my childhood questions: Did time go on forever? I looked at pictures of my parents and grandparents and tried to imagine their parents, and so on, back through the generations, back and back through time. Does time go on forever? Or is there some beginning of time? And if so,what came before? When I grew up, I became a professional astrophysicist. Although I never answered any of these questions, they continued to challenge me, to haunt me, to drive me in my scientific research, to cause me to live on tuna fish and no sleep for days at time while I was obsessed with a science problem.


  These same questions, and questions like them challenge and haunt the leading scientists of today. Einstein once wrote that "the most beautiful experience we can have is the mysterious. It is the fundamental emotion which stands at the cradle of true art and true science." What did Einstein mean by “the mysterious?" I don't think he meant that science is full of unpredictable or unknowable or supernatural forces. I think that he meant a sense of awe, a sense that there are things larger than us, that we do not have all the answers at this moment. And a sense that we can stand right at the boundary between known and unknown and gaze into that cavern and be exhilarated rather than frightened.


  Scientists are happy, of course, when they find answers to questions. But scientists are also happy when they become stuck, when they discover interesting questions that they cannot answer. Because that is when their imaginations and creativity are set on fire. That is when the greatest progress occurs. One of the Holy Grails in physics is to find the so-called "Theory of Everything," the final theory that will encompass all the fundamental laws of nature. I, for one, hope that we never find that final theory. I believe in the creative power of the unknown. I believe in the exhilaration of standing at the boundary between the known and the unknown. I believe in the unanswered questions of children.