June 7, 2010— -- Celebrated physicist Stephen Hawking knows more about the universe than almost any other person ever to walk the planet, but some answers still escape even him.
When asked by ABC News' Diane Sawyer about the biggest mystery he'd like solved, he said, "I want to know why the universe exists, why there is something greater than nothing."
During Hawking's 30 years in the post, he gave his colleagues new ways to look at the universe. But he also gave the public, through his many books and occasional appearances, a way to connect with the often obscure world of theoretical physics.
"Stephen has had a tremendous impact on our understanding of the universe, particularly of warp space and warp time in the universe, black holes, the origin of the universe," said physicist Kip Thorn at last week's World Science Festival event honoring Hawking.
Hawking's most well-known book, "A Brief History of Time," sold more than 9 million copies and is an international best-seller. He's even made brief cameos in pop culture staples like "The Simpsons" and "Star Trek."
But exploring the origins of time inevitably leads to questions about the ultimate origins of everything and what, if anything, is behind it all.
"What could define God [is thinking of God] as the embodiment of the laws of nature. However, this is not what most people would think of that God," Hawking told Sawyer. "They made a human-like being with whom one can have a personal relationship. When you look at the vast size of the universe and how insignificant an accidental human life is in it, that seems most impossible."
When Sawyer asked if there was a way to reconcile religion and science, Hawking said, "There is a fundamental difference between religion, which is based on authority, [and] science, which is based on observation and reason. Science will win because it works."