"We are in danger of destroying ourselves by our greed and stupidity. We cannot remain looking inwards at ourselves on a small and increasingly polluted and overcrowded planet."

"I want to know why the universe exists, why there is something rather than nothing."

"I have always been very optimistic about the future of the human race."

"The downside of my celebrity is that I cannot go anywhere in the world without being recognized. It is not enough for me to wear dark sunglasses and a wig. The wheelchair gives me away."

"I am an optimist, but I am a realist who understands that science is a slow process."