"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."

"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'm an optimist. I think that the human race will find a way to survive."

"I'm a physicist, and I believe in science. I don't believe in miracles."

"I believe that we are alone in the universe, but I hope we are not."