"I still believe in e=mc², but I can't believe that in all of human history, we'll never ever be able to go beyond the speed of light to reach where we want to go," said Clark. "I happen to believe that mankind can do it.

"I've argued with physicists about it, I've argued with best friends about it. I just have to believe it. It's my only faith-based initiative." Clark's comment prompted laughter and applause from the gathering.