What do you believe is true, even though you cannot prove it?

That's what John Brockman asked scientists, futurists and other creative thinkers. Some replies:

Randolph Nesse, University of Michigan: 'I'm pretty sure that people gain a selective advantage from believing in things they can't prove. Those who are occasionally consumed by false beliefs do better in life than those who insist on evidence before they believe and act.'

Stanislas Dehaene, Institut National de la Sant, Paris: 'We vastly underestimate the differences that set the human brain apart from the brains of other primates.''

Carlo Rovelli, Centre de Physique Thorique, Marseille: 'Time does not exist.'

Seth Lloyd, Massachusetts Institute of Technology: 'I believe in science. Unlike mathematical theorems, scientific results can't be proved. They can only be tested again and again, until only a fool would refuse to believe in them.'

Daniel Hillis, chairman, Applied Minds Inc: 'I know that it sounds corny, but I believe that people are getting better. In other words, I believe in moral progress.'

Craig Venter, president, J Craig Venter Science Foundation: 'Life is ubiquitous in the universe.'

Janna Levin, Columbia University: 'I believe that there is an external reality, and you are not all figments of my imagination.'"

I wonder if he talked to any psychiatrists. We can't prove any of our theories. But I do believe in unconscious drives, and in defense mechanisms. I think that denial may be one of the strongest forces on earth!

How would you answer Mr. Brockman?