"When I discover I'm wrong, I change my mind. What do you do?"

“Absence of evidence is not evidence of absence.”

“We’re all depressingly ‘lay’ outside our specialisms — my own knowledge, of recent biological advances, such as it is, comes largely from ‘popular’ books and journalism.”

“Once the threshold is crossed when there is a self-sustaining level of life in space, then life's long-range future will be secure irrespective of any of the risks on Earth . Will this happen before our technical civilisation disintegrates, leaving this as a might-have-been? Will the self-sustaining space communities be established before a catastrophe sets back the prospect of any such enterprise, perhaps foreclosing it for ever? We live at what could be a defining moment for the cosmos, not just for our Earth.”

“2005 TED talk: Is this our final century?”

“Our Universe and Others”

“No one can say which approach is the right one — so no one can say how close we are to a solution.”