How do we decide what's important? How do we balance the priorities of the here and now with the big picture challenges that will determine the future of human civilisation? HARDtalk speaks to Sir Martin Rees, one of the world’s leading astrophysicists, who has recently been gazing into the future of our own planet. The next century, he says, will determine humanity's long term destiny; so are the prospects good, or grim?Image: Sir Martin Rees (Credit: Getty Images)