You're listening to a podcast from the BBC World Service. This is Hard Talk with me, Stephen Sacker.

Thanks for downloading this edition of the program. I do hope you enjoy it.

Welcome to Hard Talk on the BBC World Service with me, Stephen Sacker.

My guest today is a world-renowned astrophysicist and cosmologist whose cutting-edge science is rather belied by the

historical splendor of his title of Astronomer Royal here in the UK. Martin Rees is internationally

renowned for his work on black holes, dark matter, and the complex science of the origins of the universe in the so-called

Big Bang. But in recent years, Martin Rees has increasingly trained his scientific gaze on the

future of our own small blue planet. In a series of books, he's described our current 21st century

as a crossroads for humanity.

Decisions we take now will determine whether human civilization survives and thrives,

very possibly to explore worlds far beyond our own, or whether it collapses,

overwhelmed by the failure to tackle man-made existential threats,

from climate change to weapons of mass destruction.

Human beings, he says, must learn to respect education and science

and act on the basis of long-term rather than short-term priorities.

So we've arrived at the crossroads, but are we capable of finding the right route?

Martin Rees, welcome to Hard Talk.

Good to be here.

We are used to you training your gaze to the furthest most corners of the universe,

and yet here you are, having just published a book on the prospects for humanity.

So now your focus is here on the blue planet, on Earth,

and you appear to believe that this century we are living in

...