Professor Stephen Hawking will be celebrating his 70th birthday in two days and marked the occasion by answering questions from callers on BBC Radio 4's Today Programme. Among other topics, Hawking discussed his belief that the human race will need to colonize space to survive long-term — he feels it's "almost certain" a catastrophic event will take place on Earth in the next 1,000 years, like nuclear war or global warming. Not the most positive of statements to make, but Hawking claims he is optimistic about our ability to make self-sustaining colonies on Mars or other planets and that humans will eventually spread beyond the reaches of the solar system.

He wasn't quite so positive when asked about the outcomes of meeting intelligent life elsewhere in the universe. Hawking said the discovery of other intelligent life would be the biggest scientific breakthrough in history, but then compared alien creatures visiting the earth to Europeans encountering Native Americans for the first time: "that did not turn out well for the native Americans." You can listen to the entire interview over on the BBC's website.