Humanity won't survive another 1,000 years unless it escapes Earth, physicist Stephen Hawking warns
He made the assessment in his first Australian address at Sydney's Opera House, where he appeared through the use of holographic technology from his office in the University of Cambridge in Britain.
"We must continue to go into space for the future of humanity," Mr Hawking said.
"I don't think we will survive another 1,000 years without escaping beyond our fragile planet."
He was filmed by two cameras in his office to create the holographic effect, with the footage sent to San Jose for processing, and then on to the Sydney Opera House.
Both his lectures on Saturday and Sunday night were sold out - the enthusiastic audience keen to hear the 73-year-old speak about the universe, black holes, and the history of time.
"I want to share my excitement and enthusiasm about this quest, so remember to look up at the stars and not down at your feet," Mr Hawking said.
"Try to make sense of what you see and wonder about what makes the universe exist.
"Be curious. And however difficult life may seem, there is always something you can do, and succeed at."
The wheelchair-bound scientist is perhaps the world's most famous sufferer of motor neurone disease.
He was introduced to the stage by his daughter — author Lucy Hawking, who was in Sydney — and kept his sense of humour throughout the lecture.
Asked: "What do you think is the cosmological effect of Zayn leaving One Direction and consequently breaking the hearts of millions of teenage girls across the world?"
His answered: "Finally, a question about something important."
Professor John Webb, the director and co-founder of the Big Questions Institute at the University of New South Wales (UNSW), made the lecture possible by an initiative he launched, along with Mr Hawking, to tackle some of the fundamental questions in science.
"He's worried about the future of the human race. You know, he thinks that human beings are, I suppose naturally aggressive," Mr Webb said.
"That may have been useful at some point in the early history of humanity enabling us to find food and get a partner and things like that, but he thinks that aggression that remains with us today is now the thing that could well end up destroying us.
"I think he's put a time on it to make us realise we've got to take better control of what we're doing."
Mr Webb said he hoped Mr Hawking's appearance would encourage a new generation to engage with scientific discovery.
"We want to appeal to young people and get them into science, we want to try and encourage governments to fund the fundamental sciences more," he said.
However, he said the development of new technology needed to be given time.
"The trouble with the fundamental sciences, the sort of things that Stephen Hawking is interested in, is there's no immediate capital return," Mr Webb said.
"Governments tend to think short term and that doesn't help get in funding for the pure sciences.
"We want to make people excited about science, we want to bring the best minds into science and we want governments to realise that there is so much interest in science that there may even be political capital there too."
Professor Merlin Crossley, the Dean of Science at UNSW, said uncertainty over federal and state funding of the sciences in Australia made presentations from people like Mr Hawking vital.
"That's the important thing ... having a culture of wanting to understand," he said.
"That's why we wanted Stephen Hawking here, to help inspire Australia not to lose faith in the importance of science discovery for improving people's lives and because it's good fun."