The venture is said to be the biggest yet in support of the search for extra-terrestrial intelligence.

The 10-year effort will listen for broadcast signals from a million of the stars closest to Earth.

Prof Stephen Hawking has launched a new effort to answer the question of whether there is life elsewhere in space.

The venture is said to be the biggest yet in support of the search for extra-terrestrial intelligence.

The 10-year effort will listen for broadcast signals from a million of the stars closest to Earth.

The £64m ($100m) initiative was launched by the Breakthrough Initiatives group at the Royal Society in London.

Speaking at the launch, Prof Hawking said: "Somewhere in the cosmos, perhaps, intelligent life may be watching these lights of ours, aware of what they mean.

"Or do our lights wander a lifeless cosmos - unseen beacons, announcing that here, on one rock, the Universe discovered its existence. Either way, there is no bigger question. It's time to commit to finding the answer - to search for life beyond Earth.

"We are alive. We are intelligent. We must know."

Those behind the initiative claim it to be the biggest scientific search ever undertaken for signs of intelligent life beyond Earth. They plan to cover 10 times more of the sky than previous programmes and scan five times more of the radio spectrum, 100 times faster.

It will involve access to two of the world's most powerful telescopes. - the Green Bank Telescope in West Virginia and the Parkes Telescope in New South Wales, Australia.

Among those involved in the search is Lord Martin Rees, the Astronomer Royal.

The £64m initiative was launched at the Royal Society in London

"The search for extra-terrestrial life is the most exciting quest in 21st-century science. The Breakthrough Initiatives aim to put it on the same level as the other ultimate scientific questions," he said.

The public will be invited to participate in efforts to find a signal from another world through the SETI@home project.

Yuri Milner, a high tech US based-billionaire and founder of the initiative said technology had developed to a point where it was possible to put listening for signs of extra-terrestrial intelligence on a proper scientific footing.

He said: "Current technology gives us a real chance to answer one of humanity's biggest questions: Are we alone?

"With Breakthrough Listen, we're committed to bringing the Silicon Valley approach to the search for intelligent life in the Universe. Our approach to data will be open and taking advantage of the problem-solving power of social networks.

Prof Hawking added that he believed the search was one of humanity's most important scientific endeavours.

"To understand the Universe, you must know about atoms - about the forces that bind them, the contours of space and time, the birth and death of stars, the dance of galaxies, the secrets of black holes," he explained.

"But that is not enough. These ideas cannot explain everything. They can explain the light of stars, but not the lights that shine from planet Earth.

"To understand these lights, you must know about life. About minds."