"We believe that life arose spontaneously on Earth, so in an infinite universe, there must be other occurrences of life.
"Somewhere in the cosmos, perhaps intelligent life might 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 better question.
"It's time to commit to finding the answer, to search for life beyond Earth. The Breakthrough initiatives are making that commitment. We are alive. We are intelligent. We must know," Hawking said.
The project is funded by Silicon Valley technology investor Yuri Milner, who was trained as a physicist.
"In 1961, John F. Kennedy announced his dream of landing a man on the moon by the end of this decade. Forty-six years ago, man made the first steps on the moon.
"That same year, 1961, Yuri Gagarin became the first human in space. It was an important year for humanity; we stepped out into the solar system. And it was an important year for me; I was born. My parents were so inspired by Gagarin's voyage that they named me Yuri.
"Later, I was told by my mother, who is right here in this room, that she wanted me to be inspired by what he did," Milner said.