Professor Stephen Hawking is backing a new search for alien intelligence on an astronomical scale that within 10 years could reveal if we are alone in the universe.
The renowned cosmologist and best-selling author has lent his personal support to the 100 million dollar (£64 million) decade-long project launched by a Russian silicon valley billionaire.
Other big name scientists, including the Astronomer Royal, Lord Rees, are also involved in the endeavour which dwarfs previous underfunded and piece-meal attempts to eavesdrop on alien civilisations.
Yuri Milner, who made his fortune through investments in technology companies, said the Breakthrough Listen project he is funding will use three of the world's most powerful telescopes and gather more information in one day than previous Seti (Search for Extraterrestrial Intelligence) attempts managed in a year.
Speaking through his trademark voice synthesiser at today's launch event at the Royal Society's headquarters in London, Prof Hawking said: "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.
"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. 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 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 our rock, the universe discovered its existence?
"Either way, there is no bigger question. It is time to commit to finding the answer - to search for life beyond Earth."
Listen, the first of two Breakthrough Initiatives, will harness both state-of-the-art analytical software and the combined power of nine million personal computers around the world via a "citizens' science" network already used by Seti researchers.
Cutting edge computing technology being developed for the project will make it possible to sift through billions of radio frequencies at once, looking for the tell-tale signs of an intelligent signal.
The search will take in a million nearby star systems, the centre of our Milky Way galaxy, and even reach out across unimaginable distances to 100 other galaxies. As well as scouring vast numbers of radio channels, the scientists will also watch for messages transmitted by laser light.
All the information collected will be made publicly available. There is no question of anything being kept secret or covered up - whatever is found, insist the scientists involved in the project.
Recent discoveries, largely from the American space agency Nasa's Kepler space telescope, have revealed that habitable planets may be as common as they are in popular science fiction.
Data from Kepler suggest at least 10% of stars in the Milky Way harbour a planet of almost Earth size with mild temperatures conducive to life. In a galaxy containing hundreds of billions of stars, that greatly increases the odds of life existing beyond the solar system.
Lord Rees, who will chair the project's advisory committee, said: "It's a huge gamble of course, but the pay off will be so colossal ... that the investment is well worth while.
"The chances of finding life have been raised a billion-fold when you realise that habitable planets are not rare but there are billions of them."
Speculating on the kind of intelligent life that might exist among the stars, Lord Rees said: "The biggest uncertainties in the origin of life are the biological ones.
"We don't know what we'll see out there. It may be organic life. It may be machines made by a long-dead civilisation. But any signal, even if it's hard to decode, if it's manifestly artificial, will tell us that the concepts of logic and physics aren't limited to the hardware in human skulls. It is elsewhere, and it will transform our view of the universe."
If evidence of intelligent life is found, the second Breakthrough Initiative will come into play. Known as Breakthrough Message, this will organise a competition with prizes totalling one million dollars (£640,000) to find the best ways of communicating with aliens - probably by means of pictures or movies rather than any kind of language.
The search will centre on three top observatories, including the Green Bank telescope in West Virginia, US, the world's largest steerable radio telescope.
The two others are the 64-metre Parkes dish in New South Wales, Australia, which recorded the first images of Apollo astronaut Neil Armstrong walking on the moon on 1969, and the Lick observatory in California, US, which will be used to look for laser signals.
Among other leading lights in astronomy involved in the project are Professor Frank Drake, the founding father of Seti, and Professor Geoff Marcy, from the University of California at Berkeley, who pioneered the search for extra-solar planets orbiting distant stars.
Prof Drake made the first attempt to look for an intelligent transmission from outer space in 1960 and formulated the Drake Equation that provides a method of calculating the likely number of alien civilisations in the universe.
His own solution to the equation estimates that there could be as many as 10,000 intelligent civilisations in the Milky Way alone.
The professor described how 55 years ago he pointed his antenna at the star Epsilon Eridani, 10 light years from Earth, and immediately picked up what appeared to be an artificial signal.
"We were astonished - could it really be this easy?" he said. "But unfortunately that signal was one that was coming from us, mimicking a signal from another star."
Since then numerous searches have revealed nothing to indicate that the human race has any intelligent company in the cosmos.
But Prof Drake pointed out that the technical and funding limitations had seriously hampered Seti scientists up until now.
He added: "There are just so many stars with so many frequency channels that you must make a very comprehensive search using very sophisticated equipment that allows us to search the whole radio spectrum in a very short time.
"Things have come together to make this possible. We have the large telescopes; we also have major developments in digital technology that allow us to construct radio receivers that can monitor literally billions of channels at the same time."
Mr Milner's "massive" donation meant that Seti scientists would no longer be confined to the role of "poverty stricken" guest observers, said Prof Drake.
"We will have the most powerful search, and enduring search, that has every been launched," he said. "This is a very great milestone."
Prof Marcy stressed that both habitable planets and the organic chemicals of life were abundant in the universe.
"The universe is apparently bulging at the seams with the ingredients of biology," he said. "Given all that, who among us could doubt that basic single-celled life is common in the universe? I would bet my house that in the 100 closest star systems single-celled organisms are flourishing.
"The more difficult question is how commonly life evolves into intelligent species, and how long it lasts.
"We will be examining something like 10 billion frequencies of radio waves simultaneously. In fact we will listen to a cosmic piano every time we point the telescope - a piano not with 88 keys but 10 billion keys."
Mr Milner, who was named after the first man in space, Russian cosmonaut Yuri Gagarin, said: "Today we are launching the most comprehensive search programme ever. Just in one day Breakthrough Listen will collect more data than a year of any previous search.
"The scope of our search will be unprecedented - a million nearby stars, the galactic centre, the entire plane of the Milky Way and 100 nearby galaxies.
"Breakthrough Listen takes the search for intelligent life in the universe to a completely new level."
Giving pre-recorded answers to questions, Prof Hawking said that even if the scientists failed to find any evidence of intelligent life that in itself would be a "very interesting result".
He added: "It will not prove that we are alone. But it will narrow the possibility and is likely to produce data that is fascinating in its own right."
Asked if he believed intelligent aliens existed, he said: "They might be there, they might not. But recent experiments like the Kepler mission have changed the game.
"We now know there are so many worlds and organic molecules are so common that it's quite likely life is out there, but intelligence is a great unknown. It only took 500 million years for life to evolve on Earth. But it took two and a half billion years to get from the earliest cells to multi-celled animals, and technological intelligence has appeared only once, so it may be very rare. And when it does evolve we only have to look in the mirror to know it can be fragile and prone to self-destruction."
The project will - at least initially - only listen for signals and avoid actively transmitting news of our presence to the cosmos.
So-called "active Seti" would not be the best use of resources, and may cause unnecessary anxiety among those who fear the consequences of revealing ourselves to a super-advanced civilisation, say the scientists, who do not believe the risk is real.
Their view is not shared by Prof Hawking, who in the past has warned of the folly of such a move.
Answering a question today, he said: "We don't know much about aliens, but we know about humans ..
"A civilisation reading one of our messages could be billions of years ahead. If so, they will be vastly more powerful and may not see us as any more valuable than we see bacteria."