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Stephen Hawking

When Stephen Hawking, one of the world’s leading astrophysicists, worries that alien “nomads” could potentially arrive at Earth “looking to conquer and colonize,” should humanity worry?

Is Mr. Hawking wrong to speculate about whether extraterrestrial life might pose a threat?

Well, at this point, says Fabio Favata of the European Space Agency, such musings are probably premature. There's no data either way.

“Many, many scientists are of the opinion that life is very likely to be common, but, quite frankly, until you discover it, it’s as much a philosophical statement as anything else. As a scientist you base your views on actual measurements,” says Mr. Favata, head of the ESA’s science planning and community coordination office. “Whether there are other life forms or not, I would say, is one of the oldest questions that mankind has asked itself.”

As far back as the third century before Jesus Christ, noted Greek philosopher Epicurus postulated that humans are not alone in the universe. “There are infinite worlds both like and unlike this world of ours. For the atoms being infinite in number, as was already proven, ... there nowhere exists an obstacle to the infinite number of worlds,” he wrote.

Since Epicurus’ time - and especially in the last 20 years - much evidence has emerged to give further credence to scientists like Hawking who theorize that other forms of life exist somewhere in the universe.

New technology and techniques for finding planets has revealed hundreds of extrasolar planets. Moreover, scientists have found that there are a wide variety of solar systems, some with small rocky planets close and others with large gaseous planets close to their star.

Now that scientists understand planets are not rare outside our solar system, the question is how do we find other life forms, if they do indeed exist? To date, scientists have found nothing to prove the assumption that out of an estimated 100 billion galaxies in the universe, some must host extraterrestrial life.

And it's not for lack of trying. A half century ago, Frank Drake started the first SETI (Search for Extraterrestrial Intelligence) program to scan the cosmos for radio signals. We have yet to tune in to an Elvis from the Alpha Centauri system - or any other.

But Hawking does have some company. Fermi scientist Richard Carrigan suggests that we shouldn't be transmitting radio signals willy-nilly into the universe. Who knows who might come to investigate us.

“Before worrying about communicating with extraterrestrials, I think most scientists are first of all trying to establish whether there is any form of extraterrestrial life and that is likely to take, still a certain number of years before one can make any definite statement, and I’m talking here whether there is anything in terms of primitive life let alone intelligent life,” says Favata.