what are they trying to signal?

Video - Into the Universe with Stephen Hawking Aliens

Guardian | "Extremophiles" are species that can survive in places that would quickly kill humans and other "normal" life-forms. These single-celled creatures have been found in boiling hot vents of water thrusting through the ocean floor, or at temperatures well below the freezing point of water. The front ends of some creatures that live near deep-sea vents are 200C warmer than their back ends.

"In our naive and parochial way, we have named these things extremophiles, which shows prejudice – we're normal, everything else is extreme," says Ian Stewart, a mathematician at Warwick University and author of What Does A Martian Look Like? "From the point of view of a creature that lives in boiling water, we're extreme because we live in much milder temperatures. We're at least as extreme compared to them as they are compared to us."

On Earth, life exists in water and on land but, on a giant gas planet, for example, it might exist high in the atmosphere, trapping nutrients from the air swirling around it. And given that aliens may be so out of our experience, guessing motives and intentions if they ever got in touch seems beyond the realm's even of Hawking's mind.

Paul Davies, an astrophysicist at Arizona State University and chair of Seti's post-detection taskforce, argues that alien brains, with their different architecture, would interpret information very differently from ours. What we think of as beautiful or friendly might come across as violent to them, or vice versa. "Lots of people think that because they would be so wise and knowledgeable, they would be peaceful," adds Stewart. "I don't think you can assume that. I don't think you can put human views on to them; that's a dangerous way of thinking. Aliens are alien. If they exist at all, we cannot assume they're like us."

Answers to some of these conundrums will begin to emerge in the next few decades. The researchers at the forefront of the work are astrobiologists, working in an area that has steadily marched in from the fringes of science thanks to the improvements in technology available to explore space.