Feature: ET, when will we see you? (3)

Chinese scientists have also actively participated in the preparations for the Square Kilometer Array (SKA), a large multi-radio telescope project to be built in Australia and South Africa.

The SKA will eventually use thousands of dishes and up to a million antennas, which will enable astronomers to monitor the sky in unprecedented detail and survey the entire sky much faster than any system currently operating. The search for extraterrestrial life is one of its key science programs.

Scientists have surveyed the entire sky with radio telescopes for a half-century now, and they have found interesting signals occasionally.

On August 15, 1977, a strong narrow-band radio signal, bearing the expected hallmarks of extraterrestrial origin, was detected by astronomer Jerry R. Ehman while working on a SETI project at the Big Ear radio telescope of Ohio State University. The signal appeared to come from the constellation Sagittarius and lasted 72 seconds.

Ehman circled the signal on the computer printout and wrote the comment "Wow!" beside it, which the event is now commonly called. But it has never been detected again.

"Some strange signals have been found, but it's hard to confirm their origins, because these signals do not repeat," Li Di says.

"We look for not only television signals, but also atomic bomb signals. We shall give full play to our imaginations when processing the signals," Li says. "It's a complete exploration, as we don't know what an alien is like."

Sometimes, radio telescopes are "confused" by signals from astronomical objects. For example, astronomers once mistook signals from a pulsar for extraterrestrial signs, because a pulsar can also give out very stable periodical signals.

"We don't know when earthlings will discover ET. It could be 1,000 years from now, or in our lifetimes. It could be next year, when FAST gets going on the sky surveys," Werthimer said.

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However, with no clues of extraterrestrial life over the past five decades, questions are constantly asked as whether the search methods are appropriate.

Even on Earth, land and sea host completely different forms of life. "It is highly possible that life on other planets is entirely different from that on Earth, and it might not be carbon-based," says Jin Hairong, deputy curator of Beijing Planetarium.

Liu Cixin, a Chinese science fiction writer and winner of the Hugo Award for his novel The Three Body Problem, points out the current method assumes that aliens also communicate in radio waves. "But if it's a truly advanced civilization, it is possible to use other more advanced forms of communication, such as gravitational waves."

But Mao Shude believes many methods deserve a try: "Who knows what they are and how they think?

"When we study the origin of life, we risk going down a blind alley if we only have one sample from Earth," Mao says. "If we could find more samples in the universe, we could look at the puzzle more comprehensively and solve it more easily."

He gives an example in astronomy to explain the limitations of a single sample. "When scientists started to look for planets around Sun-like stars, they thought it must be difficult as their period might be as long as a year. However, the first such planet discovered outside our solar system takes only four days to orbit its host star - much faster than astronomers expected. At that time, some people doubted it, showing how the example of our solar system narrowed their thinking."

"If we really discover extraterrestrial life, I'd like to know how life spreads in the universe. Is it distributed uniformly in space, or clustered?" Mao wonders.

However, the idea communicating with aliens comes with concerns.

British astrophysicist Stephen Hawking has warned that communicating with aliens could be a threat to Earth: "If aliens visit us, the outcome would be much as when Columbus landed in America, which didn't turn out well for the Native Americans."

The Three Body Problem by Liu Cixin depicted the universe as a jungle with every civilization as a hidden hunter. Those who are exposed will be eliminated.

But Han Song, another leading Chinese science fiction writer, believes humans naturally want to connect, citing the Internet as proof.

"I think aliens might think similarly. It is a biological instinct to connect with each other. Everyone wants to prove that they are not alone in the universe. Loneliness is intolerable to humans," he says.

He also points out that the contact will be driven by curiosity and real requirements. "Humans will ultimately go to space to find resources and expand their living area, so it will be hard to avoid aliens. Contact with them, especially those with more advanced intelligence, may help us leap forward in civilization."

Regardless of the theoretical debate, scientists have never wavered in the search.

"I think we shall call out. As a matter of fact, we have been yelling for years, and our radios and televisions are broadcasting in space all the time," Mao says, "Aren't you curious what our counterparts would look like?

"If they are inferior or equal to us in terms of civilization, we won't be easily destroyed. If they are much more intelligent than us, they wouldn't be so narrow-minded as to compete with us. Some worry they will come to rob us of our natural resources, but they likely have the power to transform the entire globe already. What's the point of eliminating a much lower civilization?"

Mao believes the result will be significant however it turns out. "If we find other life, it will undoubtedly be the most important scientific discovery in our history; if not, it shows that life on Earth is unique and we should respect life and cherish each other.

"No matter the outcome, we shall never stop searching, and I hope to hear more voices and contributions from Chinese scientists." Endi