英国著名物理学家史蒂芬·霍金近日发出警告，称外星生物可能真的存在，但是人类与他们接触可能会带来毁灭性的后果。

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Aliens may exist but mankind should avoid contact with them as the consequences could be devastating, British scientist Stephen Hawking warned Sunday.

Aliens may exist but mankind should avoid contact with them as the consequences could be devastating（毁灭性的） , British scientist Stephen Hawking warned Sunday.

"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," said the astrophysicist（天体物理学家） in a new television series, according to British media reports.

The programs depict³（描画，描述） an imagined universe featuring alien life forms in huge spaceships on the hunt for（寻找） resources after draining（枯竭，排水） their own planet dry.

"Such advanced aliens would perhaps become nomads⁴（流浪者，游牧民） , looking to conquer and colonize⁵ whatever planets they can reach," warned Hawking.

The doomsday scenario⁶ is suggested in the series "Into the Universe with Stephen Hawking" on the Discovery Channel, which began airing in the United States on Sunday.

On the probability of alien life existing, he says: "To my mathematical（数学的） brain, the numbers alone make thinking about aliens perfectly⁷ rational（理性的，合理的） .

"The real challenge is to work out what aliens might actually be like."

Glowing squid-like creatures, herds⁸（人群，大量） of herbivores（食草动物） that can hang onto a cliff face and bright yellow predators⁹ that kill their prey¹⁰ with stinging tails are among the creatures that stalk the scientist's fantastical cosmos¹¹.

Mankind has already made a number of attempts to contact extraterrestrial（地球外的） civilizations.

In 2008, American space agency NASA beamed the Beatles song "Across the Universe" into deep space to send a message of peace to any alien that happens to be in the region of Polaris（北极星） -- also known as the North Star -- in 2439.

But the history of humanity's efforts to contact aliens stretches back（回溯到） some years.

The US probes Pioneer 10 and 11 were launched in 1972 and 1973 bearing plaques¹²（斑块，瓷片） of a naked man and woman and symbols seeking to convey the positions of the Earth and the Sun.

Voyager 1 and 2, launched in 1977, each carry a gold-plated copper¹³ phonogram（音标符号，录音片） disk with recordings¹⁴ of sounds and images on Earth.