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Should We Call the Cosmos Seeking ET? Or Is That Risky?

Astronomers have their own version of the single person’s dilemma: Do you wait by the phone for a call from that certain someone? Or do you make the call yourself and risk getting shot down?

Instead of love, of course, astronomers are looking for alien life, and for decades, they have sat by their telescopes, waiting to hear from E.T. It didn’t happen, and so now some of them want to beam messages out into the void and invite the closest few thousand worlds to chat or even visit.

Others scientists, including Stephen Hawking, think that’s crazy, warning that instead of sweet and gentle E.T., we may get something like the planet-conquering aliens from “Independence Day.” The consequences, they say, could be catastrophic.

But calling out there ourselves may be the only way to find out if we are not alone, and humanity may benefit from alien intelligence, said Douglas A. Vakoch, whose title — for real — is director of interstellar message composition at the SETI Institute in Mountain View, California. SETI stands for Search for Extraterrestrial Intelligence, and until now it’s been mostly a listening-type thing.

This dispute — which mixes astronomy, science fiction, philosophy, the law, mathematics and a touch of silliness — broke out Thursday and Friday at a convention in San Jose of the American Association for the Advancement of Science.

And this week several prominent space experts, including Space X founder Elon Musk and planet hunter Geoff Marcy, started a petition cautioning against sending out such messages, saying it is impossible to predict whether extraterrestrial life will be benign or hostile.

Vakoch is hosting a separate conference Saturday at the SETI Institute on the calling-all-aliens proposal and what the messages should say.

The idea is called active SETI, and according to Vakoch would involve the beaming of messages via radar and perhaps eventually lasers.

We’ve been inadvertently sending radio and TV signals out to the cosmos for some 70 years — though less now, with cable and satellite sending shows directly down to Earth. In fact, each day a new far-off planet may be just now catching the latest episode of the 1950s sitcom “I Love Lucy,” said astronomer Seth Shostak, a senior astronomer at the SETI Institute.

There have been a few small and unlikely-to-work efforts to beam messages out there in the past, including NASA sending the Beatles song “Across the Universe” into the cosmos in 2008. NASA’s Voyager probe recently left the solar system with a “golden record” created by Carl Sagan with a message, and the space agency’s New Horizon probe will also have greetings on it by the time it exits the solar system.

But what scientists are now talking about is a coordinated and sustained million-dollar-a-year effort with approval from some kind of science or international body and a message that people agree on.

It’s an “attempt to join the galactic club,” Vakoch said. He assured a crowd of reporters: “There’s no danger of alien invasion from active SETI.”

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But as a science fiction author, as well as an astrophysicist, David Brin thinks inviting aliens here is a bad idea. Even if there is a low risk of a nasty creature coming, the consequences could be extreme.

“I can’t bring myself to wager my grandchildren’s destiny on unreliable assumptions” about benevolent aliens, Brin said.

Brin noted that European explorers brought slaughter and disease to less technologically advanced people in the Americas more than 500 years ago. He called for the science community to put efforts on hold for an ethical and scientific discussion on “why it won’t go the same way as between Cortez and the Aztecs.”

As Brin, Shostak, Vakoch and others sparred at a news conference, 84-year-old Frank Drake sat in the back quietly. Drake, a pioneer in the search for extraterrestrial life, created the formula called Drake’s Equation that scientists use to estimate the chances that other life is out there. More than 40 years ago, Drake and Sagan beamed a message into space to look for aliens, a first for Earth.

It was a short message from the Arecibo Observatory in Puerto Rico, and it was aimed at a star cluster called Messier 13. It will take 25,000 years to get there, Drake said.

“The probability of succeeding is infinitesimally small,” Drake said, rolling out calculations about the incredible amount of time it takes messages to go back and forth and his estimate that the average civilization will last only 10,000 years.

So why’d he do it? Curiosity, Drake said. And it doesn’t matter if our civilization is gone by the time E.T. answers, if he does.

“We get messages from the ancient Greeks and Romans and Socrates all the time, long since gone. Still valuable,” Drake said. “We’re going to do the archaeology of the future.”

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Online:

SETI Institute: http://www.seti.org

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Berkeley statement cautioning against active SETI: http://setiathome.berkeley.edu/meti_statement_0.html

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New Horizons messaging initiative: http://www.oneearthmessage.org

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Depiction of black hole in space by artist

Evaporating black holes? Explained

Can the concepts of relativistic quantum field theory be carried over to curved space-times, which include gravitational sources and are described by Einstein’s theory of general relativity? The answer is a “Yes”. Stephen Hawking, the most famous physicist of recent time, took the most notable step in this direction in the 1970s.

Hawking examined a model of quantum particles not in the gravity-free environment of special relativity, but in a space-time containing a black hole. The result was surprising: The mere presence of the black hole means that, even if at early times not a single particle was present, at late times, there is a steady stream of them escaping to infinity. In other words: a black hole emits quantum particles! This conjectured radiation is known as “Hawking radiation“. While it has not yet been observed, convincing reasons for its existence appear to be built right into the foundations of quantum theory.

Higher the mass of the black hole, lower will be the temperature and intensity of Hawking radiation. The following table shows a few black hole masses, corresponding Schwarzschild radii (which measure the size of a spherical black hole) and the temperature (measured in Kelvin) of the radiation it emits. Each entry has as a background the characteristic colour of thermal radiation with the given temperature:

MassSchwarzschild radiusTemperature
Solar mass3 kilometres (1.9 miles)1 tenth of a millionth Kelvin
Mass of the earth9 millimetres0.02 Kelvin
Mass of the moon1/10 millimetres1.7 Kelvin
1/10 mass of the moon1/100 millimetre17 Kelvin
1/100 mass of the moon1 millionth of a metre170 Kelvin
1/1000 mass of the moon1/10 millionth of a metre1700 Kelvin
1/2000 mass of the moon1/20 millionth of a metre3300 Kelvin
1/5000 mass of the moon1/50 millionth of a metre8400 Kelvin

 

As the colours show, astrophysical black holes – such as stellar and supermassive black holes – are indeed black. Black holes lighter than about a hundredth of the mass of the earth’s moon, however, glow in the dark. Even lighter ones – a five-thousandth the mass of the moon – are white-hot objects, and look the part. For holes that are lighter still, most radiation is emitted as UV radiation, X-rays or even highly energetic gamma radiation.

The table doesn’t indicate intensities. In fact, the black holes shown are dark. For black holes with lesser masses, however, significant fractions of mass and energy are radiated away – the smaller the mass, the greater the power. This leads to a runaway process in which the black hole evaporates with a final, gigantic flash of energy

If at all “mini black holes” with very little mass have formed in our universe, some might now have reached the stage where such violent evaporation occurs. But till now we haven’t found any astronomical evidence for highly energetic evaporation processes, and Hawking radiation remains purely theoretical.

In calculations like Hawking’s initial derivation of radiating black holes, the matter is described in quantum terms, but the concepts of classical general relativity are used to describe the space-time environment. However, there are situations when this semi-classical treatment is insufficient. To fully understand our universe, these situations indicate that it is necessary to formulate a quantum theory of gravity, in which space and time are subject to the laws of the quantum world as well.