Astronomy190 - Topics in Astronomy
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Astronomy190 - Topics in Astronomy
Astronomy and Astrobiology
Lecture 21: Search for Extraterrestrial Intelligence
Ty Robinson
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Questions of the Day
• What is the Drake Equation, and why is it useful?
• Even if life arises, will it inevitably evolve towards intelligence?
• What are the methods SETI uses to search for intelligence today?
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Are We Alone?
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The Drake EquationEstimating the number of civilizations in the Milky Way with which we might hope to communicate
Nc = Ns x fp x Ne x fl x fi x fc x L
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The Drake Equation
number of stars in the galaxy(~200 billion)
Nc = Ns x fp x Ne x fl x fi x fc x L
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The Drake Equation
QuickTime™ and a decompressor
are needed to see this picture.
fraction of stars that have planets(> 10%)
Nc = Ns x fp x Ne x fl x fi x fc x L
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The Drake Equation
number of terrestrial planets per planetary system in the Habitable Zone
QuickTime™ and a decompressor
are needed to see this picture.
Nc = Ns x fp x Ne x fl x fi x fc x L
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The Drake Equation
fraction of such planets on which life actually evolved
QuickTime™ and a decompressor
are needed to see this picture.
Nc = Ns x fp x Ne x fl x fi x fc x L
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The Drake Equation
fraction of inhabited worlds that develop intelligent life
Nc = Ns x fp x Ne x fl x fi x fc x L
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The Drake Equation
fraction of worlds with intelligent beings that produce a civilization capable of interstellar communication
QuickTime™ and a decompressor
are needed to see this picture.
Nc = Ns x fp x Ne x fl x fi x fc x L
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The Drake Equation
the lifetime of such civilizations (divided by the age of the galaxy)
Nc = Ns x fp x Ne x fl x fi x fc x L
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Fermi Paradox
What if Nc is much larger than 1?
Where are they?
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Alone in the galaxy?
What if Nc is less than 1?
Is anybody out there?
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fi : the Question of Intelligence
Is the evolution of intelligence inevitable?
Nc = Ns x fp x Ne x fl x fi x fc x L
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fi : the Question of Intelligence
• two schools of thought1. intelligent (radio telescope building) life is rare
• we’ve had life for 3.5 Gyrs, but radio and TV signals for only the last 50 yrs.
• intelligence evolved as the result of random chance
• remember: evolution is not goal-oriented!
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fi : the Question of Intelligence
• two schools of thought2. there is evolutionary pressure for intelligence
• natural selection promotes greater intellectual capability
• if humans hadn’t developed technology-building intelligence, something else would have
• maybe there is a widespread selection pressure for intelligence
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Convergent Evolution• organisms of different evolutionary backgrounds
that occupy similar ecological niches will eventually come to resemble one another
Is there an evolutionary trend favoring intelligence?
• maybe intelligence increases fitness so much that if that niche is not filled, species will be selected for intelligence via convergent evolution
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Measuring Intelligence
big brainsmall brain
EQ= encephalization quotient
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Evolution to Higher Intelligence?
Enc
epha
lizat
ion
Quo
tient
(E
Q)
Time (millions of years ago)
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Evolution to Higher Intelligence?
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Intelligence = Technology?
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The Search for Extraterrestrial Intelligence
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Radio SETI: Where to look?
• a “hailing signal” would need to have a narrow bandwidth signal component– easier to see against “noise” from interstellar gas, distant
galaxies, the radio receiver
• first proposed to be tuned to 1420 MHz, the
frequency of H gas in the interstellar medium– for comparison: NPR is at 94.9 MHz
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Categories of Signals• signals used for local communication where
intelligent beings live
• signals used for communication between a civilization’s home world and some other site
• intentional signal beacons
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Finding and Decoding Signals• some things to look for:
1,679 bits
23 x 73
–broadcast in a strong, narrow wavelength–flashing on/off or switching frequencies–repetition–prime numbers? π? e?
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Where do we look?
• targeted search– not all locations in space are
equally probable for intelligent life
• sky survey– no assumptions made about where they might be
located
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Questions of the Day
• What is the Drake Equation, and why is it useful?
• Even if life arises, will it inevitably evolve towards intelligence?
• What are the methods SETI uses to search for intelligence today?
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Quiz
3 - What is one thing you did not understand from today’s lecture?
2 - What term in the Drake Equation will NASA’s Kepler mission be the first to measure?
1 - Explain why methane on Mars is a biosignature but methane on Titan is not.