Transcript Planet Detection - University of Washington

Astronomy190 - Topics in Astronomy
Astronomy and Astrobiology
Lecture 21: Search for Extraterrestrial Intelligence
Ty Robinson
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?
Are We Alone?
The Drake Equation
Estimating 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
The Drake Equation
Nc = Ns x fp x Ne x fl x fi x fc x L
number of stars in the galaxy
(~200 billion)
The Drake Equation
Nc = Ns x fp x Ne x fl x fi x fc x L
fraction of stars that have planets
(> 10%)
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The Drake Equation
Nc = Ns x fp x Ne x fl x fi x fc x L
number of terrestrial planets per planetary system in the
Habitable Zone
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The Drake Equation
Nc = Ns x fp x Ne x fl x fi x fc x L
fraction of such planets on which life actually evolved
QuickTime™ and a
decompressor
are needed to see this picture.
The Drake Equation
Nc = Ns x fp x Ne x fl x fi x fc x L
fraction of inhabited worlds that develop intelligent life
The Drake Equation
Nc = Ns x fp x Ne x fl x fi x fc x L
fraction of worlds with intelligent beings that produce a
civilization capable of interstellar communication
QuickTime™ and a
decompressor
are needed to see this picture.
The Drake Equation
Nc = Ns x fp x Ne x fl x fi x fc x L
the lifetime of such civilizations
(divided by the age of the galaxy)
What if Nc is much larger than 1?
Where are they?
What if Nc is less than 1?
Is anybody out there?
Nc = Ns x fp x Ne x fl x fi x fc x L
fi : the Question of Intelligence
Is the evolution of intelligence inevitable?
fi : the Question of Intelligence
• two schools of thought
1. 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!
fi : the Question of Intelligence
• two schools of thought
2. 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
Convergent Evolution
• organisms of different evolutionary backgrounds
that occupy similar ecological niches will
eventually come to resemble one another
• maybe intelligence increases fitness so much that if that
niche is not filled, species will be selected for intelligence
via convergent evolution
Is there an evolutionary trend favoring intelligence?
Measuring Intelligence
big brain
small brain
EQ= encephalization quotient
Encephalization Quotient (EQ)
Evolution to Higher Intelligence?
Time (millions of years ago)
Evolution to Higher Intelligence?
Intelligence = Technology?
The Search for
Extraterrestrial
Intelligence
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
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
Finding and Decoding Signals
• some things to look for:
–broadcast in a strong, narrow wavelength
–flashing on/off or switching frequencies
–repetition
–prime numbers? π? e?
1,679 bits
23 x 73
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
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?
Quiz
1 - Explain why methane on Mars is a biosignature
but methane on Titan is not.
2 - What term in the Drake Equation will NASA’s
Kepler mission be the first to measure?
3 - What is one thing you did not understand from
today’s lecture?