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 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

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

The Drake Equation

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fraction of stars that have planets(> 10%)

Nc = Ns x fp x Ne x fl x fi x fc x L

The Drake Equation

number of terrestrial planets per planetary system in the Habitable Zone

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Nc = Ns x fp x Ne x fl x fi x fc x L

The Drake Equation

fraction of such planets on which life actually evolved

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Nc = Ns x fp x Ne x fl x fi x fc x L

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

The Drake Equation

fraction of worlds with intelligent beings that produce a civilization capable of interstellar communication

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Nc = Ns x fp x Ne x fl x fi x fc x L

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

Fermi Paradox

What if Nc is much larger than 1?

Where are they?

Alone in the galaxy?

What if Nc is less than 1?

Is anybody out there?

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

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!

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

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

Measuring Intelligence

big brainsmall brain

EQ= encephalization quotient

Evolution to Higher Intelligence?

Enc

epha

lizat

ion

Quo

tient

(E

Q)

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:

1,679 bits

23 x 73

–broadcast in a strong, narrow wavelength–flashing on/off or switching frequencies–repetition–prime numbers? π? e?

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

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.