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SETI
Extra Terrestrial Intelligence
• Is there intelligent life on other planets?
• If so,
– Can we find them?
– Can we try to communicate?
• SETI is the Search for Extra Terrestrial Intelligence
Evolution of Intelligence
• If a planet has life, will intelligence evolve?
– Within the last 2 million years on Earth
– Less than 1/1000 the time since life appeared
• How probable is the development of technology?
– Radio communications for just 100 years
– Less than 1/10,000 the time since humans appeared
• How long will an intelligence survive?
Drake Equation
• In 1960 Frank Drake
created a way to estimate
the number of planets with
civilizations capable of
interstellar
communication.
– The Drake equation
– Rate in years







R* = 1; rate of stars forming
fp = 1; fraction with planets
ne = 0.1; earth-like planets
fl = 1; fraction with life
fi = 1; intelligence fraction
fc = 1; communicating aliens
L = 100; lifetime of
civilization
N  R*  f p  ne  f l  f i  f c  L  Total = 10 in the galaxy
Communicating with ET
• Sending a spaceship is too slow (25,000 mph
= 11 km/s).
– 300,000 years to reach the nearest star
• Radio communication is much faster
(300,000 km/s).
– 4 years to the nearest star
– Earth radio to stars within 100 light years
• A planet 60 ly away could be watching “I
Love Lucy”.
Searching for Signals
• Civilizations may also be
sending information.
• Radio waves (including TV) are
easy to detect.
• Radio telescopes scan the sky
for radio objects.
• Searches analyze data in parallel
with other experiments.
SETI @ Home
• Data must be scanned for
signals.
– Weak signals, lots of noise
– Needs lots of computer time
• SETI@home uses volunteer
computers.
• So far, the fluctuations seem
to be random.