The Search for
Extraterrestrial
Intelligence
Can E.T. hear me know?
Goals
• How likely is intelligent life in the Universe?
Life in the Universe
• What are the odds of intelligent life elsewhere in
the Universe?
• How many communicating civilizations are
there in the Milky Way?
• How do you guess?
• How do you guess the number of jellybeans in a
jar?
• Break the problem down into things you can
guess.
The Drake Equation
N  R *  f p  n e  fl  fi  fc  L
N = Number of communicating civilizations in
our galaxy right now.
And what about the rest?
Star Formation Rate: R*
N  R *  f p  n e  fl  fi  fc  L
• There are 100 billion stars in the Milky Way.
• The Milky Way is 10 billion years old.
R* = 100 billion stars/10 billion years
R* = 10 */year
Fraction with Planets: fp
N  R *  f p  n e  fl  fi  fc  L
• What fraction of stars have planets?
• Extrasolar planet research since 1995:
– 851 confirmed planets
– 126 multi-planet systems
– 1 star has six
fp = 1/4
Number of Earths: ne
N  R *  f p  n e  fl  fi  fc  L
• How many habitable planets are there in each
of these planetary systems?
• Habitable zone: water should be a liquid
• Depends on star.
– No O or B
– No M
– No binaries
ne = 1/5
Fraction with life: fl
N  R *  f p  n e  fl  fi  fc  L
• On what fraction of habitable planets does life
evolve?
• Look at our Solar System.
• 2 planets in habitable zone, life has evolved on 1
(or maybe 2).
fl = ?
Fraction with intelligence: fi
N  R *  f p  n e  fl  fi  fc  L
• What fraction of life bearing planets have life
evolve to intelligence?
• Is intelligence inevitable?
fi = ?
Fraction that communicate: fc
N  R *  f p  n e  fl  fi  fc  L
• What fraction of intelligent civilizations
become technological enough that we could
communicate?
• Is technology inevitable?
• Desirable?
fc = ?
Lifetime: L
N  R *  f p  n e  fl  fi  fc  L
• How long does a civilization last?
• Do we have time to communicate with them?
• For us: L = 80 years!
L = ? years
What’s the Answer?
N  R *  f p  n e  fl  fi  fc  L
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R* = 10 */year
fp = 1/4
ne = 1/5
fl = ?
fi = ?
fc = ?
L = ? year
N = _____  # of technological
civilizations in Milky Way, right now.
But space is vast
• Milky Way is a giant cylinder (disk).
– Radius = 15000 pc
– Thickness = 1000 pc
• Volume = p(Radius)2 x Thickness
• V = 7 x 1011 pc3 = 700 billion cubic parsecs!
How far to the neighbors?
• If there are 100 civilizations in 700 billion
cubic parsecs, then:
– 1 civilization in every 15 billion cubic parsecs
• Imagine every civilization surrounded by a
bubble in which it is alone.
• V = 15 billion cubic parsecs
• R = 3 kpc
• Distance between civilizations:
3 kpc = 900 LY (optimistically)!
R
R
How Can We Know?
• How can we tell if there are extraterrestrial
civilizations?
• Go visit. Is this practical?
• Look for visitors? Is there evidence?
• Look, or listen, for signals from E.T.
SETI
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Search for Extraterrestrial Intelligence
Several organized searches over the last 30 years.
Use a radio telescope to try to detect signs of E.T.
Why?
The Earth floods space with radio waves.
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TV
Radio
Cellular phones
etc
E.T. FM
• Most natural radio sources are broadband.
• Radio stations are narrowband.
Tuning the Dial
• Nearly all searches have been looking for
extremely narrow radio signals.
– But there are millions and billions of frequencies
to listen to.
– And millions and billions of stars
• Concentrate on nearby sun-like stars.
– No luck.
• Point in the sky randomly.
– No luck yet. But you can help.
SETI@Home
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Receiver piggybacks on Arecibo telescope.
Constantly searches as telescope observes.
Millions of channels.
Thousands of hours.
Lots of data.
Needs lots of computer power.
Your power.
SETI@Home
“Is there anybody out there?”
We have made three attempts
to communicate.
1. The Arecibo broadcast to
Hercules Cluster.
Here’s my card.
2. The Pioneer 10 and 11 plaques.
Pioneer 10 is now 12 billion km from Earth – 80 AU  11.3 light hours!
The Voyager Record Club
3. Voyagers 1 and 2 contain a plaque and a record.
Voyagers 1 and 2
• Greetings 55 languages
• 115 images
• Music
Sumerian"May all be well."
Arabic"Greetings to our friends in the stars. We wish that we will meet you someday."
Urdu"Peace on you. We the inhabitants of this earth send our greetings to you."
Italian"Many greetings and wishes."
Ila (Zambia)"We wish all of you well."
Akkadian"May all be very well."
Romanian"Greetings to everybody."
Hindi"Greetings from the inhabitants of this world."
Nguni"We greet you, great ones. We wish you longevity."
Nyanja"How are all you people of other planets?"
Hittite"Hail."
French"Good day everybody." recorded by Alexandra Littauer
Vietnamese"Sincerely send you our friendly greetings."
Sotho"We greet you, O great ones."
Swedish"Greetings from a computer programmer in the little university town of Ithaca on the planet Earth."
Hebrew"Peace."
Burmese"Are you well."
Sinhalese"Greetings."
Wu"Best wishes to you all."
Ukrainian"We are sending greetings from our world, wishing you happiness, goodness, good health and many
years."
Aramaic"Peace."
Spanish"Hello and greetings to all."
Greek"Greetings to you, whoever you are. We come in friendship to those who are friends."
Korean"How are you?"
Persian"Hello to the residents of far skies."
English"Hello from the children of planet Earth."
Indonesian"Good night ladies and gentlemen. Goodbye and see you next time."
Latin"Greetings to you, whoever you are; we have good will towards you and bring peace across space."
Armenian"To all those who exist in the universe, greetings."
Serbian"We wish you everything good from our planet."
Portuguese"Peace and happiness to all." recorded by Janet Sternberg
Kechua"Hello to everybody from this Earth, in Kechua language."
Japanese"Hello? How are you?"
Polish"Welcome, creatures from beyond the outer world."
Luganda"Greetings to all peoples of the universe. God give you peace always."
Cantonese"Hi. How are you? Wish you peace, health and happiness."
Dutch"Heartfelt greetings to everyone."
Punjabi"Welcome home. It is a pleasure to receive you."
Nepali"Wishing you a peaceful future from the earthlings."
Amoy (Min dialect)"Friends of space, how are you all? Have you eaten yet? Come visit us if you have time."
Russian"Be healthy - I greet you."
German"Heartfelt greetings to all."
Turkish"Dear Turkish-speaking friends, may the honors of the morning be upon your heads."
Mandarin Chinese"Hope everyone's well. We are thinking about you all. Please come here to visit when you
have time."
Marathi"Greetings. The people of the Earth send their good wishes."
Thai"We in this world send you our good will."
Bengali"Hello! Let there be peace everywhere."
Welsh"Good health to you now and forever.“
Gujarati"Greetings from a human being of the Earth. Please contact.“
Kannada"Greetings. On behalf of Kannada-speaking people, 'good wishes'."
Telugu"Greetings. Best wishes from Telugu-speaking people."
Oriya"Greetings to the inhabitants of the universe from the third planet Earth of the star Sun."
Hungarian"We are sending greetings in the Hungarian language to all peace-loving beings in the Universe."
Czech"Dear Friends, we wish you the best."
Rajasthani"Hello to everyone. We are happy here and you be happy there."
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Bach, Brandenburg Concerto No. 2 in F. First Movement, Munich Bach Orchestra, Karl Richter, conductor. 4:40
Java, court gamelan, "Kinds of Flowers," recorded by Robert Brown. 4:43
Senegal, percussion, recorded by Charles Duvelle. 2:08
Zaire, Pygmy girls' initiation song, recorded by Colin Turnbull. 0:56
Australia, Aborigine songs, "Morning Star" and "Devil Bird," recorded by Sandra LeBrun Holmes. 1:26
Mexico, "El Cascabel," performed by Lorenzo Barcelata and the Mariachi México. 3:14
"Johnny B. Goode," written and performed by Chuck Berry. 2:38
New Guinea, men's house song, recorded by Robert MacLennan. 1:20
Japan, shakuhachi, "Tsuru No Sugomori" ("Crane's Nest,") performed by Goro Yamaguchi. 4:51
Bach, "Gavotte en rondeaux" from the Partita No. 3 in E major for Violin, performed by Arthur Grumiaux. 2:55
Mozart, The Magic Flute, Queen of the Night aria, no. 14. Edda Moser, soprano. Bavarian State Opera, Munich,
Wolfgang Sawallisch, conductor. 2:55
Georgian S.S.R., chorus, "Tchakrulo," collected by Radio Moscow. 2:18
Peru, panpipes and drum, collected by Casa de la Cultura, Lima. 0:52
"Melancholy Blues," performed by Louis Armstrong and his Hot Seven. 3:05
Azerbaijan S.S.R., bagpipes, recorded by Radio Moscow. 2:30
Stravinsky, Rite of Spring, Sacrificial Dance, Columbia Symphony Orchestra, Igor Stravinsky, conductor. 4:35
Bach, The Well-Tempered Clavier, Book 2, Prelude and Fugue in C, No.1. Glenn Gould, piano. 4:48
Beethoven, Fifth Symphony, First Movement, the Philharmonia Orchestra, Otto Klemperer, conductor. 7:20
Bulgaria, "Izlel je Delyo Hagdutin," sung by Valya Balkanska. 4:59
Navajo Indians, Night Chant, recorded by Willard Rhodes. 0:57
Holborne, Paueans, Galliards, Almains and Other Short Aeirs, "The Fairie Round," performed by David
Munrow and the Early Music Consort of London. 1:17
Solomon Islands, panpipes, collected by the Solomon Islands Broadcasting Service. 1:12
Peru, wedding song, recorded by John Cohen. 0:38
China, ch'in, "Flowing Streams," performed by Kuan P'ing-hu. 7:37
India, raga, "Jaat Kahan Ho," sung by Surshri Kesar Bai Kerkar. 3:30
"Dark Was the Night," written and performed by Blind Willie Johnson. 3:15
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Beethoven, String Quartet No. 13 in B flat, Opus 130, Cavatina, performed by Budapest String Quartet. 6:37
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