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The Search for The Search for Extraterrestrial Extraterrestrial

IntelligenceIntelligence

E.T. phone home using 10-10-220

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GoalsGoals

• How likely is intelligent life in the Universe?

• How can we find out if there is?• How could we communicate with it?• Should we?

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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.

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The Drake Equation

N = Number of communicating civilizations in our galaxy right now.

And what about the rest?

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R* = 10 */year

Star Formation Rate: R*

• There are 100 billion stars in the Milky Way.

• The Milky Way is 10 billion years old.

R* = 100 billion stars/10 billion years

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Fraction with Planets: fp

• What fraction of stars have planets?• Extrasolar planet research in the last

7 years:– 87 stars are known to have at least one

planet.– 9 stars have more than one planet.– 2 stars have three planets

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fp = 1 Optimistic!

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Number of Earths: ne

• 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

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ne = 1/10

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fl = 1/3

Fraction with life: fl

• On what fraction of habitable planets does life evolve?

• Look at our Solar System.• 3 planets in habitable zone, life has

evolved on 1 (or maybe 2).

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Fraction with intelligence: fi

• What fraction of life bearing planets have life evolve to intelligence?

• Is intelligence inevitable?

LfffnfR N cilep*

fl = 1 Inevitable!

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Fraction that communicate: fc

• What fraction of intelligent civilizations become technological enough that we could communicate?

• Is technology inevitable?• Desirable?

LfffnfR N cilep*

fl = 1 Inevitable!

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Lifetime: L

• How long does a civilization last?• Do we have time to communicate with

them?• For us: L = 70 years!

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L = 1000 years

Optimistic?

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What’s the Answer?

• R* = 10 */year• fp = 1• ne = 1/10• fl = 1/3• fi = 1• fc = 1• L = 1000 year• N = 330! 330 technological

civilizations in the Milky Way, right now.

LfffnfR N cilep*

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But space is vast

• Milky Way is a giant cylinder (disk).– Radius = 15000 pc– Thickness = 1000 pc

• Volume = (Radius)2 x Thickness• V = 7 x 1011 pc3 = 700 billion cubic

parsecs!

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How far to the neighbors?

• If there are 330 civilizations in 700 billion cubic parsecs, then:– 1 civilization in every 2 billion cubic parsecs

• Imagine every civilization surrounded by a bubble in which it is alone.

• V = 2 billion cubic parsecs• R = 1 kpc• Distance between civilizations:

1 kpc = 3300 LY (optimistically)!

R

R

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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.

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SETI

• 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.

– TV– Radio– Cellular phones– etc

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E.T. FM

• Most natural radio sources are broadband.

• Radio stations are narrowband.

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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.

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SETI@Home

• 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.

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SETI@Home

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“Is there anybody out there?”

We have made three attempts to communicate.

1. The Arecibo broadcast to Hercules Cluster.

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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!

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The Voyager Record Club

3. Voyagers 1 and 2 contain a plaque and a record.

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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

• Beethoven, String Quartet No. 13 in B flat, Opus 130, Cavatina, performed by Budapest String Quartet.

6:37

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A Pale Blue Dot

Credit – Voyager 1990

43 AU