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22 - SETI ( S earch for E xtra T errestrial I ntelligence)

22 - SETI ( S earch for E xtra T errestrial I ntelligence). Prelude. If L ic > 100 years, "they" will probably be more advanced than us. Our radio, TV, defense radar signals are already 50 l.y. away by now - there is no easy way to “ hide ” We also need to make some choices: Where to look

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22 - SETI ( S earch for E xtra T errestrial I ntelligence)

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  1. 22 - SETI(Search for ExtraTerrestrial Intelligence)

  2. Prelude • If Lic > 100 years, "they" will probably be more advanced than us. • Our radio, TV, defense radar signals are already 50 l.y. away by now - there is no easy way to “hide” • We also need to make some choices: • Where to look • What frequencies to search • Separate “noise” and human signals from ET

  3. Fundamentals • Light - energy is proportional to the frequency - radio is cheaper than Vis-IR • Interstellar dust is transparent to radio, more opaque at VIR • High information rates - “bits” - requires large bandwidth • Seeing the signal above background noise easier for narrow bandwidth • Signal will spread in frequency due to: • Doppler shift - motion of source w.r.t. us • Interstellar gas effects

  4. Signal Types - Radio Quietest radio region near 1420 MHz H line and OH bands - all technical societies with interest in the universe will know this

  5. Search Strategies Directed - use a major facility for short periods of time. Target Search - look at specific, promising stars Sky Survey - look everywhere Shared - use observations from other projects. You can analyze old data, or make "parasitic" observations. Dedicated - use a facility exclusively (or at least primarily) for SETI work (in Target Search or Sky Survey)

  6. OZMA - The first modern radio search 1959 - David Morrison & Giuseppi Cocconi propose radio search for signals from intelligent extraterrestrials (September 19 issue of Nature) 1960 - Frank Drake looks at 2 stars (Tau Ceti & Epsilon Eridani) at 1 wavelength (H I 21-cm line) with 85-ft NRAO dish for a few months. SETI established as an experimental science

  7. Programs - Past, Present, and Future 1960 - Ozma Frank Drake 1973-1997 - OSU

  8. Megachannel Extraterrestrial Assay (META) Paul Horowitz META Processors Harvard 26-m radio telescope

  9. NASA SETI Sky Survey 16 million channels - 1-10 GHz - equivalent to 10 billion “Ozmas” Target Search 14 million channels - 1-3 GHz - looking at 1000 stars Project cancelled by US Congress after 2 megachannel receiver/processor began.

  10. Main BETA rack - containing 63 FFT boards (each processing 4 million channels) BETA BETA Destruction of the antenna by nature

  11. SETI Institute (founded in 1984) &Project Phoenix Continuation of Target Search under Private Funding! Parkes 210-ft, Green Bank 140-ft, Arecibo 1000-ft telescopes

  12. Allen Telescope Array

  13. Optical SETIProposed in 1961 by R. Schwartz & C. Townesrst carried out in 1990 by Stuart Kingsley in Columbus, OH High-power narrow-band lasers can outshine the Sun at the emitting wavelengths Look for short pulses with coincidence counters

  14. What Would a Message Look Like? How would it be composed? Need a signal that is instantly recognizable as non-natural Prime numbers: 1,2,3,5,7,11,13,17,19,.. Mathematical relations & diagrams - circles, triangles Pictures (these were the same as the ideas of Gauss & von Littrow)

  15. 2D Pictures • Use BINARY - 0 (off), 1 (on) • How to make it quickly recognizable? - fewest permutations • Example: a “message” with 12 bits can make 6 different 2D pictures - arranged as: • 1 x 12 (boring 1-D) • 2 x 6 • 3 x 4 • 4 x 3 • 6 x 2 • 12 x 1 (boring 1-D) • 15 bits only has 4! - notice that 15 is the product of two prime numbers! • 1 x 15 (boring 1-D) • 3 x 5 • 5 x 3 • 15 x 1 (boring 1-D) • So some choices are better than others!

  16. Example Message: 11111100001000011110000010000111110 This contains 35 bits and can be arranged as either 5x7 or 7x5 WE recognize the first as an arabic numeral but maybe ET uses the other one!

  17. Some “Test” Messages Message sent by Drake using the Arecibo radio telescope in 1974 - consisted of 1679 bits: (Transmitting frequency: 2380 MHz = 12.6 cm) 00000010101010000000000001010000010100000001001000100010001001011001010101010101 01010010010000000000000000000000000000000000000110000000000000000000110100000000 00000000000110100000000000000000010101000000000000000000111110000000000000000000 00000000000001100001110001100001100010000000000000110010000110100011000110000110 10111110111110111110111110000000000000000000000000010000000000000000010000000000 00000000000000000010000000000000000011111100000000000001111100000000000000000000 00011000011000011100011000100000001000000000100001101000011000111001101011111011 11101111101111100000000000000000000000000100000011000000000100000000000110000000 00000000100000110000000000111111000001100000011111000000000011000000000000010000 00001000000001000001000000110000000100000001100001100000010000000000110001000011 00000000000000011001100000000000001100010000110000000001100001100000010000000100 00001000000001000001000000011000000001000100000000110000000010001000000000100000 00100000100000001000000010000000100000000000011000000000110000000011000000000100 01110101100000000000100000001000000000000001000001111100000000000010000101110100 10110110000001001110010011111110111000011100000110111000000000101000001110110010 00000101000001111110010000001010000011000000100000110110000000000000000000000000 00000000001110000010000000000000011101010001010101010100111000000000101010100000 00000000000101000000000000001111100000000000000001111111110000000000001110000000 11100000000011000000000001100000001101000000000101100000110011000000011001100001 00010100000101000100001000100100010010001000000001000101000100000000000010000100 0010000000000001000000000100000000000000100101000000000001111001111101001111000

  18. Counting to 10 in binary Elements 1, 6,7,8,15 (H,C,N,O,P - in DNA) Nucleic base pairs, deoxyribose, phosphate - note that the placement’s meaning has changed - now its how many of #1, #6, etc. is included There is one #15 and 4 #8’s - PO4 - phosphate Shape of SNA double-helix # nucleotides in human DNA Human Height of human in unit’s of signal’s wavelength (12.6 cm) Human population (on Earth, of course) Pluto, Neptune, Uranus, Saturn, Jupiter, Mars, Earth (offset), Venus, Mercury, SUN Arecibo dish Size of dish in unit’s of signal’s wavelength “start bit”

  19. What if We Hear “Them”? - SETI Protocol 1. Is it really extraterrestrial? 2. Get confirmation from other astronomers. (If extraterrestrial, tell your government about it). 3. If convincing: announce to International Astronomical Union, Secretary General of the UN, inform SETI groups. 4. Make the first public announcement 5. Make data available to all. 6. Everyone carefully record & disseminate signals 7. Protect frequencies. 8. Don't broadcast back to the ETs! Requires Debate. 9. Study signals. The SETI Committee of the International Academy of Astronautics keeps a list of experts to call on.

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