22 - SETI (Search for ExtraTerrestrial Intelligence)

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22 - SETI(Search for ExtraTerrestrial
Intelligence)
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Prelude

• If Lic gt 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

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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

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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
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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)
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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
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Programs - Past, Present, and Future
1960 - Ozma Frank Drake
1973-1997 - OSU
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Megachannel Extraterrestrial Assay (META)
Paul Horowitz
META Processors
Harvard 26-m radio telescope
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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.
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Main BETA rack - containing 63 FFT boards (each
processing 4 million channels)
BETA
BETA
Destruction of the antenna by nature
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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
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Allen Telescope Array
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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
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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)
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2D Pictures
Use BINARY - 0 (off), 1 (on) How to make it
quickly recognizable? - fewest permutations Exampl
e 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!
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Example
Message 11111100001000011110000010000111110 Thi
s 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!
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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)
00000010101010000000000001010000010100000001001000
100010001001011001010101010101 0101001001000000000
00000000000000000000000000001100000000000000000001
10100000000 00000000000110100000000000000000010101
000000000000000000111110000000000000000000
00000000000001100001110001100001100010000000000000
110010000110100011000110000110 1011111011111011111
01111100000000000000000000000000100000000000000000
10000000000 00000000000000000010000000000000000011
111100000000000001111100000000000000000000
00011000011000011100011000100000001000000000100001
101000011000111001101011111011 1110111110111110000
00000000000000000000001000000110000000001000000000
00110000000 00000000100000110000000000111111000001
100000011111000000000011000000000000010000
00001000000001000001000000110000000100000001100001
100000010000000000110001000011 0000000000000001100
11000000000000011000100001100000000011000011000000
10000000100 00001000000001000001000000011000000001
000100000000110000000010001000000000100000
00100000100000001000000010000000100000000000011000
000000110000000011000000000100 0111010110000000000
01000000010000000000000010000011111000000000000100
00101110100 10110110000001001110010011111110111000
011100000110111000000000101000001110110010
00000101000001111110010000001010000011000000100000
110110000000000000000000000000 0000000000111000001
00000000000000111010100010101010101001110000000001
01010100000 00000000000101000000000000001111100000
000000000001111111110000000000001110000000
11100000000011000000000001100000001101000000000101
100000110011000000011001100001 0001010000010100010
00010001001000100100010000000010001010001000000000
00010000100 00100000000000010000000001000000000000
00100101000000000001111001111101001111000
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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
placements meaning has changed - now its how
many of 1, 6, etc. is included There is one
15 and 4 8s - PO4 - phosphate Shape of SNA
double-helix nucleotides in human
DNA Human Height of human in units of signals
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 units of
signals wavelength
start bit
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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.