Lecture 22 Life beyond our Solar system SETI - PowerPoint PPT Presentation

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Lecture 22 Life beyond our Solar system SETI

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... intelligent life broadcasting across space. Drake equation (terms) ... How long (in years) will it take to go across the galaxy at the current Voyager's speed? ... – PowerPoint PPT presentation

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Title: Lecture 22 Life beyond our Solar system SETI


1
Lecture 22 Life beyond our Solar system (SETI)
2
SETI
  • Search for Extra Terrestrial Intelligence
  • What is intelligence?
  • In reality we search for some signs/manifestation
    of another technology
  • What types of technology?

3
Visible signs of technological civilization
(based on ours)
  • Energy production
  • Waging wars
  • Transportation (including interstellar travel)
  • Communication (unintentional leakage or
    deliberate beacons)

4
The best information carrier for interstellar
communications
  • Minimum energy per bit of information
  • Max possible velocity
  • Easy to generate, launch, and capture
  • Not be appreciably absorbed by the interstellar
    medium
  • Go where aimed
  • Go photons!

5
Nine-dimensional cosmic haystack
  • Direction (any)
  • Distance (100,000 light years)
  • Time continuous signal vs. periodic
  • Polarization right and left
  • Frequency frequencies lower than 100 kHz are
    absorbed by interstellar medium
  • Modulation
  • Signal strength

6
Background
  • Ultraviolet, X-ray, gamma-ray blocked by
    atmosphere (absorption on ozone, oxygen, nitrogen
    etc.) space based telescope
  • IR and mm effectively absorbed by water vapor
    telescope on the mountain-top
  • SETI concentrated on 1-10GHz (30-3 cm in
    wavelength)
  • Recently communication via visible light was also
    considered

7
Visible vs. Radio search
  • Radio photons are less energetic ? less energy to
    generate a signal
  • Visible photons are easier to focus

8
Arecibo radio telescope (Puerto Rico) diameter
305 m
9
Signal and noise
  • PR (PE x AR) / 4?r2
  • PR the amount of signal power collected by
    receiver
  • PE effective isotropic radiated power
  • AR effective area of the receiver
  • PN k x T x B
  • B 0.01 Hz k 1.381 x 10-23 Joules/Kelvin
  • We want PR 10 x PN
  • r ?

10
(No Transcript)
11
Drakes equation
  • The number of civilizations, N, broadcasting
    their existence in our Galaxy
  • N Rb T
  • T time over which civilizations broadcast
  • Rb R pp nE pl pi pc
  • R rate at which suitable stars are formed
  • pp probability of planets forming around a
    suitable star
  • nE average number of suitable planets in HZ
  • pl probability of life
  • pi probability of intelligence developing in
    life
  • pc probability of intelligent life broadcasting
    across space

12
Drake equation (terms)
  • R - 20 stars per year are born in our Galaxy
    but only 10 are solar-like.
  • pp 0.1-0.2
  • ne 1 and lt10
  • pl ?
  • pi ?
  • pc ?

13
Fermi Paradox
  • Our planet is not special
  • If even one civilization had originated before us
    then it should have already colonized the entire
    galaxy
  • So where is everybody? (Enrico Fermi, 1950)

14
  • Size of the Milky Way galaxy 100,000 light
    years
  • Speed of the Voyager 1 (launched in 1977) is 17
    km/sec
  • Speed of light 300,000 km/sec
  • How long (in years) will it take to go across the
    galaxy at the current Voyagers speed?
  • Age of the galaxy oldest stars 13 Gyr ago
    Galactic thin disk formation 10 Gyr ago

15
Possible solutions to the paradox
  • We are alone
  • Civilizations are common but no one has colonized
    the galaxy
  • a) technological difficulties
  • b) sociological considerations
  • c) self-destruction
  • There is a galactic civilization, but it has
    deliberately avoided contact

16
Sociological considerations
  • Civilization has to maintain desire and
    enthusiasm for colonization for millions of years
  • SETI does not have a government funding NASAs
    SETI was terminated 1993
  • Unless extra funding provided NSF will close
    Arecibo in 2011

17
Self-destruction
  • Nuclear weapons
  • Global warming
  • Population growth
  • Diseases

18
Galactic civilization
  • No interest in us we are too primitive
  • Zoo hypothesis (wildlife refuge) humans like
    other animals are supposed to have their own
    habitat
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