Extra-terrestrial Civilizations

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Extra-terrestrial Civilizations
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Are we alone? Contact

• Direct contact through traveling to the stars and
  their planets
• Will be a challenge because of the vast distances
  involved and the (slow) speeds we can travel

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Are we alone? Contact

• Radio communication more likely possibility for
  contact
• Electromagnetic radiation travels at the speed of
  light.

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Civilizations

• Will life always develop technology? Some
  societies on Earth have not developed the means
  to communicate with ETs.
• Will a society want to communicate? A society
  may develop the means to search for ET but elect
  not to attempt to reach out.

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Consider ...

• How many intelligent civilizations exist?
• How long on average do they last?
• How does communication proceed?

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Drake Equation

• One possible way to estimate the number, N, of
  civilizations.
• N
• Ns x fs x ps x ls x lc x L

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Stars in the Galaxy, Ns

• The number of stars in the Milky Way galaxy
  about 300 billion.

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Suitable stars (fraction), fs

• Star must be old enough to allow life to develop
  spectral types F, G, K
• Star must have enough heavy elements to form
  planets 0.005

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Suitable planets in a Solar System, ps

• To date, extra-solar planets have been hot
  Jupiters
• Planets to sustain life need to be in the
  habitable zone around a star 1.0

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Fraction of planets suitable for life, ls

• Very speculative sample of 1 only to date
  (Earth)
• If a planet is suitable for life, good reason to
  think life will develop
• Conservative approach suggest Earth and Mars
  could produce life 0.5

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Life develops a civilization, lc

• Again, very speculative.
• Simple life started on Earth nearly 3.5 billion
  years ago.
• Extinction level events common for example 250
  and 65 million years ago.

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Life develops a civilization, lc

• As long as some form of life exists after an
  extinction event occurs, natural selection should
  continue and life redevelops.
• Assuming life develops then a case can be made
  that a form of civilization is inevitable 0.33

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Lifetime of a civilization, L

• Firstly, the age of our Milky Way galaxy is 10
  billion years.
• How long have we had the ability to communicate
  with ET about 50 years.
• How many times have we sent a communication not
  many!
• Radio telescope, Pioneer and Voyager

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Drake Equation Result

• Substituting into
• N Ns x fs x ps x ls x lc x L
• N 300x109x0.005x1x0.5x0.33xL/10x109
• L/40
• Large numbers top and bottom tend to cancel out.

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Range of answers

• Depending upon your optimism or pessimism, N can
  vary significantly
• From 10L (Carl Sagan,1978) to a very optimistic
  120L to a pessimistic L/10 billion
• If civilization survives for 100s or 1,000s of
  years then N could be very large indeed.

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Survival lifetimes

• Dinosaurs lived for 150 million years can we
  survive for longer thus increasing L
  substantially?
• Some species of life have lived for over 200
  million years on Earth.
• Humans are living outside the laws of Natural
  Selection may well reduce L.
• Upper limit based upon life of a star 10
  billion years.

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More than the Milky Way

• Ours is not the only galaxy in the universe

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Why communicate at all?

• Curiosity
• The urge to talk and listen!
• The hope to learn/gain knowledge
• The need for resources and/or living space
• Because we can!

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Why not?

• Fear (enslavement, destruction, etc)
• Inertia happy as we are
• Economics expensive to try and need to deploy
  resources appropriately.
• Of course, contact may happen by accident
  leakage of radio and TV signals.

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How far away is a civilization?

• Even assuming optimistic values for the Drake
  Equation, the closest civilization maybe 100s of
  light years away!
• Average stellar separation in the outskirts of a
  galaxy 5 to 10 light years.
• Two way communication then becomes a problem.

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The urge to explore

• In our Solar System, we seem keen to explore and
  colonize

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Types of civilizations

• Kardashev spawned the following classification
  scheme
• Type 0 inability to communicate with ET
• Type 1 like us with limited technology
• Type II almost 100 utilization of parent
  stars energy (Dyson spheres)
• Type III utilization of a galaxy of stars
  energy!